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Discussion Starter · #1 ·
1996 3500 dually Fishbiting at operating temp.

All the things we have done to this truck so far-
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Upgraded battery cables
New batteries
New harmonic balancer
New front seal
New PMD relocated to bumper
Deleted vacuum pump
Installed manual wastegate
New lift pump
New sending unit with diesel sock
New fuel lines from lift pump to FFM
Clear line to IP (not seeing any bubbles)
Swapped bed for flatbed.
Checked all grounds.
Ive run it with/without gas cap, and drilled a tiny hole in it
Installed boost gauge

Things happening-
Fishbiting at temp, sometimes worse than others. When its bad, I have to double foot at stops to keep it from dying. Sometimes its little bumps, sometimes its really jerky.
RPMs arent surging when it happens.
I do have exhaust? coming up from right behind the motor, if that might have anything to do with anything.
Low coolant light will come on randomly or when I hit a bump hard enough.
The only codes I currently have are P0251, and P1656, which I assume is because of the manual wastegate?

These are the previous codes that were cleared out, none have come back though.
0231- fuel pump feedback low voltage
0238- turbo boost sensor circuit high voltage
0251- injection pump cam system
0370- timing reference high resolution
0380- glow plug circuit performance
0606-PCM internal communications interrupted

(Digging in here is like going into WebMD with a cough and coming out with cancer lol)
From searching in here, it could be one or some of these things-
Bad PMD/harness
Optic sensor (does the 96 have the OS sensor)
Tuna can
Cam shaft sensor.

I dont have the stuff currently to check the fuel pressure, but can see if anyone around me might.

What is the "proper" order of operations on how to eliminate possible non-issues?

· Registered
5,157 Posts
If you have verified that there is no air in fuel with the clear fuel line. Check the wiring and connections for the OS. If all good. Then your Optical Sensor is most likely bad. The optical sensor also functions as the cam position sensor. The OS is located on the top of the IP. A bad OS can cause fish biting and stalling.
1656 is most likely because you went with a manual wastegate control. OBD2 does not like manual control. You will have to live with wastegate and boost trouble codes and possible defueling, Unless you get a custom tune for the manual wastegate.
To start I would not adjust the controller to give more than 8 lbs of boost. You can then adjust it up slowly to find the sweet spot where It does not trip codes all the time.
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