First off, thank you for the years of experience I've found on this forum. It has been very helpful with all of my OBS trucks. This has me stumped. 1996 f250, 4x4 351w. Idles completely fine. Goes in and out of gear perfect. Timing was off when I got it (someone times it w/o removing the spout). Fixed that. Fuel pressure was 25psi at idle. Put a new pump in. 33 idle, 35 regulator vacuum removed. TPS was jumpy on the diagnostic so I replaced it (0.83-4.55 now). If I move the throttle slowly (crawl speed) it revs up fine. But any harder acceleration and it starts to cut out and I lose fuel pressure. As if the ECM is shutting the pump down. Let go of the throttle and it comes back. It doesn't lose spark when this happens and timing is advancing with the tps. Codes pulled are for egr and o2 sensor. Sensor is gone from having headers and egr line is plugged (previous owner). But that shouldn't stop it from acceleration. 108k on the clock. Any advice and tests for the crank, cam, or heard maybe MAF sensors? And the ECM was replaced and programmed by some guy called the cheap computer king. Tried emailing him with no response. Thank you in advance.

 

Have you checked the IAC? If not, try cleaning your IAC (idle air control) valve. Same thing had happened to a truck that my friend had owned. It is cheap to do and fix if that is the problem. Just use some brake cleaner on the valve to clear up any blockage.

 

I haven't taken it off yet. I pulled the plug on it and the idle dropped very low. Thought it was working correctly. I'll pull it off tomorrow. I performed the hertz test on the map sensor today and it passed.

 

If I'm reading this right, then that is a problem. The O2 sensor needs to be mounted back in the exhaust stream, right at the collector or as close to it as possible.

If you're still using the factory injectors and MAF, then pull the chip out from the ECU and see how it runs.

 

I can't seem to find the original wiring in the harness for the o2 sensor. Expected to see it zip tied somewhere back there, but nothing. Thinking I will have to find a harness from the junkyard. And from my understanding the MAF was optional. Mine doesn't have one on the air box or at the throttle body. Build date on the door is 09/95.

 

Yeah it not likely an F250 would be MAF unless it was a Cali truck originally. And the PCM in that thing is not programmable as we understand it today with modern OBD-2 vehicles.. you don't just plug in a handheld device and flash the prom.. there is no prom, so an external module has to be added that overrides the on-board memory. If your truck has one of these add on modules remove it.. there is no need for it and who knows what they messed with. And as already stated get the O2 sensor reinstalled, the EFI system is totally crippled without it you may as well have carb on the motor. The harness for it runs up over top of the trans or along the frame and up behind the battery with the main ground cable, should be a round connector with 3 or 4 wires.

 

Ill look there for the harness tonight. Misscomunication, not programmed but remanufactured. Sorry.

 

Found it! Had my boat do this, so it gave me the idea. The rubber part of the fuel line coming off of the filter had partially collapsed. So it would prime and idle fine, but not enough fuel when I get on it. Cut the piece out and rigged a piece of fuel line in. Revs happy and no loose of power. Thank you for the tips guys. And yes, I will be hunting down that harness and adding the o2 sensor. Thanks

 

If this is an EFI engine why am i totally confused..