E38 Street Sweeper no start / no crank signal

I am trying to start a 6.0 liter street sweeper with an E38 (well two E38s :anitoof:)
The previous mechanic put a crank sensor in it and also replaced the ECM. It was towed in for programmimg. I programmed the new ECM but it won't initiate the theft learn (MIL keeps flashing at all times, not steady for 10 minutes then off in VTD learn.) The only codes it has are Crank Variation Learn not performed, which can't be done until it runs anyway. The old E38 does not flash the MIL, but still does not learn the VTD, just stays solid long after the 10 minutes. Same codes, and no start. Scan tool says VTD is not learned, but fuel IS enabled, however... no crank RPM on either one. So therein lies my problem I think. :nixweiss:

This vehicle does not have a VTD module that I am aware of, it is an Isuzu and has a PIM (integration module).

I will now try to figure out the 0 RPM during cranking and try to start this thing. Any advice is appreciated, I will post the results. I can post schematics if anyone cares.

:banana:

I have no Cam Angle and no Mass Air Flow grams /s in the scan tool while cranking. I unplugged the MAF, it should start without that. I cut off the melted together Knock Sensor connector, it should start without that. After that it did the weirdest thing, it tried to start for just a split second, but again nothing and it never tried to start again.

Crank and crank, their is fuel in the rail but no injector pulse or spark. I checked all 3 wires to the Crank sensor and all the fuses to the ECM.

So basically it's as if half of the ECM is dead, according to the data list. Keep in mind it's doing this with 2 different ECMs.

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Originally Posted by Boost

So basically it's as if half of the ECM is dead, according to the data list. Keep in mind it's doing this with 2 different ECMs.

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Missing power somewhere? :nixweiss:

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Originally Posted by Boost

After that it did the weirdest thing, it tried to start for just a split second, but again nothing and it never tried to start again.

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Intermitent power somewhere...

Thank you for your reply Mark! I admit this truck has throughly kicked my butt the entire day yesterday. So here I am trying to salvage my pay for the week this morning. A part of the confusion is that I have people that are smarter and more experienced helping me and I feel they are skipping steps.

We have still not proven that the brand new crank sensor is good. I verified the part # is correct for the application but have not ohmed it or swapped it with a known good one. All three wires have been checked, it has 5 volt reference and everything else. But the connection at the ECM is not yet proven (looks good). I would focus on this simple circuit as I feel it is the main issue (possibly?).

The only reason I think it blurped one time to start is dieseling - if this is possible with the compression of this engine. It happened for a split second only and never again, just after we cut off the melted Knock Sensor connector and unplugged the MAF. There is still no spark, pulse, or cam angle.

Another thing that is a bit confusing is that this ECM seems to have 5 volts as well as 12 volts. (what is the 12 volt used for? The cam actuator?) None the less I think the Crank circuit is 5 volts, despite an apparent mistake in the service literature.

Ckecked all power and grounds to the ECM, seems good. There is also something in Service Information about having to use a special multi meter due to the sensitivity (E38 guys chime in?)

There seems to be some sort of a ground issue that I'd like to prove this morning (28 Ohms), and one of the 5 Volt refs. is at 4.5 while the other is right at 5. (not sure if normal of symptom of ground issue). Anyways as you can tell I am struggling but will be post outcome. Thanks!

Not sure how it could diesel when cold and without fuel?

How did knock sensor connector get melted? Could have already burned up second PCM replacement?

Just throwing out ideas from what you have said, sometimes I go blind looking for an issue and already have it figured out, just need another set of fresh eyes. HTH!

Thanks, and you are absolutely right. Truck is fixed now, it was the PTO (power take off) for the sweeping equipment in the back tapped into the crank signal wire by the column. Once I cut that out it fired right up. Still have a P0340 that I need to diagnose, may just need a cam sensor or further electrical issues. I chased my tail on this one, these sweepers get lots of problems and have custom equipment. I think / thought it was an LY6, but the 8th VIN digit is B (?)

No kidding? Wonder how it ever ran like that? Or did something fail in PTO to fail the crank?

Glad it helped without any real technical info... :anitoof:

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Originally Posted by EagleMark

Or did something fail in PTO to fail the crank?

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This.

Thanks!!!

:thumb_yello:

Good job :cheers:

( why did they hack into the CKP signal for the PTO...? )


28 ohm issue: measure the voltage drop across this connection with power applied (key on, engine running), if it's less than 0.2V it should be ok.

Thanks Joe! I see the strangest projects. My goal is to use all this to improve my confidence and my diagnostic skills at the same time as trying to make a living. I really enjoy the GM related ones but in this case I just overlooked something simple.