[hopdup95]

My 2000 f250 7.3 surges real bad and shakes like you're on a bumpy road at low rpms but then runs like a bat outta hell when I step on it. Doesn't throw a check engine light, doesn't always idle rough (only a couple of times), but always cuts out when barely touching the pedal. The previous owner said it was getting too much fuel when I bought it from him, changed out the fuel pressure spring and nothing.

It's got a TS chip (always set at 75hp), intake, and an old edge programmer that doesn't have any settings on it, just used as a reader for egt etc.

Any help would be greatly appreciated! THanks
Rob

 

[RT]

Does it still do this in stock setting? I'd try unplugging the ICP sensor and see if it smooths out.

 

[hopdup95]

Yes still does it in the stock setting. I will try unplugging icp later to see if that helps. Doesn't it need the sensor tho? Why would it do better without it? Thank you!

 

[RT]

With the sensor unplugged, the PCM uses default tables. It basically guesses at what the IC pressure should be considering all other parameters. It definitely needs it in the long run, but to test if the sensor is bad, unplugging it is the quick and dirty test.

As to why it would run better unplugged. Lets say your ICP sensor is biased by 200 psi. Your PCM wants 500 psi at idle (random examples) and your ICP sensor is reporting back the pressure is 700 psi (even though it really is 500). The PCM responds by opening the IPR valve slightly to bleed off the excess pressure dumping the actual pressure to 300 psi (ICP sensor now reporting 500). At this pressure, the engine begins to stall, the PCM closes the IPR valve to raise the pressure, the engine smooths out, then the cycle repeats. Over and over and over.