Probably at the back of the cylinder head or thereabouts.
Realized I was mistakenly testing for short before on the non signal wire. (doh!) There is no short to the engine.
Left injectors 2 and 3 plugged in, and checked for shorts at ECM harness plugs. Both I confirmed to be shorted; of course 1 and 4 did not. So the short is in the harness, amazing. The 5 pin plug is so close to the injectors its sad, http://imgur.com/NMchGIg (clipped to the dipstick) so Iām hoping its in the plug itself, as there is a lot of wire between it and the ECM.
Do the injector ground wire continuity tests with all connectors unplugged. Since the injectors share the positive wires with the fuel pump, if you check for continuity of an injector ground wire at the PCM plug with the injector plug connected, you will see an apparent short because the current path connects through the injector to the positive wire, and then through the fuel pump to ground.
Re: no noid light but the injectors are squirting?
One idea, the noid light might only light at a certain minimum voltage difference between the injector pulse pin, and injector ground. While the injector might open with a smaller voltage.
Re: no injector pulses without ignition module
They put safety features in the computer software to try to prevent fuel spills after an accident. For example the injectors wonāt usually pulse unless the computer detects the engine is rotating. Likewise, there may be something that prevents injector pulsing unless the ignition system is functioning.
If I had this problem Iād try a couple of things first, before trying to debug a wiring harness or computer problem
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verify none of the injectors squirt any gas during cranking when they are completely unplugged from the wiring harness.
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verify you can pulse the injectors manually (with an injector-pulser gadget or a home-made equivalent using a push button switch), and that they only squirt gas when the pulse is on.
checked for short to ground as you suggested, and couldnāt find any short to ground no matter what I tried. None in the harness now, none in the injector harness, nada. So there must be a reason the injectors are filling up the cylinders, that isnāt electrical? Gas was getting in the oil before of course, and the pressure in the fuel line bled out when you did a pressure test at the pump. I later replaced the regulator, now this.
This is all started with a code for P0300, and a code for a TPS which I repaired. Still have the P0300 and still have the gas in the oil/leak down problem from before, and now this problem.
I can try pulsing them, but yes when they are not plugged up they donāt fill up the cylinders. Iām very confused.
Should i remove the injectors and reseat them? If i did install them incorrectly, what should i look for? Surely if their is no short, gas must be getting into the cylinders from the injector area?
That would imply that none of the injectors is stuck open and that the problem must be electrical. However, it shouldnāt happen with the key off or key on/engine off, since there would be no positive voltage at the injectors, unless the fuel pump relay or the oil pressure switch were stuck closed, as mentioned earlier.
You say there are no shorts in the harnesses, but did you check for shorts to ground at the PCM injector driver pins? You can do this from the injector plugs on the ground side with all PCM connectors connected. Try it with both key off and on.
I checked for shorts from the injector harnesses to ground (no ECM connected) and at the end of the main harness via the plugs/pins that connect to the ECM, and checked the harnesses at the injectors again with the ECM plugged in. No shorts, with a confirmed good body ground. And yes, I checked both the signal wire and ground wire for shorts at the injector ends, with the ECM connected, with the key on and off. No shorts.
What usually happens is I turn the key to the on position, the pump primes, the rail fills up and it seems almost immediately the cylinders start filling. If I attempt to crank the engine shortly after the system is primed; by the second short crank the cylinder is almost 1/4 full of gas. If the injectors are not plugged in, then the system primes and the engine cranks normally and no evidence of fuel is seen.
The old set of injectors, when I pulled the plugs, cylinder number 4 was wet fouled, cylinder 3 and 2 were dry fouled, and cylinder 1 was halfway to being gas fouled.
I have a parasitic loss somewhere as the battery loses voltage daily. Something, is being constantly energized. Iāll double check the ECM and wiring for shorts, and edit this post with the results, just to make sure.
EDIT: On a hunch moved 5 pin connector around after another round of tests. (wondered if the short was intermittent based on position of the connector) This time with KEY ON OR OFF, the meter read shorts to the ground side of the injector harnesses. So, am I correct in assuming the injector driver in the PCM has a short? Or the 5 pin connector has an issue? Both?
above post updated as promised
Youāre just gonna have to keep plugging away until you find the exact location of the short(s).
If you again isolate the harness from the PCM and redo the tests while wiggling the 5-pin connector and still find short(s), you can probably rule out the PCM.
The parasitic draw will have to be diagnosed on its own. It may or may not be related to your injector problem.
Do you have a way to post the wiring schematic for the injector circuits? If you have one, take a photo of it w/your cell phone and upload it to this thread.
I disconnected the ECM, and then I unplugged the injector harness from main harness. When checked, no short. Next I checked the plug at the main harness, (engine bay) and I got a confirmed short. Itās the ā0.8 GRY 120ā ground wire in the above diagram.
Now, Iām a novice at best at deciphering wiring diagrams in general. It looks like the wire goes to 4 different places? The fuel pump, then āground distribution cell 14ā, (wherever that is) the fuel pump relay, and the oil pressure switch. I think Iām getting closer to where my problem is?
The gray wires are the positive supply for the fuel pump and injectors. Power comes from the fuel pump fuse and through the pump relay and oil pressure switch to the in-harness splice labeled S136. From there power goes to the pump and injectors. The connector labeled C102 with pins A thru E is the 5-pin fuel injector harness connector.
As mentioned before, youāre getting an apparent short on that wire because youāre reading continuity through the fuel pump motor to ground. This is normal.
Even if as mentioned ive had the fuel pump fuse removed this entire time?
The fuse is on the āupstreamā side of the connector from which you are probing, and is isolated by the open relay and oil pressure switch anyway, so it is irrelevant here. Your continuity flow is heading ādownstreamā through the fuel pump.
Donāt worry about the gray wire. If it were shorted, the fuel pump fuse (if installed) would blow when the key is turned on. Concentrate on the injector ground wires. One is black and the other three have black stripes on green, pink, and blue.
Key on/off no shorts on injector harness at signal/ground wires now. Iāll have to downgrade from novice rank to dullard rank haha.
Okay, so if the injectors only fill up the cylinders when they are actually connected, and there is no short apparently making them constantly pulse, then what other reasons would this occur?
If the O rings had been all damaged, they would allow fuel in the cylinders regardless of power or ground correct? Should I check the injector harness for voltage with the key off/on? If soā¦ wouldnāt the fuel pump fuse being removed stop the injector harness from getting power?
EDIT: Yep no voltage, tested with test light and DVM.
Yes, the fuel pump fuse is required to be in place to get power at the injectors. Again, there should only be power at the injectors with key on during pump priming, and key on with engine cranking or running. With key off or key on engine off after the pump prime cycle, there should be no power.
From the beginning, Iāve been visualizing the wrong type of injector for this application. Now that I know the correct setup, yes, it is very possible that fuel is getting around the injector inner o-rings and into the cylinders. It doesnāt seem likely that you would have damaged all four, but the only way to know is to pull the injectors and have a look. You are putting two o-rings (one large and one smaller) on each injector, right? The o-rings should be lubricated with a bit of engine oil before injector installation.
One unlikely possibility is that the lower intake manifold has a crack and is allowing fuel into the cylinders through the crack from the fuel rail (if thatās even possible), which is cast into the manifold. Unless there is major crackage though, one would think only one cylinder would be affected.
Well I just came back to talk about the O rings, but you beat me to it. I got all 4 injectors new off Amazon for 85.00 plus shipping. I just pulled the upper intake and the injectors.
All 4 injector upper O rings were pinched in various places, and the lower O rings are VERY loose. One had actually split in two pieces. Now, Iām no electrical expert, but Iām pushing 50 and I use to rebuild hydraulic cylinders a couple times a week when I worked for a logging company for many years. Iām thinking to cut corners, the O rings supplied with the injectors are ill-fitting and of very cheap quality. When I installed the injectors I took the level of care I always have with O rings and installing them. In all my years of work, I can remember maybe twice I damaged an O ring installing it.
I think the original injectors were dying, at least very worn and clogged. I think the number 4 injector was leaking, and the number 1 injector was starting to get as bad. This makes sense as 4 is near the return line, and 1 is near the inlet. (I could be crazy) I think 4 was causing my P0300 code, and the source of my fuel pressure leakdown and the source of gasoline in my oil as well.
Ive had bad luck with O rings from Oreillys, Advance, and Autozone either not fitting properly, or being off in some way. I want to do this right, I wonder if GM has an OE O ring kit available?
You didnāt install the o-rings dry, did you?
Many service manuals specify to lube the injector o-rings with engine oil . . . not sure if this applies to your engine, though
Napa auto parts would be a good place to get an o-ring set. Iād go there, before going to Autozone, FWIW
https://www.napaonline.com/napa/en/p/FPBES71188/FPBES71188_0232960538