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I have two 1998 Olds 88 LS cars, one runs fine and the other misses when warmed up and only when moderate to full acceleration. I initially found the intake manifold was warped above the #6 cylinder (thus the P0306 code). The manifold was replaced which helped the missing but not completely. Then I swapped the ECM/PCM unit and the stumble / misfire issue remained the same. Also, the stumble / misfire issue occurs in all gears, not just third when the torque converter normally locks. I also swapped the ignition module, but also no solution. The sensation of the stumble is more like a misfire, sporadic, which only occurs with moderate to strong accelerating when the timing advance drops below 15 degrees. With all of the self-troubleshooting that I and my mechanic friend have performed (yes, I even replaced the plugs and wires), we are both stumped. Nothing appears as a malfunction on my Autoxray scanner, nor my mechanics scanner. Also, if you accelerate easily, or the engine is below 150 degrees F., the misfire is barely (if at all) noticable. Other than the missfire, the car acts and drives very well. Still stumped in Richmond, Va. Thanks....JCT
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Hi John
Check your fuel injectors,ohm check them and see what the values are,anything under 12.5 ohms and over 17.0 ohms is cause for a failed injector,also make sure you have good firing from the coils,what i do is cut 1/2in lengths of vacuum line and insert them between the ign wires and the coil terminals,then i ground a test light and use the test light prob end near each of the vacuum lines,the spark will jump to the test light and you can check for a possible weak ign coil,the spark should be blue in color,if yellowish then it may be a weak ign coil.let me know what you find,Thanks
ED
Thanks Ed, the injectors were the next thing my friend checked after he replaced the warped intake manifold. And as for the ignition system, remember that I swapped another complete unit (which worked fine) onto this car(plugs and wires also replaced), however there was no improvement. The warped manifold initially caused the same sensation, however he rechecked the new manifold and it appears still to be tight and OK.
Also, the misfire ONLY occurs when the car reaches operating temperature and ONLY during moderate to full acceleration. I think that it may be some sensor that goes nuts when it gets hot, but there are no pending or trouble codes that I can review. I have read of a couple of other peoples inquiries into very similar situations, however none had any answers. Oh well. Any other suggestions?
Thanks a bunch.
JCT
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John
I was thinking about your problem,have you checked the Mass air flow sensor,try swaping it out and see if that works,the thing i thought about was i had a simular problem with a 3800 a few years back,what i found and that was through an Internal bulliten through GM,was the TPS was causing this sensation,it wasnt a strong miss just what they call a fish bite,it happened on accel,what caught me off guard was i was monitoring all sensor data with our GM Tech2 scanner,i even snapshoted the data and scoped it,but i never scoped TPS data,well the bulliten stated that the TPS is so fast in reacting that the TECH2 could not pick up on the fault,well i decided to jumper the TPS with my meter,i set it to rec,and sure enough when i laid into the throttle it went from 2.4v to a drop at 1.08v the PCM thought i was in decell for about 1.3 sec and leaned fuel it just so happened #3 got the first lean fuel in the firing order,missfired and flagged a missfire code,something to think about,ill give you a new bulliten issued by GM it is #1702215,try the TPS...and let me know on this one ok
ED
Ed, you are great in staying with me on this problem. I have not have a chance to swap the MAF sensor, nor the TPS, however, I did scan both cars (my good running burgundy 1998 Old 88 and my no-so-good running silver 1998 Olds 88) with my AutoXray scanner and the MAF, MAP, TPS and O-2 sensor readings are very nearly the same (at varing RPMs). I did notice that while performing the scan, for the good car's scan, all functional tests indicated they were complete, whereby on the not-so-good car, some of the same funtional tests indicated not-complete - inparticular the EGR and O-2 tests. Does this mean anything to you. Also remember that I swapped each cars computer which made no difference in the not-so-good cars performance.
Also, the misfire is not subtle. When it occurs, it feels like the car is running on 4 cylinders (kinda like when bad wires get wet). It is worse from a dead stop, versus passing acceleration, in particular as the engine stumbles to gain speed (gets worse with more pedal). Perhaps a shark attack instead of a fish bite!
As for the GM bulletin #1702215, I have no way of finding or viewing it.
Thanks again for taking time to ponder my plight and hopefully you will have more comments.
JCT
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John
With the scanner you have are you able to veiw live data,can you get data on what the O2's the MAF MAP etc are doing when the missfire happens,man, i just am leaning towards either the TPS or MAF,{im trying not to use the magic wand}but it just seems like a lean condition...im going to a TAC meeting {technical assistance GM} tomorrow,im going to run this across some friends and see what they come up with.i have to admit i love a challange. :)
ED
Ed, my scanner, when viewing engine operational data in real time between my two cars, does not show much difference. The #1 O-2 sensor fluctuates wildly between say .1 and .9 and the #2 sensor does the same, but much slower (will stay close to the same value under constant RPM). The air flow rate and MAP sensor output data also appear to be very similar between cars.
When you discuss this with your TAC guys, make sure you tell them that this is a problem that is mostly un-noticable when the engine is cold, but very noticable when the engine is hot...especially upon accelerating from a stop or say when you hit the pedal hard to pass someone. Also tell them all of the stuff that I have swapped.
It is kind of rainy this weekend here on the east coast, so I will try to swap out the sensors you recommended soon.
Thanks again!!!
JCT
Answer -
John
Some things to keep in mind,did talk to TAC about it,asked about compression,asked to do a running compression test,they think you may have a valve or guide thats is failing,also to check for a crack in a rocker, bent pushrod,lifter,they think you may have a mechanical problem.and compression would let you know.
ED
Hi Ed, thanks for the previous suggestions.
I checked the compression on the #6 cylinder. However, I could not really get the device all that tight into the cylinder head (hard to get to in the rear of the engine) and I know that there was some leakage. Nevertheless, it looked like I was getting at least 100 PSI.
I am confused. If there was mechanical issues as your TAC guys may have suggested, wouldn't this cause the engine to miss all of the time, not just when hot and being aggressively accelerated? Also, remember that this car only has about 27,000 miles on it, was driven by a 75 year old man who meticulously maintained the car.
I don't know. The sensation really feels like a bad wire or fouled plug, but those have been changed out, along with the ECM and ignition module. Perhaps it is a fuel problem, but my mechanic friend said all of that checked out OK as well.
Oh well, unless you have any other ideas (always appreciated), I guess I will have to take it into a dealership (which scare the Hell out of me), unless you have some guidance on good, honest shops in the Richmond, Va area.
Thanks again...JCT
AnswerJohn
Yes i thought the same but i have seen some pretty wild things and i wouldnt rule out a mechanical problem,but if you were able to isolate the cyl that is causing the problem,try to swap the injectors with that cyl,say #6 was the guy thats causing this,swap #6 injector with #4 and see if it follows to that cyl,that way you can either flow test the injectors or replace it,have you swaped the injectors with the good car to the bad one?
Ill give you my Email address if you need more help,like i said i am curious as to what is going on with this,it is: eds69z@yahoo.com
ED
