Calgary Jeep Association
4x4 Related Groups => Tech Talk => Topic started by: birdo on February 17, 2011, 10:28:12 PM
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Greetings,
99 Jeep TJ 4.0 liter, 5-speed.
Starts up fine and settles into smooth idle. Under load as the engine warms, she coughs and sputters and surges for a couple of minutes and then settles down and runs just fine. No "check engine" lights...ever. As soon as the engine gets up to temp, everything is fine. If I let it cool down a few minutes,restart it, it does the same until it gets back up to temp.
I get the impression that this is occurring while the injection system is in open loop mode.
So far I have:
Changed plugs, cap, rotor and wires.
Replaced Engine Coolant Temperature Sensor (CTS)
Replaced Air Temperature Sensor (ATS)
Cleaned Throttle Body
Cleaned Idle Air Controller (IAC)
Have ordered a MAP sensor.
Have checked for vacuum leaks.....throttle gasket, intake/exhaust gasket, injectors, crankcase ventilation. All is good.
Took it to a local dealer (big mistake) who said they couldn't find anything and I have my doubts that they did any checks at all. (coz they didn't charge me for it)
Any ideas.....I'd be willing to take it to a good mechanic who really knows Jeeps. Recommendations?
Cheers
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Jay at Chanda.......... aka lemon-aid Jay....... he knows his stuff..............
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Give me a call tomorrow at the shop and will see what we can do for you. 403 287 3350
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Took the beast in to see Jay today. He couldn't have been more helpful. Spent a very cold morning checking for vacuum leaks and ran the gizmo over the computer and everything came up trumps. Jay has suggested I replace the TPS and if it ever warms up, I'll put it in and see what happens. Watch this space.
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Took the beast in to see Jay today. He couldn't have been more helpful. Spent a very cold morning checking for vacuum leaks and ran the gizmo over the computer and everything came up trumps. Jay has suggested I replace the TPS and if it ever warms up, I'll put it in and see what happens. Watch this space.
Well hell, it was good to meet you today John, hopefully you get the ole girl straightened out....................she was probably just fumed at you for making her pull that pickup out of the snow bank.
I was the guy with the Mango Rubi that picked up the winch :)
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Ok...replaced TPS.......no change...arrggghhhhh! This really has me stumped.
Ha,ha...I never did pull that guy out....if he had asked nicely I might have. His truck is still stuck. Could be until it thaws...or he eats some crow and apologizes. Common courtesy will get ya a lot further in this world than cussing and swearing.
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It could be your upstream O2 sensor between the Cat and the engine. Unplug it on cold start up and see if it fixes it.......if you have no rough idle on start up it needs to be replaced. Worked for me.
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I was thinking O2 sensor too. Good luck.
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Worth a shot...I'll give it a try and let you know.
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Just a footnote on this...rough idle is not really the issue.....the problem occurs shortly after engine start (or restart) when the normally smooth engine starts the misbehave. If I try to hold a steady RPM under partial throttle the engine will speed up then slide back then speed up and slide back.....almost rhythmically. Jay will testify to this. Then after 2-3 minutes, the engine settles down and idles and runs fine. If I try to drive it, it will buck no matter how much or how little throttle I give it. Eventually it will settle down and drive as per normal.
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Now that the weather has settled down a bit, I got busy and replaced the intake/exhaust gasket. Same result I'm afraid. Now I'm baffled.
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did you check fuel pressure, compression/ leakdown test. Injectors? grounding? fuel pump? check all fuel pump connectors.
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did you replace that MAP?
mine does the same thing when i start it up in the morning. it'll stutter an dstall out if i give it gas. i have a stored MAP code but it doesn't throw a CEL. i've learnt to live with it ;) after it runs for 30 seconds it goes away. might be similar, maybe not?
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Just throw as many parts at it that you can think of.
Probably just needs belt dressing.....
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not everyone should fix jeeps like you do trevor!
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O2 sensors are not operational during warm up (open loop). Cmon guys, you know better then that.
Tap the map with a screw driver during warm up and see if anything changes.
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Well......took a long-shot and went and saw Jay on Thursday. We poked and prodded, swapped PCM, did OBD checks, scratched our heads and looked up at the sky a lot. Jay suggested I might try replacing the pre-Cat O2 sensor. Friday, and with a lot of swearing wrenching and penetrating, oil I got the old sensor out and replaced it with a new one.........I might be jumping the gun here, but I did a lot of stop and start errands Friday and so far so good...no belching, farting, bucking and other non-sense. Maybe....just maybe we finally got it fixed. O2 sensor......never threw a code.....wow! ;D
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Glad you got it sorted out!
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Well......took a long-shot and went and saw Jay on Thursday. We poked and prodded, swapped PCM, did OBD checks, scratched our heads and looked up at the sky a lot. Jay suggested I might try replacing the pre-Cat O2 sensor. Friday, and with a lot of swearing wrenching and penetrating, oil I got the old sensor out and replaced it with a new one.........I might be jumping the gun here, but I did a lot of stop and start errands Friday and so far so good...no belching, farting, bucking and other non-sense. Maybe....just maybe we finally got it fixed. O2 sensor......never threw a code.....wow! ;D
Hopefully its worked out for you. Still makes no sense though.
Either your description of the problem was wrong, or the computer you swapped did something.
An o2 sensor should never effect the running of a vehicle during open loop. Its virtually impossible unless there's faulty programing involved.
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Hopefully its worked out for you. Still makes no sense though.
Either your description of the problem was wrong, or the computer you swapped did something.
An o2 sensor should never effect the running of a vehicle during open loop. Its virtually impossible unless there's faulty programing involved.
This is Chrysler we are talking about... ::)
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I think you guys will find this interesting...it's a primer on heated O2 sensors. It might dispel a few myths about these gizmos.
http://www.picoauto.com/applications/lambda-sensor.html
The section on "Heated Oxygen Sensors" is very interesting.
Why my failed sensor never threw any codes remains a mystery.
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Yeah interesting enough, but still doesnt explain why a sensor that isnt active during warm gave you issues..................during warm up.
All that article explains is how 02's work, and what the symptoms are when they are failing. Again, all closed loop diagnostics.
The fact that your symptoms were exhibited during warm up (open loop) still indicates that it should not be 02 sensor related. Im pretty sure you inadvertantly fixed while you were messing around with everything else.
Either that, or its possibly an intermittent issue thats gone away for the time being.
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Not too sure about the 'closed loop' aspect of it but this is common occurance with Jeeps that have the upstream O2 sensor. I had the same problem and received the same advice on JeepForum.com. There are literally tons of posts/threads on it all have the same outcome; ' if you're having issues on start-up first unplug the O2 sensor and if the problem goes away the sensor needs to be replaced'..........fixed mine too.
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I have to rule out any tinkering we did. There is no doubt in my mind that the O2 sensor was the culprit. When I drove over to the parts place to get the sensor, the Jeep was still bucking and snorting on the short ride over. On the way home (approx 30 kms) as soon as the engine got up to heat, it ran fine. Same old pattern. The next morning I replaced the O2....fired it up and not a burp, hiccup or misfire. Been fine ever since.
All I can tell you is that if your Jeep starts to misbehave, as mine did, consider your upstream O2...especially if the one that's in there has been there for a while. Yes it should throw codes, but it may not always do so. ;)
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As you can tell this has bugged the crap out of me.
Here is the explaination of whats happening.
http://www.justanswer.com/jeep/3vwgi-misfiring-brief-period-during-warmup-driving-maybe.html
The sensor was acting up after your jeeps were "warm" and went into closed loop.
By the way, according to these guys you should disco the batt for a while and clear the fuel mapping memory for the best results when you change that sensor.
Oh, and that also explains why it never threw a code. The voltage remains within acceptable range, its just slow to bleed down. It will only throw a code if the voltage spikes outside of the operating range, one way or another.
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