LY6 crankshaft position sensor mystery
05-16-2016, 11:27 PM
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LY6 crankshaft position sensor mystery Background: In the finishing stages of my 2007 LY6 and 4l60e swap into a volvo station wagon.
During the wiring harness install, I inadvertently left the crankshaft position sensor unplugged. Didn't care too much at first, as initial engine testing showed the engine would turn over and idle fine. When I realized the sensor was unplugged, I was pretty astonished the engine would even turn over, let alone idle smoothly.
Recently, I have been checking all the little things on the to-do list up, including plugging the crankshaft position sensor in. Immediately, the engine would barely turn over, and idled to the point that I though the aftermarket cam had collapsed valve spring and half the cylineders were dead...it was that bad. Throttle wouldn't respond and the smell of unburnt fuel in the exhaust was very evident.
To test all the things I had done between the time the car ran fine, and didn't, I unplugged the crankshaft position sensor and viola, back to smooth idle, and the only CEL from the sensor being unplugged.
Took the car for a hard drive and everything went smooth through all gears, downshifts etc.
Any thoughts on why having the sensor plugged in is causing such an issue, but having no signal is allowing the car to drive fine? I'm stumped! Could the sensor be bad, and the ECU compensates when it's unplugged by switching to an alternate source for the placement of the crankshaft?
During the wiring harness install, I inadvertently left the crankshaft position sensor unplugged. Didn't care too much at first, as initial engine testing showed the engine would turn over and idle fine. When I realized the sensor was unplugged, I was pretty astonished the engine would even turn over, let alone idle smoothly.
Recently, I have been checking all the little things on the to-do list up, including plugging the crankshaft position sensor in. Immediately, the engine would barely turn over, and idled to the point that I though the aftermarket cam had collapsed valve spring and half the cylineders were dead...it was that bad. Throttle wouldn't respond and the smell of unburnt fuel in the exhaust was very evident.
To test all the things I had done between the time the car ran fine, and didn't, I unplugged the crankshaft position sensor and viola, back to smooth idle, and the only CEL from the sensor being unplugged.
Took the car for a hard drive and everything went smooth through all gears, downshifts etc.
Any thoughts on why having the sensor plugged in is causing such an issue, but having no signal is allowing the car to drive fine? I'm stumped! Could the sensor be bad, and the ECU compensates when it's unplugged by switching to an alternate source for the placement of the crankshaft?
05-20-2016, 11:09 AM
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The mystery deepens. Working on getting my tach wired last night and found there is no tach signal coming through the white wire. It's a little ambiguous on the internet, but the general consensus I can find is that the crankshaft position (CKP) sensor supplies the tach signal. Although I note arguments are out there for the tach signal coming from the camshaft position (CMP) sensor.
It's hard to nail down exactly what's happening, but the CMP sensor is used to determine what stroke the engine is on, while the CKP determines when the piston is at TDC. My guess is both sensors can be used redundantly to determine the engine's position in the case the one or the other stops working? In my case, my hard start is the ECU being unsure where the engine is at and is forced to guess how to ignite.
It seems there are differences in generation and model PCM sources for tach, so I'm hoping my missing tach signal, and the fact that when my CKP sensor is plugged in, the car runs horribly as a sign that the CKP sensor itself is bad?
My confusion at this point is why when the CKP sensor is unplugged the car runs fine, but even when plugged in, the CKP is not providing a tach signal. Is the sensor completely not working, sending a bad signal, or something entirely different? Who knows at this point?
I'll be switching the sensor out this evening to check this hypothesis.
It's hard to nail down exactly what's happening, but the CMP sensor is used to determine what stroke the engine is on, while the CKP determines when the piston is at TDC. My guess is both sensors can be used redundantly to determine the engine's position in the case the one or the other stops working? In my case, my hard start is the ECU being unsure where the engine is at and is forced to guess how to ignite.
It seems there are differences in generation and model PCM sources for tach, so I'm hoping my missing tach signal, and the fact that when my CKP sensor is plugged in, the car runs horribly as a sign that the CKP sensor itself is bad?
My confusion at this point is why when the CKP sensor is unplugged the car runs fine, but even when plugged in, the CKP is not providing a tach signal. Is the sensor completely not working, sending a bad signal, or something entirely different? Who knows at this point?
I'll be switching the sensor out this evening to check this hypothesis.
05-21-2016, 03:20 PM
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Seems like I'm talking to myself here, but here's what today's work uncovered.
New crankshaft position sensor did not solve this issue. Still same problems...so we hooked up the super-fancy shop scanner to the car and did some investigating.
First off, both cam and crank position sensors appear to be working fine, with both showing a rpm signal in the scanner and no codes thrown when everything is plugged in. Still car runs like junk with CKP sensor plugged in. When CMP sensor is unplugged, car will not start, and dies when unplugged while running. Idle runs rich and lumpy with occasional backfires and stalls if you don't keep feathering the throttle.
When crankshaft position sensor is plugged in:
o2 sensors suggest a lean fuel mixture and the engine is looking to compensate because it sure smells rich as hell and the cats are running very hot. I have the rear o2 sensors removed and they show their typical neutral value in the scanner.
The fuel trim numbers are running close to 30 and when we unplug the o2 sensors, that number swings back to around -20.
When CKP sensor is unplugged we looked at the scanner to see if that gave us any clues.
As has been the case, car idles smooth.
O2 sensors are right where they should be with large oscillation between 100-900.
Everything else seems fine, and the fuel trims are right around 1 to -5
Fuel pressure before fuel filter shows 55psi w vacuum and 58 psi w/o vacuum so the engine should be getting the correct amount of fuel pressure.
Did a throttle position relearn and idle relearn...no help
Tried a crankshaft relearn and would get past the point where the scanner asked for the rpm above 4k, but would always fail due to some odd A/C codes, which is weird, since the A/C isn't communicating whatsoever with the PCM.
Still confusing is the lack of tach signal coming from the white PCM wire. I tested the voltage at the wire, and sure enough, right around 12V coming through the wire, just no signal that the dakota digital gauge is seeing. I've confirmed the tach box is sending a correct signal to the tach with the calibration of the DD gauge. Since both CMP and CKP sensors registering and RPM on the scanner, is this indicative of an issue at the PCM output level? Something between the CKP and CMP sensor is off and when they are both plugged in, things start getting off with the fuel injection process.
New crankshaft position sensor did not solve this issue. Still same problems...so we hooked up the super-fancy shop scanner to the car and did some investigating.
First off, both cam and crank position sensors appear to be working fine, with both showing a rpm signal in the scanner and no codes thrown when everything is plugged in. Still car runs like junk with CKP sensor plugged in. When CMP sensor is unplugged, car will not start, and dies when unplugged while running. Idle runs rich and lumpy with occasional backfires and stalls if you don't keep feathering the throttle.
When crankshaft position sensor is plugged in:
o2 sensors suggest a lean fuel mixture and the engine is looking to compensate because it sure smells rich as hell and the cats are running very hot. I have the rear o2 sensors removed and they show their typical neutral value in the scanner.
The fuel trim numbers are running close to 30 and when we unplug the o2 sensors, that number swings back to around -20.
When CKP sensor is unplugged we looked at the scanner to see if that gave us any clues.
As has been the case, car idles smooth.
O2 sensors are right where they should be with large oscillation between 100-900.
Everything else seems fine, and the fuel trims are right around 1 to -5
Fuel pressure before fuel filter shows 55psi w vacuum and 58 psi w/o vacuum so the engine should be getting the correct amount of fuel pressure.
Did a throttle position relearn and idle relearn...no help
Tried a crankshaft relearn and would get past the point where the scanner asked for the rpm above 4k, but would always fail due to some odd A/C codes, which is weird, since the A/C isn't communicating whatsoever with the PCM.
Still confusing is the lack of tach signal coming from the white PCM wire. I tested the voltage at the wire, and sure enough, right around 12V coming through the wire, just no signal that the dakota digital gauge is seeing. I've confirmed the tach box is sending a correct signal to the tach with the calibration of the DD gauge. Since both CMP and CKP sensors registering and RPM on the scanner, is this indicative of an issue at the PCM output level? Something between the CKP and CMP sensor is off and when they are both plugged in, things start getting off with the fuel injection process.
11-06-2016, 10:52 PM
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I've been reading along and thinking about this (altho I don't have an answer).
Is this an E38 ECM...?
Does your engine have the 58x CKP reluctor and the 4x CMP cam sprocket...?
Is the harness wired correctly without and shorts/opens...?
Do you gave a spare ECM to try...?
Is this an E38 ECM...?
Does your engine have the 58x CKP reluctor and the 4x CMP cam sprocket...?
Is the harness wired correctly without and shorts/opens...?
Do you gave a spare ECM to try...?
11-11-2016, 01:00 PM
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MY 60-2 (58x) MY 60-2 (GM58x) should be fitted as the patent expired in 2006.
Your answer, the CAM sprocket does have the four pole design with the ability to do a "limp home" if the CS sensor fails/wire breaks/no signal.
That calibration is ALSO "fail safe" with different settings when the Mode is CS = No signal.
Those at GM, the EMS engineer, has NO CLUE about the correct name for my 60-2.
EXAMPLE :
There ARE 58 teeth on a 60-2 THOUGH the ECU will "see" the Missing Tooth as ONE tooth.
Thus one CORRECT name could be "59x" unless the EMS is BLIND!
THIS is the "mystery"
Lance
Your answer, the CAM sprocket does have the four pole design with the ability to do a "limp home" if the CS sensor fails/wire breaks/no signal.
That calibration is ALSO "fail safe" with different settings when the Mode is CS = No signal.
Those at GM, the EMS engineer, has NO CLUE about the correct name for my 60-2.
EXAMPLE :
There ARE 58 teeth on a 60-2 THOUGH the ECU will "see" the Missing Tooth as ONE tooth.
Thus one CORRECT name could be "59x" unless the EMS is BLIND!
THIS is the "mystery"
Lance