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Tom, ASE Certified Technician
Category: Car
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Experience:  ASE Certified Master Technician
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1992 Isuzu Trooper: freeway..fuel in exhaust as converter..cylinders

Resolved Question:

RE: 1992 Isuzu Trooper, 3.2L DOHC

New plugs/wires two weeks before this happened ... ran great for about 2 weeks. I use injector cleaner regularly and use only Shell/Chevron/Union 76 gas.

Then while driving on freeway, Trooper suddenly lost much power. Runs rough, fuel in exhaust as converter gets glowing hot.

Identified "dead cylinders" 3 and 4 via unplugging spark wires. In-line park tester shows spark happening. These cylinders are on different spark modules.

Manifold vacuum about 20psi (low??) but steady. I don't have extender (through valve covers) to do compression check. But, decent pressure while cranking with plug removed and "hole" blocked with thumb. Have not had plug out while engine running.

I think this points toward a fuel injector issue, but don't think glowing catalytic converter fits with no fuel.

Any guidance greatly appreciated.


Submitted: 5 years ago.
Category: Car
Expert:  Tom replied 5 years ago.
What are the compression readings on all cylinders? Has the intake manifold been checked for cracks and broken gaskets?
Customer: replied 5 years ago.
Just did compression check. All #'s in psi

1 -- 180
2 -- 195
3 -- 160
4 -- 180
5 -- 160
6 -- 160

Haven't checked intake gaskets with fine tooth comb. One of my diesel mechanic buddies sprayed WD-40 around intake manifold (under plenum on both sides). Then also tried some carb cleaner. Both done with engine running. No rpm change of change in engine sound.

I do not hear any whistles or rushing air sounds.

What do you suggest for further checking of intake?
Expert:  Tom replied 5 years ago.
Ok I take should be good. Compression readings should be no more the 25 psi between cylinders so that's should be ok. Sounds like the dead cylinders are not getting fuel . I would check those fuel injectors next and make sure timing is dead on and proper distributor operation. These are the next steps. Hoped this helped. Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.
I'm not quite sure about your suggestion about checking timing and distributor operation.

This is a distributorless ignition system. Timing is all computer controlled and is not adjustable.

Please elaborate.

So far you haven't really told me anything I don't already know. And, I really need to deal with someone who knows about the many quirks of the 1992 Trooper.
Expert:  Tom replied 5 years ago.
This has a timing belt and if it jumped time it will cause this issue. Unless the coil pack or ignition control module is failing timing needs to be physically checked.
Customer: replied 5 years ago.
Back on the possible fuel issue...

Because the catalytic, muffler, and tailpipe have gotten very hot, that would suggest that excess fuel is getting into the exhaust system. But, I don't smell gas in the exhaust except at a cold start. Also, no "burbling" or any popping from fuel exploding in the exhaust.

However, I can also get up to about 55 or 60 on a flat road. It takes a while. Doesn't that suggest that timing is "not horribly messed up"?

Does this make the fuel system the top candidate? Or would you look at the timing issue first? Or do the above symptoms really tell us nothing?
Expert:  Tom replied 5 years ago.
If it's not running rough at idle timing should be fine and I would focus on a fuel issue. Sounds like the fuel pump might be weak and causing this issue or clogged filter. I would have a fuel gauge hooked up when this happens to see if it's a fuel issue next . Last could be am ECU shorting out. These are the next steps. Hoped this helped.Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.
Runs rough at idle. Almost has a burned valve kinda sound...BAP, bap,bap,bap. (Muffler got a hole in it somewhere in this deal.) But that may just be from the two cylinders apparently not working. Yes, it moves, but very shaky, quite a bit of shuddering.

I'm usually pretty good at figuring things out. I'm tight on available time and $$ on this, so I'd like to avoid the pretty extensive disassembly to verify the mechanical timing.

But, with this it seems odd that the "dead cylinders", 3 and 4 don't have much in common. They are on different sides of the engine. They are on different spark modules. They are on different fuel rails.

Since this happened suddenly, I'd have a hard time believing there are two separate problems. But, I can't think of anything that they have in common unless it is the fuel injection control.

The only manual I have on this is the Chiltons Isuzu manual. In the engine electrical for the 3.2 DOHC it shows a "common connection", i.e., parallel wiring for all of the injectors. This would suggest that they are all pulsed at once. Is this in fact the case? Or does the ECM have a separate driver and connection to each injector?

Your thoughts, if you have the time...
Expert:  Tom replied 5 years ago.
Yes they are all pulsed at once. From the description this is a timing issue and I would physically check cam and crank timing and of that checks out do a cylinder leak down to rule out a valve issue . These would be the next steps and will not cost you money just some time. There were some engines harness issues with these trucks failing also and ECUs . These are the next steps. Hoped this helped. Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.
Two last items...

Would it be worth the time to check injector operation before tearing the plenum and front engine extrenals off to get at the timing belt/chains?

Also, since this is a 20 year old vehicle, I'm concerned about breaking a connector, like the ones on the fuel injectors. There's a picture at this URL:


Expert:  Tom replied 5 years ago.
You can use a noide light to check injector pulse if you want to first . No need to worry about breaking a connector just be careful you will be fine. Sounds like a timing issue or valve issue to me. Hoped this helped.Positive feedback and bonuses greatly appreciated.
Customer: replied 5 years ago.
Is there any trick to getting the connectors off of the fuel injector?
Expert:  Tom replied 5 years ago.
Yes pull the metal clips back with a pick and then the connector slides off.
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