basic info: 1989 F-150 5.0L EFI, AOD transmission, 65K

The fuel pump is replaced and working fine, thanks.
Here is a problem noticed a year ago, but ignored until I got everything else working. Now for the experts.

1) After filling, and putting in Techron to "clean her out." I too 89Flivver out for a 65 - 80 mph run on the local highway. The engine was warm before I put in the fuel. Acceleration was fine, cruise was fine, then, after 10 - 15 miles, without warning, the engine stumbled and eventually stalled without warning. To this neophyte, it appeared that the fuel "ran out." Putting in neutral, and moving over to the curb, it started up, first rough, then fine after stepping on the gas pedal.

2) After about another 15 miles, this time going under 65 (another highway), the same thing happened, but faster. It restarted, first rough, then fine after stepping on the gas pedal.

3) I do have to step on the gas pedal when cold to keep from dying when starting, but I do not know if this is related.

 

chek your IAC a friend of mine had this prob his IAC was dirty clean it out and see if any improvements show

 

cool, ah...what is an IAC?

 

I think this is the Idle Air Control... I am having the same problem with my truck, i am going to try this out. I will let you know if it works.

 

check the codes first. See if there is anything in the continuous memory that might tell you something.

I would check the fuel pressure at the rail. If you have the 40psi when you start and while idling, then your fuel system is probably ok. It's pretty obvious when something is wrong. the fuel pressure will creep down slowly and the truck will die when it gets to around 20psi.

Do you have dual tanks, or a single tank?

But, before you throw money at the problem, check your codes and you fuel pressure. It can save a lot of time and money.

 

Have replaced the fuel filter on the rail and checked pressures. Pressure wasn't where it should've been but is at about 32 now after changing the filters. I have dual tanks.

Have checked everything I can think of, the computer is showing no codes but yet the Check Engine light comes on when accelerating only.

It only dies after it is warmed up and been running for awhile, the biggest problems when you are idiling switching from R to D or while slowing down to make turns, this problem has been driving me nuts.

 

so, you pulled the continuous codes? If your CEL comes on at all, then the computer should store those codes in the memory for later, they should tell you where to begin looking.

So, your pressure is ok all the time now? If you let the truck idle for a while, will it die?

My truck was having a similar problem. My reservoir crapped out on me. So, I wasn't getting enough fuel to the high pressure pump and it would die. Do you get this problem with either tank selected? Check that and see. If the problem only occurs with one tank, then you can narrow the problem down a little bit. If the problem occurs on either tank, then you will not have learned anything (but you won't have lost anything but time).

I don't think the IAC would hurt you while accelerating. I think the IAC only controls the idle, nothing else. A rough idle is a symptom of a bad IAC, but also a symptom of everything else in the world (vacuum leak, bad gas, electrical trouble, PMS).

Make sure that there are no continuous codes stored in the memory. Even if the CEL light isn't on, there should be codes left over from when the light did flick on during acceleration. Then, verify that you get in trouble with either tank.

Sorry to keep hanging on the fuel and CEL codes, but I threw WAY too much money at mine (replaced fuel pump, fuel filter, fuel pressure regulator, EEC relay and FP relay before I did other tests). The CEL codes and fuel pressure are easy to check and pretty cheap (especially if you already have a fuel pressure gauge).

 

I will check the codes again.. this happens with both tanks, and the CEL only flickers when accelarting which I have never seen before. I have sunk a lot of money too into fuel filters, fuel pumps etc. Haven't changed the filter inside the tank (nor do I want to).

I will also try to check the PSI after it has been running for awhile.. although once it is warmed up it has a horrible time staying running.

I tried to take my two boys on a trail ride the other day and gave up cause it kept dying everytime I would slow down to take a turn or go down an incline or anything.

 

So I did this last night.. It was fairly easy to get to and remove. I was done in about 30 minutes tops (minus the cleaner I sprayed in my eye). The truck is running like a top! Next for the exhaust!

Now if I would have only checked into this sooner I'd save a lot of time and money on fuel filters & pumps.. oh well they need changed sooner or later.


Thanks for all of your advice, I'll be checking back here frequently!

Amy