FQ2013

Continuing Cummins M11 fuel pump issues... I'm starting to feel pretty familiar with these by now! You may remember I was having problems with losing prime and well, it got a lot worse. Truck couldn't start on it's own anymore because it would pull the batteries down before it could self prime and purge the air. When I initially started working on this truck it would build 22 +/- psi cranking. When I pulled it in the shop it would barely make 10 which is no good at all. In my research I found a TSB from 15 years ago regarding above tank filter mounting. Apparently Cummins decided the best fix was a check valve in a fitting at the filter...

Along with a reman fuel pump I was sure the problem would be resolved. Nope, although the original pump had stripped the splines on the drive gear (Causing the low pressure) it was not the ultimate problem. With a pressure gauge hooked up while cranking it will read zero but spike up to 20 psi every 10 seconds or so until it starts. Hmmm, the check valve eliminated any drain back and air intrusion so what's going on now? FSS is 12v powered with ignition on but only "pings" while cranking (explaining the pressure reading). What the heck? According to Cummins the FSS is powered when the ECM senses the ignition is on and only turns it off with the key switch or engine over speed. On further research some ECM's are programmed to shut off fuel until it get's a reading from the engine position sensor. Performed Cummins ohm testing procedure and sensor tested out fine. I'm not sure I'm convinced that it isn't the problem though.

Week: 60