Any Duramax FICM experts in existence? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 07-18-2016, 09:45 AM   #1 (permalink)
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Any Duramax FICM experts in existence?

I've got an LB7 FICM on the bench that I'm trying to operate with a non-GM ECU and I'm trying to drive 8 injectors from an ISB.

It isn't firing injectors, I'm monitoring the CAN channels and I've got two CAN messages that I don't have definitions for.

I'm sending low side .5msec pulses for all 8 cylinders in firing order, I measured LCR on all 8 injectors and they are right around what an lb7 injector is (about .4 ohms R). I'm sending a tach signal to the engine speed pin that is a 50% duty cycle 0-5v wave with 2 pulses per rev.

I think I need to find someone who rebuilds or bench tests these to see if they can offer insight.

My next step is to buy the ECU for the truck and use that to read FICM diagnostics with a scanner.

Unfortunately these don't seem to fail like the Ford 6.0L FICM's do so there is VERY little info out there on them.
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Last edited by [email protected]; 07-18-2016 at 09:46 AM.
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Old 07-18-2016, 11:13 AM   #2 (permalink)
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I thought the Duramax FICM had some step up voltage and ran at 19V+.

Don't know why that's standing out in my head but it is.
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Old 07-18-2016, 11:45 AM   #3 (permalink)
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Quote:
Originally Posted by miniwally View Post
I thought the Duramax FICM had some step up voltage and ran at 19V+.

Don't know why that's standing out in my head but it is.
I've read as high as 60
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Old 07-18-2016, 11:50 AM   #4 (permalink)
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That's pretty much what it does, it boosts the battery voltage up to 50-70 volts for the peak portion of the injector opening, then holds it at a regulated current for the duration of the injection event.

The early dmax used a separate module (ficm) until an ecu with injector drivers built in on board came around after the lly/lb7.

The FICM basically allows a gasoline ecu to fire diesel injectors because each PFI injector wire from the ecu goes to the FICM and low side drives the ficm's control wire.
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