I took my snowplowing truck out of storage recently... it had been sitting for ~4 months.

[1990 F-150 Custom... 5.0 EFI, 4x4, 5-speed.]

It started fine, ran well, then, when it began to get warm... started to have problems. At first I thought I had run out of gas (tank was nearly empty)... I was near a gas station, filling the tank didn't fix anything.

Idle ran really rough, and when I'd press on the gas pedal, the engine wouldn't want to go above ~1,500 RPM... it would start to choke at that point and I would have to press the clutch to keep it from dying...

Also, the exhaust smelled like unburnt gas...

The current situation:

- There's a difference in the way it runs (cold vs hot) so any explanation has to take that into account

- All cylinders have good fire, and the spark plugs, wires, distributor cap and rotor are all brand new.

- All eight cylinders were between 150 and 160 psi when I checked compression.

- Fuel pump is brand new, as is the filter, and I get ~40 psi at the fuel rail. Blocking the fuel return line doesn't change anything (I tried this to see if the regulator worked properly).

- I did a lot of things that are supposed to clean the injectors up, so let's assume they are clean.

- PCV valve is new, EGR valve also has been taken care of, so the problem shouldn't be there.



Now, the hint I have... when I unplug the air hoses going from the air filter to the throttle body and put my hand in front of the throttle body valves, there's absolutely no sucking of air...

I would tend to think the engine is running with a mix that is way too rich, for some reason.

What do you think??? How can I fix this??

Thanks in advance!!

 

Oh, I also forgot to add: the brand new spark plugs were completely black with deposits after a couple days of trying stuff (and having the engine run like that for minutes at a time several times).

That's another bit of info that could be useful...

(I left them like that, as I'm quite sure they aren't the cause of the problem)

 

Do you have a Chilton or Haynes manual and a multi meter? At this point at least you know your truck doesn't suck..... Anyway enough bad jokes. Any codes? I would test out all the electronic controls that you have according to the specs in the manual. The TPS, that other vaccuum control thing that you probably have on the left manifold side, I have the i6 so it's different but the manual shows all that stuff and what to test. Also did you carefully check that the air intake tubes are clear of rodents, nests and stuff. OK just some thoughts.

 

Sounds like a bad FPR to me. You need to pull the vacuum line off of it and see if it smells of fuel. If it does then replace the FPR as the diaphragm is shot. From there it's going to need NEW plugs as the ones you have are now fouled and adding to the poor running condition.

 

Mr Dave: yes, the check engine light is on and I've read the codes already, but they didn't seem directly related, so I brushed them aside. (From memory, I had ~3 codes or so).

I'll check that tomorrow and tell you guys which codes I get.

The intake tubes aren't the problem... I've tested the truck with the tubes disconnected (meaning the truck is supposed to get air directly at the throttle body valves) and it still doesn't suck air... BTW, if a rodent managed to get in there, he's a ninja.

The Chilton manual is much better than the Haynes, right? I have plenty of Haynes for my present and past vehicles, but I have none for my Ford. I will buy the "most recommended" of these two and perform the tests.

pfogle: thanks, I'll try testing the FPR that way tomorrow... Re: the spark plugs, I know, but unless you think it's essential I would rather wait to see if that damn truck will ever start again and then I'll be glad to invest in stuff not directly related to the problem.

(If I change them right now, when I'll resume testing they'll quickly turn bad exactly like the brand new ones I put in a few days ago.)



Thanks a LOT to you two!!!

I'll keep you posted, but please keep the good ideas coming!!

 

Lio45 wrote:

"Now, the hint I have... when I unplug the air hoses going from the air filter to the throttle body and put my hand in front of the throttle body valves, there's absolutely no sucking of air... "


If the truck was at idle speed-the throttle plates would be closed.When you put your hand over the throttle body-did you try to cover the IAC on the driver's side of the throttle body?? If you did---and the engine still ran---it would suggest an intake vacuum leak.

What happens when you disconnect the IAC wire when the truck is idling---will it stop running??

 

timing chain jump a tooth? Mine ran similar right before it quit.

 

Plugged exhaust?

 

Yes, I prefer the Chilton but have both. And the FPR is the other device I was referring to but brain wasn't connecting. I had a broken vaccumm connection on my 96(sold) and it caused a lot of trouble, but not as bad as yours.

 

If the plugs are black like you say they are you need to at least clean them. A piece of 200 grit sand paper between the electrodes is all that's needed to get good spark. Shine them up a bit. It won't fire correctly, and possibly not at all on some cylinders with those plugs.