Gstang117

My 89 renix 4.0 is backfiring through the air intake on a light load. Like taking off from a stop. Its a rapid pop pop pop noise. After giving it half or full throttle it goes away but once you let off it does it again. I've checked the timing chain and it is not loose. I've given it all new cap rotor plugs and wires. I'm about to head out to change the fuel filter because I heard that my problem was caused by a lean mixture but I doubt that will do any good.
Also one of the spark plugs had a white color to the tip like a vacuum leak. Could one of my injector O-rings be leaking in air?

cruiser54

Make sure your intake bolts are tight. Spray around the intake system with throttle body cleaner for vacuum leaks. Ever cleaned your throttle body?

Gstang117

Yep cleaned the throttle body, haven't checked it yet for leaks yet though.

tjwalker

Sounds like it might be running a little lean. Along with above suggestions, test your fuel pressure (should be 31 psi at idle, 39 psi with the vacuum line leading to the fuel pressure regulator) and also the MAP sensor, which plays a big role in fuel/air mixture. Be darn sure that the vacuum lines leading to the regulator and the MAP sensor are pulling good vacuum!