I've posted before about my misfire problem and after extensive searching, checking, and replacing near every sensor in the truck I have to my witts end on what is at fault. I've got a code 31-EGR position sensor below minimum voltage. My symptoms are a rough idle, a misfire when over ~half throttle, and the engine stumbles and near dies at WOT.

So far I've changed out the EGR valve, EGR position sensor, O2 sensor, Throttle position sensor, and coolant temp sensor. I've also checked voltage to the EGR position sensor and as vacuum is applied, the voltage does change HOWEVER the voltage is not consistent with a diagram I printed off Alldata (our schools online chilton's guide to every vehicle), it is reading above what it should. I was told that this wouldn't cause the problems, but it still worries me.

I had the truck in a local shop where he suggested either the O2 sensor was faulty or the injectors were dirty. I pulled and cleaned the plenum and injectors spotlessly along with doing a ignition tune-up and replaced the 02 sensor. I'm a student at Linn state technical college and have been lucky enough to get the truck in mechanics shop where they found today that the voltage from the 02 sensor was inconsistent with normal readings and that they are going to be searching for ground issues or a break in the wire harness.

I have free time tomorrow and was hoping to get in the shop and check the ground wires and test continuity from the EEC to the sensors and grounds, however I can't find a diagram anywhere on Alldata or on the internet on where the ground wires are.

Does anyone here have any suggestions on what else to check out or have a diagram of where I can find all engine grounds?

 

i had these same problems on my 88 f150. nothing seemed to work. as soon as i changed the fuel pressure regulator it ran like new. try that

 

I replaced the FPR about a year ago, and have tested that as well. Fuel pressure has been checked for both volume and pressure both checked out.

 

If you're checking all these sensors then why are you replacing them? Were the 02, TPS, FPR, EGR, and EVP sensor all bad at the same time? Do the symptoms go away when the EGR valve vacuum line is plugged\disconnected?

 

I replaced them all for more peace of mind then anything. The symptoms do not go away when the EGR vacuum line is plugged and when vacuum is applied to the EGR valve at idle, the engine stumbles meaning the EGR valve is opening and closing.

 

I bet the Ford parts that you tested OK are better than the replacements from chinaland.

They arn't "ground" wires per say, all the sensors have a signal return to the 5v from the computer. Read up on fordfuelinjection.com

Adrianspeeder

 

Thanks for the link adrianspeeder! I did a lot of research on that website today and it had some great data on it.

After reading through it, I wanted to test my MAP sensor but I don't have a multimeter that reads hertz. I unplugged the electrical plug from the sensor and the truck idles perfectly and the RPM's dropped much quicker when revved than when it was plugged in. It was the best the truck has run for months. Would this be a sign of a bad MAP sensor?

 

It could be, but it is also the sig of a vacuum leak, have you hooked up a vacuum gauge?

 

I've checked every vacuum line and repalced a few of them. I also run ~25 pounds of steady vacuum at idle.

 

Then I'd try a new MAP sensor, but keep the receipt and take it back if it doesn't fix the problem of course.

 

Sounds like a plan boss I won't be back in town till friday but I'll get it swapped out and let you guys know. Thanks for the help so far!

 

That would qualify as an electrical part. Most parts places have a "no returns on electrical parts" policy.

 

Hmm, I've done it before, but needless to say the guys at the parts counter know me well. When I have a bucking\surging\backfiring problem I tried a new MAP sensor and it didn't do anything for it, so I took it back. Later I found out that my distributor shaft bearings were bad causing the distributor\rotor to drag.

 

I've got a good friend who works the counter at O'Reilly's, he can help me out with that no-return policy. And a great perk to going to a state tech school is 10% off autoparts with student ID.

Your symptoms sound similar to mine booba5185 with the bucking and surging. Is it possible to regrease distributor bearings? Even if its temporary fix, it will single out my problem before dropping more money and pulling the dizzy.

 

Not really, I just replaced the distributor. The way I singled it out was I pulled the distributor and spun the rotor by hand, it squeeked and I could feel the drag.