2 of 4 injectors not firing

Home  \  Repairs & Maintenance  \  2 of 4 injectors not firing

This is driving me nuts, hopefully someone else has had this issue...

Car is a '89 Grand Am, 2.3L Quad 4, manual trans.

Friday, all of a sudden the car started stumbling pretty bad, as though a plug wire were missing from my past experience. Very little power, idled very rough.

I have replaced the coil tower, plugs, and boots, since I heard this was a common problems on the Quad 4 engines. I also swapped coils from a junkyard to eliminate the coils as the problem.

No dice. The exhaust manifold is cold to the touch near the exhaust ports of cylnders 1 and 4 (which curiously share the same coil) while 2 and 3 seem fine.

Today, I tested the Throttle Position Sensor, and disconnected the IAC and O2 sensor just for kicks to see if anything changed. This problem is the same upon cold start though, so it's happening in open loop too.

I then pulled the fuel rail, and injectors 1 and 4 are not firing at all. When I compared the resistance of #4 with #3, #3 showed 2.0 ohms, and #4 showed 1.2 ohms.

Is there something that fires the #1 and #4 injectors that could break, like maybe there are 2 crank position sensors on this thing or something?

It did show a Code 13 (O2 sensor circuit), I presumed because of the ultra rich condition caused by 2 cylinders not firing, but once I cleared the code it has not recurred. (and of course, there would not be a rich condition with the 2 injectors not firing)

It seems odd that 2 injectors would fail simultaneously, maybe there is a driver circuit in the computer that goes bad?

posted by  PeteC

More craziness - threw Code 24 at me this morning, after a brief drive.

My book shows this for code 24:

Vehicle was not in park or neutral for 20 seconds when throttle position signal was over 7% with engine speed between 1600 and 3600 RPM and the MAP signal showed low manifold vacuum.

I am going to assume this was because I tried various throttle settings, including WOT, and the engine speed/vacuum was not right because of it running on 2 cylinders.

posted by  PeteC

i checked the ALLDATA for u.
yes, #1 and #4 share the same drive circuit in the ECM。
so check the ground wire from the injectors to the ECM (the BLUE wire), usig a scope if u have.

posted by  autecfan

Thanks, will do. I don't have a scope, but I'll try my meter, which has a frequency counter.

The wiring has become a bit of concern, I realized that this car has a broken front engine mount, causing excessive rocking that could conceivably yank a wire apart or otherwise damage the harness. :oops:

I have located a junkyard ECM for $15, so I'll probably pick that up in the morning and give it a shot as well, providing I find no glaring issues with the wiring.

posted by  PeteC

The #1 and #4 injectors test at 1.2 ohms each, while the 2 and 3 injectors show 2 ohms. Less resistance = more current = shortened driver life. Is 1.2 ohms below the allowable tolerance?

Looking at the wiring diagram, looks like the #1 and #4 injectors fire together, and are attached to the same driver. I thought that this injector type was supposed to test at about 2.2ohms.

posted by  PeteC

I replaced the ECM with no change, but before I could change the injectors, the car caught fire and burned up at my friend's house Friday night!!!!!!!!!!!!!!!!!!!! :screwy: :doh:

I guess it might have been a wiring issue, eh? :ohcrap:

Thus ends the saga of the 2 injectors not firing.......

posted by  PeteC

I'm sorry, that was the funniest end to any of the posts I've ever read. Time to buy a new beater, eh?

posted by  Nichol Bolas

Yep :laughing:

Hell, I considered setting the thing on fire myself a few times, as irritated as I was about this problem. Too bad it had $100 worth of new ignition parts on it.

Obviously, I didn't have any full coverage insurance, so the car is a loss.

I DID notice, when I had been letting the injectors spray onto a piece of cardboard to test them a few days ago, that the car cranked slow even with a new battery, AND that the starter seemed to smoke a little even a long time after cranking. I assume that's how it started. Luckily there was no damage to anything else but the car.

My next beater is a 1998 Ford Escort ZX2, with only 64,000 miles that I got for $400. Of course, that's because it has thrown a rod. I'll put a new engine in it for about $500, and it should be good to go. Book value on it will be about $3500, so it will be a much better investment of my time than the Flaming Grand Am.

posted by  PeteC

Your Message