I have a 89 D100 with a 318 automatic.The problem is it runs pretty good when its cold unless you give it full throttle then it wants to die but if I dont beat on it it's ok. But as i drive it and it gets warmer the hesitation gets worse until I have to feather the pedal to get it up to speed.After an hour of driving it wont go over 55.The check engine light is on but its been on for years and it didnt have this problem. Any thoughts would be helpful.

 

What is the code from the check engine light?

 

I'm sorry I meant the required maintenance light is on. The check engine light comes on when you start it then goes out.

 

Sounds like a fuel issue.

 

Yes I'm pretty sure it's a fuel issue but where to start. I did the full tune up on it a couple months ago,cap,rotor,plugs,wires,Fuel filter but I'm not really about all the sensors. I was going to start with the O2 sensor and see if that helps other wise its digging into the throttle body and randomly changing sensors until I get the right one.

 

And I'm reading this Chilton manual and it says nothing about the maintenance required light. What is this light telling me and how do i clear it?

 

Maintenance light is so you can take it back to the dealer and they can charge you for it. All it is a timer that after a certain amount of run time passes the light will come on. It has nothing to do with how the truck runs. You need a scanner to shut it off/reset it. I would see what kind of fuel pressure you have at the throttle body. Might want to look and see if both injectors are working. I seen a post about one stopped working because one of the wires was loose.

 

OK. changed the o2 sensor and the fuel injectors. Didnt change anything. don't know what to do now.

 

turn ignition switch on & off 3 times. write down the number of check engine light flashes. There will be a brief pause between flashes to seperate the number. also the beginning and ending code will be 55. let us know.

 

Meant to say leave switch on to read after cycling switch.