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Replaced engine 996 now has long crank before starting


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we rebuilt an engine in a 2001 c4s

the car now has a long crank before starting

has new alternator and battery and wiring harness for starter

we replaced the crank sensor and cleared the code

the P1579 code keeps coming back for crank sensor - tried 2 new sensors

long crank all hot or cold conditions

I checked crank sensor connector and cleaned with dieelectric grease

fuel pressure is good and does not have any leak down

sometimes will crank 7 times then start some times 20 or more

Im chasing my tail on this one

Im open for all suggestions

Thank You

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we rebuilt an engine in a 2001 c4s

the car now has a long crank before starting

has new alternator and battery and wiring harness for starter

we replaced the crank sensor and cleared the code

the P1579 code keeps coming back for crank sensor - tried 2 new sensors

long crank all hot or cold conditions

I checked crank sensor connector and cleaned with dieelectric grease

fuel pressure is good and does not have any leak down

sometimes will crank 7 times then start some times 20 or more

Im chasing my tail on this one

Im open for all suggestions

Thank You

Did you change the flywheel during the rebuild?

And please do not double post, it is against the forum rules you agreed to when you signed up.............

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sorry, I did not know I double posted

No we did not change out the flywheel

and I looked at every tooth on the flywheel for damage

also I pin tested for the signal from the plug on crank sensor to the main pin #10 ground in the harness plug and have continuity and #9 signal has a continuity

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Use an oscilloscope to check the DME side (pin #46 signal and pin #32 GND) to make sure it's actually seeing the proper signal?

I do not have and oscilloscope im going to try using a bosch hybrid multimeter set on the ms-pulse setting to test it that way

Im trying to avoid spending 2000.00 for an ocilloscope

typically this tool im using is used to test for example the injector pulse

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Use an oscilloscope to check the DME side (pin #46 signal and pin #32 GND) to make sure it's actually seeing the proper signal?

I do not have and oscilloscope im going to try using a bosch hybrid multimeter set on the ms-pulse setting to test it that wayIm trying to avoid spending 2000.00 for an ocilloscopetypically this tool im using is used to test for example the injector pulse
Not sure the hybrid mutlimeter can verify all the info of the waveform though, especially the reference mark signal as shown herehttp://www.renntech.org/forums/topic/40945-cam-position-sensor-resistance-readings/?p=217349I have a 2-(analog)channel DSO203 ($170 from eBay. 2 analog channels. It also has 2 digital channels but that's irrelevant for our usage) and it works well for occasional use (not rugged enough for a shop environment).I've read some threads about issues of the gap between the sensor and the flywheel tooth. Someone had to use a washer to space out the distance a bit but if you're using the correct OE parts, I don't see how this is a problem. Edited by Ahsai
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Can you check that you are getting a spark when cranking (but not firing?)

Good point. If the crank signal is weak/not proper, I think the DME would not even try to fire the plugs.

Experts: After starting is CPS still used? Is there anything duramatic that can be monitored? thanks, Mike

No expert by any strech of imagination but I'm pretty sure the CPS is continuously monitored since there are so many other functions depending on it (e.g., relative camshaft position, misfire detection, etc.) As far as I know, there's nothing in durametric that directly displays CPS signal. There's a rough running value, which itself is based on the CPS measuring the acceleration/decceleration of the flywheel. Not sure what we can derive from that though.The mystery here is why it doesn't work when cranking but it does when the engine is up and running.
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Can you check that you are getting a spark when cranking (but not firing?)

Good point. If the crank signal is weak/not proper, I think the DME would not even try to fire the plugs.

Experts: After starting is CPS still used? Is there anything duramatic that can be monitored? thanks, Mike

No expert by any strech of imagination but I'm pretty sure the CPS is continuously monitored since there are so many other functions depending on it (e.g., relative camshaft position, misfire detection, etc.) As far as I know, there's nothing in durametric that directly displays CPS signal. There's a rough running value, which itself is based on the CPS measuring the acceleration/decceleration of the flywheel. Not sure what we can derive from that though.The mystery here is why it doesn't work when cranking but it does when the engine is up and running.

This is exactly the mystery.. at times it will crank 3 times and start.. other times it will crank 15 times to start... other times seems like it cranks 30 times to start...I think I am going to take the transmission out and look at the flywheel again.. I looked at the teeth through the CPS hole while manually turning it over.. Maybe there is more to it once I get it on the table in front of me

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Have you actually watched the fuel pressure during one of the cranks but won't start sessions? Along with providing the DME with the crank position data, if the DME looses the CPS signal, it will shut the fuel pump off because it thinks the engine is not turning. It would be very interesting to see the CPS signal via a pin out box at the DME because if there is any interruption of the signal (pinched or frayed wire, etc.) the DME would promptly shut the fuel supply off...............

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If the CPS is monitored while running -- AND it is the cause of the non-started -- I would think you would get engine running issues.

In my experience, when the CPS has gone south -- it tends to lead to starting issues only. Typically hot start issues.

NOTE: I'm a shade tree Boxster mechanic at best -- but I have seen 2 CPS go out on two different cars.

Neither exhibited running issues -- just eventually failure to start.

That is why I'm not convinced that is is continually monitored but I have no real evidence.

Mike

Edited by txhokie4life
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If the CPS is monitored while running -- AND it is the cause of the non-started -- I would think you would get engine running issues.

In my experience, when the CPS has gone south -- it tends to lead to starting issues only. Typically hot start issues.

NOTE: I'm a shade tree Boxster mechanic at best -- but I have seen 2 CPS go out on two different cars.

Neither exhibited running issues -- just eventually failure to start.

That is why I'm not convinced that is is continually monitored but I have not real evidence.

Mike

I'm pretty sure it has to be monitored at all times Mike, we have had more than one car towed in because the owner thought it had a dead fuel pump that turned out to be a bad CPS. Normally, when the CPS goes, you get hard starting, particularly when hot; but not always. The CPS is also the DME's reference for ignition timing (it has to know exactly where the engine is in its rotation cycle in order to pick the correct moment to fire the plugs in relation to that rotation). It is also the baseline reference for cam deviation values.

If the OP has a loose, pinched, or frayed wire carrying the CPS signal to the DME (remember, the car has just been apart), all Hell can break loose for the DME......

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Have you actually watched the fuel pressure during one of the cranks but won't start sessions? Along with providing the DME with the crank position data, if the DME looses the CPS signal, it will shut the fuel pump off because it thinks the engine is not turning. It would be very interesting to see the CPS signal via a pin out box at the DME because if there is any interruption of the signal (pinched or frayed wire, etc.) the DME would promptly shut the fuel supply off...............

+1

If the CPS is monitored while running -- AND it is the cause of the non-started -- I would think you would get engine running issues. In my experience, when the CPS has gone south -- it tends to lead to starting issues only. Typically hot start issues. NOTE: I'm a shade tree Boxster mechanic at best -- but I have seen 2 CPS go out on two different cars.Neither exhibited running issues -- just eventually failure to start. That is why I'm not convinced that is is continually monitored but I have no real evidence. Mike

I see your dilemma and reasoning. As JFP said, if the CPS signal disappears, the DME will shut down the fuel pump. That itself means the CPS is monitored all the time.My speculation is at cranking, there's no reference point for the DME to synchronize with the CPS signal so the DME is looking for the "reference mark signal" to syncronize with it so it's less tolerant to any imperfect waveforms. However, once synchronized, the DME is still continuously monitoring the waveform but it's tolerant for small variations so the engine still runs fine even the CPS is not optimal?The DME complain is pretty clear though. The mystery continuous....
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today we took out the transmission and removed the drive plate and what we found was

1 bent tooth on the drive plate. The bent tooth was right below the bolt hole.

We are putting it back together now and hopefully if all our research proves correct

the long crank problem should go away.

I will post the results tomorrow.

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today we took out the transmission and removed the drive plate and what we found was

1 bent tooth on the drive plate. The bent tooth was right below the bolt hole.

We are putting it back together now and hopefully if all our research proves correct

the long crank problem should go away.

I will post the results tomorrow.

The Verdict is in ...... The drive plate bent tooth was without doubt the reason for the long crank problem.

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Sorry for asking but to take out the transmission do you have to take out the engine? I'm new.

no you do not have to take out the engine to remove the transmission on this car

But you do need to support the engine with the transmission out.

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today we took out the transmission and removed the drive plate and what we found was 1 bent tooth on the drive plate. The bent tooth was right below the bolt hole. We are putting it back together now and hopefully if all our research proves correctthe long crank problem should go away. I will post the results tomorrow.

The Verdict is in ...... The drive plate bent tooth was without doubt the reason for the long crank problem.

:thumbup:

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Sorry for asking but to take out the transmission do you have to take out the engine? I'm new.

no you do not have to take out the engine to remove the transmission on this car

But you do need to support the engine with the transmission out.

thanks.

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