ECM differences

[justacruzr2]

Sounds to me like you might've lucked up and are able to run the car with the basics at least. If you're getting a code 41, then SOMETHING is setting the code, although for some reason it's not puting you in limp home mode. IIRC, a code 41 by itself will go pig rich with locked base timing if you don't also have a Code 12 set. A Code 12 will not set. But the 41 will. Your reference signal is coming from the "R" terminal of the ignition module, through the "B" terminal of the distributor harness to ECM. A white/purple wire going to pinout #10 on the back of the ECM.

There may be peripheal equipment that isn't sending or getting any signals to the ECM. This MIGHT make it do weird things.

The 83 ECM is NOT 100% compatible with the 84. It just isn't.

A code 41 setting with key on and engine not running may mean your MAP or differential pressure sensor (VAC, aka D/P sensor) to the manifold is showing a running voltage when engine is off. Meaning the sensor could be hosed.

This is all based on an 84 307 5.0L troubleshooting procedures. GP SHOULD have the same, but the CSM would have the right info in it.

But if you like it, then go with it.

Thanks. All the sensors were replaced for this project. The 83 had the 305 4bbl also. There's no gas smell coming from the exhaust and from what I can determine, it's getting real good gas mileage.

 

[justacruzr2]

What scanner arevyou using? The ECMs are setup to go into a weird diagnostic mode with limited timing advance anytime a scanner is plugged into ALDL port. Could just be something in your scanner causing a false code 41. Bitflipper's modified ZZ4 chip has this odd function edited out.

The Snap-On Solus.

 

[Clone TIE Pilot]

The Snap-On Solus.

I am not familer with that scanner, I use a Alltest Brainmaster and a Actron analog dwell meter.

Something to try to rule out the scanner is to disconnect the battery to clear the codes and run the engine without the scanner plugged in and see if the code pops back up.

I double checked my repair manuals for causes for Code 41 and found one cause that was not listed by your sources. A defective pickup coil in the distributor can trip a code 41. So I would test the pickup coil as follows with a ohmmeter.

• Connect an ohmmeter to each terminal of the pick-up coil connector or wire and ground (one terminal at a time). The ohmmeter should indicate infinite resistance. If it doesn't, the pick-up coil is defective.

• Connect the ohmmeter between both terminals or wires of the pick-up coil connector. If a vacuum advance unit is attached to the distributor, apply vacuum from an external source and watch the ohmmeter for indications of intermittent opens (if no vacuum unit is used, flex the wires by hand). The ohmmeter should indicate one steady value within the 500 to 1500 ohm range as the wires are flexed. If it doesn't, the pick-up coil is defective.
• If the pick-up coil fails either test. replace it.

Computer controlled HEIs usually have less pickup coil failures as there is no vacuum advance to flex the wires which eventually leads to breakage. Still with age anything will eventually go bad.

 

[justacruzr2]

I am not familer with that scanner, I use a Alltest Brainmaster and a Actron analog dwell meter.

Something to try to rule out the scanner is to disconnect the battery to clear the codes and run the engine without the scanner plugged in and see if the code pops back up.

I double checked my repair manuals for causes for Code 41 and found one cause that was not listed by your sources. A defective pickup coil in the distributor can trip a code 41. So I would test the pickup coil as follows with a ohmmeter.

• Connect an ohmmeter to each terminal of the pick-up coil connector or wire and ground (one terminal at a time). The ohmmeter should indicate infinite resistance. If it doesn't, the pick-up coil is defective.
• Connect the ohmmeter between both terminals or wires of the pick-up coil connector. If a vacuum advance unit is attached to the distributor, apply vacuum from an external source and watch the ohmmeter for indications of intermittent opens (if no vacuum unit is used, flex the wires by hand). The ohmmeter should indicate one steady value within the 500 to 1500 ohm range as the wires are flexed. If it doesn't, the pick-up coil is defective.
• If the pick-up coil fails either test. replace it.

Computer controlled HEIs usually have less pickup coil failures as there is no vacuum advance to flex the wires which eventually leads to breakage. Still with age anything will eventually go bad.

OK. The distributor is new and comes with a new ignition module, and pickup. I suppose that doesn't necessarily rule out a defective one. Working at an auto parts store as I do we see a small percentage of defective parts that are new. I can still check it to be sure.

 

[69hurstolds]

Is the pickup the right polarity for your car? Just asking. For that matter, the coil polarity, too?

Look at the last couple pages of this pdf file on HEI component interchangability. Thing is, it may be a Pontiac, but has an SBC in it, so I'm not sure if you'd use Pontiac junk or Chevy junk in it. If I were to guess, you'd go with Chevy stuff.

https://www.gmcmi.com/wp-content/uploads/2014/05/HEI-Distributors.pdf

 

[Clone TIE Pilot]

Is the pickup the right polarity for your car? Just asking. For that matter, the coil polarity, too?

Look at the last couple pages of this pdf file on HEI component interchangability. Thing is, it may be a Pontiac, but has an SBC in it, so I'm not sure if you'd use Pontiac junk or Chevy junk in it. If I were to guess, you'd go with Chevy stuff.

https://www.gmcmi.com/wp-content/uploads/2014/05/HEI-Distributors.pdf

Its probably Chevy style pickup coil. The factory just dropped LG4s into the GPs. Through I think most 7 pin module are revearse of most older 4 PINs. That is most computer controlled 7 PIN HEI modules use a + to - transition signal.

 

[rfpowerdude]

I have spare Olds 1988 ECMs if you think you might want one. 1228330. Olds 307 application though.

 

[justacruzr2]

Is the pickup the right polarity for your car? Just asking. For that matter, the coil polarity, too?

Look at the last couple pages of this pdf file on HEI component interchangability. Thing is, it may be a Pontiac, but has an SBC in it, so I'm not sure if you'd use Pontiac junk or Chevy junk in it. If I were to guess, you'd go with Chevy stuff.

https://www.gmcmi.com/wp-content/uploads/2014/05/HEI-Distributors.pdf

Thanks for the info. I downloaded the PDF and will give it a look see. Car is running fine though. And one other thing I forgot to mention is according to the scanner, it's cycling between a rich and lean condition and that's exactly what it should be doing and it is in closed loop and that's evidence that it's not running in "limp mode".

 

[justacruzr2]

I have spare Olds 1988 ECMs if you think you might want one. 1228330. Olds 307 application though.

Thanks for the offer but that probably wouldn't work right.

 

[Clone TIE Pilot]

Another issue that can affect the pickup coil is if the magnet develops rust. A rusty magnetic ring can produce a noisy reference pulse to the ECM and ignition module. However, its hard to see the magnetic ring in the distributor.