Mechanics

CHANGED FUEL INJECTORS AND CAR STARTED KNOCKING. WHY?

1990 Chevrolet Lumina • 68,000 miles

PLEASE HELP!
Okay so we changed out the fuel rail and injectors from a car at the junk yard. All injectors read between 12 and 12.3 ohms. Car started making a horrible knocking noise and acting like it was miss firing. It isn't rod knock. Its not a constant knock. It sounded like something was knocking around the intake. So we decided to take the intake off and make sure nothing had accidentally fallen in one of the holes for the injectors. We power washed both the intake and the plenum cleaning it inside and out. Made sure there was no debris under it. Put in new gaskets of course, new grommets and rings where needed, new coolant temp sensor, thermostat, oxygen sensor, new plugs, wires were good quality and about 1 yr old, and new crank sensor. Still knocking and running horrible. Decided to put the old fuel rail back on and replace the 2 bad injectors (with other used ones not from the other rail). It is running better but still knocking. Any ideas? Can fuel injectors be plugged and still show good resistance on an ohm meter? Is there anyway to check for clogged injectors and clean them individually. Just asking because I've heard plugged or malfunctioning injectors can cause knocking.
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Tinkergirl
November 1, 2011.




If you dropped something into the intake, it is most likely in one of the cylinders. It wont be anywhere you can see. If it is the case, you would have to remove the heads to find what and where the object has settled.

Roy

We don't think anything dropped into the intake and if it was in the one cylinders wouldn't we have seen damage on the spark plugs. They looked pristine as we had just changed them the week before. It was just a possibility. The knocking is intermittent not constant. If I rev the engine the knocking stops.
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Tiny
Tinkergirl
Nov 1, 2011.
I am going by your desription of the noise. If it is bouncing around inside, it may not hit the plug now but may later. Meantime, it may be doing damage inside the cylinder.

Many times I have dropped things into a motor without knowing and the same result has happened and lengthened the job.

Roy

Is it possible for an injector to be plugged without being bad?

Tiny
Tinkergirl
Nov 1, 2011.
It can have the correct resistance or ohm reading and be clogged, yes. It would produce an engine miss not a noise resulting from the injector.

Roy


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