I have an 88 with the 4.0 renix. I got it for free and it didn't run. It had a fuel pump that went bad. Replaced it and the filters. Also changed the water pump cause it was shot. It ran great for the winter and then started knocking, ticking, and hardly idling. Now the knock is gone but the tick is still there and it seems to be misfiring. It is like it is backfiring into the air filter?


Here is what ive done recently to try and fix it:

new rotor/cap
new wires
new champion copper plugs
new starter(old one lock up)
new oil/filter

This made it smoother but didn't stop the misfire/tick and it still runs like $#!+!

Any ideas would be greatly appreciated.

 

sounds like it could be a stuck lifter at the least, the worst a bad intake valve. you could try some marvel mystery oil (or rislone valve stuff) in the crankcase to maybe free up a possible bad lifter. if an oil change is due some engine flush let it go about 5 min longer than recommended follow the directions otherwise. when you refill use a thinner oil and some
marvel that should clean out the system and unstick the valve or lifter. other than that a head job is in order.


1990 renix sport 5spd 422,346mi

 

Backfiring into the intake can indicate a lean fuel/air mixture.

The first thing I would do if this were my vehicle is to test fuel pressure. Get a gauge; they can be rented from many big box parts stores.

For the 87-90, you should have 31 psi at the fuel rail. Then disconnect the vacuum line leading to the fuel pressure regulator and the fuel pressure should jump to approximately 39 psi.

Don't throw parts at this. Test your way to a solution.

 

Thanks for the input guys! I will buy a gauge tomorrow cause i need one anyways!

 

I finally got around to checking the fuel pressure and it checked out good. I also cleaned the IAC and throttle body. Runs better but still has the tick and misfire. At this point im stumped and hope its not a stuck valve.