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

Wheel end control...

On the topic of ABS and stability control

Computer is getting feedback from wheel end sensors but they must be using individual leveling valves or a single modified valve that can control the suspension independently.

ABS valves

The brake modulator is used to control individual or in this case LH side of the tandem drive. Using the input from the wheel speed sensors the computer will command the modulator to cycle exhausting service brake air to the atmosphere and preventing the wheel from locking up. A three wire connector is used to control the inlet and exhaust solenoids in the valve. During normal operation the service air bypasses the exhaust port and is routed directly to the brake chambers.

And there were pictures...

In the process of repairing an intermittent short in the headlight system I found these. None of which were the problem.

The corroded off wire in the first picture was in the wiring loom directly behind the RH steer tire. No tape, shrink tube, etc... had been used. Someone then skived the insulation off of wire 22D coming out of the RH headlight relay and ran a light gauge jumper wire to front of the truck. A crossover wire was used to hook the headlights together but was left hanging across the front cross member. It is pictured below. I repaired the damage to the harness in the loom and completely re-did everything from the end of the frame rail forward. New pins in the metripac connectors at the headlights and the harness is now back to OEM original using numbered wire.

FQ2013

Learning the art of repairing what has been done before you... Driver complained of the headlights flickering on/off constantly. In the process of finding the short I found these. None of which were the problem.

... or not. Company phone won't connect to the server to upload the pictures. I'll put them up in another post as soon as it works.

Week: 50
Total: 418

FQ2013

Found another purpose for my test gauge setup... Intermittent hard start with a Cummins M11. Fuel pressure while cranking jumps from 0 - 20 with hang time on the 0 until it finally starts. Extended crank after sitting for a few hours. If only shut down for 5 minutes it will start right up but will take up to 30 seconds cranking the first time in the morning. I'm suspicious of the check valve sticking letting the fuel drain back. Fuel pump is identical to the N14 I've been working on.

Week: 50
Total: 368

FQ2013

Adjusting wheel bearing end play using TMC RP618...

Initial torque 200 ft-lbs while rotating wheel

Back off 1/2 turn

Back up nut torqued to 300 ft-lbs

Checking for end play... Initially at 0 (Bearing pre-loaded). Backed off inner nut slightly and ended up with 10 thousandths which is still no good. After close inspection the inner nut would rotate approximately an 1/8th of a turn while torquing the back up nut. The locking ring has worn to where it allows the inner nut a 1/4 turn free movement. I have a new lock ring etc... on order. After fighting it for a while I was able to get end play set to 0.003" within the acceptable range of 0.001 - .005.