Re: New Cam, Jeep will only run without TPS
 

I went through this a while back after replacing a distributor cap, it
was driving me nuts because the engine started fine and while it seemed
a bit off it only ran a little rough until I gave it some gas and
brought the revs up, then it started spitting, backfiring and raising a
fuss. As first I thought it was a vacuum leak but it turned out to be
the wires were one position off.

If the TPS isn't functioning how does the FI system know how much fuel
to deliver? With a carburatorated engine the vacuum naturally would
pull more fuel out of the jets, but with FI something has to tell the
computer.

Will the computer figure something out from the 02 sensor telling it the
engine is running too lean?

Jeff DeWitt

bllsht wrote:
> There is a big difference between not being able to compute the
> optimal fuel and timing demands (no TPS signal), and having spark in
> the wrong cylinder and no spark in the right cylinder.
>
> You don't need a TPS to start the engine. You do need spark in the
> right cylinder.
>
> On Sun, 29 Oct 2006 21:41:32 GMT, Jeffrey DeWitt
> <JeffDeWitt@nc.rr.com> wrote:
>
>
>>It seems at least as likely as the thing running with the TPS unplugged!
>> THAT one I don't understand at all.
>>
>>Jeff DeWitt
>>
>>bllsht wrote:
>>
>>>Not likely. If it ran at all in that condition, unplugging the TPS
>>>wouldn't improve it.
>>>
>>>On Sun, 29 Oct 2006 13:30:11 GMT, Jeffrey DeWitt
>>><JeffDeWitt@nc.rr.com> wrote:
>>>
>>>
>>>
>>>>That's a good point, could you have put the wires on the distributor cap
>>>>one position off? I've done that and the engine will run, but sounds
>>>>off and backfires when revved.
>>>>
>>>>Jeff DeWitt
>>>>
>>>>bllsht wrote:
>>>>
>>>>
>>>>>First thing that came to my mind is that you may have the distributor
>>>>>indexed incorrectly.
>>>>>
>>>>>With cyl. 1 at TDC, the trailing edge of the ign. rotor should be
>>>>>about .020" PAST the #1 post in the distributor cap.
>>>>>
>>>>>With the TPS disconnected, the PCM may not be advancing the timing and
>>>>>that may be enough for it to 'fire' the correct post.
>>>>>
>>>>>In other words, the rotor isn't pointing in the right direction when
>>>>>the PCM fires the coil.
>>>>>
>>>>>
>>>>>
>>>>>On 28 Oct 2006 12:31:01 -0700, "jeepinacreek"
>>>>><jeepinacreek@hotmail.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
>>>>>>was a great mod with out totaly stroking the motor. After completing
>>>>>>the buildup and starting it for the first time, I thought great it
>>>>>>runs. Then I ran up and it starting backfiring at around 1800+ RPM.
>>>>>>This has been my battle for the last three months.
>>>>>>
>>>>>>A little about my Jeep;
>>>>>>Doug thorley header
>>>>>>bored out 62mm throttle
>>>>>>MSD ignition
>>>>>>New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
>>>>>>Curry Enterpise lift 33in tires, 4:10 gears, lockers
>>>>>>
>>>>>>What I have done to fix this so far;
>>>>>>-Took it the dealer, they wouldn't touch it.
>>>>>>-I currently have timing chain retarded -5 degree's due to pinging, cut
>>>>>>down on backfiring.
>>>>>>-I also had it advanced +5 degree's, caused a lot more backfiring.
>>>>>>-I also ran the cam at TDC with no advance or timing. This is the
>>>>>>original way I built it.
>>>>>>-Changed TPS
>>>>>>-Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
>>>>>>ignition which I disconnected and the Jeep barely ran. Connected it
>>>>>>back up and seems to be the only thing keeping it running. So I know
>>>>>>the MSD works -changed O2 sensors -changed fuel pump and filters in
>>>>>>tank, gas cap to.
>>>>>>-Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
>>>>>>an air/fuel ratio gauge on it.
>>>>>>
>>>>>>So my latest attempt to get this thing running right truely has me
>>>>>>scratching my head, I left the TPS wire connected disconnected, drove
>>>>>>it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
>>>>>>hesitate or ping or miss or run rich. It runs great, I can drive it on
>>>>>>the freeway now.
>>>>>>
>>>>>>I am on my last leg with this thing. Anyone have any ideas or
>>>>>>suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

I went through this a while back after replacing a distributor cap, it
was driving me nuts because the engine started fine and while it seemed
a bit off it only ran a little rough until I gave it some gas and
brought the revs up, then it started spitting, backfiring and raising a
fuss. As first I thought it was a vacuum leak but it turned out to be
the wires were one position off.

If the TPS isn't functioning how does the FI system know how much fuel
to deliver? With a carburatorated engine the vacuum naturally would
pull more fuel out of the jets, but with FI something has to tell the
computer.

Will the computer figure something out from the 02 sensor telling it the
engine is running too lean?

Jeff DeWitt

bllsht wrote:
> There is a big difference between not being able to compute the
> optimal fuel and timing demands (no TPS signal), and having spark in
> the wrong cylinder and no spark in the right cylinder.
>
> You don't need a TPS to start the engine. You do need spark in the
> right cylinder.
>
> On Sun, 29 Oct 2006 21:41:32 GMT, Jeffrey DeWitt
> <JeffDeWitt@nc.rr.com> wrote:
>
>
>>It seems at least as likely as the thing running with the TPS unplugged!
>> THAT one I don't understand at all.
>>
>>Jeff DeWitt
>>
>>bllsht wrote:
>>
>>>Not likely. If it ran at all in that condition, unplugging the TPS
>>>wouldn't improve it.
>>>
>>>On Sun, 29 Oct 2006 13:30:11 GMT, Jeffrey DeWitt
>>><JeffDeWitt@nc.rr.com> wrote:
>>>
>>>
>>>
>>>>That's a good point, could you have put the wires on the distributor cap
>>>>one position off? I've done that and the engine will run, but sounds
>>>>off and backfires when revved.
>>>>
>>>>Jeff DeWitt
>>>>
>>>>bllsht wrote:
>>>>
>>>>
>>>>>First thing that came to my mind is that you may have the distributor
>>>>>indexed incorrectly.
>>>>>
>>>>>With cyl. 1 at TDC, the trailing edge of the ign. rotor should be
>>>>>about .020" PAST the #1 post in the distributor cap.
>>>>>
>>>>>With the TPS disconnected, the PCM may not be advancing the timing and
>>>>>that may be enough for it to 'fire' the correct post.
>>>>>
>>>>>In other words, the rotor isn't pointing in the right direction when
>>>>>the PCM fires the coil.
>>>>>
>>>>>
>>>>>
>>>>>On 28 Oct 2006 12:31:01 -0700, "jeepinacreek"
>>>>><jeepinacreek@hotmail.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
>>>>>>was a great mod with out totaly stroking the motor. After completing
>>>>>>the buildup and starting it for the first time, I thought great it
>>>>>>runs. Then I ran up and it starting backfiring at around 1800+ RPM.
>>>>>>This has been my battle for the last three months.
>>>>>>
>>>>>>A little about my Jeep;
>>>>>>Doug thorley header
>>>>>>bored out 62mm throttle
>>>>>>MSD ignition
>>>>>>New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
>>>>>>Curry Enterpise lift 33in tires, 4:10 gears, lockers
>>>>>>
>>>>>>What I have done to fix this so far;
>>>>>>-Took it the dealer, they wouldn't touch it.
>>>>>>-I currently have timing chain retarded -5 degree's due to pinging, cut
>>>>>>down on backfiring.
>>>>>>-I also had it advanced +5 degree's, caused a lot more backfiring.
>>>>>>-I also ran the cam at TDC with no advance or timing. This is the
>>>>>>original way I built it.
>>>>>>-Changed TPS
>>>>>>-Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
>>>>>>ignition which I disconnected and the Jeep barely ran. Connected it
>>>>>>back up and seems to be the only thing keeping it running. So I know
>>>>>>the MSD works -changed O2 sensors -changed fuel pump and filters in
>>>>>>tank, gas cap to.
>>>>>>-Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
>>>>>>an air/fuel ratio gauge on it.
>>>>>>
>>>>>>So my latest attempt to get this thing running right truely has me
>>>>>>scratching my head, I left the TPS wire connected disconnected, drove
>>>>>>it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
>>>>>>hesitate or ping or miss or run rich. It runs great, I can drive it on
>>>>>>the freeway now.
>>>>>>
>>>>>>I am on my last leg with this thing. Anyone have any ideas or
>>>>>>suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

I went through this a while back after replacing a distributor cap, it
was driving me nuts because the engine started fine and while it seemed
a bit off it only ran a little rough until I gave it some gas and
brought the revs up, then it started spitting, backfiring and raising a
fuss. As first I thought it was a vacuum leak but it turned out to be
the wires were one position off.

If the TPS isn't functioning how does the FI system know how much fuel
to deliver? With a carburatorated engine the vacuum naturally would
pull more fuel out of the jets, but with FI something has to tell the
computer.

Will the computer figure something out from the 02 sensor telling it the
engine is running too lean?

Jeff DeWitt

bllsht wrote:
> There is a big difference between not being able to compute the
> optimal fuel and timing demands (no TPS signal), and having spark in
> the wrong cylinder and no spark in the right cylinder.
>
> You don't need a TPS to start the engine. You do need spark in the
> right cylinder.
>
> On Sun, 29 Oct 2006 21:41:32 GMT, Jeffrey DeWitt
> <JeffDeWitt@nc.rr.com> wrote:
>
>
>>It seems at least as likely as the thing running with the TPS unplugged!
>> THAT one I don't understand at all.
>>
>>Jeff DeWitt
>>
>>bllsht wrote:
>>
>>>Not likely. If it ran at all in that condition, unplugging the TPS
>>>wouldn't improve it.
>>>
>>>On Sun, 29 Oct 2006 13:30:11 GMT, Jeffrey DeWitt
>>><JeffDeWitt@nc.rr.com> wrote:
>>>
>>>
>>>
>>>>That's a good point, could you have put the wires on the distributor cap
>>>>one position off? I've done that and the engine will run, but sounds
>>>>off and backfires when revved.
>>>>
>>>>Jeff DeWitt
>>>>
>>>>bllsht wrote:
>>>>
>>>>
>>>>>First thing that came to my mind is that you may have the distributor
>>>>>indexed incorrectly.
>>>>>
>>>>>With cyl. 1 at TDC, the trailing edge of the ign. rotor should be
>>>>>about .020" PAST the #1 post in the distributor cap.
>>>>>
>>>>>With the TPS disconnected, the PCM may not be advancing the timing and
>>>>>that may be enough for it to 'fire' the correct post.
>>>>>
>>>>>In other words, the rotor isn't pointing in the right direction when
>>>>>the PCM fires the coil.
>>>>>
>>>>>
>>>>>
>>>>>On 28 Oct 2006 12:31:01 -0700, "jeepinacreek"
>>>>><jeepinacreek@hotmail.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
>>>>>>was a great mod with out totaly stroking the motor. After completing
>>>>>>the buildup and starting it for the first time, I thought great it
>>>>>>runs. Then I ran up and it starting backfiring at around 1800+ RPM.
>>>>>>This has been my battle for the last three months.
>>>>>>
>>>>>>A little about my Jeep;
>>>>>>Doug thorley header
>>>>>>bored out 62mm throttle
>>>>>>MSD ignition
>>>>>>New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
>>>>>>Curry Enterpise lift 33in tires, 4:10 gears, lockers
>>>>>>
>>>>>>What I have done to fix this so far;
>>>>>>-Took it the dealer, they wouldn't touch it.
>>>>>>-I currently have timing chain retarded -5 degree's due to pinging, cut
>>>>>>down on backfiring.
>>>>>>-I also had it advanced +5 degree's, caused a lot more backfiring.
>>>>>>-I also ran the cam at TDC with no advance or timing. This is the
>>>>>>original way I built it.
>>>>>>-Changed TPS
>>>>>>-Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
>>>>>>ignition which I disconnected and the Jeep barely ran. Connected it
>>>>>>back up and seems to be the only thing keeping it running. So I know
>>>>>>the MSD works -changed O2 sensors -changed fuel pump and filters in
>>>>>>tank, gas cap to.
>>>>>>-Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
>>>>>>an air/fuel ratio gauge on it.
>>>>>>
>>>>>>So my latest attempt to get this thing running right truely has me
>>>>>>scratching my head, I left the TPS wire connected disconnected, drove
>>>>>>it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
>>>>>>hesitate or ping or miss or run rich. It runs great, I can drive it on
>>>>>>the freeway now.
>>>>>>
>>>>>>I am on my last leg with this thing. Anyone have any ideas or
>>>>>>suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

On Mon, 30 Oct 2006 01:22:21 GMT, Jeffrey DeWitt
<JeffDeWitt@nc.rr.com> wrote:

>I went through this a while back after replacing a distributor cap, it
>was driving me nuts because the engine started fine and while it seemed
>a bit off it only ran a little rough until I gave it some gas and
>brought the revs up, then it started spitting, backfiring and raising a
>fuss. As first I thought it was a vacuum leak but it turned out to be
>the wires were one position off.


>
>If the TPS isn't functioning how does the FI system know how much fuel
>to deliver? With a carburatorated engine the vacuum naturally would
>pull more fuel out of the jets, but with FI something has to tell the
>computer.

MAP sensor.

>
>Will the computer figure something out from the 02 sensor telling it the
>engine is running too lean?

With no TPS it's gonna be in open loop, using a pre programmed
strategy. The PCM is ignoring the O2 at this point.


>
>Jeff DeWitt
>
>bllsht wrote:
>> There is a big difference between not being able to compute the
>> optimal fuel and timing demands (no TPS signal), and having spark in
>> the wrong cylinder and no spark in the right cylinder.
>>
>> You don't need a TPS to start the engine. You do need spark in the
>> right cylinder.
>>
>> On Sun, 29 Oct 2006 21:41:32 GMT, Jeffrey DeWitt
>> <JeffDeWitt@nc.rr.com> wrote:
>>
>>
>>>It seems at least as likely as the thing running with the TPS unplugged!
>>> THAT one I don't understand at all.
>>>
>>>Jeff DeWitt
>>>
>>>bllsht wrote:
>>>
>>>>Not likely. If it ran at all in that condition, unplugging the TPS
>>>>wouldn't improve it.
>>>>
>>>>On Sun, 29 Oct 2006 13:30:11 GMT, Jeffrey DeWitt
>>>><JeffDeWitt@nc.rr.com> wrote:
>>>>
>>>>
>>>>
>>>>>That's a good point, could you have put the wires on the distributor cap
>>>>>one position off? I've done that and the engine will run, but sounds
>>>>>off and backfires when revved.
>>>>>
>>>>>Jeff DeWitt
>>>>>
>>>>>bllsht wrote:
>>>>>
>>>>>
>>>>>>First thing that came to my mind is that you may have the distributor
>>>>>>indexed incorrectly.
>>>>>>
>>>>>>With cyl. 1 at TDC, the trailing edge of the ign. rotor should be
>>>>>>about .020" PAST the #1 post in the distributor cap.
>>>>>>
>>>>>>With the TPS disconnected, the PCM may not be advancing the timing and
>>>>>>that may be enough for it to 'fire' the correct post.
>>>>>>
>>>>>>In other words, the rotor isn't pointing in the right direction when
>>>>>>the PCM fires the coil.
>>>>>>
>>>>>>
>>>>>>
>>>>>>On 28 Oct 2006 12:31:01 -0700, "jeepinacreek"
>>>>>><jeepinacreek@hotmail.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
>>>>>>>was a great mod with out totaly stroking the motor. After completing
>>>>>>>the buildup and starting it for the first time, I thought great it
>>>>>>>runs. Then I ran up and it starting backfiring at around 1800+ RPM.
>>>>>>>This has been my battle for the last three months.
>>>>>>>
>>>>>>>A little about my Jeep;
>>>>>>>Doug thorley header
>>>>>>>bored out 62mm throttle
>>>>>>>MSD ignition
>>>>>>>New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
>>>>>>>Curry Enterpise lift 33in tires, 4:10 gears, lockers
>>>>>>>
>>>>>>>What I have done to fix this so far;
>>>>>>>-Took it the dealer, they wouldn't touch it.
>>>>>>>-I currently have timing chain retarded -5 degree's due to pinging, cut
>>>>>>>down on backfiring.
>>>>>>>-I also had it advanced +5 degree's, caused a lot more backfiring.
>>>>>>>-I also ran the cam at TDC with no advance or timing. This is the
>>>>>>>original way I built it.
>>>>>>>-Changed TPS
>>>>>>>-Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
>>>>>>>ignition which I disconnected and the Jeep barely ran. Connected it
>>>>>>>back up and seems to be the only thing keeping it running. So I know
>>>>>>>the MSD works -changed O2 sensors -changed fuel pump and filters in
>>>>>>>tank, gas cap to.
>>>>>>>-Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
>>>>>>>an air/fuel ratio gauge on it.
>>>>>>>
>>>>>>>So my latest attempt to get this thing running right truely has me
>>>>>>>scratching my head, I left the TPS wire connected disconnected, drove
>>>>>>>it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
>>>>>>>hesitate or ping or miss or run rich. It runs great, I can drive it on
>>>>>>>the freeway now.
>>>>>>>
>>>>>>>I am on my last leg with this thing. Anyone have any ideas or
>>>>>>>suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

On Mon, 30 Oct 2006 01:22:21 GMT, Jeffrey DeWitt
<JeffDeWitt@nc.rr.com> wrote:

>I went through this a while back after replacing a distributor cap, it
>was driving me nuts because the engine started fine and while it seemed
>a bit off it only ran a little rough until I gave it some gas and
>brought the revs up, then it started spitting, backfiring and raising a
>fuss. As first I thought it was a vacuum leak but it turned out to be
>the wires were one position off.


>
>If the TPS isn't functioning how does the FI system know how much fuel
>to deliver? With a carburatorated engine the vacuum naturally would
>pull more fuel out of the jets, but with FI something has to tell the
>computer.

MAP sensor.

>
>Will the computer figure something out from the 02 sensor telling it the
>engine is running too lean?

With no TPS it's gonna be in open loop, using a pre programmed
strategy. The PCM is ignoring the O2 at this point.


>
>Jeff DeWitt
>
>bllsht wrote:
>> There is a big difference between not being able to compute the
>> optimal fuel and timing demands (no TPS signal), and having spark in
>> the wrong cylinder and no spark in the right cylinder.
>>
>> You don't need a TPS to start the engine. You do need spark in the
>> right cylinder.
>>
>> On Sun, 29 Oct 2006 21:41:32 GMT, Jeffrey DeWitt
>> <JeffDeWitt@nc.rr.com> wrote:
>>
>>
>>>It seems at least as likely as the thing running with the TPS unplugged!
>>> THAT one I don't understand at all.
>>>
>>>Jeff DeWitt
>>>
>>>bllsht wrote:
>>>
>>>>Not likely. If it ran at all in that condition, unplugging the TPS
>>>>wouldn't improve it.
>>>>
>>>>On Sun, 29 Oct 2006 13:30:11 GMT, Jeffrey DeWitt
>>>><JeffDeWitt@nc.rr.com> wrote:
>>>>
>>>>
>>>>
>>>>>That's a good point, could you have put the wires on the distributor cap
>>>>>one position off? I've done that and the engine will run, but sounds
>>>>>off and backfires when revved.
>>>>>
>>>>>Jeff DeWitt
>>>>>
>>>>>bllsht wrote:
>>>>>
>>>>>
>>>>>>First thing that came to my mind is that you may have the distributor
>>>>>>indexed incorrectly.
>>>>>>
>>>>>>With cyl. 1 at TDC, the trailing edge of the ign. rotor should be
>>>>>>about .020" PAST the #1 post in the distributor cap.
>>>>>>
>>>>>>With the TPS disconnected, the PCM may not be advancing the timing and
>>>>>>that may be enough for it to 'fire' the correct post.
>>>>>>
>>>>>>In other words, the rotor isn't pointing in the right direction when
>>>>>>the PCM fires the coil.
>>>>>>
>>>>>>
>>>>>>
>>>>>>On 28 Oct 2006 12:31:01 -0700, "jeepinacreek"
>>>>>><jeepinacreek@hotmail.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
>>>>>>>was a great mod with out totaly stroking the motor. After completing
>>>>>>>the buildup and starting it for the first time, I thought great it
>>>>>>>runs. Then I ran up and it starting backfiring at around 1800+ RPM.
>>>>>>>This has been my battle for the last three months.
>>>>>>>
>>>>>>>A little about my Jeep;
>>>>>>>Doug thorley header
>>>>>>>bored out 62mm throttle
>>>>>>>MSD ignition
>>>>>>>New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
>>>>>>>Curry Enterpise lift 33in tires, 4:10 gears, lockers
>>>>>>>
>>>>>>>What I have done to fix this so far;
>>>>>>>-Took it the dealer, they wouldn't touch it.
>>>>>>>-I currently have timing chain retarded -5 degree's due to pinging, cut
>>>>>>>down on backfiring.
>>>>>>>-I also had it advanced +5 degree's, caused a lot more backfiring.
>>>>>>>-I also ran the cam at TDC with no advance or timing. This is the
>>>>>>>original way I built it.
>>>>>>>-Changed TPS
>>>>>>>-Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
>>>>>>>ignition which I disconnected and the Jeep barely ran. Connected it
>>>>>>>back up and seems to be the only thing keeping it running. So I know
>>>>>>>the MSD works -changed O2 sensors -changed fuel pump and filters in
>>>>>>>tank, gas cap to.
>>>>>>>-Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
>>>>>>>an air/fuel ratio gauge on it.
>>>>>>>
>>>>>>>So my latest attempt to get this thing running right truely has me
>>>>>>>scratching my head, I left the TPS wire connected disconnected, drove
>>>>>>>it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
>>>>>>>hesitate or ping or miss or run rich. It runs great, I can drive it on
>>>>>>>the freeway now.
>>>>>>>
>>>>>>>I am on my last leg with this thing. Anyone have any ideas or
>>>>>>>suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

On Mon, 30 Oct 2006 01:22:21 GMT, Jeffrey DeWitt
<JeffDeWitt@nc.rr.com> wrote:

>I went through this a while back after replacing a distributor cap, it
>was driving me nuts because the engine started fine and while it seemed
>a bit off it only ran a little rough until I gave it some gas and
>brought the revs up, then it started spitting, backfiring and raising a
>fuss. As first I thought it was a vacuum leak but it turned out to be
>the wires were one position off.


>
>If the TPS isn't functioning how does the FI system know how much fuel
>to deliver? With a carburatorated engine the vacuum naturally would
>pull more fuel out of the jets, but with FI something has to tell the
>computer.

MAP sensor.

>
>Will the computer figure something out from the 02 sensor telling it the
>engine is running too lean?

With no TPS it's gonna be in open loop, using a pre programmed
strategy. The PCM is ignoring the O2 at this point.


>
>Jeff DeWitt
>
>bllsht wrote:
>> There is a big difference between not being able to compute the
>> optimal fuel and timing demands (no TPS signal), and having spark in
>> the wrong cylinder and no spark in the right cylinder.
>>
>> You don't need a TPS to start the engine. You do need spark in the
>> right cylinder.
>>
>> On Sun, 29 Oct 2006 21:41:32 GMT, Jeffrey DeWitt
>> <JeffDeWitt@nc.rr.com> wrote:
>>
>>
>>>It seems at least as likely as the thing running with the TPS unplugged!
>>> THAT one I don't understand at all.
>>>
>>>Jeff DeWitt
>>>
>>>bllsht wrote:
>>>
>>>>Not likely. If it ran at all in that condition, unplugging the TPS
>>>>wouldn't improve it.
>>>>
>>>>On Sun, 29 Oct 2006 13:30:11 GMT, Jeffrey DeWitt
>>>><JeffDeWitt@nc.rr.com> wrote:
>>>>
>>>>
>>>>
>>>>>That's a good point, could you have put the wires on the distributor cap
>>>>>one position off? I've done that and the engine will run, but sounds
>>>>>off and backfires when revved.
>>>>>
>>>>>Jeff DeWitt
>>>>>
>>>>>bllsht wrote:
>>>>>
>>>>>
>>>>>>First thing that came to my mind is that you may have the distributor
>>>>>>indexed incorrectly.
>>>>>>
>>>>>>With cyl. 1 at TDC, the trailing edge of the ign. rotor should be
>>>>>>about .020" PAST the #1 post in the distributor cap.
>>>>>>
>>>>>>With the TPS disconnected, the PCM may not be advancing the timing and
>>>>>>that may be enough for it to 'fire' the correct post.
>>>>>>
>>>>>>In other words, the rotor isn't pointing in the right direction when
>>>>>>the PCM fires the coil.
>>>>>>
>>>>>>
>>>>>>
>>>>>>On 28 Oct 2006 12:31:01 -0700, "jeepinacreek"
>>>>>><jeepinacreek@hotmail.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
>>>>>>>was a great mod with out totaly stroking the motor. After completing
>>>>>>>the buildup and starting it for the first time, I thought great it
>>>>>>>runs. Then I ran up and it starting backfiring at around 1800+ RPM.
>>>>>>>This has been my battle for the last three months.
>>>>>>>
>>>>>>>A little about my Jeep;
>>>>>>>Doug thorley header
>>>>>>>bored out 62mm throttle
>>>>>>>MSD ignition
>>>>>>>New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
>>>>>>>Curry Enterpise lift 33in tires, 4:10 gears, lockers
>>>>>>>
>>>>>>>What I have done to fix this so far;
>>>>>>>-Took it the dealer, they wouldn't touch it.
>>>>>>>-I currently have timing chain retarded -5 degree's due to pinging, cut
>>>>>>>down on backfiring.
>>>>>>>-I also had it advanced +5 degree's, caused a lot more backfiring.
>>>>>>>-I also ran the cam at TDC with no advance or timing. This is the
>>>>>>>original way I built it.
>>>>>>>-Changed TPS
>>>>>>>-Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
>>>>>>>ignition which I disconnected and the Jeep barely ran. Connected it
>>>>>>>back up and seems to be the only thing keeping it running. So I know
>>>>>>>the MSD works -changed O2 sensors -changed fuel pump and filters in
>>>>>>>tank, gas cap to.
>>>>>>>-Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
>>>>>>>an air/fuel ratio gauge on it.
>>>>>>>
>>>>>>>So my latest attempt to get this thing running right truely has me
>>>>>>>scratching my head, I left the TPS wire connected disconnected, drove
>>>>>>>it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
>>>>>>>hesitate or ping or miss or run rich. It runs great, I can drive it on
>>>>>>>the freeway now.
>>>>>>>
>>>>>>>I am on my last leg with this thing. Anyone have any ideas or
>>>>>>>suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

you have to set the timing gears bac to straight up and then you have to
properly resync the dist(.need factory manual for procedure) and get the dist
rotor past #1 cylinder tower of the dist.cap to get it in the correct place
even if it means spinning oil pump drive a hair and it should drop in

"L.W.(Bill) ------ III" wrote:

> I am a total loss as to how it would run without the Crankshaft
> Position Sensor. It should default into the safe mode, with no spark
> advance. Maybe you have your distributor installed in such a way so that
> it's Cam Position Sensor somehow takes over??????? What's the timing
> light show, initial and total?
> God Bless America, Bill O|||||||O
> mailto:-------------------- http://www.----------.com/
>
> jeepinacreek wrote:
> >
> > I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
> > was a great mod with out totaly stroking the motor. After completing
> > the buildup and starting it for the first time, I thought great it
> > runs. Then I ran up and it starting backfiring at around 1800+ RPM.
> > This has been my battle for the last three months.
> >
> > A little about my Jeep;
> > Doug thorley header
> > bored out 62mm throttle
> > MSD ignition
> > New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
> > Curry Enterpise lift 33in tires, 4:10 gears, lockers
> >
> > What I have done to fix this so far;
> > -Took it the dealer, they wouldn't touch it.
> > -I currently have timing chain retarded -5 degree's due to pinging, cut
> > down on backfiring.
> > -I also had it advanced +5 degree's, caused a lot more backfiring.
> > -I also ran the cam at TDC with no advance or timing. This is the
> > original way I built it.
> > -Changed TPS
> > -Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
> > ignition which I disconnected and the Jeep barely ran. Connected it
> > back up and seems to be the only thing keeping it running. So I know
> > the MSD works -changed O2 sensors -changed fuel pump and filters in
> > tank, gas cap to.
> > -Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
> > an air/fuel ratio gauge on it.
> >
> > So my latest attempt to get this thing running right truely has me
> > scratching my head, I left the TPS wire connected disconnected, drove
> > it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
> > hesitate or ping or miss or run rich. It runs great, I can drive it on
> > the freeway now.
> >
> > I am on my last leg with this thing. Anyone have any ideas or
> > suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

you have to set the timing gears bac to straight up and then you have to
properly resync the dist(.need factory manual for procedure) and get the dist
rotor past #1 cylinder tower of the dist.cap to get it in the correct place
even if it means spinning oil pump drive a hair and it should drop in

"L.W.(Bill) ------ III" wrote:

> I am a total loss as to how it would run without the Crankshaft
> Position Sensor. It should default into the safe mode, with no spark
> advance. Maybe you have your distributor installed in such a way so that
> it's Cam Position Sensor somehow takes over??????? What's the timing
> light show, initial and total?
> God Bless America, Bill O|||||||O
> mailto:-------------------- http://www.----------.com/
>
> jeepinacreek wrote:
> >
> > I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
> > was a great mod with out totaly stroking the motor. After completing
> > the buildup and starting it for the first time, I thought great it
> > runs. Then I ran up and it starting backfiring at around 1800+ RPM.
> > This has been my battle for the last three months.
> >
> > A little about my Jeep;
> > Doug thorley header
> > bored out 62mm throttle
> > MSD ignition
> > New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
> > Curry Enterpise lift 33in tires, 4:10 gears, lockers
> >
> > What I have done to fix this so far;
> > -Took it the dealer, they wouldn't touch it.
> > -I currently have timing chain retarded -5 degree's due to pinging, cut
> > down on backfiring.
> > -I also had it advanced +5 degree's, caused a lot more backfiring.
> > -I also ran the cam at TDC with no advance or timing. This is the
> > original way I built it.
> > -Changed TPS
> > -Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
> > ignition which I disconnected and the Jeep barely ran. Connected it
> > back up and seems to be the only thing keeping it running. So I know
> > the MSD works -changed O2 sensors -changed fuel pump and filters in
> > tank, gas cap to.
> > -Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
> > an air/fuel ratio gauge on it.
> >
> > So my latest attempt to get this thing running right truely has me
> > scratching my head, I left the TPS wire connected disconnected, drove
> > it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
> > hesitate or ping or miss or run rich. It runs great, I can drive it on
> > the freeway now.
> >
> > I am on my last leg with this thing. Anyone have any ideas or
> > suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

you have to set the timing gears bac to straight up and then you have to
properly resync the dist(.need factory manual for procedure) and get the dist
rotor past #1 cylinder tower of the dist.cap to get it in the correct place
even if it means spinning oil pump drive a hair and it should drop in

"L.W.(Bill) ------ III" wrote:

> I am a total loss as to how it would run without the Crankshaft
> Position Sensor. It should default into the safe mode, with no spark
> advance. Maybe you have your distributor installed in such a way so that
> it's Cam Position Sensor somehow takes over??????? What's the timing
> light show, initial and total?
> God Bless America, Bill O|||||||O
> mailto:-------------------- http://www.----------.com/
>
> jeepinacreek wrote:
> >
> > I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
> > was a great mod with out totaly stroking the motor. After completing
> > the buildup and starting it for the first time, I thought great it
> > runs. Then I ran up and it starting backfiring at around 1800+ RPM.
> > This has been my battle for the last three months.
> >
> > A little about my Jeep;
> > Doug thorley header
> > bored out 62mm throttle
> > MSD ignition
> > New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
> > Curry Enterpise lift 33in tires, 4:10 gears, lockers
> >
> > What I have done to fix this so far;
> > -Took it the dealer, they wouldn't touch it.
> > -I currently have timing chain retarded -5 degree's due to pinging, cut
> > down on backfiring.
> > -I also had it advanced +5 degree's, caused a lot more backfiring.
> > -I also ran the cam at TDC with no advance or timing. This is the
> > original way I built it.
> > -Changed TPS
> > -Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
> > ignition which I disconnected and the Jeep barely ran. Connected it
> > back up and seems to be the only thing keeping it running. So I know
> > the MSD works -changed O2 sensors -changed fuel pump and filters in
> > tank, gas cap to.
> > -Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
> > an air/fuel ratio gauge on it.
> >
> > So my latest attempt to get this thing running right truely has me
> > scratching my head, I left the TPS wire connected disconnected, drove
> > it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
> > hesitate or ping or miss or run rich. It runs great, I can drive it on
> > the freeway now.
> >
> > I am on my last leg with this thing. Anyone have any ideas or
> > suggestions?????? Please help or i may put the stock cam back in.

Re: New Cam, Jeep will only run without TPS
 

are u in michigan by any chance???

"L.W.(Bill) ------ III" wrote:

> I am a total loss as to how it would run without the Crankshaft
> Position Sensor. It should default into the safe mode, with no spark
> advance. Maybe you have your distributor installed in such a way so that
> it's Cam Position Sensor somehow takes over??????? What's the timing
> light show, initial and total?
> God Bless America, Bill O|||||||O
> mailto:-------------------- http://www.----------.com/
>
> jeepinacreek wrote:
> >
> > I recently put a new cam in my 1997 Jeep Wrangler 4.0L. I figured it
> > was a great mod with out totaly stroking the motor. After completing
> > the buildup and starting it for the first time, I thought great it
> > runs. Then I ran up and it starting backfiring at around 1800+ RPM.
> > This has been my battle for the last three months.
> >
> > A little about my Jeep;
> > Doug thorley header
> > bored out 62mm throttle
> > MSD ignition
> > New catalatic convertor, Flowmaster 50 exhaust Cold air intake 4in
> > Curry Enterpise lift 33in tires, 4:10 gears, lockers
> >
> > What I have done to fix this so far;
> > -Took it the dealer, they wouldn't touch it.
> > -I currently have timing chain retarded -5 degree's due to pinging, cut
> > down on backfiring.
> > -I also had it advanced +5 degree's, caused a lot more backfiring.
> > -I also ran the cam at TDC with no advance or timing. This is the
> > original way I built it.
> > -Changed TPS
> > -Changed spark plugs, wires, cap, rotor, and coil. Currently run MSD
> > ignition which I disconnected and the Jeep barely ran. Connected it
> > back up and seems to be the only thing keeping it running. So I know
> > the MSD works -changed O2 sensors -changed fuel pump and filters in
> > tank, gas cap to.
> > -Changed fuel injecters to 21LB injectors, stock is around 23.5LB -Put
> > an air/fuel ratio gauge on it.
> >
> > So my latest attempt to get this thing running right truely has me
> > scratching my head, I left the TPS wire connected disconnected, drove
> > it and it runs fine. No backfire at 1800+ RPM, it doesn't surge,
> > hesitate or ping or miss or run rich. It runs great, I can drive it on
> > the freeway now.
> >
> > I am on my last leg with this thing. Anyone have any ideas or
> > suggestions?????? Please help or i may put the stock cam back in.