Help!

[Rawze]

What model/year engine is it?
some history?


CM570/Sig. Series ISX.
Fault Code: 121 -- No engine speed signal detected from the crankshaft engine position sensor.


If it is not the crank position sensor, or the wiring, crank shaft damper is good, ecm is good, it could be that the tone wheel is slightly loose on the crank. - I have seen this before. Check to see if there is any free-play in the tone wheel to the crank.

It can also be from too much play in the crank bearings. If it has had a recent inframe or those bearings were replaced, someone needs to plastigauge the bearings and ensure they did not install the wrong ones. read through this post for some related issues known about the ISX and bottom end bearings that a lot of people simply do not know any more about them: http://rawze.com/forums/showthread.php?t...5#pid32065

lastly, if someone has installed the wrong program in it, or has made a custom program for it resulting in too high of a final crank angle (the point where peak cylinder pressure happens is too low of an angle) then it will cause the crank to vibrate internally. A person usually cannot feel this going down the roads, but over time, it beats the bearings up in the bottom end and also causes liner fretting prematurely. -> if it is bad enough, it can weaken the crank bearings and eventually start to cause crank position alarms as the bearings slowly get hammered out, the problem getting worse over time, eventually destroying the engine.

just some things that have been seen in the past on them, thoughts. nothing more.