90 F-350 cab/chassis 460 5-speed 93k
this truck sat about 7 years and ended up with both fuel pumps being replaced (junkyard pumps) everything worked well once that problem was solved. been driving the truck around the pasture and it performed great. Slight high idle but I know what caused that (dirty ABP). Have been trying to get the truck road ready, the only thing it really needed was a new muffler. Being a weldor by trade I just cut off the OEM muffler and tailpipe and welded a 26" glasspack behind the CAT. That was the end of good times. The truck idles very nice, but will not accelerate under load at all. RPM can be raised gradually when stationary and runs fairly well. But when you give full or partial full throttle suddenly it falls on it's face, backfires through carb and only hits on a few cyls.
Here is what I have done:
CK fuel pressure- marginal at 35-38 psi
CK flow- good
CK spark at idle- hits on every cyl
CK for vac leaks- none
CK fuel pressure reg- appears functional
CK fuel filter- new after fuel pump change
CK EGR valve- mechanically functional and has vacuum when running
Even tried building baffle plate after new muffler to simulate backpressure of old OEM set-up- no difference.
Pulled Codes:
KOEO:
14-PIP circuit failure
34- PFE or EVP circuit failed
KOER:
14
34
95- Fuel pump secondary circuit failure EEC to ground
96- Fuel pump secondary circuit failure Battery to EEC

Ihave read and searched this foroum till I am blue in the face and can find nothing that helps. I'm not one to just go replacing parts and hope it works. I want somthing to test and visually, mechanically or electrically find a problem with and fix that. It may not fix the big problem but it isn't unnecessary either.
Thank you for any responses.

 

I'd go after the code 14 first. The ignition module can be tested at some parts stores. If that's good, then either the pickup in the distributor or the circuit to the computer could be bad. Here's a good reference book for troubleshooting these things:
https://www.ford-trucks.com/lc/lc.ph....htm?code=GFF9
I don't know what the fuel pump circuit faults would cause.

 

Since you replaced the muffler with a glasspack and now you have problem accelerating under load, the problem is more than likely partially clogged exhaust system.

The muffler you took out probably has some holes inside or around it's external surface and helped flow the slow moving exhaust coming from the cat.

Verify if you have a clogged cat by using a exhaust backpressure gauge. You just remove your O2 sensor and plug this device and start the engine. Any pressure above 3 PSI indicates a clogged exhaust system.

You might have to replace your cat with a free flowing cat.