Hi everybody!

I'm having some issues with my 96 Ford F-250 EFI 5.8L and I'm looking for diagnostic advice.

Had the truck for about six months and it always had an issue where when idling occasionally the CEL would come on and it would idle a bit rough and surge.

Last week it started give me fits when driving. It seems like if I press the accelerator anywhere up to about 15-20% throttle it will buck and surge if driving and surge when idling. It doesn't matter if I'm on flat ground or going up a hill. If I give it more gas it'll hesitate a bit and then pickup and run pretty well. The exhaust smells kinda funky, but it's not raw fuel smell.

I borrowed a scanner last night and did a KOEO test and got 111 followed by 327 and 334. I cleared the memory and drove it for a while today and then checked it again and got 111 and 327.

I didn't get a chance to really get into it since it was getting dark, but I checked a few things. I unplugged the vacuum line off of the EGR valve and applied a bit of vacuum and it caused rough idle and it held the vacuum. I couldn't backprobe it and test it while running because I didn't have an extra hand or two to keep everything in place.

I checked the voltage at the EVP sensor harness and it read 4.78v with KOEO. I unplugged the connector and checked the sensor. The resistance between VREF and SIG was 4.55kohms and between SIG RETN and SIG was 673ohms.

I was just wondering if anyone had a little more logical approach to diagnosing this problem or if the problem I described is even consistent with that code. I searched quite a bit, but I keep getting conflicting information.

Thanks and have a good one!
JD

 

Try a simple check: Pull the throttle position sensor connector and put an ohmmeter across the wiper and one of the end terminals, and slowly open and close the throttle. The resistance should change smoothly. It's best to do this with an analog meter, if you can get one. If the reading jumps around, then the TP sensor has gone bad, and will give your engine fits as you try to change throttle positions. It's a cheap part, around $30.

 

Xlt4wdford - That is what I initially suspected before I scanned it and I ordered a Motorcraft replacement and the required gaskets for the throttle body, etc, but the weather hasn't been cooperating on my days off. As soon as I get a chance I'm going to install it and check out the throttle body and stuff.

Today I picked up an EVP sensor and took it for a short ride and no CEL, no surging and the motor sounded better over all. I'll know for sure when I go to work in the morning.

Thanks

Jd

 

I've encountered at least 2 bad TPS that caused intermittent stumbling without registering any errors in the EEC self test. So it may not show up in a scan.

Also, unless you need to remove the TB for something else, it's not necessary to do that in order to replace the position sensor.

good luck.

 

Yeah I have had them fail without any codes, too. Going to find out shortly how it runs now.

I wanted to take the throttle body off anyway because the gasket is looking kind of sketchy, though I wasn't aware that you could change them on the 5.8L without removing it due to the mounting location.

bjd

 

A quick update.


Fired it up this morning in the cold (2F outside) and let it warm up real good and it idled great.


Drove it in to the shop and drivability has increased 10x. I can still feel a flat spot in the throttle response about midway through, but the bucking and surging are gone and I didn't spill my coffee on the dashboard! I figure it's probably the TPS acting silly on me.


The CEL did come on and it stayed on the whole way in, but I'm a wuss and it's cold so I didn't scan it yet. Could this be caused by the new sensor? I unhooked my negative cable before I went to get the sensor and hooked it back up after the new sensor was installed, but I didn't hook up and manually clear the memory.


Thanks and have a good one.


bjd

 

Looks like you got at least one thing fixed. You may want to rescan the EEC to try to find the cause of the CEL. That seems to be a hard error that should record error codes.