Hello everyone. New to the forums. Recently inherited a ol truck after my grandfathers passing. They basically drove it once a week or less, when needing to haul. It sat for most of its life. The truck will start almost instantly. No issues there. Idling is not too smooth. Once in gear, it sounds like it's going to die, but doesn't. When driving, the truck is not smooth at all. There is very little power (will not break the tires loose on wet pavement). I have replaced the plugs but instead of just going through part after part, I figured I'd ask and see where you guys thought I should start? Thanks.

 

Do a complete tuneup. Plugs, wires, cap, and rotor. Put Techron in the gas to clean the injectors. Change the fuel and air filters.

While the plugs are out, do a compression test.

 

Some of that years production trucks had very high gears in the rear. Some as high as 2.73:1. You might want to see what the axle code is. You'll find it on the door jamb, drivers side. The codes are online. More than likely, this is the problem with low power. My uncles had the 3.08 axle and his wouldn't burn rubber when new on slick wet asphalt. Since it's been sitting a lot, make sure the gas is fresh. I'd pull the gas out of it and only half fill a tank and then put 2 bottles of Techron in the gas to clean the injectors. They can foul pretty easy. Might consider taking the throttle body off of the engine and give it a cleaning. DO NOT spray any cleaner in the intake on the engine unless you just like pulling the intake system and replacing the gaskets. You have an IAC on that engine and it could be that's the bad idle. I'd look up the test procedure to check it out. It's not a hard item to replace. The IAC sits on the side of throttle body. IAC= Idle Air Control. It's function is to control the idle speed. It keeps the idle constant while the A/C cycles off and on, in neutral or in a gear, etc. If you pull the throttle body to clean it, you can clean the pintle inside the IAC and make it work like new, if the servo is still working right. No replacement gaskets are required as all are a dry fit gasket and reusable. That truck most likely has a MAP sensor on it. Once you get the right gas in it, I'd suggest on a warm engine, disconnecting the vacuum line to it. It will make the injectors go wide open which means it will run extremely rich, might even kill the engine. Give it enough throttle to make it run a few seconds can clean the injectors. If it does nothing when you disconnect it, you have other issues. The MAP on that truck should be on the passenger side firewall and has a vacuum line and an electrical plug in to it. Obviously, on that old of a truck check all vacuum lines for breaks and leakage. The engine control system can't account for air coming into the engine and will make it run like crap. I'd also check the brake booster for any leak down. This can cause an engine of that era to run bad due to air the system can't account for. While probably a neat ol truck, they were never a powerhouse. The straight 6 of the day would pull a trailer far better and on less gas. The straight 6 was the bulletproof 300 Cu In engine. The 5.0 was 302 Cu Ins but the 6 had a much longer stroke which makes more torque. Best of luck with it.
Axle codes

 

Thanks for the responses guys. I do understand about the high gear ratio, however the last time i drove the truck (3 years ago) it ran great and had much more power than it does now. It is really struggling. I'll go through all of the suggestions and see what I come up with.

Thanks again.

Andy