My 93 F150 has a 5.8L in it. I gutted the front cat and cut the back one off. It ran great for a while and now it's missing at idle and missing and bucking at cruise and during acceleration. I have replaced the wires, plugs, cap & rotor and the coil. I am also having fuel pump problems. If I run the front tank it pumps to the back tank AND the fuel rail. The back tank does not pump to the front tank. I run on the back tank only. Tomorrow morning I plan on checking the fuel rail pressure. I also want to fool the ECM by bypassing the O2 sensor with a resistor that gives it a false median reading. Anyone know what the resistor value would be? Or the median voltage so I can find the resistor value?
Kenny

 

Sounds like your rear fuel delivery module is bad in the rear fuel tank. Replace it and see if that fixes your problems.

Fuel Delivery Module (FDM):
http://i54.photobucket.com/albums/g9...nceAutoFDM.jpg

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Thanks

 

this is exactly what my truck was doing at first. mine has just progressed to stalling in reverse. my front fuel pump doesn't work at all

 

The filling tank would have the bad check valve in its FDM.
With a bad check valve your fuel pressure can be low and cause drive ability problems.

 

I did a fuel pressure check today. When the key is turned on and left on the fuel pressure goes to 45psi. As soon the key was turned off the pressure dropped to zero. Also the engine sounds like it is running lean when it is accelerating. It sounds like it's on the right side which would make sense if the fuel can't keep. The right side fuel rail is the furthest away from the fuel regulator. I'm putting in a new fuel pump on Saturday. Does anyone have an answer about the resistor size in the O2 sensor circuit?
Kenny

 

I have not heard of anyone putting a resister in the O2 circuit. I have heard of them doing it to a EGR sensor (EVP) circuit.

 

I have seen some for sale on the internet but a few years ago I did some research on a "chip" that would give your vehicle a power boost. The "chip" was a resistor, packaged nicely, that plugged into the cars IAT sensor and fooled the PCM into thinking the Inlet Air Temp was 70 degrees. I thought if I could do the same with the O2 sensor it keep the ECM running the fuel delivery in the mid-range. The info is out there I just have to find it.

 

A resistor will not do it, you would need a circuit with a chip.
I think this is what you are looking for:
http://www.mkiv.com/techarticles/oxy...sor_simulator/

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Replaced the fuel pump on Sunday, it helped a lot, no more lean running problems but it still missed. I realized that the plug wires that I installed the other day had been on my shelf for a few years so I put new plug wires on this morning. Viola! Problem solved. Thanks for all the help.