I have a 91 F150 , 5.0 with the crappy M5OD tranny. I've been having engine performance problems for a while (rough idle, acceleration and cruise stumble). The engine light never came on until recently. After reading and rereading the "Ford Fuel Injection & Electronic Engine Control" by Charles Probst, I found a way to download the fault without spending hardly a cent (by triggering the self test function using a jumper wire between the STI and signal return, and observing the engine light). Anyways, the self test (KOEO) first indicated system pass, but the memory code signaled code 33 (EGR Valve opening not detected). The KOER test also indicated the same code. Mr. Probst's book gives parameters for testing the EGR valve position sensor, which I will accomplish in the next few days, to determine if the the sensor, valve, or wiring are faulty. ANY SUGGESTIONS?

I purchased an EGR valve and wanted to replace it anyway since the truck has over 105000 miles on it. Anyone out there ever had difficulty loosening the nut that attaches the EGR valve to the tube, mine seems to be extreemly tight and I don't want to break anything trying to remove it.
ANY SUGGESTIONS?

One last thing; engine RPM hangs at times between shifts, the idle seems a bit high and a little rough. Gooseing (sp?) it drops the RPMs but it still hangs. Found a way to temporarily eliminate it; shortly after the engine is running, I goose the throttle and the hanging problem goes away, but opposite happens; RPM drops off abruptly. The the performance problem as stated above still occurs. Replaced the ISC-BPA valve and slaved in a used TPS. No change. No fault codes for either two components during recent testing. I have a new TPS on hand. SUGGESTIONS?

SORRY ABOUT THE LONG DISSERTATION-thanks to anyone who will be of help!

 

Step #1 for your type problem is to clean the throttle bore where it interfaces with the throttle plate and disassemble and clean the bypass (BYB) valve. Small amounts of gunk really impacts the ability of the valve to maintain idle. Use a soft brush and carb cleaner or lacquer thinner to remove the crud. Fords are famous for this problem and many a troop has dropped big $ at the local garage on parts when this was the problem.

 

Anytime I know I'll have to work on anything exhaust related,I spray penetrant every 1/2 day or so for the entire week before the weekend when I did the work. Also,every time you spray,rap the nut a few times with the ball of a ball pein hammer. This hasn't failed me yet! Thinking about your fault code, I'm wondering if a busted diaghram which would not move the valve pintle,causing a no position sensed,and also cause a vacuum leak while in operation,possibly contributing to your erratic idle.
Phillip

 

Thanks for your suggestions. The original bypass valve was replaced with a brand new one from Ford less than a year ago. It was the first thing I did when the idle started acting up. I did clean the T-body just recently using Simple Green; the throttle was sticking after the engine had been off for a while. It still sticks even after I cleaned it. Perhaps I should try the thinner as you mentioned.

Since the self test I did didn't point to the TPS, should it be ruled out as it being a contributing factor in the idle problem?

 

Thanks for the tip, I'll keep spraying on the penetrant and this time tap on the nut. I'll be using a vacuum tester to open the valve to check the resistance at the EGR position sensor, if it doesn't hold a vacuum then your theory may be right-will let you know.

 

>Thanks for your suggestions. The original bypass
>valve was replaced with a brand
>new one from Ford less than
>a year ago. It was the
>first thing I did when the
>idle started acting up. I did
>clean the T-body just recently using
>Simple Green; the throttle was sticking
>after the engine had been off
>for a while. It still sticks
>even after I cleaned it. Perhaps
>I should try the thinner as
>you mentioned.
>Since the self test I did didn't
>point to the TPS, should it
>be ruled out as it being
>a contributing factor in the idle
>problem?

One would think so, however, some BBS contributors have indicated a new TPS fixed their problem even though they did not have a fault code. I changed my TPS when I had an idle problem (88 Bronco) even though I had no fault code (desparation) and than got the fault code with the new TPS. I put the old one back in and the fault code stopped. My gremlin turned out to be the gunk problem. When you get it fixed we would like to learn from your experience.

 

You used the wrong stuff... Use spray carb cleaner.

 

On anything exhaust related, I always spray it with penetrating oil. Warm up the engine for a couple of minutes, then break it loose.