A little long, but I wanted you to have all the info................

I've been having trouble getting my 1987 Z28/LB9/Auto to start lately and the one time it finally did start it ran very rough and wouldn't idle. I felt around the exhaust manifolds for hot spots and the driver's side was hot all the way down, as you'd expect, but the entire passenger side manifold was as cold as a stone. This motor is bone stock except for the swap from MAF to MAP and serpentine belt. Here are the facts: at key-on the SES light gives the checksum wink then stays on; fuel pressure at key-on is 42 psi and stays steady while cranking; cranking compression test showed ~170 psi all around; getting spark to the plug boots; both injector fuses are good. Also, the engine has been running fine since the S/D swap until lately so I don't think that's it.

Other things I've done: ohmed the injectors at ~16 ohms each; pulled the harness plugs from the ECM and shorted the injector banks one at a time to ground through my Fluke ammeter and got about 2.6 amps on each bank which is about right according to Ohm's law; inspected the ECM harness and found nothing out of the ordinary, even tried all 3 of my '730 ECMs, no difference. Also, no trouble codes. The plugs on the passenger side were wet with gas, so it is obviously getting fuel.

That's all I know at this point. What could possibly keep an entire cylinder bank from firing when all seems normal? I can usually keep prodding around and find the problem but this one has me stumped. Any ideas?

 

there isn't anyway for spark to not be getting to all 4 holes on one bank. my guess would be to check for fuel on the dead side. rereading it i also doubt there's anyway you could have the engine running with 4 dead holes.

 

You'd think so, but it did run as long as I held the throttle open, albeit extremely rough and it would restart a couple of times but it would not idle. A real head scratcher, ha??

 

Check your fuses there is one fuse for each side of injectors, Inj1
Inj2

 

This may sound stupid but check your plug wires. Like if you had 2&4 swapped and 6&8 swapped.

 

Firing order is correct, and as stated, the injector fuses are good. At this point I'll take any suggestions you have and thanks for the responses so far.

 

If everything you say is correct then it has to be one of two things: Something is causing the ECM to leave that bank if injectors "firing" (continuously on) or there is an obstruction in the exhaust for that side of the engine. If the engine was running and the plugs were wet on that side then there is excessive fuel to that side. If you have a cylinder on a running engine that should be firing but has no spark then you will still pull out a dry plug. The "breeze" of the intake charges coming thru will keep it dry. It either has too much fuel or no "breeze". If you can get it to run again check the INJ- voltage to that bank of injectors. Should average over 6 volts at idle. Also make sure something "silly" hasn't happened to the exhaust.
EDIT: Compare the INJ- voltages for both banks they should be the same.

 

Supervisor, you may be on to something there with excessive fuel, I'll look into that. I guess I need to borrow a noid light from my mechanic buddy and also check the injector voltage. Seems odd though that the symptoms are there on 3 different ECMs and moreso seeing as how there's only one injector driver. Another thing: about 150 miles ago (i don't drive it much!) I removed the injectors and sent them to Cruzin Performance to be cleaned & flow checked and they were returned with a clean bill of health.

 

My bad. I was looking at the schematic for my '88 and the ECM has an output for each side (bank).

 

Pardon my ramblings while I muse through your problem and data:

It could be caused by mechanical blockage in the RH fuel rail. That seems strange, since the FPR is mounted there, but it's remotely possible.



It seems highly unlikely that BOTH crossovers would be damaged/restricted, and a pressure tester would show that. The test you performed seems to indicate that fuel is present, so disregard that possibility.

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As long as the 'noid light fires on that bank while all the other injectors are connected, the ECM and injector power source would be O.K. If the light doesn't flash with the rest of the injectors connected, you may have a problem with the injector power supply (INJ1/INJ2 fuses). Since you've load tested each bank and read 2.6A, that possibility doesn't exist.

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You measured spark at all holes, but also mentioned that the plugs on the RH bank are wet with fuel. Plugs with wet insulators will shunt the spark energy directly to ground (the shell) without ever allowing a spark. If those plugs are soaked, try clean, dry plugs in those holes. If the fuel is present as you suggest, and the spark energy is present, even if the wires are out of order, there should be an afterfire or backfire. If they somehow magically all end up on the correct plugs, it should run. If you don't have a set of clean plugs handy, swap a couple of the easier ones from bank-to-bank. See if the dead cylinders move.

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There is nothing that of which I am aware that will cause a massive vacuum leak in that one bank alone. Even then, once it is running, the cylinder should fire (albeit lean) and generate some heating of the exhaust manifolds. ]

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Speaking of exhaust manifolds, if it is a dual exhaust, is the RH bank exhaust system crushed, collapsed, or damaged?

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Another observation is that even though the plugs are "wet", we still don't know whether a 'noid light will fire when the rest of the injectors in that bank are connected and the engine is "running". If the grounded side of the injector circuit is poorly connected, the ECM may not be operating the injectors. Remember that you externally shunted the injector bank to ground when you read the 2.6A load current? What happens if the ECM is allowed to switch ground to that bank? I know that the banks are internally connected at the ECM, but not in the harness all the way back to the ECM. You could temporarily jumper the grounding (ECM) side of the injector circuits across the banks and see if they all fire.

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I'd suggest the clean, dry plugs first, then checking the injector bank firing while keeping the engine running by tweaking the throttle.

 

That's correct, there are two injector connections leaving the ECM but they are connected to the one driver inside the box.

 

This could be the one..........
This problem has been such a pain that I may not have been thinking clearly. Off to get a noid light and maybe a cold beer.............

 

Actually, that might help. Sometimes it's good just to get away from a problem for a while and return with a more open (or at least, numbed) mind.

 

I had to get some distance between me and this problem, but I got it fixed today, thanks to ya'll, especially The Helmeted One. I bought a noid light set, hooked it up and it flashed when the injectors fired so that was one less thing. After some more cussin' I bought new spark plugs, gapped and installed them (with even more cussin'), hit the key and the biotch fired right off. Vader was correct in that the gas had apparently ruined the plugs. It seems to be OK now. Thanks everyone, especially Vader, for the help.