i have a 1990 f150 with a5.0, runs fine for about 20 minutes, then starts to miss. everything is new, plugs, plugs wires, cap is in good shape.i already ran 2 cans of sea foam within a couple weeks.i dunno if it could be injectors they have never been replaced the only way id know is to hook it up to a pressure test right?? forgot to mention..pedal to the floor it goes but if you tryin n slowly accel.it cuts up

 

What is your fuel pressure when it's running rough? If you have 2 gas tanks, mine did this when the o-ring in my selector valve was swollen. Let me know if you have dual tanks and if switching from tank-to-tank has any impact

 

well i actually elliminated the rear tank its just the side tank.my truck has been running good for a while and it just started doin it on a cold day. my buddy was sayin take the distributor cap off and look to see if there is moisture, it was fine.i dont think i have an ignition problem deff fuel problem did the same thing today once it warms up it starts running ****ty.im almost positive its injectors i just wanna be a little more sure.need sum more input...

 

When you took out the rear tank did you take out the fuel selector valve on the frame? If not, then it is still a dual tank, without the rear tank (you still have the option to select the rear tank), so that o-ring can still swell up.

 

No, the injectors are among the least-likely causes. Get a Haynes manual & test the TPS & MAP. If you can zip into a U-Pull-It JY and snag a spare MAP or 3, that might be quicker. You can get one from any '87-93 Bronco or gas F-series, and some later trucks.



I doubt it's fuel-related, and a '90 doesn't have the valve that an '89 does. A bad coil can do this, though, and Haynes has an excellent diagnostic procedure for the ignition system.

How exactly did you delete the rear tank? What did you do with the fuel lines?

 

More than likely a bad MAP but don't rule out the TFI on it. Both will give you the same symptom. The MAP is the easiest to replace.
TFI= Thin Film Ignition- it's the little black box on the distributor. When they get warm they start to break down and yields a miss. It will get worse over time if it's the TFI and probably leave you some where.

 

when i eliminated the rear tank i just connected the lines from the side tank directly to the lines that run aling the frame..i dont think there is a selector on the frame i just replaced that little sensor on the side of the distributor not too long ago maybe 5 6 months ago what is the MAP and TFI.sensors would cause it to break up after 15 minutes??i dont really understand its pretty difficult trial and error ive been buying parts like crazy i just put a new coil in it..mad it a little better.but you say its most likely not a fuel problem?

 

i havent hooked up a fuel pressure test yet im gunna do that tmrw i was thinkin.. would a computer diagnose the problem..would it find the erroe for sumthing like this?my check engine light isnt even on.

 

when i drive the truck if you try to slowly accelerate it cuts up but if you mash the gas it up and goes..thanks for all the help guys

 

Actually, it's Thick-Film Integrated-IV (4th generation) Ignition Control Module.

Automotive Terms & Abbreviations

 

That's not right, and it's probably a major contributor to your problems. You have to treat the fuel lines like the 2nd tank was never there: plug them - don't connect them to anything. But it's VERY difficult & dangerous to plug them because the pressure can go over 100psi, so even a small leak can create a BIG fire. You should either reinstall the tank with a working fuel pump, or remove your 2-tank lines & install single-tank lines.Stop. It's wasting money, time, & effort, and it's making diagnosis more difficult. Keep any parts you've removed because they're probably fine.

 

there is only 2 lines running down the side of the frame then it splits into a y and there was a set of lines running to the rear tank..those i took off and deleted the Y connector. The fuel pressure im pretty sure is the same or my truck wouldnt have ran right??..my truck has been running for almost a year like this

 

i just replaced my ICM and its still driving the same way

 

I thought you meant you had connected the 2 lines from the deleted tank - the way you did it is correct.Why? Did you follow the procedure in the Haynes manual?

 

my truck is still doing the same *******ING thing. new coil, new ICM, plugs. ignition is pretty much brand new i dont have resources to hook it up on a computer not alot of people cqn hook up a 1990..my light came on for about a minute then went off its really bothering me!!breaks up at 2-3000 RPM but it doesnt do it every single time o come to a stop it happens eevery so often SOMEBODY HEEELP!