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My mother in law has a cranking no start, fortunately in my sister in laws garage. All I've done so far is confirmed good fuel pressure at the rail. Compression sounds good. No spark.
Initially I'm thinking CPS or CKS, hoping for the cam because it's easier to get to and doesn't require pulling the harmonic balancer and securing the crank.
I am looking at a diagram and have questions about the a b c that I've circled. What do those symbols mean?
I'm guessing A (logic) is saying that the chain starts by seeing a signal on the l bl/wh wire and moves to the left, basically stating that you'll have no cam signal without crank? Total guess there.
Tutti57 wrote: My mother in law has a cranking no start, fortunately in my sister in laws garage. All I've done so far is confirmed good fuel pressure at the rail. Compression sounds good. No spark.
Initially I'm thinking CPS or CKS, hoping for the cam because it's easier to get to and doesn't require pulling the harmonic balancer and securing the crank.
I am looking at a diagram and have questions about the a b c that I've circled. What do those symbols mean?
I'm guessing A (logic) is saying that the chain starts by seeing a signal on the l bl/wh wire and moves to the left, basically stating that you'll have no cam signal without crank? Total guess there.
C is gonna be the CMP signal itself. FYI, I'm reasonably sure this engine will start and run without the CMP. It's only there for injector phasing, and the PCM will figure it out on it's own if you crank it long enough.
I wouldn't read too deeply into A. 'Logic' just means that the module does its own thing based on inputs and such. It's GM for, "There's a ton of circuits in here that we're not gonna show you."
If it's no spark, then I'd suggest looking into the 3X signal, as that's the only one required for spark. If you've got the 3X signal, then it may be down to powers and grounds for the ICM.
Great info, thank you. I'm going to look back but now that you mentioned that, I believe Paul has a video with this engine as the example, explaining ignition inputs maybe?
The Mitchel diagram has two signal wires on the CKS. One is called low and one is high. Would the 3x be the low and 18x be high?
Here's what I came up with tonight:
- No cam or crank signal on scan tool and no counts on either as well
- Have power and ground on the ICM
- The cks didn't produce a square wave on the signal wires. I only saw a few very small peaks for a moment on initial cranking, then nothing
- I didn't see any voltage on the 12v ref wire but I believe that could be just based on the crank position
- I didn't see injector pulsing. Correct me if my test for this is not correct. I connected my test light to B+ and probed the control wire on the injector. It stayed light prior to cranking and went off and didn't flash during cranking.
Is what I have enough to condemn the crank sensor or does anyone have other tests I should perform?
Yeah, that video was exactly what I needed. I'm going to do the signal test again tomorrow, then a bypass test.
I'm not sure why my injector test had my test light shining while it wasn't cranking here, then it went off during cranking. I was def on a control wire, going to B+.
This car has the 3800 series III and while it's a very similar setup to the one in the video, this sensor is a pull-up design. I tested for signal again and got a very small amount of fuzz right away, then nothing. I was able to do a bypass test, which was successful, so the wiring is good. I'm going to call the CKS on this one unless anyone objects to that!
I'm not sure why my injector test had my test light shining while it wasn't cranking here, then it went off during cranking. I was def on a control wire, going to B+.
I've observed the same behavior before, on multiple different makes/engines. I think it has to do with the light finding a ground through the power side of the injector? It never ended up being the problem, so I never took the time to trace it out on a diagram. :silly:
- I didn't see any voltage on the 12v ref wire but I believe that could be just based on the crank position
Are you sure? :blink: Pin N at the ICM doesn't have 12V? That'd be a red flag on the ICM. Or, am I misunderstanding?
I'm not sure why my injector test had my test light shining while it wasn't cranking here, then it went off during cranking. I was def on a control wire, going to B+.
I've observed the same behavior before, on multiple different makes/engines. I think it has to do with the light finding a ground through the power side of the injector? It never ended up being the problem, so I never took the time to trace it out on a diagram. :silly:
- I didn't see any voltage on the 12v ref wire but I believe that could be just based on the crank position
Are you sure? :blink: Pin N at the ICM doesn't have 12V? That'd be a red flag on the ICM. Or, am I misunderstanding?
I know I had power and ground at the ICM. I'm not sure what I was talking about there, ha. I'll double check when I go back over there in a bit.
I'm not sure why my injector test had my test light shining while it wasn't cranking here, then it went off during cranking. I was def on a control wire, going to B+.
I've observed the same behavior before, on multiple different makes/engines. I think it has to do with the light finding a ground through the power side of the injector? It never ended up being the problem, so I never took the time to trace it out on a diagram. :silly:
- I didn't see any voltage on the 12v ref wire but I believe that could be just based on the crank position
Are you sure? :blink: Pin N at the ICM doesn't have 12V? That'd be a red flag on the ICM. Or, am I misunderstanding?
New lesson learned. Look at the pin out. I thought one wire was yellow but its actually the white/black ref. That does not have 12v on it.
Can I put 12v to that pin and see if that changes anything or could the components in the module be messed up where that might not be of any help? I guess direction has changed to replacing the module here.
Tutti57 wrote: New lesson learned. Look at the pin out. I thought one wire was yellow but its actually the white/black ref. That does not have 12v on it.
Ah OK, glad I asked. :lol: I was looking over your results super closely, because changing the crank sensor is kinda crappy on this motor. Gotta have the special balancer puller and all that. Didn't want to see you go to all that effort for nothing!
Can I put 12v to that pin and see if that changes anything or could the components in the module be messed up where that might not be of any help? I guess direction has changed to replacing the module here.
I guess you could? But I think I'd be more worried about a short to ground at this point. That 12V ref is shared between the CKP and the CMP, and a short in either sensor or the wiring will cause this. In fact, Paul covered this exact issue in a different video. Different engine, but same idea:
Tutti57 wrote: New lesson learned. Look at the pin out. I thought one wire was yellow but its actually the white/black ref. That does not have 12v on it.
Ah OK, glad I asked. :lol: I was looking over your results super closely, because changing the crank sensor is kinda crappy on this motor. Gotta have the special balancer puller and all that. Didn't want to see you go to all that effort for nothing!
Can I put 12v to that pin and see if that changes anything or could the components in the module be messed up where that might not be of any help? I guess direction has changed to replacing the module here.
I guess you could? But I think I'd be more worried about a short to ground at this point. That 12V ref is shared between the CKP and the CMP, and a short in either sensor or the wiring will cause this. In fact, Paul covered this exact issue in a different video. Different engine, but same idea:
So you're saying you hold off on replacing the module and check the wires on the sensors?
Tutti57 wrote: New lesson learned. Look at the pin out. I thought one wire was yellow but its actually the white/black ref. That does not have 12v on it.
Ah OK, glad I asked. :lol: I was looking over your results super closely, because changing the crank sensor is kinda crappy on this motor. Gotta have the special balancer puller and all that. Didn't want to see you go to all that effort for nothing!
Can I put 12v to that pin and see if that changes anything or could the components in the module be messed up where that might not be of any help? I guess direction has changed to replacing the module here.
I guess you could? But I think I'd be more worried about a short to ground at this point. That 12V ref is shared between the CKP and the CMP, and a short in either sensor or the wiring will cause this. In fact, Paul covered this exact issue in a different video. Different engine, but same idea:
So you're saying you hold off on replacing the module and check the wires on the sensors?
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If im getting power and ground to the ICM and not out, on that 12v ref that goes to both sensors, wouldn't the problem be the ICM? I would think if either of those sensors had a short to ground, I would still have 12v at the ICM pin. I guess I'll have to watch that video you mentioned to understand this.
Yeah it's a bit misleading. It's not B+ 12V coming from the ICM to the sensors. Think of it more like a 5V reference that happens to be 12V.
You could try disconnecting the ICM and checking the reference for a short to ground with an ohm meter. Or, cut the reference wire close to the ICM (somewhere easily repairable, of course), and see if you now get 12V out of the module. If you don't, module time. Of you do, find the short.
Tyler wrote: Yeah it's a bit misleading. It's not B+ 12V coming from the ICM to the sensors. Think of it more like a 5V reference that happens to be 12V.
You could try disconnecting the ICM and checking the reference for a short to ground with an ohm meter. Or, cut the reference wire close to the ICM (somewhere easily repairable, of course), and see if you now get 12V out of the module. If you don't, module time. Of you do, find the short.
Ok, gotcha. I just hooked the scope back up and unplugged both sensors while watching the 12v ref. It stayed at 0v, so I think that rules out shorted sensors. I pushed and pulled on all of the wires I could find coming from the sensors and module and didn't see squat change on the scope.
You're probably good to go on the ICM, then. I would expect several thousand ohms of resistance to ground with the sensors plugged in.
If you don't suspect a short, then you could definitely try supplying 12V on that wire. Maybe try a test light first? I figure the sensors can't draw more than a few mA.
Tyler wrote: You're probably good to go on the ICM, then. I would expect several thousand ohms of resistance to ground with the sensors plugged in.
If you don't suspect a short, then you could definitely try supplying 12V on that wire. Maybe try a test light first? I figure the sensors can't draw more than a few mA.
Got it going. Phew. It was the ICM. I cut the 12v wire and still didn't have 12v on it. I installed the new module and still didn't have 12v on it! Checked for power and had now lost that, but I had it before. Blown fuse. Replaced the fuse and started it up.
No problem! Glad to hear it's up and running again. I'm sure your mother in law will be thrilled.
Just curious, did you ever try supplying power on that 12V ref wire? I've never seen this kind of ICM failure, so I've never got to try supplying a 12V ref before. :silly:
Tyler wrote: No problem! Glad to hear it's up and running again. I'm sure your mother in law will be thrilled.
Just curious, did you ever try supplying power on that 12V ref wire? I've never seen this kind of ICM failure, so I've never got to try supplying a 12V ref before. :silly:
Yes, she is!
I did use my test light on there and watched the data pids. Nothing changed. I don't know at what point I lost the b+ power to the module though.
I'll inquire about that one.
I'm sure your mother in law will be thrilled.