Best plan of attack for injector issue?

[Fubar1764]

We did a compression test on all 4 cylinders. No problems there. We also did a spark test (live) and again no problem there. So that leaves fuel supply/injection.

My guess is the electronic fuel injection went screwy rather than the injectors themselves. The reason why I think this is because the issue happened suddenly. If it had been a physical injector issue, I would think the motor would have gradually gotten rougher.

So, my question: what should be my plan of attack in diagnosing?

[Doc Fizzix]

My guess is the electronic fuel injection went screwy rather than the injectors themselves. The reason why I think this is because the issue happened suddenly. If it had been a physical injector issue, I would think the motor would have gradually gotten rougher.

Jack I do not mean to send you off course or make you try something just for the fun of it but your problem reminded me of the hell I went through about a year after I bought Dereks old Elan and the problem came on suddenly, in fact it was over night with no warning. The day before the car ran great and then the next day it would only run on one cylinder, for the next month and then some I went through every possible sinario and tested or replaced everything. I am not sure if you even tried this but I will mention it one more time and then stop bringing it up and bugging you with it.

Check the connectors going to the injectors, pull each connector and then clean the terminals on both the injector and the connector, I used a Dremal with a small wire brush.

I had tried everything even to the point of swapping out the ECU, coils, re-traced every electrical line, you name it I replaced it. I also did the same as you, tested compression and spark, all was good. It was not until I was removing the fuel rail that I discover that the connections between the injectors corrode up very easily. I also checked my spare motor and discovered that it also corroded in a very similar way. I ended up replacing all the connectors when I rebuilt the motor with some gold plated connections just to make sure that never happens again.

[Fubar1764]

Jack I do not mean to send you off course or make you try something just for the fun of it but your problem reminded me of the hell I went through about a year after I bought Dereks old Elan and the problem came on suddenly, in fact it was over night with no warning. The day before the car ran great and then the next day it would only run on one cylinder, for the next month and then some I went through every possible sinario and tested or replaced everything. I am not sure if you even tried this but I will mention it one more time and then stop bringing it up and bugging you with it.

Check the connectors going to the injectors, pull each connector and then clean the terminals on both the injector and the connector, I used a Dremal with a small wire brush.

I had tried everything even to the point of swapping out the ECU, coils, re-traced every electrical line, you name it I replaced it. I also did the same as you, tested compression and spark, all was good. It was not until I was removing the fuel rail that I discover that the connections between the injectors corrode up very easily. I also checked my spare motor and discovered that it also corroded in a very similar way. I ended up replacing all the connectors when I rebuilt the motor with some gold plated connections just to make sure that never happens again.

Thanks! I wanted to get the easy stuff out of the way first. Since the wires looked old, I figured I'd replace them anyways as well as the plugs. Coil packs, well, I'm sure they were original as well. Again, swapping them wasn't a big deal since they're old parts that could use some swapping anyways.

At this point, I plan to follow your lead on the problem. If the injector connection is the weak link, then that's the first thing I'll look at. Thanks Doc!

[GeoffSmith]

Jack,

If it all started happening at the same time then maybe it's a fault common to all injectors i.e. return or earth connection. Obviously, if the connectors on the injectors are a bit corroded then it's not going to help, but it's probably worth checking anything that's common at the same time.

Good luck.

Geoff

[Doc Fizzix]

At this point, I plan to follow your lead on the problem. If the injector connection is the weak link, then that's the first thing I'll look at. Thanks Doc!

Lets hope for the best


Like anything, it may be the problem and then your troubles are over or at least you can rule this out and move to the next thing. I should have also given you a warning, the plastic connections get old and brittle over time so be careful pulling them off. Don't pull them off by tugging on the wires, try to get behind then with a small screw driver or something to pry them off, also, if you do this be careful where you pry, it is best to pry at the top side of the connector. If I remember correctly, I busted the tab on one of the connectors and it still worked but I ended-up finding an exact replacement at Carquest and removed the old connector and then soldered in the new one. (I will look up the part number if you need it, I still have the box)

Here is to wishing you luck

[ESM]

We did a compression test on all 4 cylinders. No problems there. We also did a spark test (live) and again no problem there. So that leaves fuel supply/injection.

My guess is the electronic fuel injection went screwy rather than the injectors themselves. The reason why I think this is because the issue happened suddenly. If it had been a physical injector issue, I would think the motor would have gradually gotten rougher.

So, my question: what should be my plan of attack in diagnosing?

For start don't assume the problem lies with the injectors or injector drivers. A faulty CTS, MAT or MAP sensor would mess up fuelling even if the injectors and injector circuits were working perfectly.

[Fubar1764]

Here's the latest:
We looked at the electrical schematic and traced the wiring back as far as we could. The connectors within reach all seemed old but not corroded and still working. My friend borrowed an injector testor. I removed the electrical injector lead and tried each out. We discovered that injectors 2 and 4 weren't getting an electrical signal to spray fuel. Turns out the clean plugs were the ones that weren't firing! The dirty plugs were just working overtime to compensate and not firing well. So now, we're thinking it might be the EM computer or maybe a resistor pack (a trusted GM mechanic made that suggestion. . .he's somewhat familiar with the Isuzu version).
Do you think the ALDL cable and ElanScan will be helpful? Also, I can't find anywhere where there's a description of where wiring connectors are. Does such a thing exist or is it a matter of dig and ye shall find?
Thanks!

[ESM]

Which wiring connectors are you looking for? I suppose you are only interested in those where the two injector circuits are separate (the ECU -> injector rather than the injector -> earth side) and the only connectors that meet that criteria are:
1) ECU -> ECU harness,
2) ECU harness to injector harness (2 connectors in front of the coolant bottle)
3) and injector harness to injectors.
If you've got continuity from the plug that goes into the ECU (pin C15 or D15, depending on which circuit is out) to the injector plugs and no short to ground then you'd be looking at a dud injector driver in the ECU. I'm a bit surprised you haven't got an injector circuit code set if its stuffed.

The circuit diagram indicates that the Elan only has resistors in-line with the injectors in the NA version.

[Fubar1764]

Well, if it sounds like I'm a retard and haven't really worked engines, that would be right!

BTW, everyone, thank you for helping me with this!


Ok, back to work. . .

The wiring I was looking for is described in Sheet 4A in the Section MJ notes. On that page, about bottom-half of the center-left of the page, there's a diagram of injection connectors to Cylinders 1, 2, 3, and 4. From this diagram, I conclude (and please correct me if I'm wrong) that the electrical signal to the 1 and 3 injectors and 2 and 4 injectors are grouped together. So, I'm thinking that if 2 and 4 went out together, THAT would be the most likely place to look for a corroded connection. ESM, this is the connection that I'm trying to find!

Failing this conncetion, I'm thinking it's an ECU issue.

Meanwhile, no check engine light has come on, so I haven't done a paperclip test. I suppose it couldn't hurt to do one, if unlikely to produce any fruit.

As for resistors, the GM mechanic may be thinking of the N/A version as that was the most common version in the Geo Storm in which that engine sat. Many thanks for looking that up!

[Fubar1764]

And the woes continue. . .

Ok. We got a Bosch injector diagnose thingee to test out the electronic signal telling the injectors to squirt. Well, the signal isn't going to cylinders 2 and 4. So, we're definitely looking at a connection issue somewhere between the brain and the connection into the injector.

It's not the brain. Nitroman lent me his spare brain (may explain some recent emails he's been sending out!). Same problem when we tried that. So with a known good brain (again, that would be Nitroman's), 2 and 4 still aren't squirting.

So, were I to guess, it's a connection issue somewhere between the brain and where the plug goes into the injectors. SIGH.

[Doug]

could you have a ground fault (loose ground) to that circuit ???

haven't seen the circuit diagram, just mustering a guess . . . .

[GeoffSmith]

There's a lot common to 2&4 - like everything!

[Fubar1764]

could you have a ground fault (loose ground) to that circuit ???

haven't seen the circuit diagram, just mustering a guess . . . .

I thought about the ground, but there's a common ground to both pairs of injectors (1 & 3 are grouped together, as are 2 & 4). If it's a grounding issue, I think all would be bad.

Going to have a friend come over and look at her tonight. I'll keep everyone posted.

SIGH.

[lotuska]

I agree with Geoff, there does seem to be a lot common...

I'd start with the IHC connector..or more specifically pin B8 as its the common link.

The IHC connector is the "Injector Harness Connector" and can be found on the right hand side of the engine bay (when looking from the front of the car to the back) between the water header tank and air filter...see picture below.

The wire from the ECM is Blue and White and to the injector is also Blue and White.

I'd try looking for dirty contacts, maybe try opening the connector and spraying with wd40.

If that doesn't work check the circuit from ECM to the connector, and then connector to injector.

[Fubar1764]

Thanks!

Actually, we did that last night. ECM to harness is clear. Harness to injector doesn't seem to be clear, but the colors aren't what they're supposed to be from injector to harness. We're checking it again tonight. I think that's where our problem is. Nitroman suggested we recheck the ground again.

[Fubar1764]

Strangest thing.
We test out the signal path from the ECM harness to the harness in the engine bay (see pic above in lotuska's post). Path clear. Then we test the path from the engine bay harness to the injector plug. 1 and 3 good, 2 and 4 not good.

So we unwrap the wires from the injector plugs to the harness. A lot of electrical tape later, we find no breaks, but we now have a clear signal path.

Now, we have clear path from ECM to harness and harness to injector, right? So everything should go right, right? Wrong-O!

We put the plugs back into the injectors and crank the motor to test. Still running rough. We pull the injector plugs out and test. Not signal. WTF?! We test the path again. Clear from ECM to harness and harness to plug. So, that should mean clear from ECM to plug. But when we test the path with a pilot light, no joy.

Lucas, Prince of Darkness is still lurking. . .

We're testing the two ECMs now. Very very unhappy.

[Doc Fizzix]

Just a sugestion:

Have you unplugged the wire harness and tested the injector wire lines for conductivity? To do this you will have to pull off the connectors for injectores 1 & 3 then touch the block and the lines for 2 & 4 and see if you have conductivity.

[Fubar1764]

If I'm reading your description correctly, yes, I have.

The wiring goes from the ECM to the harness (A-B), then from the wiring harness to the injectors (B-C). We have continuity from A-B and B-C. One would expect to have continuity then from A-C. Right? Wrong!

I've cleaned the leads on the harness to both sides. Still no joy. SIGH.

[lotuska]

Very odd....

Only 2 things I can think of:

1. You have a connector issue. What I mean is that the phyical connector isn't making contact when plugged onto the injector and/or the IHC connector.

2. You have what looks like a good wire, but it is infact broken inside the insulation. You get continuity when you use your meter because you are having to move the cable to a different position than normal.

However having said all of that you can probably narrow the issue down to a certain point. Can you see where the 2 wires to injectors 2 & 4 join? (The manual isn't much help). The likelyhood that both electrical connectors on injectors 2 & 4 have the same fault is low, therfore the problem is probably either at or before the point they both connect to.

Assuming that you are happy that you have checked continuity between all connectors my plan of action would be:

1. connect everything as normal

2. cut the wire that comes out of the IHC connector, leaving enough so that you can splice a new wire in...

3. check continuity from ecm to this cut wire (don't remove the connector leave it in situ).
If this doesn't work then your problem is in the IHC connector or the length of wire you left from step 2 above. You need to fix this.
If you have continuity then the problem is engine side, i.e. somewhere between your cut and the injector connector, you need to do step 4.

4. cut one of the wires on injector 2 or 4 connector. Same as before, leave in stiu, leave enough to splice in a new wire, but this time check continuity from the injector wire (not connector side) back to the cut wire at IHC connector.
If there's no continuity then your problem is with this wire. I would then splice a new length of wire in and check.
If there's continuity then the problem has to be with the injector connector. You will probably need to replace this.

All of that sounds extreme but what have you got to lose? You are only cutting the engine harness. You could use a razor blade to strip back the insulation and check continuity rather than cut wires.

Hope that helps...

[Doc Fizzix]

Do you have someone down there that you can try their ECU? Worth a shot to rule the ECU out