A lot of symtoms, not sure what is related to what.

• RPMs drop to zero when travelling over 50 mph (sensor maybe?)
• Had issue where it wouldn't start, had to replace fuel pump, but still hesitates to start
• Drove it with a loose oil plug for a month, obviously not on purpose
• Running sluggishly
• Gas gauge stayed on 1/4, but I think fuel pump replacement corrected that problem

Now (2 weeks after fuel pump replacement), I started it up and a horrible knocking, like someone is trying to get out from under the hood. I didn't attempt to drive anywhere, I just shut it down to avoid any further injury.

What things should I look in it to try to fix my truck? Thanks for any help.

 

I have an 84 Honda. The diaphram went bad on it, and filled the oil pan with gas. I replaced the fuel pump and changed the oil and filter, and it runs fine now, altho I didn't drive it much before I did the repairs. If you have a knocking in the engine, you have a serious problem that will take a mechanic to fix. I'm sorry I didn't see this post before or I would have been prompt to answer you.

 

Is your truck smoking bad even in low rpm? If so have a compression test just to have an idea of its engine health.