myronXJ

My 01 XJ has had an engine knock / tick for a while. Not sure what it is, took the valve cover off, all the rockers are great and everything's clean under the cover. Hoping it's not piston slap.

Anyways, I was getting ready to splice in new injector harness pigtails (cause the original ones suck) and I took my circuit tester out for sh*ts and giggles. I put the tester to the wires on the first injector pigtail. When I put the tester on the rear wire of the first injector pigtail (see photo), the tester lights up of course... But my engine knock goes away almost instantly. Also, it seems to idle a little rough and my exhaust smells super rich like gas.




I did some reading and found out that the injectors are energized when the recieve a momentary ground. SO. I believe, when I put the circuit tester on that wire I give it a constant ground, causing the injector to be constantly energized and to constantly spit gas.

This would explain the exhaust smelling super rich (the injector spitting gas constantly). But why would that cause my engine knock to go away?

Thanks in advance!

superj

maybe you have a timing issue so its got a slight preignition knock?

myronXJ

Interesting. Didn't think of that!

NorthernerXJ

I'm going to follow this because I have the weirdest sounding knock in mine. It's only there when the engine warms up (except in winter, then it's 50/50 if it's there in startup), and it comes/goes as it pleases. Maybe it's timing related, I am curious if that's what yours will be !

myronXJ

Yeah I'll fiddle with it again tonight. I do have some 12 port fuel injectors, a coil pack and plug wires and some new spark plugs on the way. (ditching the crappy stock coil rail).

I'll let you know if that fixes the knock when they come in the mail but it won't be for a little while.

Also my knock is loudest when it's cold and somewhat goes away when it warms up. It also seems to get louder as I rev the engine.

awg

maybe I am misunderstanding, but the PCM grounds each injector via an internal Mosfet in the PCM

If that is failed, the injector wont fire, (but you would expect an engine missfire)

what happens when you disconnect the relevant spark plug ?