P1351 after replacing ignition coil and icm

[doncaruana]

Sounds like it's time to diagnose that ICM and/or circuit.

Brand new ignition coil and 2nd new ICM (this one is AC Delco) as well as distributor assembly and spark plug wires. I don't think it's the ICM although there might be a funky connection on one of those components.

 

[doncaruana]

If you have the original iCM still, maybe try swapping it back, clear the code, and see if it latches the P1351 again?

I don't and this is 2 new ICMs that throw the code, the current one being AC Delco oem part.

 

[YukonGTmaster]

How does you connector look at your Crankshaft Position Sensor? You started having issues when it was raining. Maybe water ingress into the connector?

 

[exp500]

Loosen the dist hold down bolt. That is your adjuster as explained above. Rotate dist and recheck until it reads 0+- 1 degree above 1000 rpm steady. Tighten hold down! After that then we work on what remains.
Your mechanic made a mistake, not the first guy to do that.
There are a couple fixes if it is still a problem. Ground wire at firewall/ ICM connector bad/corrosion water in computer plug.
Did you notice your Tach bouncing 1-200 rpm?

 

[doncaruana]

Loosen the dist hold down bolt. That is your adjuster as explained above. Rotate dist and recheck until it reads 0+- 1 degree above 1000 rpm steady. Tighten hold down! After that then we work on what remains.
Your mechanic made a mistake, not the first guy to do that.
There are a couple fixes if it is still a problem. Ground wire at firewall/ ICM connector bad/corrosion water in computer plug.
Did you notice your Tach bouncing 1-200 rpm?

Tach was pretty normal. I've got to get the timing addressed and check the connections (at coil, etc) at the same time. It's surely a head scratcher.

 

[east302]

Plus the mechanic said there is no adjustment for this distributor, just like in the screenshot above (which is actually from Mitchell OnDemand) where it says the distributor is installed in a fixed, nonadjustable position for HVS (which I may or may not have??). So, of course, I'm utterly confused...

Some aftermarket distributors come with a fixed hold-down bracket which doesn’t allow the CMP offset to be set. The fix is to swap the hold down with the original one in order to do the replacement correctly. Not sure if you have that one or not.

P1345 is the CMP correlation, as others said it is adjustable on these.

For P1351, the factory manual has the step-by-step diagnostic tables for it. This site has PDFs of them for most years up to 1998:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

An alternative would be alldatadiy.com which is a subscription site and has the same information (verbatim generally) as the factory manual. They went up in price recently (it’s now around $60/yr) so I let my subscription expire or I would copy the sections for you.

Edit: here is P1351 from the 98 PDF manual…

 

[exp500]

I was not aware of the non adjustable hold down issue, thanks east302.
Using only GM/Delco/Delphi ICM's, Coils, CPS, have fixed the P1351 for my fleet mostly. Also replaced the ICM connector 3 or4 times, CPS connector twice. A few ground issues, repairing firewall grounds was usually it. Twice I have repinned a new white wire from VCM to ICM, on these two I added a ground on VCM. The Tach bouncing is a bad CPS or connector. These are hi mile work trucks all over 200k some over 300k miles. Hope this helps.

 

[east302]

For me, it was a Summit brand distributor that had that issue. While it had aluminum tabs for the cap screws (versus plastic OEM), the hold-down was keyed on there. Some of the reviews suggested that it was for “universal” applications or perhaps the 4.3L, but I couldn’t say for sure.

 

[doncaruana]

I was not aware of the non adjustable hold down issue, thanks east302.
Using only GM/Delco/Delphi ICM's, Coils, CPS, have fixed the P1351 for my fleet mostly. Also replaced the ICM connector 3 or4 times, CPS connector twice. A few ground issues, repairing firewall grounds was usually it. Twice I have repinned a new white wire from VCM to ICM, on these two I added a ground on VCM. The Tach bouncing is a bad CPS or connector. These are hi mile work trucks all over 200k some over 300k miles. Hope this helps.

I took it back over and told him we've got to get the cam retard set regardless and to check the connections while he's at it. Gotta peel the onion and the first layer is that offset.

 

[doncaruana]

Some aftermarket distributors come with a fixed hold-down bracket which doesn’t allow the CMP offset to be set. The fix is to swap the hold down with the original one in order to do the replacement correctly. Not sure if you have that one or not.

P1345 is the CMP correlation, as others said it is adjustable on these.

For P1351, the factory manual has the step-by-step diagnostic tables for it. This site has PDFs of them for most years up to 1998:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

An alternative would be alldatadiy.com which is a subscription site and has the same information (verbatim generally) as the factory manual. They went up in price recently (it’s now around $60/yr) so I let my subscription expire or I would copy the sections for you.

Edit: here is P1351 from the 98 PDF manual…

View attachment 364567
View attachment 364568
View attachment 364569

Thank you!!