Why when key on injectors just begin dumping fuel into cylinders?
10-18-2007, 09:00 PM
#1
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Why when key on injectors just begin dumping fuel into cylinders?
I got a weird problem that has the mechanics working on my vette and me completely baffled. Ok 86 I bought no motor or trans. The 383 Tpi was going in fine and it was going to be fired up today. The mechanic tried it and it would turn over but not fire the injectors, well he notices the injector fuse is missing so he puts one in, and all the injectors start dumping into the cylinders (he had a pulse test light on them, and it just stayed lit). So he turns the key off and pulls the battery leads. He then pulls the spark plugs and fuel pours out of every cylinder. No one at the shop has ever seen this before, usually the problem is the injectors wont fire, here they wouldnt stop firing. Ok here are the specs on the motor 383 tpi, bosch 30lb injectors, pcm for less chip, msd 6al box with pro billet distributor. All the wiring looks fine no obvious missing grounds or shorts. What we are thinking so far is either an ecm problem, or a problem with the msd box. Any help would be greatly appreaciated.
10-18-2007, 09:09 PM
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2023 C7 of the Year Finalist - Unmodified
injectors.
All eight pumping gas? 86 is batch fire. Sounds like ecm? Remember they are always positive to them. The grounding signal is what fires them. Dont know if that helps. Just my .02
Last edited by CorvetteMike2024; 10-18-2007 at 09:12 PM.
10-18-2007, 09:25 PM
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Yes all 8 started dumping, and by the way it did not throw a code. After all this it blew the fuse for the fuel injectors that was missing, and now each time you try to start it, the same fuse blows.
10-18-2007, 09:49 PM
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I agree on a short of some sort. My question is that there should be minimal chance that both banks could short out simultaneously, unless someone has been monkeying with the harness. I would be curious to see if a solenoid lamp would reveal a short with the key off (ECM disabled), or do the injector low sides only conduct when the ECM is energized.
10-18-2007, 10:53 PM
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injectors
you can check injectors with a digital multi function testor I believe. OBD1, I have had problems without throwing any codes. Sometimes those injector wiring harnesses that run along the valve covers get pretty toasted.
10-18-2007, 11:13 PM
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btdt
1) keyoff/engine off.
2) unplug all 8 injector elec connectors.
3) remove battery GROUND cable.
4) unplug ecm connectors.
5) reconnect battery.
6) key on/ engine off.
7) replace any blown ''inj'' fuse
8) probe all injector connectors, both terminals, for +12v...one terminal should have power, the other should not...probe the ''unpowered'' terminal for continuity to ground... if continuity is demonstrated , you have short to ground in wiring harness.
9) if no ground at injector plug, check each injector, either terminal ...no grounded terminal should be found, if grounded that injector is junk...resistance from any injector terminal to the other terminal of same injector should be 12-16 ohms (varies for different years),the same for all injectors within 2 ohms.
10) if no harness or injector is grounded, ecm is defective.
check dipstick for oil dilution by gasoline, immediate oil change mandatory if level has gone up or smells like gasoline.
2) unplug all 8 injector elec connectors.
3) remove battery GROUND cable.
4) unplug ecm connectors.
5) reconnect battery.
6) key on/ engine off.
7) replace any blown ''inj'' fuse
8) probe all injector connectors, both terminals, for +12v...one terminal should have power, the other should not...probe the ''unpowered'' terminal for continuity to ground... if continuity is demonstrated , you have short to ground in wiring harness.
9) if no ground at injector plug, check each injector, either terminal ...no grounded terminal should be found, if grounded that injector is junk...resistance from any injector terminal to the other terminal of same injector should be 12-16 ohms (varies for different years),the same for all injectors within 2 ohms.
10) if no harness or injector is grounded, ecm is defective.
check dipstick for oil dilution by gasoline, immediate oil change mandatory if level has gone up or smells like gasoline.
Last edited by redrose; 10-18-2007 at 11:21 PM.
10-19-2007, 02:19 AM
#10
Le Mans Master
It is going to either be a wiring problem between the injectors and ECM, as CFI stated, or a bad ECM. Sounds like there is a constant ground keeping the injectors open.
10-19-2007, 02:18 PM
#12
Safety Car
the ground side is shorted to ground or the PCM bit the dust
10-19-2007, 06:48 PM
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Ok I spend all day today working on this problem and we still havent got anywhere. The previous owner really butchered the engine wiring, and we spent a couple hours double checking everything was where it was supposed to be and not shorting out. One question we had was how to wire in a msd 6al box and an msd probillet distributor on an 1986 tpi. I searched the forums and got the msd kit and coil i thought was correct but it is for an 1987 and up tpi. The difference is 86 was coil on cap, and 87 was external coil, and the electrical connectors are completely different. I am not sure how to tie it in with the ecm, becuase doesnt the ecm have to know where the pistons are at in order to control the fuel.
10-20-2007, 06:09 AM
#14
- 1986 Original Owner -
10-20-2007, 12:33 PM
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vettes, some cadillacs, got the better ''big'' dizzy (coil-on cap) until 91...camo's, trucks, etc got the little cheapo (remote coil) 87 and up...connectors are different, but color of wires was the same (some have 3 of the 4 wires in ''standard'' color with the 4th wire varied, just hook up the three that do match and connect the odds)...all l98's are ''batch'' fired injectors and ecm doesn't care, as long as it gets a signal from the dizzy that the engine is turning over it will pulse the injectors.
