Re: 1994 YJ Help! Is the computer the problem
 

How about the gas tank vent on those? That would be the charcoal
canister... If you open the gas cap and it goes whoosh and then it runs
ok again, the air filter on the gas tank vent is plugged up with mud or
dirt or just too old.

On a 94... Gas filter? Does it have one on the frame rail just in front
of the tank? If so, I would change that too....

Worn away new HT wires, as in pleural!!!!! Say what????????

That just plain isn't supposed to happen. Ever. Something is seriously
wrong with those wires....

If the core was exposed on the coil wire or any other, they are dead
wires and need to be replaced. If the insulation is falling off, it
didn't cure or was a bad mix or something.

I would just plain take those wires back and get new ones. That could
be all your latest issues.

Mike

aj wrote:
>
> Thanks for the suggestion, but my problem is still there. I made it
> 11.4 miles this time.. I got some contact cleaner and grease. I
> cleaned the contacts on every sensor I could find. In my search I
> found a wire that the insulation had worn off, fixed that. I also
> found the insulation on the coil lead of my new set of wires was warn
> away in one spot. I am not sure just how this happened but it could
> have been when the dealer or mechanic connect computer or timing light.
>
> Mike Romain wrote:
> > The 4.2 is a carburetor engine so you are going to get all kinds of
> > wrong advise....
> >
> > You later state it is a 2.5.....
> >
> > I would be suspecting the electrical connections on the throttle body.
> > When they get corroded, the gas pedal response can act like you
> > describe.
> >
> > The pins are very small computer signal pins and can look perfectly
> > clean but be corroded enough to interfere with the signal.
> >
> > I recommend a good clean of every sensor connection you can get your
> > hands on with a spray contact cleaner. I then use dielectric grease on
> > the plug's seal skirts. The best spray is sold at electronic shops, but
> > in a pinch, WD40 will work as an electrical cleaner.
> >
> > I would try the clean before tossing any expensive parts at it.
> >
> > A massive vacuum leak at the TB is just plain -------- I am sorry to
> > tell you. A vacuum leak at the TB causes 'high' idle, not low idle,
> > they lied to you.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> > Canadian Off Road Trips Photos: Non members can still view!
> > Aug./05 http://www.imagestation.com/album/in...?id=2120343242
> > (More Off Road album links at bottom of the view page)
> >
> > aj wrote:
> > >
> > > My 94 YJ 4.2L MPFI, 104000 miles started acting up a few weeks ago. It
> > > has since been to the my local mechanic and the dealer. The problem
> > > starts after 14 to 20 miles of driving. The engine starts running a
> > > little rough just barely noticeable until you push in the clutch. Then
> > > the idle drops off very quickly to about 200 to 300 rpm. When you let
> > > out the clutch and give it the gas its like driving into a very strong
> > > head wind. If you push on most of the time the engine will surge a
> > > couple of times and start running ok again. I have had the problem
> > > show up both when the engine was cold but mostly it happens after
> > > driving it a while. Once the problem occurs if you rev the engine from
> > > idle it will backfire out the throttle body. The timing appears to be
> > > advanced. There are no codes stored except the usual 12, 33 (I dont
> > > have AC). I have listened to the injectors with a mechanics
> > > stethoscope and they are all just clicking away.
> > >
> > > My mechanic thinks it's the computer, but from what I have read here
> > > computers dont go bad very often. I brought it to the dealer for a
> > > diagnostic they found a massive vacuum leak at the throttle body and
> > > replaced. They also suggested the cat converter may be bad.
> > >
> > > The dealer said the compression was good and my mechanic said he
> > > checked the grounds.
> > >
> > > I have replaced
> > > Rotor
> > > Distrib Cap
> > > Plug Wires
> > > Coil
> > > Plugs
> > > Radiator (it needed it lots of fins were gone)
> > > Coolant Temperature Sensor
> > > Vehicle Speed Sensor
> > > Throttle body
> > > Cat Converter
> > > Oil
> > > Oil Filter
> > > I have also added a bottle of fuel injector cleaner in the gas.
> > >
> > > When its not acting up it runs like a dream, all kinds of power,
> > > well at least for a 4.2L. I really dont want to replace this one I just
> > > got it setup the way I wanted it.
> > >
> > > The computer is next.
> > >
> > > Does anyone have any ideas.

Re: 1994 YJ Help! Is the computer the problem
 

How about the gas tank vent on those? That would be the charcoal
canister... If you open the gas cap and it goes whoosh and then it runs
ok again, the air filter on the gas tank vent is plugged up with mud or
dirt or just too old.

On a 94... Gas filter? Does it have one on the frame rail just in front
of the tank? If so, I would change that too....

Worn away new HT wires, as in pleural!!!!! Say what????????

That just plain isn't supposed to happen. Ever. Something is seriously
wrong with those wires....

If the core was exposed on the coil wire or any other, they are dead
wires and need to be replaced. If the insulation is falling off, it
didn't cure or was a bad mix or something.

I would just plain take those wires back and get new ones. That could
be all your latest issues.

Mike

aj wrote:
>
> Thanks for the suggestion, but my problem is still there. I made it
> 11.4 miles this time.. I got some contact cleaner and grease. I
> cleaned the contacts on every sensor I could find. In my search I
> found a wire that the insulation had worn off, fixed that. I also
> found the insulation on the coil lead of my new set of wires was warn
> away in one spot. I am not sure just how this happened but it could
> have been when the dealer or mechanic connect computer or timing light.
>
> Mike Romain wrote:
> > The 4.2 is a carburetor engine so you are going to get all kinds of
> > wrong advise....
> >
> > You later state it is a 2.5.....
> >
> > I would be suspecting the electrical connections on the throttle body.
> > When they get corroded, the gas pedal response can act like you
> > describe.
> >
> > The pins are very small computer signal pins and can look perfectly
> > clean but be corroded enough to interfere with the signal.
> >
> > I recommend a good clean of every sensor connection you can get your
> > hands on with a spray contact cleaner. I then use dielectric grease on
> > the plug's seal skirts. The best spray is sold at electronic shops, but
> > in a pinch, WD40 will work as an electrical cleaner.
> >
> > I would try the clean before tossing any expensive parts at it.
> >
> > A massive vacuum leak at the TB is just plain -------- I am sorry to
> > tell you. A vacuum leak at the TB causes 'high' idle, not low idle,
> > they lied to you.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> > Canadian Off Road Trips Photos: Non members can still view!
> > Aug./05 http://www.imagestation.com/album/in...?id=2120343242
> > (More Off Road album links at bottom of the view page)
> >
> > aj wrote:
> > >
> > > My 94 YJ 4.2L MPFI, 104000 miles started acting up a few weeks ago. It
> > > has since been to the my local mechanic and the dealer. The problem
> > > starts after 14 to 20 miles of driving. The engine starts running a
> > > little rough just barely noticeable until you push in the clutch. Then
> > > the idle drops off very quickly to about 200 to 300 rpm. When you let
> > > out the clutch and give it the gas its like driving into a very strong
> > > head wind. If you push on most of the time the engine will surge a
> > > couple of times and start running ok again. I have had the problem
> > > show up both when the engine was cold but mostly it happens after
> > > driving it a while. Once the problem occurs if you rev the engine from
> > > idle it will backfire out the throttle body. The timing appears to be
> > > advanced. There are no codes stored except the usual 12, 33 (I dont
> > > have AC). I have listened to the injectors with a mechanics
> > > stethoscope and they are all just clicking away.
> > >
> > > My mechanic thinks it's the computer, but from what I have read here
> > > computers dont go bad very often. I brought it to the dealer for a
> > > diagnostic they found a massive vacuum leak at the throttle body and
> > > replaced. They also suggested the cat converter may be bad.
> > >
> > > The dealer said the compression was good and my mechanic said he
> > > checked the grounds.
> > >
> > > I have replaced
> > > Rotor
> > > Distrib Cap
> > > Plug Wires
> > > Coil
> > > Plugs
> > > Radiator (it needed it lots of fins were gone)
> > > Coolant Temperature Sensor
> > > Vehicle Speed Sensor
> > > Throttle body
> > > Cat Converter
> > > Oil
> > > Oil Filter
> > > I have also added a bottle of fuel injector cleaner in the gas.
> > >
> > > When its not acting up it runs like a dream, all kinds of power,
> > > well at least for a 4.2L. I really dont want to replace this one I just
> > > got it setup the way I wanted it.
> > >
> > > The computer is next.
> > >
> > > Does anyone have any ideas.

Re: 1994 YJ Help! Is the computer the problem
 

I replaced the fuel filter still the same problem. I also checked gas
cap for the whoosh no whoosh.

I am not going to be able to work on it again until this weekend, gotta
go back to work so I can pay for all these sensors.
I will be checking the fuel pressure this weekend. If thats not it
guess the next sensor will be either the camshaft position sensor or
the crank position sensor?
I did think about the crank position sensor. Everything I have found
so far says you won't be able to start with a bad crank sensor. I am
currently able to get it started, give me some time and I am sure I
can make it not start.

Thanks again for all the help,
If you have any other ideas I am more than willing to give them a try.

Re: 1994 YJ Help! Is the computer the problem
 

I replaced the fuel filter still the same problem. I also checked gas
cap for the whoosh no whoosh.

I am not going to be able to work on it again until this weekend, gotta
go back to work so I can pay for all these sensors.
I will be checking the fuel pressure this weekend. If thats not it
guess the next sensor will be either the camshaft position sensor or
the crank position sensor?
I did think about the crank position sensor. Everything I have found
so far says you won't be able to start with a bad crank sensor. I am
currently able to get it started, give me some time and I am sure I
can make it not start.

Thanks again for all the help,
If you have any other ideas I am more than willing to give them a try.

Re: 1994 YJ Help! Is the computer the problem
 

I replaced the fuel filter still the same problem. I also checked gas
cap for the whoosh no whoosh.

I am not going to be able to work on it again until this weekend, gotta
go back to work so I can pay for all these sensors.
I will be checking the fuel pressure this weekend. If thats not it
guess the next sensor will be either the camshaft position sensor or
the crank position sensor?
I did think about the crank position sensor. Everything I have found
so far says you won't be able to start with a bad crank sensor. I am
currently able to get it started, give me some time and I am sure I
can make it not start.

Thanks again for all the help,
If you have any other ideas I am more than willing to give them a try.

Re: 1994 YJ Help! Is the computer the problem
 

Were I a betting man, my money would be on the fuel pump, but I work too
hard for my money to burn it up gambling.

Before you pony up for a CPS and go through the pain of replacing it,
grab a Chilton's and see if there isn't a diagnostic you can run on it
with an ohm meter. For some model years you could check it and see if
you were getting the couple of hundred ohms the spec called for.

I gather that usually when the CPS goes it is dead dead dead. You get
no spark and no fault codes (at least in older models) -- because the
computer doesn't know the engine is spinning over. But something I read
recently was about finding an intermittant break at the CPS connector --
in one position it would run fine, in another the wire would open up
just enough to make it run crappy and stall frequently. Just something
to keep in mind.


aj wrote:
> I replaced the fuel filter still the same problem. I also checked gas
> cap for the whoosh no whoosh.
>
> I am not going to be able to work on it again until this weekend, gotta
> go back to work so I can pay for all these sensors.
> I will be checking the fuel pressure this weekend. If thats not it
> guess the next sensor will be either the camshaft position sensor or
> the crank position sensor?
> I did think about the crank position sensor. Everything I have found
> so far says you won't be able to start with a bad crank sensor. I am
> currently able to get it started, give me some time and I am sure I
> can make it not start.
>
> Thanks again for all the help,
> If you have any other ideas I am more than willing to give them a try.
>

Re: 1994 YJ Help! Is the computer the problem
 

Were I a betting man, my money would be on the fuel pump, but I work too
hard for my money to burn it up gambling.

Before you pony up for a CPS and go through the pain of replacing it,
grab a Chilton's and see if there isn't a diagnostic you can run on it
with an ohm meter. For some model years you could check it and see if
you were getting the couple of hundred ohms the spec called for.

I gather that usually when the CPS goes it is dead dead dead. You get
no spark and no fault codes (at least in older models) -- because the
computer doesn't know the engine is spinning over. But something I read
recently was about finding an intermittant break at the CPS connector --
in one position it would run fine, in another the wire would open up
just enough to make it run crappy and stall frequently. Just something
to keep in mind.


aj wrote:
> I replaced the fuel filter still the same problem. I also checked gas
> cap for the whoosh no whoosh.
>
> I am not going to be able to work on it again until this weekend, gotta
> go back to work so I can pay for all these sensors.
> I will be checking the fuel pressure this weekend. If thats not it
> guess the next sensor will be either the camshaft position sensor or
> the crank position sensor?
> I did think about the crank position sensor. Everything I have found
> so far says you won't be able to start with a bad crank sensor. I am
> currently able to get it started, give me some time and I am sure I
> can make it not start.
>
> Thanks again for all the help,
> If you have any other ideas I am more than willing to give them a try.
>

Re: 1994 YJ Help! Is the computer the problem
 

Were I a betting man, my money would be on the fuel pump, but I work too
hard for my money to burn it up gambling.

Before you pony up for a CPS and go through the pain of replacing it,
grab a Chilton's and see if there isn't a diagnostic you can run on it
with an ohm meter. For some model years you could check it and see if
you were getting the couple of hundred ohms the spec called for.

I gather that usually when the CPS goes it is dead dead dead. You get
no spark and no fault codes (at least in older models) -- because the
computer doesn't know the engine is spinning over. But something I read
recently was about finding an intermittant break at the CPS connector --
in one position it would run fine, in another the wire would open up
just enough to make it run crappy and stall frequently. Just something
to keep in mind.


aj wrote:
> I replaced the fuel filter still the same problem. I also checked gas
> cap for the whoosh no whoosh.
>
> I am not going to be able to work on it again until this weekend, gotta
> go back to work so I can pay for all these sensors.
> I will be checking the fuel pressure this weekend. If thats not it
> guess the next sensor will be either the camshaft position sensor or
> the crank position sensor?
> I did think about the crank position sensor. Everything I have found
> so far says you won't be able to start with a bad crank sensor. I am
> currently able to get it started, give me some time and I am sure I
> can make it not start.
>
> Thanks again for all the help,
> If you have any other ideas I am more than willing to give them a try.
>

Re: 1994 YJ Help! Is the computer the problem
 

Its fixed!
It was an intermittent Crank Position Sensor.
It didn't set a code and tests with an ohm meter were within spec.
Since it was the cheapest of all fixes in my current list of guesses I
figured I would try a new one anyway.
Went to the parts store got a cheap after market - figured it would
work well enough.
Crawled under the jeep with my socket wrench.
Now for the interesting part, when I went to loosen the bolts, those
bolts turned Real easy. Not finger tight but it sure wasn't the 14 ft.
lbs. of torque suggested. Once I got the CPS out I found very slight
scores on the face. Not knowing the tolerances between the sensor and
the flywheel, I can only guess that it had contacted the flywheel at
some point.
Since these things seem to be really sensitive, I suspect because the
sensor was loose it would move out of position. Then the computer
couldn't figure out what was going on. I can't explain why it seemed
to be only after it warmed up (all but one time).

One good thing did come out of all this, my jeep has NEVER run as good
as it is running right now. I have a hard time not turning the tires
over at the stop signs. I don't know if I am just not use to all this
new power or that there is a 1/4 inch of ice on everything up here in
Vermont ;)

Hope I am able to return the favor some day.
GoodOnYa...! All

Re: 1994 YJ Help! Is the computer the problem
 

Its fixed!
It was an intermittent Crank Position Sensor.
It didn't set a code and tests with an ohm meter were within spec.
Since it was the cheapest of all fixes in my current list of guesses I
figured I would try a new one anyway.
Went to the parts store got a cheap after market - figured it would
work well enough.
Crawled under the jeep with my socket wrench.
Now for the interesting part, when I went to loosen the bolts, those
bolts turned Real easy. Not finger tight but it sure wasn't the 14 ft.
lbs. of torque suggested. Once I got the CPS out I found very slight
scores on the face. Not knowing the tolerances between the sensor and
the flywheel, I can only guess that it had contacted the flywheel at
some point.
Since these things seem to be really sensitive, I suspect because the
sensor was loose it would move out of position. Then the computer
couldn't figure out what was going on. I can't explain why it seemed
to be only after it warmed up (all but one time).

One good thing did come out of all this, my jeep has NEVER run as good
as it is running right now. I have a hard time not turning the tires
over at the stop signs. I don't know if I am just not use to all this
new power or that there is a 1/4 inch of ice on everything up here in
Vermont ;)

Hope I am able to return the favor some day.
GoodOnYa...! All