I have an 89 4.0 and I just got done doing the o-rings on my injectors. after a good swap, I've run into 2 problems. 1 I have an almost constant hissing from my fuel rail, it APPEARS to be coming from an injector, but it's not running rough and there's no visible leak. the hissing also sounds more like air being sucked in than fuel spraying out. but I have no vacuum leaks. also, turning up allong with this problem, is my fuel gauge, when COMPLETELY stationary, is moving back and forth about a 16th of a tank. it'll hold a possition, then move, hold, move. repeating this cycle. I'm at a loss for what to do.

 

Look on yhw side of you throttle body. One of your lones prolly popped out.

 

I suck at typing on iphone lol

 

i'd say that, but all my vacuum lines are attatched properly, and there's non of the rough idle associated with a vacuum leak. its so weird and stupidly confusing. i also have some smoke coming from by the fuel rail but i think my manifold gasket just got soaked in fluid is all.

 

My money is on an injector seal that got torn upon installation. How did you check for vacuum leaks? Did you lube the injector seals?

 

Yar. This happened to me! Tore the number one head side oring just a bit. All of a sudden there was a deadly viper under the hood...oy its too early for me...

 

That seemed to be the problem. I'm glad I kept the old seals, I threw one that was in good shape on and I no longer have a "deadly viper under the hood". Thanks for the help guys.