I have a 1994 F-150 4.9 i6 with the E4OD transmission. The truck has only 121k miles on it. It runs great and hasn't skipped a beat. Plugs, wires, cap, rotor, coil, filters all have been changed recently and on schedule. This truck is in great shape inside and out..

Last week when leaving work I started the truck, and it idled like normal. Put it in gear and gave it some gas and it wanted to bog down and stall out right as I was leaving the parking lot. The truck would start and stay running, but would not do cooperate under any throttle. It puffed gray smoke (looked to be fuel) when trying to give it throttle.

But then after 5 or so minutes it somehow runs perfectly normal! It drove perfectly all the way home. I tried to get the truck to act up the rest of the evening and it wouldn't skip a beat. Then I started it the following morning and it ran perfectly! So I let it sit for the day. When I came back in the afternoon I started it and had the same symptoms. It would once again clear up after 5 or so minutes. It has done this now day after day..

So somehow my truck will not run correctly after sitting in the afternoon heat. I'm at a loss for what it could be.

I've checked fuel pressure on both tanks, that checked out. Pulled codes, nothing to be found. No check engine lights.

Further background, I live in the Houston TX area. It's hot and humid here in the summer. Afternoon temps are regularly in the 90s, sometimes the 100s. My truck is black, so the sheet metal can get pretty toasty..

Anyone have any idea why my truck is doing this?

 

I took the truck to a trusted mechanic and they gave up on diagnosing it. They said it was too difficult for them to diagnose since it only exhibits the symptoms for 5 minutes out of the day.
I'm sure they don't deal with much EEC IV stuff nonetheless..

 

Anyone??????

 

I dont have an answer to your problem, but I kind of have the same problem with my 4.9 heres my post and no one seems to have an answer either. No check engine light. No codes. I was thinking of just replacing the TPS and ICM. If that doesnt do it then ill take a look at the fuel pumps. Maybe dirty fuel tanks? clogged strainers? Old fuel pumps?? But Yes, it happens more when it's hot outside.
Loss of Power 4.9

 

It's definitely strange. Its only when its hot out and when the engine is cold. It won't act act up if you've driven the truck earlier in the afternoon.

The rear tank fuel pump is weak on the truck. The front however is strong. Maybe some sort of cross flow issue could cause this?

I'm planning on checking out the ACT (Air Charge Temp, later changed 95+to IAT sensor) sensor. It's on the manifold by the number 1 cylinder. I hear they can get gummed up and oily. Mine doesn't look to have been touched ever on the truck.
Has anyone dealt with a cruddy ACT sensor causing issues?

 

what fuel pressure readings are you getting, and have you pulled codes ?

 

Sounds like capacitors inside the ECU are failing, there are a few threads about this. Lots of weird problems occur due to capacitors leaking.

Another thing could be the MAP sensor failing, that sensor can cause the engine to run rich(gray smoke) when it's on the frits .

 

Don't Rule out the TFI module it goes for a crap they won't always throw a code.

 

TFI module same as Ignition Control Module (ICM). Correct?
Also! Most auto part stores will give you the Gray ICM, And apparently this part is the wrong part for these trucks.
You want to make sure you ask for Motorcraft Part# DY1077 Black ICM.
For some reason the Gray (part# DY1075) ICM is not the same and you will notice a difference on performance.
Accel also has a Black ICM for these trucks but after reading threads on here, they also DON'T WORK!!
Correct me if I'm wrong.

 

Yes the TFI module is called the ICM in later applications with the heat sink on them.

 

Failed ignition probably won't do this, focus on the throttle and airflow related tips mentioned earlier.

Failed ignition = no start usually. Not a rich, smokey mixture.

 

Usually but not always and a TFI module on it's way out can exhibit exactly these symptoms. There was even a TSB regarding this on early EEC IV TFI's displaying these exact symptoms.
Just saying don;t rule it out.

 

Well I will be rebuilding my engine this time off but you are more than welcome to come up and use my diagnostic tools. Not sure if that would help you but you can if you want. I have a Thexton Breakout box and Snap On Oscilloscope have I used them before nope, but as soon as my truck is running I will LOL I live in Conroe shoot me a PM if you want to stop by.

 

Having very similar issue, the truck bucks and runs poorly once its warmed up, loss of power, etc. I replaced the fuel pumps, ignition module, tps, etc etc. Crankshaft position sensor maybe?

 

Thank you everyone for your comments and advice. The culprit ended up being the ACT sensor. After a little deductive reasoning I decided to check the resistance on the ACT sensor. Sure enough, it wasn't reading the correct resistance. I removed the sensor and you can see what I found..

Below you can see the old sensor on the left. I bought an O'Reilly's replacement sensor. I'll get a Motorcraft one in time. But the truck runs great, it no longer has the issue at startup that I was having.