1990 F150 4x4 5.0 My check engine light comes on when I accelerate. Still runs great Though. Oil pressure is fine too. I was thinking maybe old transmission fluid? Could that cause this?

 

Welcome to F150Forum.com!

There's a sticky link right on the main section of this forum. It extensively details how to pull OBDI codes from your truck. Read over that, pull codes, and report back to us. Even though the light doesn't stay on, it will still be saved in your computer. We can't really help you much without more information.

Just taking guesses until you report back, but it sounds like it may be an EGR issue. Does your truck knock or ping now that it is throwing the code? TPS comes to mind as well.

 

Truck is running great like it always has. No pings, no nothing. When I give it gas to pass someone the check engine light comes on. But when I take my foot off the gas or my speed levels out it goes off. I live in the desert (literally) and the nearest shop I can take it to is quite a ways away. I don't want to kill the truck trying to get there but I guess I might just have to try.

 

A) your not going to kill an OBD1 truck driving with the check engine light on, especially if it is running fine. Its probably just polluting too much.

B) you may not need to take it to a shop. Read the sticky thread on how to pull codes, post them here. It may be a very easy fix.

 

I am new to this site and can't find the "sticky thread" Can you please
paste it here so I can click on it

 

Here's the forum page:

https://www.f150forum.com/f10/how-re...es-obdi-10907/

Here's a good YouTube video as well:


You might understand the process better from the video. Pretty much just plug in a little jumper and count the blinks.