Hi all- still working out quirks with my 90 f150

changed fuel filter, air filter, plugs and wires, ran injector cleaner, sprayed tb cleaner..all that jazz.

Truck ran ok for a few days after that, definately was wasting fuel though (I estimate 5mpg?) and could smell something gassy in the cab.

Now miraculously, after being parked with no issues, she turns on and idles (rough, shakes to hell) for 30 seconds then idle drops as it used to before but won't maintain.. cuts off.

I assume fuel pressure is good if I've been wasting gas - again plugs brand new, havent changed dizzy tho..

Tips? Thanks!

 

Check MAF, IAC valve, and TPS..........

 

^ +1. Suggest to inspect the IAC first. Our vintage (87-91) seemed to crud up pretty regular.

May want to double check the wires. I've been tripped up by getting the wires to the right cylinders, but landing them 1 post off on the cap. IIRC, the #1 cylinder is typically identified by a '1' embossed on the cap.

Not sure if you have the MAF or the MAP. A leak in the MAP vacuum line will cause some headaches.

 

Thanks for the tips guys...

It sounds almost like it's running out of gas when this happens- but both tanks were working the day before this happened, and both have gas..

the misfire or ridiculous shaking happens intermit. during the first 30 sceonds the motors on when its running at higher rpms.. itll go like 10 seconds sounding perfect though so its not like a constant shudder every time cylinder x fires.

ill try and check wiring, i did em one at a time in effort to not mix it up and before that the truck had sat since it was last operational a few years before.

im kinda thinkin in running it recently somethings gotten gunked up to point of crappin out. i'll mess around with it tomorrow if weathers good and post my findings. Thanks you guys.

 

Well I thought I was on to something and bought iac.. no go, same issue exactly - so i'll return that.

today i gave it enough gas (for about 2 mins) to keep it alive then threw it in to reverse..and it stayed running without me giving it any gas..went forward, back, few times.. then park and idle..and it stayed alive, but missing every few seconds and running like crap all in all. took her out for a spin and stayed alive the whole time but again not running well.

guess more sensors? i trusted teh gap out of the box for the autolite plugs but now wodnering- though it ran fine tho fuelrich for 50 miles before started acting up.

 

• It may be running rich, eventually making the plugs too wet to run well. Check the plugs for carbon fouling.
• If the plugs are carbon fouled, then it's running too rich, check or replace the coolant temperature sensor (the sensor just above the thermostat) and the air temperature sensor (you already replaced this).
• Check the fuel pressure. Get an inexpensive fuel pressure gauge from the auto parts store. There's a valve on the fuel rail next to the injectors to test the fuel pressure. The pressure should be around 35 psi when the engine is running. If it's closer to 40 psi or above, then replace the fuel regulator.
• As the fuel pressure regulator spring gets older, it gets weaker, the fuel pressure slowly rises. Eventually, the high fuel pressure causes the injectors to dump too much fuel into the manifold each time they fire, causing the engine to run rich. The regulator is located in the engine compartment at the back of the fuel rail close to the firewall.