I have a 168k 1995 f250 XLT 4wd extended cab truck with 7.5l and 5 speed that has been acting up recently. Truck isn't driven much, and it has been trouble free for the past 5 or so years that I've owned it.

The symptoms:

Truck is down on power and bucks while trying to accelerate from approximately 1700rpm. I say accelerate, but I guess it is when you are trying to simply maintain speed. If you hold your foot on the gas, you can tell it is being sluggish, but then it will randomly start running fine after bucking for a bit. I don't notice it missing. The jerking seems to be from no power/normal running swapping. It feels as if you are running out of fuel and then it magically starts running fine again. Then you get to repeat the cycle. It only seems to do it after it has warmed up a bit. I've left it running in the driveway for 10-15 minutes before a test drive, and it drives normally for 8 or so miles. I then parked it at the grocery store for a bit while I did some shopping (wife wanted me to multitask), and when I came out, it starts running strangely again. One time it took another 6 miles of driving before acting up, but last time it did it as soon as I left the parking lot. Truck will always idle smoothly and does not try to die when it is acting up.

The check engine light came on for about a minute right when this problem started, but it has not returned since. Pulling codes, the only thing in memory was 512 KAM failure. I did KOEO and KOER and both came back with no codes 1 1 1.

I checked the ground on the ECM by the battery, and it seems good. Got the same 512 code after disconnecting that (as I would expect). There is a little corrosion on the positive battery terminal. Things I've done since the issues started -- some general preventative maintenance that should have been done long ago, and some random guesses that I did because they were cheap:

Coil
Plugs
Wires
Cap
Rotor
fuel filter
TPS

Any ideas on what to check now (or what I should have checked) -- or random guesses based on your experience?

 

Check the fuel pressure at idle, idle w/vacuum line removed from the fuel pressure regulator, and under load.

 

That was a thought I had. Will do that this week when I get a chance.

 

Have not had a chance to check under load or when generally running funky yet, but idle shows 32psi and disconnected shows 42psi.

 

That means the fuel pressure regulator is operating as expected. Now to find out what happens under load.

 

Drabcat,
I don't have experience with Ford Diesel P-U trucks, but do with semi tractor trailers. What you described was always the symptoms of a becoming clogged primary fuel filter on a 250 Diesel Cummins that I drove in an old International Trans Star tractor (moonlighting hauling mail).

 

The OP has a 7.5L gas engine in their truck.

 

Did a test drive this morning with the fuel pressure gauge connected. Since it only has like an 18" hose, my plan was to drive until it acted funny and then hop out and do the pressure checks with the regulator vac line pulled. Problem is that it never ran weird.

I did finally get a trouble code: 173

Truck ran normally the entire drive, but the code came on after about 18 miles. When I returned home (approx 25 miles of driving), fuel pressure showed 35psi at idle.

 

Running rich,could be map sensor or the o2, another problem I have found in the past is the harness on the o2 sensor.

 

The plot thickens...

Drove the truck last night before having chance to really test anything further. Truck did fine on 5 miles trip to store, but when I started driving home, experienced the same symptoms I've been having - crappy running without any check engine light. Then the check engine light came on, and the truck started running more normally. I can't say it was 100%, but after what it was doing, it felt like normal running. So no light when running really bad, and light on when it starts running fine. I didn't have a chance to check the code last night though I assumed it would be the same rich code I got last time. Upon checking it this morning, I found it gave me 111 and 512 again. So...something is causing the computer too lose codes. Makes me wonder if it is partially causing the bad running.

 

If you are removing a battery cable to clear the stored codes then Code 512 is coming from that. If you did not, that indicates a problem with the computer. Since you did get a CEL while operating and there is nothing in CM that does point to a possible bad computer. Time to pull it out for an inspection.

 

I agree with rla on this. PCM needs to come out and I'm betting the capacitors are leaking or failing fast.

Anything with 20+ year capacitors are gonna fail.

 

I agree too! And no, the battery has not been disconnected between code setting and checking.

Will pull PCM this afternoon. Where is a good place to get a replacement or repair? I'm finding lots of places with wildly varying prices, and I don't want to spend money I don't need to -- or spend money on crap.

 

Nobody carries good re-manufactured computers (PCM) anymore. Most are carrying Cardone rebuilt units. Their QC is pretty bad. Best bet is to pull yours out and inspect. If there are obvious signs the capacitors are leaking, but no damage to the board, you stand a chance it can be repaired. Start there IMHO.

 

I have two leaking capacitors. So even if it isn't THE problem, that is a problem. So cardone is suspect. Any idea who I could send this one too? I'd hate to buy "reman" and simply get a 23 year old board that hasn't failed yet.



Leaking capacitors on top left and right