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Fuel Injector Testing on 2001 XJ 784's

Redsnake

NAXJA Forum User
Location
Tulsa, OK
I've been chasing a slight low RPM miss for a while now on my '01 XJ. I've had the 0331 head replaced, cooling system is top notch and works great, also replaced my OE fuel injectors ~ 18 months back w/some re-built 784's.

This past week I replaced my Coil Pack w/a new one (fixed another issue I was having but the slight miss still seems to be there). Plugs are like new NGK's, Fuel Pressure is good.

It could be a placebo effect, but I'm wondering if it's a defective Injector. I ran a tube to each FI to listen for clicking to see if they were all firing when I replaced the Coil Pack and noticed the #6 FI is clicking much louder than any of the other 5. The 5 click nice a quiet and steady and the #6 injector was quite loud when listening to it. Almost like a pop vs click... if that makes sense.

This miss only seems present at idle or just off-idle and more so when the engine is cold. I haven't noticed a lack of power when giving it throttle, just the sound like a miss.

So... back to my question. Could it be a faulty injector and how does one test it w/just basic garage mechanic tools?
 
First you can check the resistance of each of the injectors.

You can rig up a test with a 12 volt source, a momentary switch, some wire and an old injector plug or some alligator clips Run compressed air or some compressed liquid (non flammable is good) and pulse the injector while watching the pattern.
 
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Measuring from pin-to-pin on the injector with an Ohmmeter, you should see 12 +/- 1.2 Ohms @ 68*F. 784 injctors are advertised at 12.5 Ohms.

Thanks... I was searching for this info.

Appreciate all the info from all here. Is it possible to have an injector that works, but doesn't work the way it should that would cause a slight miss or are they normally Working or Not Working?
 
Thanks... I was searching for this info.

Appreciate all the info from all here. Is it possible to have an injector that works, but doesn't work the way it should that would cause a slight miss or are they normally Working or Not Working?

Take a look at this gif. You can see that that if the solenoid is moving the plunger you will hear the clicking, but if the holes in the end of the injector are plugged little or no fuel will pass, either that or the spray pattern will be screwed up.



350px-Injector3.gif
 
I checked the resistance and all 6 injectors showed 12.2

I haven't had a chance to pull the FI's and flow test them but I'm starting to think it could be a slight exhaust leak or something else. I'll keep checking a few things and report back if I find anything.
 
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