Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

1996 Vortec: CKP and CMP Waveforms both glitching badly

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4 years 7 months ago #33015 by martyparish
Thanks for looking! Please don't forget to look at the attached scope waveforms! I'm looking for ANY ideas but the scope is showing issues with the 2 sensors.

1996 GMC Suburban K1500
5.7 Vortec (260,000 miles)

Symptoms: I've been having issues for months now. Truck will just randomly DIE while driving down the road OR just idling.

I've thrown some parts at it already. I know that's the the "Scanner Danner way" and I"m trying to improve my diag skills(see below). In my defense, these parts needed replacing anyway.

Codes haven't been consistent but I have gotten crank sensor code (can't remember the actual code) before and after replacing it. recently it's been giving cylinder 3 misfire code (p0303). I believe I've gotten p0300 but usually it's cyl. 3

So I have replaced:

Fuel pump (it was 10 years old and LOUD)
CKP sensor (it had a fairly deep groove cut into it because it deteriorated and went in too far)
Distributer (probably a waste but it was the original and it did have gear wear)
Coil (this was just "stab", didn't even confirm it was bad... arg)
Ignition module (same as above)

LATELY(since fuel pump), the truck has been running steady and hasn't died on the road BUT it has bucked/missed on occasion. Pretty hard buck too. I thought for sure it was going to die but then it would continue on.

So finally I went and purchased myself a scope after seeing a lot of Paul's excellent videos. It's a low end scope but seems like it'll work for me for a while anyway. (Hantek 6022BE)

The attached images are showing the CKP and CMP sensors.

They look ROUGH... Any ideas on what could cause this? Both sensors are new. They are cheap knock offs but I still doubt they would both be bad right?

Thanks for any thoughts!!!


Marty
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4 years 7 months ago #33017 by Andy_
Is there anyway you could find out exactly what crank sensor code it is and post it here?

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4 years 7 months ago #33021 by martyparish
Thanks Andy.

I just pulled the obd codes again and only have p0303.

I'm 99% sure it was p1345. It' hasn't come back in a while now. Maybe a month or so.

Appreciate the help!

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4 years 7 months ago #33022 by Andy_
P1345 isn't a 'crank sensor' code, at least in the traditional way. I should say its not a crank performance or electrical circuit DTC. It's a cam/crank correlation code.

With that said, did you adjust the CMP retard after you installed the new distributor?

The P1345 could have been setting before with the worn distributor gear, but still setting now if you never adjusted the CMP retard. It's a really easy procedure with a scan tool.

If you answer this, then we'll go from there.

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4 years 7 months ago #33024 by martyparish
I did adjust the cam retard. I used torque app(or maybe dash command). I haven't had that code for a while now and possibly it stopped after the new dizzy. Sorry my recollection is pretty bad and I didn't document anything.

Have you glanced at those images that i attached? Don't they looks whacked out? Maybe it's my cheap scope... I need to test it on a known good vehicle.

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4 years 7 months ago #33025 by Andy_
I did glance at the images. Not too sure what to make of them, without being able to blow them up and really zoom in it's hard to say. The CMP is so close to the coil and wires that it could even be induced voltage.

If you're not getting the P1345 anymore I'd move on to the P0303. One other quick thing about the CMP retard. It's supposed to be set above idle. Did you do it with the RPM's raised a bit?

How repeatable is the misfire? Does it misfire at idle, or only under a load?

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4 years 7 months ago #33026 by martyparish
Thanks again for your help Andy!

I just went out and checked the retard and it's at 2.2 degrees with the rpm between 1000-1200.

I will dig into the 303 error. I already switched wires and it didn't move, so I will swap a couple plugs next to see if it moves.

I know those aren't the largest images(it's all Hscope will give me), but I can see clear dropouts in the cam signal. I can see them on the CKP signal too, but not as clearly.

Thanks!

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