I've had a problem with fuel delivery, and the output shaft speed sensor. I've completely rebuilt the fuel filter housing, and primer. I did find trash inside the molded gasket that has a retention spring inside the fliter housing, so thats all good and clean now, before I did that I wasn't able to prime the system and it would crank no start. I've replaced the inlet and outlet fuel lines from the filter. I also replaced the speed sensor closest to the drive shaft on the transfer case, before changing it my speedometer was all over the place now it's more consistent and I can finally feel the gear shifting where I was stuck in 2nd, but now I'm still seeing the needle bounce around 55 60 mph. When I get in the trottle going down the the road it restricts my throttle to where I don't have any pull and I can only get about 2500 rpms out of the truck. I'm still throwing a code but haven't checked it. I was detecting a fuel leak code, a p0721speed sensor, and a p0380 glow plug heat circut. Any ideas on where to look next? Should I change the other 2 speed sensors? Also how do you know when it's time to change the injectors?
LB7: Air leak and speed sensor troubles, can't find the source help me please!
- Thread starter DieselDean
- Start date
Whoa, that's a difficult read. So let me see if I understand:
It appears you had a problem with the fuel filter head (a common thing to happen), but it seems you got it started again now?
You also had a problem with the speedometer not working right, and replaced the output speed sensor on the transfer case, and now your speedometer mostly works. But, you have it hang in gear and other weirdness.
That is all understandable. The Allison transmission needs very accurate RPM readings from the various pieces inside it (and the output shaft, measured in the transfer case) to shift.
If the sensor went bad inside the transfer case, it could be because of a failure inside the transfer case. If the new speed sensor is acting up, you might want to check the transfer case is in good shape internally. Eventually, the oil pump rubs a hole in the case, and dumps all the fluid out, then the internals go out pretty quick.
To really diagnose this, you need to get a good scanner that can talk to all the modules in the truck (not just the ECM), and see what codes are there. If you do have a speed sensor code currently, check/replace that sensor and see what happens.
And finally, it appears you have some injector/fuel system issues besides the fuel filter head you are trying to identify? On a LB7, as the injectors start to fail, you typically get a haze when idling, and when leaving stoplights. You can also have fuel filling up the crankcase, either in addition to or instead of the smoke at idle. Finally, they can just return too much fuel, becoming hard to start when warm, again in addition to or instead of the other failure methods.
It appears you had a problem with the fuel filter head (a common thing to happen), but it seems you got it started again now?
You also had a problem with the speedometer not working right, and replaced the output speed sensor on the transfer case, and now your speedometer mostly works. But, you have it hang in gear and other weirdness.
That is all understandable. The Allison transmission needs very accurate RPM readings from the various pieces inside it (and the output shaft, measured in the transfer case) to shift.
If the sensor went bad inside the transfer case, it could be because of a failure inside the transfer case. If the new speed sensor is acting up, you might want to check the transfer case is in good shape internally. Eventually, the oil pump rubs a hole in the case, and dumps all the fluid out, then the internals go out pretty quick.
To really diagnose this, you need to get a good scanner that can talk to all the modules in the truck (not just the ECM), and see what codes are there. If you do have a speed sensor code currently, check/replace that sensor and see what happens.
And finally, it appears you have some injector/fuel system issues besides the fuel filter head you are trying to identify? On a LB7, as the injectors start to fail, you typically get a haze when idling, and when leaving stoplights. You can also have fuel filling up the crankcase, either in addition to or instead of the smoke at idle. Finally, they can just return too much fuel, becoming hard to start when warm, again in addition to or instead of the other failure methods.
Thanks it looks like I may be taking it to the mechanic. I don't think the injectors are going from what you've described. So there might be a leak somewhere else, or there might be a fuel return issue. I think anything past what I've done is going to be way over my head. That and I don't have that good of a scanner.