P1351 after replacing ignition coil and icm

[doncaruana]

Fwiw, went out to visit my dad today and plugged the reader into his 97 suburban (same as my Tahoe but with half the miles). It read - 0.8 at 1500rpm. So I think the reader is giving me accurate measurements.

 

[drakon543]

regardless of the reader the timing needs to be checked at 1 rpm range and only that rpm range. if your not at that rpm range within a very small window which i believe is the stated above 1000 rpm or maybe 2000. if you check the timing anywhere outside of that it is entirely up the ecm where it wants the timing at as your truck has electronic timing. you either have some bad wiring in your ignition system or one of your other parts are faulty. on the front bottom left side of the main drive pulley is your crank sensor it is part of that system. inside your distributor under the rotor button mount is your cam sensor. or you could also have a faulty ignition coil or the ignition coil mount doesn't have proper grounding to the engine. any of those issues could cause your p1351 if it fails in the right way. also when the icm was replaced do you see any thermal compound at the edge or is your icm bolted directly to the ign coil mount bracket. the icm generates a significant amount of heat and its supposed to have an aluminum cooling fin block between it and the mount. ive noticed that missing before and have adequate cooling for the icm can cause it to fail rather quickly.

 

[doncaruana]

regardless of the reader the timing needs to be checked at 1 rpm range and only that rpm range. if your not at that rpm range within a very small window which i believe is the stated above 1000 rpm or maybe 2000. if you check the timing anywhere outside of that it is entirely up the ecm where it wants the timing at as your truck has electronic timing. you either have some bad wiring in your ignition system or one of your other parts are faulty. on the front bottom left side of the main drive pulley is your crank sensor it is part of that system. inside your distributor under the rotor button mount is your cam sensor. or you could also have a faulty ignition coil or the ignition coil mount doesn't have proper grounding to the engine. any of those issues could cause your p1351 if it fails in the right way. also when the icm was replaced do you see any thermal compound at the edge or is your icm bolted directly to the ign coil mount bracket. the icm generates a significant amount of heat and its supposed to have an aluminum cooling fin block between it and the mount. ive noticed that missing before and have adequate cooling for the icm can cause it to fail rather quickly.

All the readings have been done around 1500 give or take a few 100rpm. There's plenty of thermal paste on the icm as well - I watched that myself.

I want to get the timing right first and see what happens. Regardless of whether it has anything to do with the start/1351 issue, it needs to be fixed. Weather is gonna warm up here so...

 

[exp500]

Great, The P1345 is not a concern now, On to the p1351. The troubleshooting in Post 26 is great perfect info.
I tend to look for ground issues first on these trucks, However in this case because of history I'm going to point at the coil not being a GM/Delco/Delphi. My experiences for p1351. I just use these now for ICM/Coil/Crank sensor/Dist cap. Cam sensor doesn't seem to matter.
With engine running, wiggle the wires/connectors on both ICM and Coil connectors. If it misses you found it. Otherwise you have to go thru tests in post 26. These trucks are a PITA sometimes. Good luck!

 

[doncaruana]

If it misses you found it.

I'm not sure I know how to tell this. Is this something I should be able to audibly hear or visually see or am I just looking for a bunch of misfires to suddenly show up on the scan tool? Sorry to be thick - I'm not real versed on this stuff as you can tell.

 

[drakon543]

All the readings have been done around 1500 give or take a few 100rpm. There's plenty of thermal paste on the icm as well - I watched that myself.

I want to get the timing right first and see what happens. Regardless of whether it has anything to do with the start/1351 issue, it needs to be fixed. Weather is gonna warm up here so...

unless whatever is causing p1351 is stopping p1345 from coming up your timing is spot on. last post i remember reading said p1345 was gone and p1351 was back. p1351 has nothing to do with timing and you only have a 2° deviation from 0° where its supposed to be befote p1345 is set. 1500 rpm is too far off from either 1000 or 2000. your timing will fluctuate all over unless your almost right on. my gm buddy thinks it was 1000. at that rpm range the ecu doesn't care about timing and will leave it at the physical timing point of the distributor.

 

[doncaruana]

unless whatever is causing p1351 is stopping p1345 from coming up your timing is spot on. last post i remember reading said p1345 was gone and p1351 was back. p1351 has nothing to do with timing and you only have a 2° deviation from 0° where its supposed to be befote p1345 is set. 1500 rpm is too far off from either 1000 or 2000. your timing will fluctuate all over unless your almost right on. my gm buddy thinks it was 1000. at that rpm range the ecu doesn't care about timing and will leave it at the physical timing point of the distributor.

1345 never came up until after the actual distributor was changed. I only know it came up because he told me it did while he was still working on it. As far as the RPM, the official GM service info is below. The offset doesn't swing that much in general and doesn't vary much. There is nothing that says that 1500 will give a bad measurement. You set is it initially at 1000 and then raise to 2000 to see if it goes out of range. That being said, the reason I even looked for it is all the way back in post 2 exp500 said the offset would trigger the 1351, I got a scanner and got the -13 degrees I indicated. Is it really the root cause? I'm not smart enough to say it isn't. All I know is that my little scan tool says the offset is wrong on my truck and says it's right on my dad's, which is the exact same engine. So I'll go back to the mechanic tomorrow and have him plug his snap on in and see if he gets the same reading following the procedure below, which is what I followed.

 

[exp500]

I wanted you to address the P1345 before the P1351 as sometimes one causes the other, and other things too.
You can usee your scantool if you are in live data recording all cylinders for misfire, otherwise listen, watch it shake. Wiggle wires/connectors the way driving would affect them, relatively gentle.

 

[doncaruana]

I wanted you to address the P1345 before the P1351 as sometimes one causes the other, and other things too.
You can usee your scantool if you are in live data recording all cylinders for misfire, otherwise listen, watch it shake. Wiggle wires/connectors the way driving would affect them, relatively gentle.

Actually, there was no 1345 at the beginning. That didn't come until after the 2nd trip to the shop and I never saw it personally. Regardless, here's the update...

I took it back over and told them I wanted to verify my scanner. Lo and behold it read -7 degrees (same as I'm getting). So they actually adjusted it on the spot. Only got to -1 and I revved the engine to 2000rpm and it went to -2 (they don't have decimals on their readout, unlike DashCommand). I would have liked to get it closer but I can live with this. Here's where it gets interesting...
The helper guy is running the scanner (I've had issues with him in the past). He unplugs the scanner and starts to walk away. I said "Wait a minute!! Let's check it again AFTER he tightens down that bracket!"

So I turn the truck off and he plugs the scanner back in and we fire it up and he says "Look, it says 0 degrees". I immediately said "You have to get it over 1000rpm to get a reading!". So he gives it some gas and bang - we get an actual reading of -1. I plugged my scanner in and I get -1.4/-2.1 at 1000/2000 respectively. Again, I can live with that - I really don't think that tenth of a degree is going to make any difference.

Now, the helper guy was going on about the timing chain, insinuating that it lost 7 degrees after the last time I brought it home. I told him "Well, now we'll know for sure", but I suspect it was the crappy methodology above.

In the meantime, I have the AC Delco ignition coil in a sealed box still ready to go. I'm going to monitor it here and see what happens. I know that the timing isn't supposed to impact that at all, but it actually started really quick the couple of times I've started it after he fixed it (whereas previously they seemed to be kinda long cranks).

So...if the code comes back, I'll attack those wires and if that doesn't do it, goodbye autozone, hello acdelco.

I'll keep y'all posted and, as always, thanks for all the help and education!!

 

[Fless]

Sloppy work for that guy to not verify after the "fix."

 

[drakon543]

i hated having someone touch my 97 and my 94 in this regards because so few people actually know how to do it properly. had a shop do my 97 once after the 3rd distributor died and they fought and fought it. fixed it in 15 min when i got home after they tried to tell me the same crap. its definitely hard to diagnose without actually being there i can only go with experience from my 97. p1345 i only got when my timing was off. p1351 i only got when i was having an issue with the icm and wiring. but again not every issue will be identical so keep us posted and we will keep trying to help.

 

[doncaruana]

i hated having someone touch my 97 and my 94 in this regards because so few people actually know how to do it properly. had a shop do my 97 once after the 3rd distributor died and they fought and fought it. fixed it in 15 min when i got home after they tried to tell me the same crap. its definitely hard to diagnose without actually being there i can only go with experience from my 97. p1345 i only got when my timing was off. p1351 i only got when i was having an issue with the icm and wiring. but again not every issue will be identical so keep us posted and we will keep trying to help.

Thanks and glad I'm not alone!!! Gonna be warm tomorrow and I have a bit of a break from work so I'm going to run down those wires. One thing that I'm a bit confused on is exactly what "ICM" stands for. I thought it was "Ignition Control Module", which is a newly installed AC Delco. But the troubleshooting guide keeps referencing "ignition coil module", yet the diagram also says "Ignition Control Module". Which leaves me completely confused at to which is which...

 

[drakon543]

Thanks and glad I'm not alone!!! Gonna be warm tomorrow and I have a bit of a break from work so I'm going to run down those wires. One thing that I'm a bit confused on is exactly what "ICM" stands for. I thought it was "Ignition Control Module", which is a newly installed AC Delco. But the troubleshooting guide keeps referencing "ignition coil module", yet the diagram also says "Ignition Control Module". Which leaves me completely confused at to which is which...

either or tomAto <> tomato
like my wifes stupid dodge journey oil filter housing or oil filter adapter same thing just who are you talking to.

 

[doncaruana]

A little extra help here - apologize if these are dumb questions... Below is the wiring diagram from the P1351 troubleshooting.

Step 6 says to "Check for a faulty VCM connection." (Similarly Step 13 says "Check for a faulty ignition coil module connection.")
What exactly does that mean? Is this the "jiggle the wire" thing?

Step 9 says:

1. Connect a test lamp to B+.
2. Probe the ignition coil module harness connector terminal C.

What is B+ here? I can see from the test that it is to check that C has a good connection to ground (BLK/WHT 451), I just don't know where B+ would be to validate that. Is it the positive terminal on the battery?

\

 

[Fless]

Yes, B+ is battery positive. If the test lamp lights brightly, you have a good ground at connector C.

 

[exp500]

Step 6 is disconnect computer plugs and inspect- Warning 50 mile drive cycle and crankshaft relearn if disconnected. If you wiggle the ICM/Coil connector wires and it misses, it usually is very near the ICM or coil in the loop of wire. Last 6 inches, flex just that area next. If it misses again you could probably narrow it down to the inch.Replace a long amount, where you can reach and hide splice. The computer will relearn on its own if you disconnect, but trans shifting and everything will be a little different while learning. Use Dielectric grease on the plugs and gaskets, coil and ICM connectors.

 

[doncaruana]

Step 6 is disconnect computer plugs and inspect- Warning 50 mile drive cycle and crankshaft relearn if disconnected. If you wiggle the ICM/Coil connector wires and it misses, it usually is very near the ICM or coil in the loop of wire. Last 6 inches, flex just that area next. If it misses again you could probably narrow it down to the inch.Replace a long amount, where you can reach and hide splice. The computer will relearn on its own if you disconnect, but trans shifting and everything will be a little different while learning. Use Dielectric grease on the plugs and gaskets, coil and ICM connectors.

So of course now I'm a little worried. Lol. In step 4 it says to disconnect the Grey connector from the vcm and then check the wire that goes to the icm. You're saying once I disconnect that, it's going to make it need to relearn etc? Just the process of disconnecting it won't mess anything up right?

 

[exp500]

Me, I would wait to disconnect that. If it passes ICM/Coil wiggle tests, change coil. If it still shows P1351 then disconnect battery and unplug computer. I do not like sparks jumping around computers. Some may disagree.

If It is still showing P1351 after cleaning computer plugs, the next step is to splice a new wire into harness. You need pin removers, new Pin(s), crimpers (specialized). Your mechanic may have them, or Get info from dealer GM or service manual. See Here-https://www.tahoeyukonforum.com/threads/helpful-links.131971/

Another useful test- Multimeter on Ohms, connect red to Bat-, Black to firewall ground, eng ground, and all the grounds you can see and reach. Hi resistance will cause that voltage spike you are getting.

 

[doncaruana]

Well, given what led up to the issue, I decided to "work backward" and leave the VCM the hell alone unless I had to!! Got a $4 test light from Harbor Freight and checked the ground on connector C on the ICM plug - worked fine. Then I flipped the other side of the probe and put it on ground and checked the two outside connectors on the ICM plug (A, pink, is 12v and D, white/black goes to the coil). One of them lit up and the other didn't. Aha! Now, if I was a lot smarter, I would have made an immediate note of which one didn't light up...but I didn't. Because you can guess what happened next - I couldn't duplicate it. Took it on and off a couple of times and even tried jiggling it a bit but both lit up each time. I put it back on and made sure it was in there snug and put everything back together and tried a couple of test starts successfully.

So I know it's one of those wires and my mechanic suggested trying to replace the connector (get one from a junk yard) first before chasing the wires and I think that's a decent idea. Regardless I feel a lot better about the root cause at this point. Or I could buy a new ACDelco from Amazon ($36) or Standard Motor from Oreilly or Duralast from Autozone (both $29) .

Any other suggestions from anyone?

 

[exp500]

Good Work! These can be a pain to find. You got thru quicker than most.
Try this or alternate numbers-

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