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+--- Thread: cm870 crank no start (/showthread.php?tid=9011)
cm870 crank no start - wrenchwabbit91 - 07-19-2023
truck ran till it was shut off, cranks but wont fire "no smoke". other mechanic ran up to diagnose it. no fuel pressure at any test port. i ordered fuel pump, it was in a bad spot so we towed truck to shop swapped both pressure reliefs with out other 870. still no start, installed new fuel pump, 270psi at compuchek but still no start. i hooked up with insite. user fueling state while cranking was engine stop "should be engine cranking"
at this point i believe fuel pump was a misdiagnosis.
verified power from ignition switch at ecm, power and ground to ecm solid while cranking. swapped cam and crank position sensor from other truck, fuel shut off getting power and coil within spec. dissasembled fuel shut off, everything looked ok "nothing plugged or broken" with power to solenoid paper clip sticking to magnet.
what confuses me is if fueling state is in engine stop there should not be power at shut off correct? insite reading no more than 11psi at fuel rail
are there any other triggers to change engine state from stopped to cranking? ecm is getting power ground and ignition signal. is there any way to test ecm? any parameters on caltrm that i could monitor? driver is sitting at home, i need to get this thing going. any help would be heavily appreciated
update - just ran a data log on insite, all engine position sensors reading 0 rpm while cranking
RE: cm870 crank no start - Rawze - 07-19-2023
CM870 and 871 ecm's are notorious for going bad after they get more than 8+ years old from vibration, or someone neglects changed the crank shaft damper at 500k mile intervals (or 8+ years). Smacking one with the handle a screw driver nice and hard in certain areas makes them cut in and out when they start going bad.
Also, I have seen plenty of fuel shutoff solenoids go bad even though they are getting power to the coil. if you suspect the fuel shutoff solenoid, simply remove its guts and re-install it to see if that is holding it back.
The ecm will not fire the cylinders during cranking unless it has more than 50 psi+ of fuel pressure too. Anyone checked the fuel pressure while cranking?.