2.8L - CODE 42

lmaini · March 18, 2005

Gm-Tech,

I`m hoping you can help or maybe have some experience with the above.

Car is a 1988 Z-24 w/ 2.8 MFI & DSI. Setting a Code 42, obvious things have been replaced (i.e module, ecm, crank sensor)

Please see post at Flatrate, rather than rewriting:

http://flatratetech.com/cgi-bin/ubbcgi/ult...t=000731#000007

Thanks in advance for any light you can shed on the subject.

Lee

GM-Tech · March 18, 2005

Sounds like you've covered all the bases on this one. Does the ECM have a red, white and blue set of connectors? I know you said you snatched a used one from another vehicle, but if it's that ECM, I wouldn't be surprised if they're both bad. What a piece of junk ECM.

I'm not a fan of aftermarket electronics, but I think the odds of an aftermarket ignition module having the exact same problem as the original is pretty slim.

Other than that, I am not aware of any known concerns that I could point you to.

lmaini · March 18, 2005

Thanks GM Tech,

The ECM has 2 black plugs and a yellow. I swapped another known good ECM from a friends Beretta (same ID on ECM) and no change. My current ECM ran that car, so I have eliminated that possibility.

I have done the ohm test on the various circuits, as per the Service manual and it seems the EST circuit wiring is working as it should. Even when back probing grounds with +12 on a test light all things are working out. This one has us all stumped. I would gladly take it to the dealer, but the car is an 88, with 150K. The bill for diagonistic would be more than the car is worth and I don`t think there is anything they would do that I haven`t.

What would the plan of attack be if this problem came into your bay ?

Thanks Again

GM-Tech · March 18, 2005

What would the plan of attack be if this problem came into your bay ?

First, I would check every ground in the engine compartment and the various grounds that are provided to the ECM. And that means doing a voltage drop check with the vehicle operating.

Using a test light to 12v to test the grounds is near worthless as a test. It'd be one thing to use this method to check the ground for a tail light bulb, but on a ciruit that deals with very tiny amounts of current, no way no how. You're looking for loss in the millivolt range and no way you're going to pick that up with a test light or by using an ohmmeter.

I would also do a pin drag test on each and every terminal involved in the circuit on both ends, plus the grounds at the ECM. If that failed to turn up anything, I would run all new wiring to the ECM. I don't mean replacing the harness, but making however many new wires are necessary with the proper terminals on each end and running them from the module to the ECM, over the engine/fenders/whatever. This would just be temporary to eliminate wiring as a possible cause.

lmaini · March 18, 2005

Thanks Again GM Tech,

I`ll get to the dealer on Saturday morning and see if I can get the correct weatherpack terminals to do a pin drag on the module,ECM & Crank Position side of the harness.

You also mentioned a VD test. Having never done one can you offer some guidance, I googled it and found that it is basically using the multimeter between 2 points to determine if there is a substantial voltage drop in the system (i.e high resistance) Sound right? When you mentioned millivolts, it still sounds like I am using a meat cleaver where a scalple is needed?

Have a good weekend and hopefully I will too .

GM-Tech · March 18, 2005

You also mentioned a VD test. Having never done one can you offer some guidance

Set your DVOM on DC millivolts. Connect one lead to the battery negative right at the battery. Connect the other lead to the ground you want to check. Make sure the vehicle is on and all loads you can turn on are on.