So, I wasn't sure where exactly to throw this thread, but figured that this would be best.

I have a 1979 F-100 Custom with a 1989 LTD Crown Victoria transmission and 5.0L 302 engine. My issue is that when I'm driving, there seems to be only "steps", if you will, in the acceleration. For instance, it will accelerate smoothly up to the pedal being depressed 1/4 of the way. After that, there's hardly any acceleration from 1/4 to 1/2. After the pedal is depressed 1/2 way down, it will "kick" up the RPMs. Usually there's what I'll call a "low" kick and a "high" kick in the RPMs.

I understand why engines "kick" when you're accelerating fast. But my question is, why don't I have a smooth acceleration up to the point when the engine needs to "kick"? Seems like a dead spot. Maybe the TPS, injectors, MAF?

Any help is much appreciated! And sorry if that's not clear, I can explain more if you need me to.

 

So the motor has the original EFI system on it? If so pull the codes and post up what you get.

 

Just got home from work and ran a KOEO test. It pulled 11, 10 (separation code), and 31. From my book, 31 is EVP or PFE circuit below minimum voltage.

Also wanted to add that for the last 2 months, usually in the mornings but sometimes in the afternoon, the check engine light will flash when the pedal is depressed within a certain range. Doesn't seem to be a code, it just flashes constantly while the pedal is in that specific range (I don't have a tachometer, but lets say that range equates to 1700-2000 RPM). If the RPM is below or above that, the light is not on or flashing.

 

I'd suggest you pull the PCM out and open it up and closely inspect for leaking or exploded caps, and even if you don't find any consider getting a replacement PCM. The reason for this is the bahaviour you describe is not normal so it would seem the PCM has lost it's marbles.

 

Based on your description, a cheap item to replace just to see if it helps is the throttle position sensor. Those seem to go bad much more often than a little potentiometer should.

 

Alright, I'll open it up and check it out. Happen to have any good sites for that kind of stuff, if I do find anything funky in there?

I was thinking about doing that a couple weeks ago. I'll probably give that a shot this weekend and see what happens.

Also, either of you know what causes a code 31 besides a bad EGR?

 

The code 31 is probably from an out of spec reading from the EGR position sensor, but the valve may actually be working. If you can get a vacuum pump, you can attach it to the port on the EGR valve and pump it when the engine is idling. It should stall the engine, which indicates the valve works. If the valve is stuck open, the engine will not idle.

You can also run the KOER test, which will blip the EGR at some point, and the engine should stumble for a moment. This shows that the entire control chain of the EGR is working.

The valve gets very hot, so the sensor takes a beating, and fails often. It's just another potentiometer, so you can pull it off and test its operation with an ohmmeter.

 

You can plug the EGR and the engine will run fine with it plugged. You will get a code from that, but otherwise, everything will function.

 

Thanks for all the suggestions, guys. Sorry that it's been so long. Finally got around to trying some things out. Forgot that we had done this, but when we did the engine swap we were getting a code, I believe 34, saying that the EVP sensor voltage was above the closed limit. In order to fix it, we shaved a little metal off of the shaft on the EVP.

So, long story short, I replaced the EVP yesterday and reset the computer. Today, started it up cold, no stumbling cold idle, no stumbling at low throttle, and no flashing check engine light. Fingers crossed, but I think the new EVP has solved my problem.