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Question - Roland,This is a follow up question to my misfire problem on my1994 Chrysler Concord, I don't remember the exact date of my e-mail but it was sometime in Feb. Isince have changed fuel filter air filter coil pack and cleaned the throtle body. After replacing the coil pack Idid another diagnostic using the key method, the 77 code I mentioned befor did not come up,however I still have the misfire. I have narrowed it down tothese facts. It only misses when RPMs are at 1900 to 2100 RPMs. Below 1900, or above 2200 RPMs it runs fine, however since normal travelspeed puts the RPMs in this range it is like driving a bucking bronco. I am ready to find some dynamite to solve the problem. Help please Ihave done everything I know to do. I have worked on cars of all makes and models pretty much all my life but this one has me baffeled. Thank you, Bruce.
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AnswerHi Bruce,
I sent an answer a couple of days ago so I still had it on my list of previously answered questions. Let's try again to send it, though the Allexperts server has been acting up:
Hi Bruce,
I located the earlier q & a which was on approximately Feb 22. I wonder if you have checked the movement of the egr valve stem and tried to measure the compression of the 6 cylinders to see if they are fairly even as mentioned there?
As for new ideas, it makes me wonder if there might be some sort of a resonant vibration at the rpm range where you experience the miss which then might impact the quality of the spark signal. For example if the crank or cam sensor was varying in the strength of its signal due to a vibrating separation distance between the sensor and the metal surface it was "looking" at that might produce an inconsistent signal that could affect the spark quality without being so extreme as to set an 11 or a 54 code. To test that theory probably requires an oscilloscope to observe the signal on a synchonized video monitor.
Another possibibility that you might be able to look at with a simple ohmmeter is a subtle discontinuity in the voltage divider wiper/resistive element interface of the throttle position sensor. I am wondering if the miss might be associated with a region of the sensor when the throttle is opened at the angle which also correspondes to the rpm range of the miss occurence. So all that would require is to measure the resistance between the middle pin and either end pin of the TPS (after unplugging its three pin connector) while very gradually opening the throttle body. Look for and discontinuity in the resistance from closed to full open throttle.
Other than something like those two possibilities I can't put my finger on an rpm range sensitive miss.
If none of those bear fruit, you might ask around at Chrysler dealer shops whether their "tune-up specialist" has a long history of working on the 3.3 and 3.5L engines and decide whether to turn it over to him for a diagnostic effort. I know it is a come down to do that, but sometimes a pro with some test tools you don't have can figure it out in a few minutes. I had that experience once when my MAP sensor drifted off-value, but not so much as to set a code. The Chrysler mechanic found it in a few minutes using the DRB (diagnostic readout box), based on the pressure parameter it was showing (not the codes). I was impressed.
Let me know what happens as this progresses to a solution, which I know you will find.
Roland
