TJ 4.0 hestitates and surges - follow up x2 to Independent Mechanics
10-13-2007, 12:40 PM
#31
Guest
Posts: n/a
Re: TJ 4.0 hestitates and surges - follow up x2 to IndependentMechanics
need to hook up a fuel pressure gauge and see if it running at spec and has
volume it should also not blow any bubbles into a clear container
Rich wrote:
> THis might sound crazy, but i had a similar problem with my CJ. I has a 4.0
> head and MPFI. on cool mornings it would do the saem thing you describe
> until warmed up. By luck I had to remove the exhaust manifold to take care
> on another issue and when I put it back together everything ran fine. A few
> months later it started the cold stumble again. I remembered the manifold
> incident, so I removed it once more checked it for flatness across the
> flange and found it to be a bit out. Not much but enought to not get a
> perfect seal against the cylinder head. I had the exhaust manifold surfaced,
> and put a new exhaust gasket on... my troubles disappeared.
> I figure, the slight leak, whan cold allowed fresh air into the exhaust that
> threw off the O2 sensor reading making it rev then stumble...
> Worth checking into
>
> --
> Rich Harris
>
> "reboot" <reboot@nothere.com> wrote in message
> news:8o5ig3l1r7ivgsv7qd2lgphcc113dh4if8@4ax.com...
> > On Thu, 04 Oct 2007 00:14:27 -0400, reboot <reboot@nothere.com> wrote:
> >
> >>'99 TJ 4.0 Auto - within about 3 minutes of a cold start under part
> >>throttle (accelerating reasonably to 45 mph) the engine would start to
> >>stutter, hesitate and surge. water temperature gage shows the mid
> >>mark between cold and 210. when this happens and I open the throttle
> >>wide open it makes good power. on return to part throttle the
> >>hesitate and surge resumes. if i come to a stop while this is going
> >>on then the idle speed dips real low and sometimes stalls. runs very
> >>rough.
> >>
> >>if i drive it a few more minutes and get the water temperature all the
> >>way up it seems OK, smooth stable idle, smooth part throttle
> >>acceleration.
> >>
> >>in the first vista to the shop, they replaced the MAP sensor because
> >>it showed this code. took the truck back but the problem persisted.
> >>
> >>called the shop after this didn't fix the problem. they kept the
> >>truck overnight and tried it cold. didn't happen for them. they
> >>scanned the 'puter and no codes. they put in a set of plugs and
> >>replaced #6 spark plug wire because they said it looked corroded.
> >>
> >>told me drive it for a few weeks and call them back. if it fixed the
> >>problem we would discuss how much to pay for the 2nd visit. if it
> >>didn't ...
> >>
> >>so i've had the truck back a couple of weeks now and it happens pretty
> >>regularly. took it to Murray's this evening and hooked up a scanner -
> >>no codes, same as the shop with their good equipment and trained techs
> >>...
> >>
> >>suggestions?
> >>
> >>reboot
> >
> > well folks, i've tried many of the suggestions made w/o any success.
> >
> > i had all of the TSB / IAC / MAP / CPS and IAT electrical connectors
> > apart, cleaned both sides with QD Electronic Spray, blew them out w/
> > compressed air a re-assembled w/ dielectric silicone grease.
> >
> > i had the throttle body off and cleaned it and took apart the IAC on
> > the side and cleaned it., staining but no blockage.
> >
> > i checked the spark plug wires after dark with a spray bottle of water
> > and it looked good.
> >
> > the driving experience when it hesitates and surges is like it
> > momentary runs below the lean limit for combustion. when it
> > hesitates, if I go to WOT it catches and pulls hard. no more
> > hesitation happens at WOT. but if i take it back to part throttle the
> > condition re-occurs.
> >
> > from this I reason that the fuel rail pressure and injectors are OK -
> > if not then the problem would persist at WOT.
> >
> > i also deduce that it isn't a spark problem because the load on the
> > ignition system is greater at WOT than part throttle and it runs fine
> > at WOT.
> >
> > if there is any problem with the TPS/MAP/IAT/IAC/CPS sensors would
> > they throw a code? in other words - can i have one of these sensors
> > bad and not find a code? (should i start back-probing them and
> > comparing the values to the FSM?)
> >
> > damn - the wife is starting to doubt my wisdom in buying this jeep
> > because it was 'simple and easy to maintain and repair' (my previous
> > words which I'm beginning to doubt).
> >
> > i;m reluctant to start swapping parts because of the expense and i
> > don't have confidence taking it back to the independent mechanic, they
> > couldn't find it before.
> >
> > reboot
> >
> >>
> >>---
> >>avast! Antivirus: Outbound message clean.
> >>Virus Database (VPS): 000778-2, 10/03/2007
> >>Tested on: 10/4/2007 12:14:28 AM
> >>avast! - copyright (c) 1988-2007 ALWIL Software.
> >>http://www.avast.com
> >>
> >>
> >
> >
> > ---
> > avast! Antivirus: Outbound message clean.
> > Virus Database (VPS): 000778-5, 10/06/2007
> > Tested on: 10/7/2007 1:41:47 PM
> > avast! - copyright (c) 1988-2007 ALWIL Software.
> > http://www.avast.com
> >
> >
> >
volume it should also not blow any bubbles into a clear container
Rich wrote:
> THis might sound crazy, but i had a similar problem with my CJ. I has a 4.0
> head and MPFI. on cool mornings it would do the saem thing you describe
> until warmed up. By luck I had to remove the exhaust manifold to take care
> on another issue and when I put it back together everything ran fine. A few
> months later it started the cold stumble again. I remembered the manifold
> incident, so I removed it once more checked it for flatness across the
> flange and found it to be a bit out. Not much but enought to not get a
> perfect seal against the cylinder head. I had the exhaust manifold surfaced,
> and put a new exhaust gasket on... my troubles disappeared.
> I figure, the slight leak, whan cold allowed fresh air into the exhaust that
> threw off the O2 sensor reading making it rev then stumble...
> Worth checking into
>
> --
> Rich Harris
>
> "reboot" <reboot@nothere.com> wrote in message
> news:8o5ig3l1r7ivgsv7qd2lgphcc113dh4if8@4ax.com...
> > On Thu, 04 Oct 2007 00:14:27 -0400, reboot <reboot@nothere.com> wrote:
> >
> >>'99 TJ 4.0 Auto - within about 3 minutes of a cold start under part
> >>throttle (accelerating reasonably to 45 mph) the engine would start to
> >>stutter, hesitate and surge. water temperature gage shows the mid
> >>mark between cold and 210. when this happens and I open the throttle
> >>wide open it makes good power. on return to part throttle the
> >>hesitate and surge resumes. if i come to a stop while this is going
> >>on then the idle speed dips real low and sometimes stalls. runs very
> >>rough.
> >>
> >>if i drive it a few more minutes and get the water temperature all the
> >>way up it seems OK, smooth stable idle, smooth part throttle
> >>acceleration.
> >>
> >>in the first vista to the shop, they replaced the MAP sensor because
> >>it showed this code. took the truck back but the problem persisted.
> >>
> >>called the shop after this didn't fix the problem. they kept the
> >>truck overnight and tried it cold. didn't happen for them. they
> >>scanned the 'puter and no codes. they put in a set of plugs and
> >>replaced #6 spark plug wire because they said it looked corroded.
> >>
> >>told me drive it for a few weeks and call them back. if it fixed the
> >>problem we would discuss how much to pay for the 2nd visit. if it
> >>didn't ...
> >>
> >>so i've had the truck back a couple of weeks now and it happens pretty
> >>regularly. took it to Murray's this evening and hooked up a scanner -
> >>no codes, same as the shop with their good equipment and trained techs
> >>...
> >>
> >>suggestions?
> >>
> >>reboot
> >
> > well folks, i've tried many of the suggestions made w/o any success.
> >
> > i had all of the TSB / IAC / MAP / CPS and IAT electrical connectors
> > apart, cleaned both sides with QD Electronic Spray, blew them out w/
> > compressed air a re-assembled w/ dielectric silicone grease.
> >
> > i had the throttle body off and cleaned it and took apart the IAC on
> > the side and cleaned it., staining but no blockage.
> >
> > i checked the spark plug wires after dark with a spray bottle of water
> > and it looked good.
> >
> > the driving experience when it hesitates and surges is like it
> > momentary runs below the lean limit for combustion. when it
> > hesitates, if I go to WOT it catches and pulls hard. no more
> > hesitation happens at WOT. but if i take it back to part throttle the
> > condition re-occurs.
> >
> > from this I reason that the fuel rail pressure and injectors are OK -
> > if not then the problem would persist at WOT.
> >
> > i also deduce that it isn't a spark problem because the load on the
> > ignition system is greater at WOT than part throttle and it runs fine
> > at WOT.
> >
> > if there is any problem with the TPS/MAP/IAT/IAC/CPS sensors would
> > they throw a code? in other words - can i have one of these sensors
> > bad and not find a code? (should i start back-probing them and
> > comparing the values to the FSM?)
> >
> > damn - the wife is starting to doubt my wisdom in buying this jeep
> > because it was 'simple and easy to maintain and repair' (my previous
> > words which I'm beginning to doubt).
> >
> > i;m reluctant to start swapping parts because of the expense and i
> > don't have confidence taking it back to the independent mechanic, they
> > couldn't find it before.
> >
> > reboot
> >
> >>
> >>---
> >>avast! Antivirus: Outbound message clean.
> >>Virus Database (VPS): 000778-2, 10/03/2007
> >>Tested on: 10/4/2007 12:14:28 AM
> >>avast! - copyright (c) 1988-2007 ALWIL Software.
> >>http://www.avast.com
> >>
> >>
> >
> >
> > ---
> > avast! Antivirus: Outbound message clean.
> > Virus Database (VPS): 000778-5, 10/06/2007
> > Tested on: 10/7/2007 1:41:47 PM
> > avast! - copyright (c) 1988-2007 ALWIL Software.
> > http://www.avast.com
> >
> >
> >
10-13-2007, 12:40 PM
#32
Guest
Posts: n/a
Re: TJ 4.0 hestitates and surges - follow up x2 to IndependentMechanics
need to hook up a fuel pressure gauge and see if it running at spec and has
volume it should also not blow any bubbles into a clear container
Rich wrote:
> THis might sound crazy, but i had a similar problem with my CJ. I has a 4.0
> head and MPFI. on cool mornings it would do the saem thing you describe
> until warmed up. By luck I had to remove the exhaust manifold to take care
> on another issue and when I put it back together everything ran fine. A few
> months later it started the cold stumble again. I remembered the manifold
> incident, so I removed it once more checked it for flatness across the
> flange and found it to be a bit out. Not much but enought to not get a
> perfect seal against the cylinder head. I had the exhaust manifold surfaced,
> and put a new exhaust gasket on... my troubles disappeared.
> I figure, the slight leak, whan cold allowed fresh air into the exhaust that
> threw off the O2 sensor reading making it rev then stumble...
> Worth checking into
>
> --
> Rich Harris
>
> "reboot" <reboot@nothere.com> wrote in message
> news:8o5ig3l1r7ivgsv7qd2lgphcc113dh4if8@4ax.com...
> > On Thu, 04 Oct 2007 00:14:27 -0400, reboot <reboot@nothere.com> wrote:
> >
> >>'99 TJ 4.0 Auto - within about 3 minutes of a cold start under part
> >>throttle (accelerating reasonably to 45 mph) the engine would start to
> >>stutter, hesitate and surge. water temperature gage shows the mid
> >>mark between cold and 210. when this happens and I open the throttle
> >>wide open it makes good power. on return to part throttle the
> >>hesitate and surge resumes. if i come to a stop while this is going
> >>on then the idle speed dips real low and sometimes stalls. runs very
> >>rough.
> >>
> >>if i drive it a few more minutes and get the water temperature all the
> >>way up it seems OK, smooth stable idle, smooth part throttle
> >>acceleration.
> >>
> >>in the first vista to the shop, they replaced the MAP sensor because
> >>it showed this code. took the truck back but the problem persisted.
> >>
> >>called the shop after this didn't fix the problem. they kept the
> >>truck overnight and tried it cold. didn't happen for them. they
> >>scanned the 'puter and no codes. they put in a set of plugs and
> >>replaced #6 spark plug wire because they said it looked corroded.
> >>
> >>told me drive it for a few weeks and call them back. if it fixed the
> >>problem we would discuss how much to pay for the 2nd visit. if it
> >>didn't ...
> >>
> >>so i've had the truck back a couple of weeks now and it happens pretty
> >>regularly. took it to Murray's this evening and hooked up a scanner -
> >>no codes, same as the shop with their good equipment and trained techs
> >>...
> >>
> >>suggestions?
> >>
> >>reboot
> >
> > well folks, i've tried many of the suggestions made w/o any success.
> >
> > i had all of the TSB / IAC / MAP / CPS and IAT electrical connectors
> > apart, cleaned both sides with QD Electronic Spray, blew them out w/
> > compressed air a re-assembled w/ dielectric silicone grease.
> >
> > i had the throttle body off and cleaned it and took apart the IAC on
> > the side and cleaned it., staining but no blockage.
> >
> > i checked the spark plug wires after dark with a spray bottle of water
> > and it looked good.
> >
> > the driving experience when it hesitates and surges is like it
> > momentary runs below the lean limit for combustion. when it
> > hesitates, if I go to WOT it catches and pulls hard. no more
> > hesitation happens at WOT. but if i take it back to part throttle the
> > condition re-occurs.
> >
> > from this I reason that the fuel rail pressure and injectors are OK -
> > if not then the problem would persist at WOT.
> >
> > i also deduce that it isn't a spark problem because the load on the
> > ignition system is greater at WOT than part throttle and it runs fine
> > at WOT.
> >
> > if there is any problem with the TPS/MAP/IAT/IAC/CPS sensors would
> > they throw a code? in other words - can i have one of these sensors
> > bad and not find a code? (should i start back-probing them and
> > comparing the values to the FSM?)
> >
> > damn - the wife is starting to doubt my wisdom in buying this jeep
> > because it was 'simple and easy to maintain and repair' (my previous
> > words which I'm beginning to doubt).
> >
> > i;m reluctant to start swapping parts because of the expense and i
> > don't have confidence taking it back to the independent mechanic, they
> > couldn't find it before.
> >
> > reboot
> >
> >>
> >>---
> >>avast! Antivirus: Outbound message clean.
> >>Virus Database (VPS): 000778-2, 10/03/2007
> >>Tested on: 10/4/2007 12:14:28 AM
> >>avast! - copyright (c) 1988-2007 ALWIL Software.
> >>http://www.avast.com
> >>
> >>
> >
> >
> > ---
> > avast! Antivirus: Outbound message clean.
> > Virus Database (VPS): 000778-5, 10/06/2007
> > Tested on: 10/7/2007 1:41:47 PM
> > avast! - copyright (c) 1988-2007 ALWIL Software.
> > http://www.avast.com
> >
> >
> >
volume it should also not blow any bubbles into a clear container
Rich wrote:
> THis might sound crazy, but i had a similar problem with my CJ. I has a 4.0
> head and MPFI. on cool mornings it would do the saem thing you describe
> until warmed up. By luck I had to remove the exhaust manifold to take care
> on another issue and when I put it back together everything ran fine. A few
> months later it started the cold stumble again. I remembered the manifold
> incident, so I removed it once more checked it for flatness across the
> flange and found it to be a bit out. Not much but enought to not get a
> perfect seal against the cylinder head. I had the exhaust manifold surfaced,
> and put a new exhaust gasket on... my troubles disappeared.
> I figure, the slight leak, whan cold allowed fresh air into the exhaust that
> threw off the O2 sensor reading making it rev then stumble...
> Worth checking into
>
> --
> Rich Harris
>
> "reboot" <reboot@nothere.com> wrote in message
> news:8o5ig3l1r7ivgsv7qd2lgphcc113dh4if8@4ax.com...
> > On Thu, 04 Oct 2007 00:14:27 -0400, reboot <reboot@nothere.com> wrote:
> >
> >>'99 TJ 4.0 Auto - within about 3 minutes of a cold start under part
> >>throttle (accelerating reasonably to 45 mph) the engine would start to
> >>stutter, hesitate and surge. water temperature gage shows the mid
> >>mark between cold and 210. when this happens and I open the throttle
> >>wide open it makes good power. on return to part throttle the
> >>hesitate and surge resumes. if i come to a stop while this is going
> >>on then the idle speed dips real low and sometimes stalls. runs very
> >>rough.
> >>
> >>if i drive it a few more minutes and get the water temperature all the
> >>way up it seems OK, smooth stable idle, smooth part throttle
> >>acceleration.
> >>
> >>in the first vista to the shop, they replaced the MAP sensor because
> >>it showed this code. took the truck back but the problem persisted.
> >>
> >>called the shop after this didn't fix the problem. they kept the
> >>truck overnight and tried it cold. didn't happen for them. they
> >>scanned the 'puter and no codes. they put in a set of plugs and
> >>replaced #6 spark plug wire because they said it looked corroded.
> >>
> >>told me drive it for a few weeks and call them back. if it fixed the
> >>problem we would discuss how much to pay for the 2nd visit. if it
> >>didn't ...
> >>
> >>so i've had the truck back a couple of weeks now and it happens pretty
> >>regularly. took it to Murray's this evening and hooked up a scanner -
> >>no codes, same as the shop with their good equipment and trained techs
> >>...
> >>
> >>suggestions?
> >>
> >>reboot
> >
> > well folks, i've tried many of the suggestions made w/o any success.
> >
> > i had all of the TSB / IAC / MAP / CPS and IAT electrical connectors
> > apart, cleaned both sides with QD Electronic Spray, blew them out w/
> > compressed air a re-assembled w/ dielectric silicone grease.
> >
> > i had the throttle body off and cleaned it and took apart the IAC on
> > the side and cleaned it., staining but no blockage.
> >
> > i checked the spark plug wires after dark with a spray bottle of water
> > and it looked good.
> >
> > the driving experience when it hesitates and surges is like it
> > momentary runs below the lean limit for combustion. when it
> > hesitates, if I go to WOT it catches and pulls hard. no more
> > hesitation happens at WOT. but if i take it back to part throttle the
> > condition re-occurs.
> >
> > from this I reason that the fuel rail pressure and injectors are OK -
> > if not then the problem would persist at WOT.
> >
> > i also deduce that it isn't a spark problem because the load on the
> > ignition system is greater at WOT than part throttle and it runs fine
> > at WOT.
> >
> > if there is any problem with the TPS/MAP/IAT/IAC/CPS sensors would
> > they throw a code? in other words - can i have one of these sensors
> > bad and not find a code? (should i start back-probing them and
> > comparing the values to the FSM?)
> >
> > damn - the wife is starting to doubt my wisdom in buying this jeep
> > because it was 'simple and easy to maintain and repair' (my previous
> > words which I'm beginning to doubt).
> >
> > i;m reluctant to start swapping parts because of the expense and i
> > don't have confidence taking it back to the independent mechanic, they
> > couldn't find it before.
> >
> > reboot
> >
> >>
> >>---
> >>avast! Antivirus: Outbound message clean.
> >>Virus Database (VPS): 000778-2, 10/03/2007
> >>Tested on: 10/4/2007 12:14:28 AM
> >>avast! - copyright (c) 1988-2007 ALWIL Software.
> >>http://www.avast.com
> >>
> >>
> >
> >
> > ---
> > avast! Antivirus: Outbound message clean.
> > Virus Database (VPS): 000778-5, 10/06/2007
> > Tested on: 10/7/2007 1:41:47 PM
> > avast! - copyright (c) 1988-2007 ALWIL Software.
> > http://www.avast.com
> >
> >
> >
10-13-2007, 12:40 PM
#33
Guest
Posts: n/a
Re: TJ 4.0 hestitates and surges - follow up x2 to IndependentMechanics
need to hook up a fuel pressure gauge and see if it running at spec and has
volume it should also not blow any bubbles into a clear container
Rich wrote:
> THis might sound crazy, but i had a similar problem with my CJ. I has a 4.0
> head and MPFI. on cool mornings it would do the saem thing you describe
> until warmed up. By luck I had to remove the exhaust manifold to take care
> on another issue and when I put it back together everything ran fine. A few
> months later it started the cold stumble again. I remembered the manifold
> incident, so I removed it once more checked it for flatness across the
> flange and found it to be a bit out. Not much but enought to not get a
> perfect seal against the cylinder head. I had the exhaust manifold surfaced,
> and put a new exhaust gasket on... my troubles disappeared.
> I figure, the slight leak, whan cold allowed fresh air into the exhaust that
> threw off the O2 sensor reading making it rev then stumble...
> Worth checking into
>
> --
> Rich Harris
>
> "reboot" <reboot@nothere.com> wrote in message
> news:8o5ig3l1r7ivgsv7qd2lgphcc113dh4if8@4ax.com...
> > On Thu, 04 Oct 2007 00:14:27 -0400, reboot <reboot@nothere.com> wrote:
> >
> >>'99 TJ 4.0 Auto - within about 3 minutes of a cold start under part
> >>throttle (accelerating reasonably to 45 mph) the engine would start to
> >>stutter, hesitate and surge. water temperature gage shows the mid
> >>mark between cold and 210. when this happens and I open the throttle
> >>wide open it makes good power. on return to part throttle the
> >>hesitate and surge resumes. if i come to a stop while this is going
> >>on then the idle speed dips real low and sometimes stalls. runs very
> >>rough.
> >>
> >>if i drive it a few more minutes and get the water temperature all the
> >>way up it seems OK, smooth stable idle, smooth part throttle
> >>acceleration.
> >>
> >>in the first vista to the shop, they replaced the MAP sensor because
> >>it showed this code. took the truck back but the problem persisted.
> >>
> >>called the shop after this didn't fix the problem. they kept the
> >>truck overnight and tried it cold. didn't happen for them. they
> >>scanned the 'puter and no codes. they put in a set of plugs and
> >>replaced #6 spark plug wire because they said it looked corroded.
> >>
> >>told me drive it for a few weeks and call them back. if it fixed the
> >>problem we would discuss how much to pay for the 2nd visit. if it
> >>didn't ...
> >>
> >>so i've had the truck back a couple of weeks now and it happens pretty
> >>regularly. took it to Murray's this evening and hooked up a scanner -
> >>no codes, same as the shop with their good equipment and trained techs
> >>...
> >>
> >>suggestions?
> >>
> >>reboot
> >
> > well folks, i've tried many of the suggestions made w/o any success.
> >
> > i had all of the TSB / IAC / MAP / CPS and IAT electrical connectors
> > apart, cleaned both sides with QD Electronic Spray, blew them out w/
> > compressed air a re-assembled w/ dielectric silicone grease.
> >
> > i had the throttle body off and cleaned it and took apart the IAC on
> > the side and cleaned it., staining but no blockage.
> >
> > i checked the spark plug wires after dark with a spray bottle of water
> > and it looked good.
> >
> > the driving experience when it hesitates and surges is like it
> > momentary runs below the lean limit for combustion. when it
> > hesitates, if I go to WOT it catches and pulls hard. no more
> > hesitation happens at WOT. but if i take it back to part throttle the
> > condition re-occurs.
> >
> > from this I reason that the fuel rail pressure and injectors are OK -
> > if not then the problem would persist at WOT.
> >
> > i also deduce that it isn't a spark problem because the load on the
> > ignition system is greater at WOT than part throttle and it runs fine
> > at WOT.
> >
> > if there is any problem with the TPS/MAP/IAT/IAC/CPS sensors would
> > they throw a code? in other words - can i have one of these sensors
> > bad and not find a code? (should i start back-probing them and
> > comparing the values to the FSM?)
> >
> > damn - the wife is starting to doubt my wisdom in buying this jeep
> > because it was 'simple and easy to maintain and repair' (my previous
> > words which I'm beginning to doubt).
> >
> > i;m reluctant to start swapping parts because of the expense and i
> > don't have confidence taking it back to the independent mechanic, they
> > couldn't find it before.
> >
> > reboot
> >
> >>
> >>---
> >>avast! Antivirus: Outbound message clean.
> >>Virus Database (VPS): 000778-2, 10/03/2007
> >>Tested on: 10/4/2007 12:14:28 AM
> >>avast! - copyright (c) 1988-2007 ALWIL Software.
> >>http://www.avast.com
> >>
> >>
> >
> >
> > ---
> > avast! Antivirus: Outbound message clean.
> > Virus Database (VPS): 000778-5, 10/06/2007
> > Tested on: 10/7/2007 1:41:47 PM
> > avast! - copyright (c) 1988-2007 ALWIL Software.
> > http://www.avast.com
> >
> >
> >
volume it should also not blow any bubbles into a clear container
Rich wrote:
> THis might sound crazy, but i had a similar problem with my CJ. I has a 4.0
> head and MPFI. on cool mornings it would do the saem thing you describe
> until warmed up. By luck I had to remove the exhaust manifold to take care
> on another issue and when I put it back together everything ran fine. A few
> months later it started the cold stumble again. I remembered the manifold
> incident, so I removed it once more checked it for flatness across the
> flange and found it to be a bit out. Not much but enought to not get a
> perfect seal against the cylinder head. I had the exhaust manifold surfaced,
> and put a new exhaust gasket on... my troubles disappeared.
> I figure, the slight leak, whan cold allowed fresh air into the exhaust that
> threw off the O2 sensor reading making it rev then stumble...
> Worth checking into
>
> --
> Rich Harris
>
> "reboot" <reboot@nothere.com> wrote in message
> news:8o5ig3l1r7ivgsv7qd2lgphcc113dh4if8@4ax.com...
> > On Thu, 04 Oct 2007 00:14:27 -0400, reboot <reboot@nothere.com> wrote:
> >
> >>'99 TJ 4.0 Auto - within about 3 minutes of a cold start under part
> >>throttle (accelerating reasonably to 45 mph) the engine would start to
> >>stutter, hesitate and surge. water temperature gage shows the mid
> >>mark between cold and 210. when this happens and I open the throttle
> >>wide open it makes good power. on return to part throttle the
> >>hesitate and surge resumes. if i come to a stop while this is going
> >>on then the idle speed dips real low and sometimes stalls. runs very
> >>rough.
> >>
> >>if i drive it a few more minutes and get the water temperature all the
> >>way up it seems OK, smooth stable idle, smooth part throttle
> >>acceleration.
> >>
> >>in the first vista to the shop, they replaced the MAP sensor because
> >>it showed this code. took the truck back but the problem persisted.
> >>
> >>called the shop after this didn't fix the problem. they kept the
> >>truck overnight and tried it cold. didn't happen for them. they
> >>scanned the 'puter and no codes. they put in a set of plugs and
> >>replaced #6 spark plug wire because they said it looked corroded.
> >>
> >>told me drive it for a few weeks and call them back. if it fixed the
> >>problem we would discuss how much to pay for the 2nd visit. if it
> >>didn't ...
> >>
> >>so i've had the truck back a couple of weeks now and it happens pretty
> >>regularly. took it to Murray's this evening and hooked up a scanner -
> >>no codes, same as the shop with their good equipment and trained techs
> >>...
> >>
> >>suggestions?
> >>
> >>reboot
> >
> > well folks, i've tried many of the suggestions made w/o any success.
> >
> > i had all of the TSB / IAC / MAP / CPS and IAT electrical connectors
> > apart, cleaned both sides with QD Electronic Spray, blew them out w/
> > compressed air a re-assembled w/ dielectric silicone grease.
> >
> > i had the throttle body off and cleaned it and took apart the IAC on
> > the side and cleaned it., staining but no blockage.
> >
> > i checked the spark plug wires after dark with a spray bottle of water
> > and it looked good.
> >
> > the driving experience when it hesitates and surges is like it
> > momentary runs below the lean limit for combustion. when it
> > hesitates, if I go to WOT it catches and pulls hard. no more
> > hesitation happens at WOT. but if i take it back to part throttle the
> > condition re-occurs.
> >
> > from this I reason that the fuel rail pressure and injectors are OK -
> > if not then the problem would persist at WOT.
> >
> > i also deduce that it isn't a spark problem because the load on the
> > ignition system is greater at WOT than part throttle and it runs fine
> > at WOT.
> >
> > if there is any problem with the TPS/MAP/IAT/IAC/CPS sensors would
> > they throw a code? in other words - can i have one of these sensors
> > bad and not find a code? (should i start back-probing them and
> > comparing the values to the FSM?)
> >
> > damn - the wife is starting to doubt my wisdom in buying this jeep
> > because it was 'simple and easy to maintain and repair' (my previous
> > words which I'm beginning to doubt).
> >
> > i;m reluctant to start swapping parts because of the expense and i
> > don't have confidence taking it back to the independent mechanic, they
> > couldn't find it before.
> >
> > reboot
> >
> >>
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> >
> >
> > ---
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