Major injector/ECU/fuel problems

Here’s the diagram to which I’ve been referring (click for full size).

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. It’s the “0.8 GRY 120” ground wire in the above diagram.

Now, I’m a novice at best at deciphering wiring diagrams in general. It looks like the wire goes to 4 different places? The fuel pump, then “ground distribution cell 14”, (wherever that is) the fuel pump relay, and the oil pressure switch. I think I’m 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, you’re getting an apparent short on that wire because you’re 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 “upstream” 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 “downstream” through the fuel pump.

Don’t 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. I’ll 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 so… wouldn’t 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, I’ve 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 doesn’t 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 that’s 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, I’m no electrical expert, but I’m pushing 50 and I use to rebuild hydraulic cylinders a couple times a week when I worked for a logging company for many years. I’m 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 didn’t 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. I’d go there, before going to Autozone, FWIW

https://www.napaonline.com/napa/en/p/FPBES71188/FPBES71188_0232960538

GM part # 19178983. This may be a 2-ring kit (per injector).

ACDelco 217-3367. 2-ring kit

ACDelco 217-3113. 9-ring kit. For 4 injectors + may include fuel supply tube o-ring.

Rockauto lists kits from other brands, too. The kit that @db4690 linked to at Napa is by Fel-Pro.

Yes, GM specifies oiling the o-rings.

I ordered the Delco kit from Rock Auto shortly after making my last post.

No, I didn’t install them dry. That kinda goes against everything I wrote in my post. :wink:

I want to thank everyone who has been trying to help in this thread! While im not out of the woods yet, you guys (possibly gals) have been a tremendous help the whole way here.

No experience w/this specific fuel injection design, but I can’t see how damaged o-rings would allow fuel to flow from the injectors, unless they were somehow pushing on the pintles. At least for the injectors I’ve dealt with the O-rings are there to prevent air from leaking into the intake manifold, not to prevent gas from leaking from the injectors.

The diagram appears a little blurry on my computer, hard to read the writing, but from what I see that 120-grey wire you mention should have battery voltage on it when the pump is powered. Does it? That is the power supply for all of the injectors, and should have battery voltage on it at all times the engine is running or cranking. When a gas-spurt is needed from an injector, the engine computer grounds the other side of that injector, causing current to flow through the magnetic solenoid that surrounds the body of the injector, which creates a miniature magnet inside the injector, and the force of that magnetic field pulls on the plunger and opens the injector so fuel sprays out the end. It’s like one of those gadgets with a spring loaded handle you put on the end of a hose to wash your car, but you can’t adjust the flow rate, it is either on or off in other words. The computer adjusts the amount of fuel delivery by varying the amount of time the solenoid is grounded instead.

So if you had one of those gadgets on the end of a hose, and it sprayed all the time the water was turned on, rather than only spraying when you pulled on the handle, you’d know how to debug that, right? Probably the return spring inside has broken. Or the seal at the tip isn’t sealing. This problem seems identical to that. It’s a little more complicated of course, for one thing, gasoline is involved which is dangerous to spray around.

  • All the injectors are bad b/c their seals are not sealing or their plunger isn’t returning to home to seal them off when their “handle” is released.

  • The “handle” is being pulled all the time, meaning the other side of the injectors are being held at ground voltage all the time, instead of just the short interval when they are supposed to be injecting gas.

@GeorgeSanJose, this is a different type of fuel injector than you are used to. You’re probably thinking of an injector that mounts between the fuel rail and the intake manifold (which I was at first, too). On this engine, the injectors actually mount within the fuel rail. The fuel rail is a gallery/passage cast into the lower intake, and the injector bores intersect this gallery. Holes in the gallery connect directly to the intake ports. The injectors plug into these holes, sealed with an o-ring. Fuel enters the injectors in their middle, instead of one end.

Here’s a picture that illustrates this. The fuel gallery/passage/rail is #6, the injectors #7. If you click on the picture, It’ll open larger in another window. If you click it again, it may get even bigger (same with the electrical diagram I posted above).

Oh my, I see what you mean. That makes this problem more difficult b/c the problem could be the injector, the o-ring, or the surface it seals against. Thanks for explaining.

Exactly, I took for granted you guys knew it wasn’t an injector on rail design like normal. Its a fantastic little engine, easy to maintain, rebuild and generally work on. The injectors are held down by a long, flat forked bar and the injector housing tabs. Its… a pain.

I don’t think its a crack(s) in the rail itself, or the injectors themselves. One O ring was split (they are so loose/oversized its crazy) and another one was just… gone, so I assume it too split and is inside the fuel rail and hopefully not the cylinder. I’ll blow it all out with compressed air to be sure.

I think the lower rings were too large and probably didn’t make good/any contact with the ports. Ill test that theory today with a cheap felpro gasket kit (5 bucks). I’ll just install the injectors, plug the fuel fuse in, and try cranking it. I should know in about 30 seconds if anything has changed!

FWIW . . . Felpro generally makes pretty good gaskets

My first choice would be OEM . . . my second choice would be Felpro

I like Felpro, I’m just saying the price is cheap

I reinstalled the injectors, and no more over fueling! The upper O ring on injector 4 leaked for seemingly no reason, so I used an O ring from an older injector. The injectors went in so much better this time, like night and day. I really think the lower O rings shipped with the new injectors are too large.

So far, so good… next is the P300 sorting.

You guys were awesome with this problem, maybe you can help me with my main one?

You’re still getting the p0300 – random/multiple misfires across all the cylinders? First make sure it doesn’t go away after driving the car a few days, the computer might just have to do a re-learn now the injectors are working again.

Misfires across all cylinders usually means there’s something common to all the cylinders that is the problem. So you’re looking at a problematic ignition system, ignition timing, or faulty air/fuel mixture. Less likely, but still possible is an exhaust system problem, compression, valve timing problem, or inaccurate sensors.

Or maybe it isn’t misfiring, and it’s just a bogus code. Do you believe it is actually misfiring? If so, where I’d start is to bring all the routine engine maintenance up to date, then probably a throttle body inspection and throttle body cleaning, paying att’n to the state of the MAF. If it looks to be covered w/gunk, give it a good cleaning. A gunked up MAF is a fairly common reason for misfires across all the cylinders.

If you could figure out a way to get access to real time scanner data, that would be very helpful for this problem. Especially fuel trim data. Is that possible for your car?

BTW: Problems w/the throttle position sensor can cause this too, so correct those first before starting down this road, if you haven’t already.