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PatrickD
Dodge Dakota
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1/17/2004
22:09:13
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 Subject: Misfier Questions
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Message:
I have been tracing a single cylinder misfire in my '97 5.2 for a little over a month now. I have done everything i can think of.
It led me to thinking;
-What is a misfire?
-What does the computer concider a misfire?
-How does it detect that a specific cylinder is misfiring?
-Is there a sensor that might be faulty?
I have not been able to find any posts or literature to answer these questions. Was hoping some one here might have a little better insight. Any advice would be helpful.
Thanks.
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chief08087
Dodge Dakota
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1/17/2004
23:28:55
| RE: Misfier Questions
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ok im assuming u changed the plugs, wires, cap, and rotor. and u would think that would fix it. i know. take a look down into ur throttle body with it open so u can see in the intake manifold. i can almost garauntee u will see oil in there. ur motor is famous for leaking intake gaskets. if there is oil in there than u need a new intake gasket. the new gasket is a revised gasket. the ones that came on the motor r defective for some reason. get back to me and ket me know what u find. if that isnt ur problem then im sure i can solve ur misfire issue
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99DAK
Dodge Dakota
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1/18/2004
12:38:15
| Misfire Questions
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"if that isnt ur problem then im sure i can solve ur misfire issue"
I'll take some of that action. I've had an intermittent P0302 (cylinder #2 misfire) since I got my Dak (99, 3.9l, 47K then, 56K now). New plugs, wires, cap+rotor, belly pan appears squeaky clean, truck runs great (except for typical slightly bumpy idle), gets 22mpg hwy. Will go for several days at a time without throwing the code - when it does it usually clears itself. Compression test done, all cylinders within spec. Best guess from anyone so far? - valve deposits.
PatrickD-
Your questions:
#1 - Misfire is incomplete or no combustion on that particular cylinder's combustion stroke.
#2 - The PCM throws a code when it sees an unacceptable # of misfires within a certain # of RPMs (both depend on programming).
#3 - The crank speed sensor is able to detect momentary drops and the crankshaft position sensor tells the PCM which cylinder it is at that moment.
#4 - Unlikely if you're getting the same cylinder all the time.
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PatrickD
Dodge Dakota
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1/18/2004
15:38:30
| RE: Misfier Questions
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chief08087:
I took a look down the TB and saw only a minute amount of oil. Is this enough to need a new gasket? And i am not seeing how oil on the intake manifold can cause one specific cylinder to misfire.
99DAK:
Thanks, that answers some questions but leaves me just as confused. I have that same idle bump that you posted about. The PCM should store the specific information to where i can take it some where and have them tell me exactly what is happening, correct?
My next thing is a fuel system cleaning, which i am waiting next time have to fill up. But i doubt that this is going to have any affect.
Thanks...
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99DAK
Dodge Dakota
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1/18/2004
16:40:24
| RE: Misfier Questions
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If you saw any oil at all then yes, that may be your problem. I have seen several people post that (it's called the plenum, or belly pan, gasket) fixed the same problem we have.
Diagnostic scanners can give details about sensor information, but in the case of cylinder misfire there's no more to tell - it's good old fashioned, flow-chart-style troubleshooting at this point.
I've heard that clogged injectors can also cause this problem, so definately do the fuel system cleaning.
If you replace the plenum gasket and have no fuel or ignition issues then a compression test is next.
Good luck and keep us posted.
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PatrickD
Dodge Dakota
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1/18/2004
16:54:26
| RE: Misfier Questions
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I appoligize for my lack of knowledge, how can the plenum gasket cause the misfire?
Thanks...
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chief08087
Dodge Dakota
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1/18/2004
17:29:28
| RE: Misfier Questions
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leaking gasket casues oil to go into the cylinder. causing the plug to misfire.
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PatrickD
Dodge Dakota
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1/30/2004
08:47:31
| RE: Misfier Questions
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Got the code to clear with a fuel treatment. Still going to replace that plenum gasket since i know now that is a problem.
Thanks
Patrick...
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guess what
Dodge Dakota
JOIN HERE
1/31/2004
08:48:38
| RE: Misfier Questions
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so can a bad fuel injector!
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