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The Audi Doctor
The Audi Doctor, Technician
Category: Car
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Experience:  Over 30 years experience, 17 years with Audi, Factory trained
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Isuzu Trooper LS: 96 isuzu trooper miss fire #4 replaced plugs

Customer Question

96 isuzu trooper miss fire #4 replaced plugs copper plus switched injectors switched col packs replaced crank sensor cam sensor plenum gasket intake gasket checked spark,plug is very black but not very warm, checked camshaft for bad lobe 155 psi compression all cylinders what am i missing?
Submitted: 2 years ago.
Category: Car
Expert:  The Audi Doctor replied 2 years ago.
Hello,

Thank You for choosing Just Answer for your query. Yes, I can help you.

A) There is a misfire Technical Service Bulletin #99-020 dated June 7 1999 regarding a re-flash on the ECM.

B) These vehicles are also very sensitive to the spark plug selection. I recommend ONLY NGK PFR5G-11.

C) These injectors are prone to bleeding down and leaking fuel into the cylinders causing misfires, mainly when cold.

D) Also the fuel pressure regulator fails and leaks fuel into the vacuum line.

E) Corrosion under the coil can cause a poor ground and the coil can cause a misfire.

All common causes of misfire issues on this year model. That said, I do not think they are going to cure the misfire, but they should be checked/eliminated.

I am going to assume that this vehicle has a direct misfire in #4 cyl. that is always present. Please let me know if that is not the case, as you did not indicate this on your question, only the fact that P0304 is stored, and the plug is black. Is the spark plug back and wet, or black and dry?

Based on the fact that the spark plug is black indicates that there is fuel present, but it is not being ignited. If you have carried out all the steps listed properly I suspect the Ignition Control Module is failed.

First I suggest you inspect the wires/terminals at the ignition module, and coil. Also check for corrosion under the coil. You could also “pin out” and test the wires from, the Ignition module to the coil, or simply replace the Ignition module.
graphic

Let me know if you have any further comments or questions.

I hope I have answered your questions and addressed your concerns. Should you have further questions on this matter, please do not hesitate to ask. I want you to be 100% satisfied with my answer.

Positive feedback, referrals and bonuses are always APPRECIATED.

Thank You!
Jake “The Auto Doctor”
Customer: replied 2 years ago.
i have pined out the wires going to the coil and placed coil on a ground and checked plug spark (ok) also swapped coil 2 and 4 problem stayed at 4 and replaced the (ecm)
with a used one,fuel pressure is ok. hooked up code reader and the p0304 is always their. the plug is black and dry i have swapped injectors from 2 and 4 and the problem stayed at #4
Expert:  The Audi Doctor replied 2 years ago.
How about the "ignition" control module? Not the "engine" control module.

Also, just for curiosity you could swap the injector wires with the adjacent cylinder as they are not sequential.

Thanks Jake
Customer: replied 2 years ago.
where is the icm located? I dont think the wires from #2 will reach #4 and wouldn't that change the fuel timing? In any way would the o2 sensors be to blame i know i have a bad one their are 4 of them and they were all unplugged when i bought the car i think their plugged in the correct i spot pinned out all wires and traced them back according to a diagram provided by one of you 6 months ago. originally it all started as sluggish and low power on the bottom end but if you put it to the floor it would go sluggish then all of a sudden pick up and put you in you're seat.
Expert:  The Audi Doctor replied 2 years ago.
This is not a "sequential" system (no fuel timing).

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This is where the module is located. I sent you a close up earlier.

I don't know what has happened in the past. I am only addressing your "misfire" question.

Not being able to experience the condition first hand put’s me at a significant disadvantage. If you can better/best describe the condition, as well as anything else that has been done to try and correct the issue. Also a time line of the events that led to the condition would be quite helpful.

The quality of my answer is based directly on the quality of your question and description. So please include anything else that may help me to better understand the condition and how it all came about.

Thank you!
Jake
Customer: replied 2 years ago.
bought car
replaced tranny (5 speed)
drove would run ok on top if you got in it
pin tested o2 sensors
changed the way i had them plugged in
now constant misfire p0304 p0300
checked compression (155lbs)
replaced gaskets cleaned intake runners checked cam lobes valve lash hot and cold
replaced cam sensor
replaced crank sensor
replaced plugs
swapped coils
swapped injectors
rechecked o2 sensor wiring looks correct to diagram
replaced ecm
checked plug (black and dry)
contacted you
Expert:  The Audi Doctor replied 2 years ago.
OK, you check for spark in #4 cylinder and then you compare it to an other cylinder, how do they compare? What kind distance gap will the spark jump on both cylinders, and is it sparking as often? If #4 is weaker than the other I would replace the Ignition control module.

Thanks Jake
Customer: replied 2 years ago.
the spark is the same the gap is .035 and it sparks just as often i have timed it with a light on #2 and #4 the spark will jump off the plug about 1 to 1.5 inch on both 2 and 4
Expert:  The Audi Doctor replied 2 years ago.
OK, I think that about covers it. I would swap the injector wire connectors if they do not reach make up some extensions. If the misfire is still in #4 there is a problem in the head possibly a broken valve spring(?).

Do you have a cylinder leakage tester? It wouldn't necessarily show a broken valve spring, but could provide a clue.

Also, put a vacuum gauge on the intake manifold. Is it steady at idle?

What happens to the vacuum reading when you drive?

Is it a dead miss all the time(idle/cruise/accelerating)

Thanks Jake

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