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On my 1996 jeep grand cherokee Laredo I put seafoam in it and also changed the plugs but now it backfires and when I start it the idle is rough and 8 cylinders are misfiring but yet when it drives its super shaky and backfires but only 4 misfire. What could be the problem and could a exhaust leak or vacuum leak cause this?

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  • Cars & Trucks Master
  • 75,842 Answers

The following are the general instructions on the start of diagnosing any electronically controlled engine or transmission problem.

The engine and the automatic transmission (transmission control is only for automatics, engine is still computer controlled no matter the transmission type) in this vehicle are computer controlled and in most cases when a fault occurs a fault code is stored in the memory of the computer control module. There are exception to this, such as the Mass Airflow Meter and fuel pressure problems. What must be done is to have all the basic testing done such as a scan of the system for fault codes as well as a check with a live data scanner tool for engine functions that are not within range of normal, a trained technician is required to know what is correct and what isn't, then based on careful diagnostics done from a factory repair manual the correct part is replaced or the wiring repaired or the computer replaced (known as the PCM or ECM,ECU), which is very rarely the problem. Other basic checks must be done as well such as mechanical problems with the engine as well as engine state of tune and mileage on the engine. The transmission can have mechanical issues as well such as no gear engagement at all or a failed pump or other pressure related problems. Also engine mechanical problems can and do cause many drive-ability related problem such as rough idle and other symptoms.

Posted on Nov 02, 2012

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Posted on Jan 02, 2017

Mikey108
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SOURCE: 2002 Jeep Grand Cherokee Lardo misfiring

You say you changed the cam sensor. A1391 code is a crank sensor on the top of the trans. bell housing.

Posted on Feb 24, 2009

kirk863
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SOURCE: STILL MISFIRING!!!!! 99 Audi A6 Avant

AUDI A6 Recalls by Year

http://www.allworldauto.com/recalls/audi_a6_recalls_65-2089-1.html


Posted on Sep 22, 2009

  • 1 Answer

SOURCE: 2005 Audi A4 1.8T QT, cylinder 4 misfire p0304

I too have the same problem on my 2005 1.8t B6. I noticed a hole in the breather hose coming off the valve cover that runs to another port under the intake manifold. I have the hoses on order and should be here on Wednesday. I'll post again if that fixes my problem.

Posted on Oct 12, 2009

ZJLimited
  • 17970 Answers

SOURCE: P0308 cylinder 8 misfire detected? How to repair?

Fuel injector cleaner commonly has a low success rate, and will not help if it's more than one cylinder that is missfiring. The fact that you have a "rattle" noise, leads me to beleive the engine is not receiving fuel on one or more cylidners. If it is all the cylinders, than the fuel pump may be the culprit, or the fuel pump circuit. But if only one cylidner is missfiring than it is a possibly an injector. A code P0300 refers to all cylinder missfires, and any code between P0301-P0308 distinugiushes a particular cylinder.

Misfiring
1- a general electrical tune-up (spark plugs, wire set, cap & rotor) is a basic start to cure this issue. Wiggle the dist shaft while you are in there, if you have one.
2- Then a good carbon cleaning / throttle-body cleaning.
3- Vacuum leaks at any of the hoses that connect to the Intake manifold; especially the MAP sensor connection.
4- If that does not help then the O2 sensor could be bad or drifting.
5- Funky coil/coil-packs
6- Theoretically a microsecond glitch in either the cam or crank shaft sensors would cause this, but I am not aware of this as a typical cause.
7- Lastly a funky PCM but again it is not common for this to cause miss-firing.

Note for the V8 then also:
a) bad erg valve (this dilutes the combustion gases and hence raises the combustion temp
b) a leaky plenum/Intake manifold gasket. Leaking Intake gasket symptoms

Also can check the TSB 18-48-98 Ignition System Cross Fire/Secondary Ignition Wire Induction (Complete Version )

Hope help with this (remember rated this). Good luck and have a nice day.

Posted on Mar 05, 2010

BCAS1298
  • 3092 Answers

SOURCE: 2002 Jeep Liberty Sport 3.7L

We have an 02 Liberty 3.7L, here at my repair shop, after customer replaced, spark plug's and all coil pack's, brought it here to my shop, was running with two cylinder's miss, did cylinder compression test, no compression on two cylinder's, remove valve cover's, found two rocker arm's off, remove cylinder head's, and found that on those two cylinder's the valve seat's had drop, keeping the valve open, and that's why the two rocker arm's had come off, do a cylinder compression test, could be the same thing, hope this was very helpful.

Posted on Aug 30, 2010

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