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Chrysler Repair/'91 3.3L: Exhaust popping

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QUESTION: "1991 Chrysler New Yorker,  engine size 3.3
Hello and thank you for volunteering your time.
My Mechanic can not figure out my cars problem.  I live in NH, 3 weeks ago we had a 3 day cold spell and very windy, making the temp minus 10 or a bit more.      We went out to go somewhere and the car would turn over but would not start , not even with a truck to jump start it. So we thought frozen fuel line and put dry gas in, but since the car didn`t move, I guess the dry gas didn`t get circulated? Now after the 3 day cold spell, day 4 was warm , and lo and behold the car started right up !!! For 1 week it ran fine but we don`t drive very far each day, so on about day 7-14, we drove to next town and and within a few miles on  acceleration it begain popping, it sounded like from the carb, but there is no carb, I put carb cleaner in anyways....Honestly it seemed to help and then then the next day I started it up and OH MY GOODNESS, the exhaust was loud and black carbon was coming, so I drove it thinking the black exhaust would go away, it kind of did , exhaust was louder then it had been and popping on acceleration, , but odd is before the frozen fuel line (if that is what is was)  the exhaust was not so loud but who knows on that problem, I brought to my mechanic, said I do need exhaust work ..(which I knew already )he told me the next day , the car was running terrible, I did not ask him what he meant by that, I think just sitting there running...My mechanic thought it was camshaft , camshaft sensor is what he ordered, but he sent it back...Reason he did was because the car sat out at his garage over the weekend and on Monday it would not start, turned over with no spark is how he worded it, they brought it into the garage, when it warmed up it started up fine, like the time I thought my lines were frozen on our cold snap and then on the warm 3rd day, (in the 40`s )...He was befuddled , and that is why he sent back the sensor, he actually said he did not know what was going on, so later on he said maybe a power control module?     Okay , He said he would look some more,  now today he calls and said the car started up right away even though it was about 8 degrees,  they ran it and it seemed to run right , except for loud exhaust...He had no answer what went wrong and why it "seemed" to fix its self, so I took it home and he said drive it, don`t let it sit, so I went to go visit my brother and after a few miles, darn it, going up the small hill, it begain popping !!! So what I did was on flat road it was fine even at 50 mph, so when the next smallish hill came up, I did not accelerate and it did not pop, but it was a small hill, no popping on flat road , bigger hill was coming up and I had to accelerate some, and it popped, when it pops , I was told that is actually back firing...So my mechanic has no idea what the heck is wrong with the car...I don`t understand why he can not find the problem, oh he did say if the check engine light was on, that would help...but of course it is not on when you want it on. So I don`t know what to do, this car ran okay , minus the smaller exhaust sound, it ran fine until the fuel lines froze,  , maybe that was not even the problem. I am sorry I rambled on, I am a girl and I don`t know what this mechanic talk really means..  Thank You"

ANSWER: Hi Jen,
It is interesting to learn this history but very difficult t draw any conclusion from it. The best thing to try for diagnosis would be the self-diagnostic ability of the powertrain control module. Use your ignition switch: turn it "on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then observe the "check engine" light, which remains "on", to see it begin to flash, pause, flash, etc. Count the number of flashes between each pause. Then do it again to be sure of a repeatable set of flash counts. Then tell me the counts in the order that they appeared. The last two sets of counts should be 5 in each set. Then we'll have some idea of what might be at fault.
Based upon the counts I will give you some ideas of what to try.
Also, at the time this car was built and sold there were differences in some of the pollution control devices which depend upon where the car was originally sold/delivered. Do you happen to know that history? If so, let me know.
Roland

---------- FOLLOW-UP ----------

QUESTION: Hi Roland, thank you for your very fast reply.       I do not know where the car was sold/delievered.          I was wondering, using the ignition switch , turn on, turn off..Wouldn`t the mechanic have tried that? I haven`t asked him yet, but I think I shall. I was under the impression that he would look for all small things first, then start looking for the bigger things, and if codes could help, I would think he would use them for a diagnosis?    Even I have used the turn on, turn off , for a  mechanic years ago, (different car) He had me do that and call him at his work place.  Also, when he 1st thought camshaft sensor and then changed his mind because the car would only crank but not start until he brought inside , then after warmed it fired right up, so for that reason he decided it wasn`t the sensor and that is when he began to think powertrain module?       Would that be correct in thinking it is not the camshaft sensor due to not starting in the cold but starting up after warm?    I am not sure if the car is worth putting big bucks into it.
Power train module is like the brain of the engine?    I am very very torn between what to do, I will get those counts before the day is over. I just can`t imagine that a mechanic wouldn`t have tried that?       He is my new mechanic, as I moved away from my long time mechanic.  Thank you so much, and I will get those counts. PS: I am not sure they sell powertrain modules for a 1991 or the cost of one plus labor....I am so torn ..

Answer
Hi Jen,
I can't know whether the mechanic checked for fault codes, but you can so that is why I told you how. If the cam sensor or the pcm is bad a specific fault code will appear for each.
The reason I asked about the history is that there is a part called the exhaust gas recirculation valve which is not monitored well for being at fault. But if it gets stuck ajar then the engine will not start and not accelerate well up hills.  All the mechanic has to do is lubricate the stem of the valve with WD-40 and move it back and forth to solve that issue.
Whether the vehicle has this valve depends upon where the car was sold so that is why I asked, but in any case ask him to look and if he finds it to lubricate it. It is at the rear of the engine if so.
I would not replace anything without having done the fault code readout first. I doubt the powertrain will be found wanting.
Roland

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Roland Finston

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Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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I have do-it-yourself experience (50+ years) and a library of 100 1982-2012 Chrysler factory shop manuals and 20 multi-manual Chrysler Corp. CD's.

I was voted "Top Expert" 2010-2015, here at AllExperts, and have answered 20,000+ questions.

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Five decades as a 'do-it-yourselfer' on domestic and imported cars.

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Yahoo Autos Group called The Chrysler Lebaron Club (co-moderator)

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Advanced degrees in Physics/bruised knuckles

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"Top expert" of 2010, 2011, 2012, 2013, 2014 and 2015 here at Allexperts. Quickest "average response time" at Allexperts (currently no. 1).

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