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."