kevinc

I have a 1990 F-150 6 cylinder. I did a standard tune-up on it when I bought it about 8,000 miles ago. Plugs, wires, fuel filter, pcv valve, cap, rotor, and air filter. I bought it last fall when the weather was starting to cool off, but now with the warm weather coming in, I have a problem. The truck runs absolutely perfect when its less than 70 degrees outside. It has excellent power, runs smooth, nothing wrong. I’m experiencing a problem whenever it’s over 80 degrees and sunny outside. When it’s that warm out, the engine has a low rpm misfire. Sometimes it’s so bad that I can’t even accelerate thru the intersection. If I press the gas pedal down any further it feels like it’s running out of gas, it falls completely on its face. If I let off and feather the gas pedal I can get it back to life and eventually accelerate to speed limit. One day when it was 85 outside, the problem was so bad I couldn’t even keep it running. I drove about 2 miles from work and it was missing so bad I couldn’t even drive 20 mph so I had to pull into a gas station and call my wife to pick me up. I replaced the ignition coil at the gas station. It started up and ran good and drove it home. When I was near home the misfire came back a couple times. At that time it was less than 70 degrees out. Next morning it ran flawless until that afternoon when it was over 80 again then the low rpm misfire came back again. I checked all of my electrical connections and their all tight. I’m at a loss for what is going on. What do you think is happening.
Thank you,
Kevin C

grabill11

Well you could always move to Michigan!

kevinc

That's okay, I moved from Minnesota about 3 years ago after being there for 30 years. I won't even want to visit family there during the winter. I bought the truck last fall because my Dakota gave up the ghost.

Kevin C

NGM

Whats the fuel pressure when this happens?

tealtwotone

i have similar symptoms with my 96 6cyl. mine don't seem to be as heat-related, but if i'm out running errands with it and turn it off and on a few times that seems to bring it on. it acts like it is choking out or misfiring...the check engine diagnostic reads that the engine's running lean...i'm pretty sure it's my fuel pump. i replaced the fuel filter recently and it ran great, no check engine light, for about two weeks. i haven't done my plugs yet but i'm pretty sure it's fuel pump related. anyone know how complex the pump is to replace?

BIG D

You sould have the fuel pressure checked, as far as replacing the pump,you will have to drop the tank, the less fuel in the tank the better,it makes it easier to handle.

wde3477

Having trouble understanding what temperature has to do with things.

One off-the-wall thought is that my understanding is the inline 6's have a fan or some contraption to cool the fuel rail. If so, perhaps there is some kind of vapor lock thing happening when the temperatures rise????????

Doggone NGM - if you're going to edit the post - at least make it a font size that us older blinder people can read!!!!! :-)~

RyKR

How much fuel is in the tank when this happens? More fuel in the tank can actually help cool the pump. If it does it when it is warm and closer to empty that can help pinpoint the pump also.

I agree with everyone else though, check the fuel pressure. You can buy a guage with a long enough hose that you can attach it and drive with it taped to the window or something so you can watch it. This way if it is an intermittent problem you can check it at the time that it is acting up.

kevinc

It doesn't seem to matter how much fuel is in the tank. Its done it on vapors and full tank. The worst incident happened when the tank was about 1/4 full. Is it possible temperature can affect a fuel pumps ability to work? Since this is my first Ford truck, how do you get codes out of the computer. I haven't had a check engine light yet. Disconnecting the battery and hooking it back up doesn't seem to make a difference. Could a faulty temperature sensor cause this? I'll check into a fuel pressure gauge and see if I can catch it happening.

Thank you
Kevin C

BIG D

Usually temp. sensors will cause a no or hard start problem and poor milage,the connector,for pulling engine codes, is under the hood by the air cleaner box and you will need a scanner.You can go to your local parts store,some of them will scan for free and ask them to scan the computer.Yes,temp. can have an effect on the fuel pump.