Need help diagnosing a code 42.

[Psychopete]

I have a 1986 Delta 88 and am having problems getting it running right. It will run for a few seconds and die on it's own; but you can keep it going if you give it a lot of accelerator. Tested the TPS sensor, but not with an analog meter. I seemed smooth from .400volts to around 4.5 volts, seemed solid.

I have pulled the codes, and I got
12, 12, 12,
42, 42, 42,
12, 12, 12,
42, 42, 42,
....

I looked this up on troublecodes.net for this model year and it's indicating that the EST signal did not change when the bypass voltage was applied. What concerns me is that the EST wire on the ignition module has been trimmed to expose a small amount of wire (I sealed it better).

A mechanic that I spoke to said it could possibly be the "electronic spark control module", but looking at a diagram for the vehicle, this deals with the knock sensor and is not related to the circuit. So I am not real sure on that...

Another question that I have is how the computer displays diagnostic codes. I know a little about Ford ECC-IV systems where the computer goes into KOEO and then into CM. Am I only getting "CM" or stored memory codes, or does the computer system work the same?

Has anyone dealt with anything similar? I have done some diagnostics at the connection to the ignition module. Power seemed to be where it needed to be. I didn't find any connection to ground in the EST wire. I am dealing with 4 wires that go to the computer from the ignition module:

White - EST - Modified computer signal
Tan / Black - EST Bypass - +5 trigger to use computer timing advance
Black - Crank Ref Hi - Reference
Back / Red Crank Ref Low (GND) - Reference Ground

Here's my BIG question

I noticed this as a possible cause:

"Reference Ground circuit open or shorted to battery +."

On this article at the bottom:
http://www.troublecodes.net/articles...ndrstd42.shtml

I was poking around with my DMM and noticed that there was little resistance (.098) to the positive terminal from the Black / Red wire. I am pretty sure this isn't right, but I am not 100% sure.

Any thoughts on other things I should look at? When the computer throws a code 42, will it stop the computer from ever trying to go into bypass mode again? Or could it be switching back and fourth?

My next plan of action I am thinking is to unplug the computer (where is it located? ) and check the resistance again. If short is present, I believe that would be the problem. If not, I would want to think bad computer, but that doesn't happen too often. I just want to verify that this sounds like the problem.

Also am planning on checking the fuel pressure to make sure I am chasing the right problem. Does anyone have the spec for that by chance?

Thanks,
Pete

[thisnametooktolong]

OK:

the mechanic is correct

GM in all there wisdom decided to start the car with the ICM, then after 300-400 RPM hand the task of spark off to the ECM. This happens by the ECM monitoring the tach signal and sending a signal to the ICM. The ICM internally switches to the computer and sends a signal back to ECM saying “its all yours”

Check your schematic to make sure that I have my colors right, the white is spark control out from the ECM and the bypass agreement signal is tan and black. Make sure that those signals are getting to and from the ECM. If you back probe the ICM and you don’t have the signal I bet that the ICM is bad…… this is very common, (don’t confuse the white tach wire) If I remember right the white wire next to the plug bolt is for the tach.
Because the engine fully dies it is probably the bypass switch not connecting the signal or the spark drive to the sws amplifier. Happens all the time. The first time I saw this problem was on a 1988, 98, and I have been seeing it across the board on GM cars

On the GM ECM when you jumper the plug to pull codes you cannot and do not “see” pending codes. On the newer OBDI you can pull the pending codes and even monitor just about everything you can think of by monitoring two different engine specs.

And By the way if you swap the ICM and the coil pack or brick, they are interchangeable on the pre type I, all the way through the type II engines. I am not sure of the type III because I have not worked on a 2006 up GM YET!

I am trying to say there are two types of coils. There is a brick and individual coil types. All ICMs from brick types interchange. All individual coil types interchange. And if you swap the ICM and the coil they all interchange from car to car……….. regardless if it is a brick or a 3 coil types.

[danny_d]

Originally Posted by thisnametooktolong

Make sure that those signals are getting to and from the ECM. If you back probe the ICM and you don’t have the signal I bet that the ICM is bad…… this is very common, (don’t confuse the white tach wire) If I remember right the white wire next to the plug bolt is for the tach.

I know this is a bit of an old thread I resurrected but my problem is in this ballpark. Does anybody know what he meant by back probe the ICM, also any information or suggestions on where to go for information relative to probing and testing ignition and timing issues would be greatly appreciated. I have an "89" Olds 88 giving a code 24 and 42. Issues similar to guy above, idles fine (a little fast though) and bogs down at higher rpm. Much obliged


Danny

[Psychopete]

Forgot to thank you for the help thisnametooktolong, THANKS! Instead of dumping anymore money into it, given the current issues it had, I ended up throwing in the towel on the car.

Originally Posted by danny_d

Does anybody know what he meant by back probe the ICM

You can usually sneak a volt meter lead along the wire, into the back of the plug to test parts of the circuit, while it's plugged in.

Originally Posted by danny_d

I have an "89" Olds 88 giving a code 24 and 42. Issues similar to guy above, idles fine (a little fast though) and bogs down at higher rpm.

Not sure if they are related. My car would not idle at all. It would start and die, I am pretty sure it was an issue between the computer and the ignition module - the EST wire. Seemed like it would want to go into bypass mode, and when it did, my best guess is that there wasn't anything making it from the computer to the ignition module once it switched from the crankshaft sensor input to the computer controlled.

[danny_d]

Thanks for the reply Psychopete, I guess I realized a second after I posted that your car had different symptoms, but there was a very good dialogue on the ICM and the bypass circuit which are new to me so I thought it a good place to jump in. I have to admit to being guilty of that, I rarely start new threads. It's usually more efficient to sniff out an answer with the search engine.

So if I hear you correctly you said with all the components hooked up and the engine running use a multi-meter to probe into the appropriate wires to check for the voltage of the signal at the back of the connector? And assuming the wires are too tight or they are epoxied in then you would have to open the wire in order to make contact? Also, are the wires are tested in pairs as in this case I would need the BLK/TAN and the WHT? I'm trying to get as thorough an understanding of this as I can, I don't want to hook up wrong and burn out an IC, totally farging the ECM in the process. Thanks

[danny_d]

Yo guys, I'm still stuck with this car problem and could use some help. I really don't want to have to try fixing it by process of elimination via buying one module/sensor after another while keeping my fingers crossed. If anybody has got the knowledge would share it please?


Thanks,
Danny

[danny_d]

This board blows.