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MrDiag
MrDiag, ASE Certified Tech
Category: Car
Satisfied Customers: 168
Experience:  16 Years Of Automotive Repair and Management Experience.
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Isuzu: I have an 1990 Isuzu Trooper II, with a 4ze1 engine

Resolved Question:

I have an 1990 Isuzu Trooper II, with a 4ze1 engine and I-TEC fuel injection. Recently I had to replace the cylender head with a new head. I took very reasonable care during disassemble to color code all hoses and wires and take numerous digital photos during the dis-assembly process; however, this is not assumed to be 100% in any case. Reassembly went basically well, which included cleaning all mating surfaces, new gaskets, proper bolt torqueing and almost a complete replacement of the hoses. Otherwise, all hoses were inspected to the best that I could examine. The wire harness for the fuel injection system was quite a trick to get back into place as the space is very, very tight around the intake manifold. Prior to starting, the turned engine over for about 20 seconds without plugs to recirculate the oil and fuel system.

The problem: When I attempted to start the engine, it would run for about one or two seconds (very smoothly) and then stoped. Every repeat start attempt was the same. The first thing I checked was for a vacuum leak, of which I found one and which resulted in running for about two to three seconds before stopping. I attached a vacuum gauge to the intake manifold and a pressure gauge to the fuel line outlet hose. While the engine would run for the three seconds, the vacuum gauge indicated a steady 15 in. of vacuum and the pressure gauge on the fuel line quickly pegged my gauge and held well after the engine stopped, but this gauge only reads to 10 psi (I can try with a bigger gauge). I am only working with a Haynes (cross-your-fingers) repair manual, which does not provide any info to test the fuel injection system except for the fuel pump and the apparent related fuses.
Though the I-TEC fuel injection system does not appear to have a " cold start injector", I would still assume that there is some kind of cold start fuel enrichment system, which is all that is allowing the the engine to run for the 2 to 3 seconds (though very smoothly).

Before I start removing engine parts I first want to see if I can single out the problem. The only odd item which I have found so far is a disconnected wire connection (two wire plug) at the back end of the same wire harness which feeds through/across the intake manifold and fuel injectors; there are three (each) male wire plug ending connectors at the end of this wire harness, but I can only find two female wire recievers at this location on the engine and these two appear to match up properly by color code. Can you find an answer for my problem?

Bud Cook.
Submitted: 2 years ago.
Category: Car
Expert:  MrDiag replied 2 years ago.

MrDiag :

Hi, My name is XXXXX XXXXX I am here to help. Can you tell me what colors the wires that you are referring to are?

Customer:

The wire you can not find a receiver for has a white (or light grey) and a black wire. The other plug which this might possibly be mixed up with I have going to a black module at the b ack of the intake manufold. Those wire collors are blue and yellow. there does not appear to be a secondary trace color on that set of wires. The third plug I have plugged i nto the coil and it has a blue wire and

Customer:

a yellow wire with a green tracer

Customer:

I believe the coil set up is correct since I am getting spark

Customer:

Any ideas?

MrDiag :

Ok, let me see if I can find those wires and see where they go

Customer:

ok, thanks

MrDiag :

ok so far it shows a blue and a yellow with blue tracer going to coil. While I look for more, have you checked injector pulse to see if you lose that when it stalls?

Customer:

How do I measure the injector pulse?

MrDiag :

I also see a green and yellow with green going to the air regulator solenoid. Is there any way these two are switched? You check injector pulse with a noid light which is kind of like a test light that plugs into injector plug and flashes if there is a signal. Let's keep checking wiring for now

Customer:

The wire colors are sometimes off-shade as a result of residue from the black tape wrap, so a blue and a green wire color can get mistaken in this case. Also I will try an incondesent light bulb which is more likely to give me a more true color. The three wire pair in this case are only about 5 inches long, so where ever they go to must be relatively close by. Off hand, do you know where the air regulator solenoid is located ?? my guess is on the throttle body. I do have a test light, but it appears that in order to get access to the injector plug that would most likely have to remove the throttle body and the fuel supply bar; which is not the worst thing to do, but was hoping to avoid this if I could. However ,, if all else fails.

MrDiag :

I don't blame you for not wanting to take that apart and I would wait until you have tried everything else. It's hard for me to find an abundance of info on that year vehicle but it is possible that a plug going to another engine control might only get power during start up and then not. So if that wire were going to your coil then you could lose power to the coil causing a stall. Just speculating at this point. The yellow with blue going to the coil should have power with the key on so if you could rig up your test light to monitor that while the engine stalls and see if you lose power to the coil that might give a clue.

MrDiag :

Also is the mass air flow sensor plugged in?

Customer:

This sounds like an easer test, as earlier today I was going to try by removing the spark plugs from the head and see if they would still produce a visible spark, better yet I'll try using my timing light. But I'll start by measuring the voltage at the wire pair plug I have in the coil. What you said does make sense even if the engine will restart (for 3 seconds) every time. Yes, there is a possibility that the receiving end to the mistery plug is buried under the fuel supply bar and wraped up in the wire harnes. By the way, the pair of wires I have pluged up to the coil are blue and yellow with a green tracer (apparent green). I will return to the shop to conduct some voltage tests and get a better look at the colors. Be back soon.

MrDiag :

Ok. I hope that's it.

MrDiag :

Also make sure the mass air flow is connected properly

Customer:

Well, not to keep you up too late, but this is what I found out so far after conducting several start-up tests and more digging around:

MrDiag :

Ok

Customer:

Upps, let me start all over and not hit the "enter" key. After conducting several start-up tests and further probing around, this is what I found so far: 1. The wire, yellow with blue tracer continued to have power as long as the key was on (as it should) and continued to have power after the engine cut-out (key always left on during the test). 2. The wire, yellow with green tracer is wrapped immediately to the plug I have plugged into the coil, which has a single wire plug which goes to the coil condenser. 3. Using a timing light (which can have it's occasional no-show flashes), showed that the spark wire continued to get a charge even while the engine started to cut out but the crank was still rotating. Based on this I believe I have the proper set of plug/wires attached to the coil. 4. I did some further testing of the "mystery plug", which showed the black wire went to ground (as would be expected) and the white wire appears to never have any charge or power at any time during the testing. So I just went ahaed and grounded the white wire which resulted in no apparent change or improvement. So that is it in a nut shell. Yes, if I could only get a wiring diagram of the fuel injector system, as for one thing I would like to know if a "cold start enrichment system" exisited. Also, yes I did check the air flow sensor several days ago and it look "ok". But,, get this, when I ran the on-board diagnostics (sp??), the only problem detected was the "air flow sensor", the only item which showed up as a problem. However, this detection may have occured when I was running the starter to turn the engine un-wired (everything else disconnected) in order prime the engine with oil and fuel (I'm an old farm boy). However, I kept this in mind and cleared the on-board diagnostics system, wired everything up and following several re-starts there was no indication of any detected diagnostics problems on the on-board system. I'm not sure what to trust. Anyway, this is the latest,, good luck.

Customer:

Oh , one more thing,, it's ok to just sleep on it as I'm turning the day off. We can pick it up in the morning.

MrDiag :


MrDiag :


MrDiag :


MrDiag :

I hope this info helps. I would also check all your grounds that needed to be removed to pull head.

MeganExpertsMod40971.8104719907
MrDiag, ASE Certified Tech
Category: Car
Satisfied Customers: 168
Experience: 16 Years Of Automotive Repair and Management Experience.
MrDiag and other Car Specialists are ready to help you
Expert:  MrDiag replied 2 years ago.
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Customer: replied 2 years ago.
MrDiag.
I don't know if you got the my final message as to what the problem was. I
did in fact re-assemble everything correctly and the mystery connector plug
does not appear to have any function in this case. My best guess is that
when I conducted the cranking/priming operation, with purposely not having
all the wiring or air ducting in place, that it put the ECU (system
computer) in a tail spin, and I was surprised that I only read one
error code on the self-diagnostic system on the first try. Though I went
through the clearing procedure, showing no further errors, the engine would
still not run. When I received the wiring diagram and proceeded to check
the power status of the fuel injection and related wires; this in turn
grounded each of these individual wires through the ECU. At this same time
the self-diagnostics system then showed a correct error code this time that
one would expect to see, that these specific wires are open
and/or grounded. I proceeded to connect the wires back and continue
testing the out-put. Then to my surprise the engine started and continued
to purr like a kitten. I have heard about these kind of problems from time
to time, but this is the first time it has happened to me. We basically
had to go through a check-by-check procedure in order to rule out all
other possible problems. Kicking the ECU in the butt just so happened in
the process of testing the fuel injection wires I best figure.

So far we have been off and running.
Expert:  MrDiag replied 2 years ago.

That is great that it's running good. I didn't receive this info if you posted it before. I am glad you followed up with me and always happy to hear repair success stories. It was a pleasure working with you. Take care,

Rich

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