Just picked this truck up, cheap. Its doing some odd stuff. It won't start on its own...you have to give it a shot of either to get it to start, then it'll run seemingly normal until you try to open the throttle. If you open the throttle more than about 25%, it'll stall. It appears someone else has already been troubleshooting this problem. There's large holes drilled in the first cat (lol...) and there was a bunch of vacuum lines pulled off, including the one going to the fuel pressure regulator. Although re-installing that line didn't seem to make any difference in performance. I swapped out the plugs and did a compression check just for starters....it has 120psi on all 6 cylinders. So that pretty much rules out mechanical. It did run slightly better with the new plugs in it, but there's definitely something wrong. I haven't messed with these early F/I Fords, so I'm not familiar with any of the common fail items. I'm hoping someone recognizes these symptoms and knows exactly what's wrong with it.

 

sounds like a M.A.P. censor Manifold Absoulute Postioning Censor that'll cause black smoke and the symptms your describing, also it could be the electronic pick up in the dist. causign the rough running and dying part or it could also be a crack dist. housing, but the black smoke sounds like the MAP Censor

 

Thanks, I'll check it out. I need to pull the codes from it today I reckon. Its not displaying a CEL though...which I think is odd, given the symptoms.

 

also check fuel pressure, known for bad regulators, pressure will skyrocket cause the problems your having.

 

i would check the timing. black smoke means unburnt fuel 80% of the time. make sure the plugs and distributor are where they should be. also im not sure if the 4.9L has an electric choke or what ever it is when the truck first starts, could be stuck open

 

Yeah...the fuel pressure is definitely on my ****list. The fuel pumps themselves really do not sound that healthy to me. (Truck has dual tanks) Each pump sounds different, also.

I would think though that if the pressure was HIGH, that I would at least have some hp on tap at WOT...it runs like its lean...won't rev up...yet it chugs black smoke when its idling.

I will check the timing, it does sound retarded...but I think that's only because its lean. This truck is Fuel injected, so there's no electric choke.

 

ooops just saw that it was fuel injection my bad

 

it definatly sounds like a MAP censor to me my dads chevy was acting the same way till i put a MAP censor on it

 

Welp, had a chance to do a little more troubleshooting this evening. I geared up to read the codes from the EEC and happened to notice whenever I turn the key on, the CEL doesn't illuminate...and the fuel pump stays running...doesn't prime up and stop and wait for a run signal before coming on again. I thought this was odd. Anyway, was not able to read any codes. When the diagnostic connector was shorted out, the code signal stayed hot all the time. In other words, there was no codes flashed, not even 11 or 111. My test light just stayed on. Now I am about 99.9% certain the ECM is bad. I removed it and it has a remanufactured sticker on it.

Anyone care to expand on my diagnosis? These computers are pretty cheap, I'm probably going to go ahead and buy one.

 

Bump. Anyone have anymore input on this theory I have?

Should the CEL come on when I turn the key on, before I start the engine?

Should the fuel pump come on and run, then shut off until the engine starts?

I am hoping someone else can confirm that I do infact have an ECM failure.

 

The fuel pump should come on, prime, and go off again until the engine is started.
Not sure about the CEL, I think it should be coming on, but again, im not sure.

Before you replace the ecm, make sure ALL vac lines are intact and in good shape. On my old I6 I had to replace almost all of them due to heat damage and dry cracking. I would also check timing, make sure someone didnt set it way off. Replace cap, rotor, wires, just as cheap insurance. Check fuel pressure, on my old truck I had a bad intank pump, would pressurize to full psi when cold, but after running for a short time i wouldnt get 10psi out of the pump. Sounds like the truck has this problem w/ the po, and hes already tried to fix it. Make sure the wire harness going to the ecm is in good shape, no damaged/broken wires.

 

I did replace several vacuum lines and I feel certain the timing has not been tampered with. There is plenty of old grease around the base of the dist and there is no evidence it has been moved in a very longtime.

I did remove the ECM and open it up for a look-see. There are 3 capacitors on the board that appear to have been leaking and the board appears damaged as a result. I have read a few blurbs about these particular ford ECMs being notorious for this particular failure...leaking capacitors. They leak out their electrolyte and corrode the printed circuitry.

 

Welp, broke down and picked up a $102 replacement ecm from RockAuto and fixed this problem. Runs perfect now.

 

So when you replaced the ECM it took care of all your issues? That's interesting about the leaking capacitors. It's a good thing you decided to crack that thing open and check. That could have been a seriously costly guess-and-check process, especially with no CEL or codes. Good on you, man.

 

Yeah, it was difficult for me to make the decision to buy the ECM...I only paid $200 for the whole truck...lol. After doing some research I found out that these particular ECMs are among a group of ECMs that ford used for several years that are notorious for failing, especially when subjected to high operating temps in the southern states. The electrolyte leaks out of the capacitors and corrodes the circuit board. This was exactly what had happened to mine.