I've got a 1985 F150, 5.0 fuel injected. Starts up fine. However, when it warms up but hasn't exactly hit operating temperature, it stalls out. If I attempt to start it again, it is difficult. After I restart it a few times the problem disappears and it runs like a charm, after it reaches full operating temp. I suspect it is a faulty throttle module.


Ideas? I've gotten some GREAT feedback here in the past and with few exceptions, the feedback has been right on the money! Hoping for the same now.


Thanks in advance!!

 

First thing to do when diagnosing any computer-controlled engine is pull the codes and ask the computer what it thinks is going on.

 

Yes. I knew you'd say that as you've said that to me before. But I cannot pull the codes since I do not own a tester.


Still, I get why you say that. Nonetheless, give me an educated guess, if possible.

 

Check the basics...

1985.5 - 1986 models have a fuel filter located, um, I think near the frame someplace in a real odd location; I forget the details, Bill Vose (85lebaront2) knows, he ran a carb and tune-up shop in the era and has posted about it before but I don't remember where.

Nevertheless, if you're going to operate and maintain an old vehicle like this, you need to invest in some basic tools and diagnostic equipment... pulling codes is not hard to do and can be done using a test light... if you don't have one, then either purchase one or take the truck to a parts store and ask them to pull them for you.

But pulling OBD1 codes is more than just plugging in a reader and seeing what it says; there are three sets of odes - KOEO tests basic integrity with the engine off and lets the computer verify it can talk to all its sensors and they're all reporting readings within their ranges... CM (Continuous Memory) is what it remembers about the last N driving cycles.. both of those sets of codes are given in the KOEO test. Then there's the engine-running (KOER) test where the computer performs some manipulations and reports what the computer is seeing right then and there.

Point being, if you want to be your own mechanic, you need to do some basic diagnosis yourself.

 

You are certainly consistent! But not too helpful, this time around. Not everyone can afford the equipment you are talking about.


I have changed the fuel filter before, and yes, it is on the frame.


It seems the throttle isn't adjusting to engine temp; my guess is the throttle control.


That's pretty easy to replace, and cheaper than your recommended diagnostic tools. I don't believe I'll get nickeled and dimed to death trying to figure this out either since it really couldn't be much else. I'll try my guess first; second guess is the famed ignition module. In either case, replacing both is still just a few bucks.

 

A test light can be had for less than $10:

Performance Tool W2975C - Electrical Tester | O'Reilly Auto Parts

Circuit Tester

 

There are actually two fuel filters on 1985.5-1986 trucks. There is the obvious one on the frame in front of the high pressure pump, there is another one hidden in the fuel reservoir behind the pump. I have an album we set up for another member (maybe Chris or another admin can add it to the stickys?) go here: 1986 5.0L EFI by 85lebaront2 | Ford-Trucks.com there are several useful items in there.

 

sgauvry,

ctubutis is attempting to assist you and possibly save you some money in the process. Why not check the FTE club memberships for where you live and see if someone local can assist?

Good luck!

 

The ignition modules typically fail in a manner backwards from what you're experiencing (they fail when they heat up).

If it is truly not reacting properly to engine operating temperature, my first thoughts are of the ECT (Engine Coolant Temperature) sensor and TPS (Throttle Position Sensor). but those are just guesses; why play games and throw parts at it while attempting to guess at what might fix it when you could just let the computer help you?

But do what you will, it's your truck and your money...

 

Thanks! That's the help I needed!! I knew you'd come through!! You always do...

 

All I'm trying to do is prod you into asking the computer what it thinks is going on, that's all.

 

Just do not use an aftermarket TPS on an 85.5 or 86 EFI system.

 

I may have missed it if someone else said how to pull the codes, but here's a link on how to use a meter or testlight to do it.

EEC IV Self Test hookup

 

Thanks, Franklin2, for the codes while using a test light. I do own one of those.

Steve