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+--- Thread: CM870 731 code (/showthread.php?tid=9928)
CM870 731 code - lstrucking - 01-25-2025
Fresh overhaul on a core engine with a deleted and tuned ecm. Have set the timing to 6/6 as the ESN suggests and have this speed sensor #2 misalignment code that I cannot figure out. Have swapped sensors around checked wiring and tone wheel on crank and even pulled the gears and re timed the cams. Looking for any advice on where to look next
RE: CM870 731 code - Rawze - 01-25-2025
FC731: Crankshaft misalignment...
possible causes...
== incorrect ecm programming for the CPL.
== bad crank/cam position sensor.
== bad wiring for one of those sensors.
== damaged or loose tone wheel on the crank.
== too much clearance in crank/main bearings, allowing for it to move around too much. Worn completely out, or after-garbage brand bearings/parts.
== slipped overhead cam / incorrectly installed overhead cam.
-----------
since 90%+ of all de-mandate programming for CM870's is nothing but garbage any ways ...
Start by put the factory program that belongs in the engine into the ecm and see if your issues go away. At least that is one demon that can be eliminated before tearing into it again.
RE: CM870 731 code - lstrucking - 01-25-2025
Is there a way to check the timing thats coded into the ecm? I don’t have insite yet I will get it Monday if I need to. I swapped my ecm over from the blown up engine and the same faults appeared it’s also a 6/6 every bearing was plastigauged and well within spec and it hasn’t slipped timing I’ve rechecked it after running it and having the fault still active
RE: CM870 731 code - tree98 - 01-25-2025
What program are you running In the ECM now and what program was running this engine before you slapped your ECM on it??
Yes the timing in the programming can be checked and changed if need be but not with insite, you need C A L T E R M for that.
A word of caution though..... 870 ECM's are well known to brick when flashing them. If you don't know what your doing you could end up with a truck that won't start.
Runningrough use to do all the 870's around here but it seems he's MIA lately, you could try sending him a PM.
https://rawze.com/forums/member.php?action=profile&uid=993
RE: CM870 731 code - lstrucking - 01-25-2025
(01-25-2025 )tree98 Wrote: What program are you running In the ECM now and what program was running this engine before you slapped your ECM on it??
Yes the timing in the programming can be checked and changed if need be but not with insite, you need C A L T E R M for that.
A word of caution though..... 870 ECM's are well known to brick when flashing them. If you don't know what your doing you could end up with a truck that won't start.
Runningrough use to do all the 870's around here but it seems he's MIA lately, you could try sending him a PM.
This ecm is new to me it came with the core so I have no information on who tuned it or anything of that nature. I’ll send him a PM thanks
RE: CM870 731 code - marek4792 - 01-25-2025
You said you checked the wiring but did you check the 5volt reference and grounds on both sensors, while wiggling the harness? Oem sensors? Both positions use the same part number.
RE: CM870 731 code - lstrucking - 01-25-2025
(01-25-2025 )marek4792 Wrote: You said you checked the wiring but did you check the 5volt reference and grounds on both sensors, while wiggling the harness? Oem sensors? Both positions use the same part number.
Yep 5 volts good ground good even pulled the harness apart and visually inspected the wiring all the way to ecm plug. I took the sensors off my blown motor that were good when it was pulled and they didn’t change anything I’ll get 2 new ones Monday and see what happens
RE: CM870 731 code - lstrucking - 01-27-2025
Set timing to 4/6 and all is good. Timing in the ecm must have been changed with the tune thanks for the replies