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Injector Problem

B

Bobby@Bullydog

NAXJA Forum User
Location
Texas
Ok I have a VERY odd problem here.
Ive been having some issues with my 96 XJ lately with it mis firing on number 1 and 3.

Codes thrown are:
p0300
p0301
p0303

The weird part is at idle I can unplug the number one injector and the idle will not change....rev it up and it has a misfire and you know it because it studders....when plugged in it still idles rough but revs up very smooth. Same with Number 3
If you rev it up with the injector pulled it studders....plugged in very smooth

So I thought maybe 2 injectors were not firing at low pressure.



Now Today I put the Mustang 5.0 injectors in thinking I had a few bad injectors. Still have the same issue.

So now Im stumped

HALP!!!!
 
Another WEIRD thing.

Just for kicks to see if it was a simple connector or harness issue. I switched number one and two injector plugs and number one still wont fire at idle.

plugs are also caramel brown like they should be

Guess Its back to the drawing board.
 
Well the tester I rented from vatozone is a piece of crap and must be broken..its wont read over 20psi even hooked up to my air line which is at 130lbs right now.
BUT

I had my dad to the ole finger over the hole trick and all cylinders push pretty hard lol

And beings it revs up perfect just idles like crap tells me it does have sufficient compression.
Like i said its only at idle that it runs like crap....the CEL only comes on when im sitting idle at a light or in slow traffic. I commute 65 miles one way a day and the light only comes on right as i hit traffic in town.


There HAS to be an easy fix and im just clearly not seeing it
 
Still need to do an accurate compression test even if the problem is only at idle. Swap the plugs anyway just to be sure. BTW what brand of spark plugs?
 
Another thing that may have been overlooked is a vacuum leak on that cylinder. I usually check with some carb cleaner sprayed around various places like the intake runners (with a fire extinguisher handy), if the idle speed changes, there is the leak.
 
88 Wagonman said:
Still need to do an accurate compression test even if the problem is only at idle. Swap the plugs anyway just to be sure. BTW what brand of spark plugs?
Click to expand...
Ive swapped plugs around..no change
and they are champion copper plugs as it calls for.

and ive sprayed carb cleaner around the intake too and nothing changed other than moving dirty from one place to another lol
 
Bobby@Bullydog said:
Ive swapped plugs around..no change
and they are champion copper plugs as it calls for.

and ive sprayed carb cleaner around the intake too and nothing changed other than moving dirty from one place to another lol
Click to expand...

After you check the compression check the fuel pressure, then put a timing light on all the spark plug wires one at a time and look for missing or no fire at idle. You just about have me stumped too, but post your results and we'll go from there.
 
You have extra injectors laying around, right?

Get yourself a clear glass jar, hook up an extra injector to the harness for a good running cylinder, and observe how it operates at idle.

Then repeat for the poor running cylinders. If there is an observable difference in the injector performance then you know it is upstream electronics from there.
 
joe_peters said:
You have extra injectors laying around, right?

Get yourself a clear glass jar, hook up an extra injector to the harness for a good running cylinder, and observe how it operates at idle.

Then repeat for the poor running cylinders. If there is an observable difference in the injector performance then you know it is upstream electronics from there.
Click to expand...
Good idea!
BUT....how am i supposed to have it running...while having it spraying fuel into the jar....with the rail bolted down so none of the others are spraying out.
 
Bobby@Bullydog said:
Good idea!
BUT....how am i supposed to have it running...while having it spraying fuel into the jar....with the rail bolted down so none of the others are spraying out.
Click to expand...

Hell, never mind. I was having a senior moment.:twak:

Ok, try this (Plan B)--pull the harness from a known good firing cylinder and measure the voltage for that connector at idle. Then repeat for a known poor cylinder connector and compare.
 
Last edited:
joe_peters said:
Hell, never mind. I was having a senior moment.:twak:

Ok, try this (Plan B)--pull the harness from a known good firing cylinder and measure the voltage for that connector at idle. Then repeat for a known poor cylinder connector and compare.
Click to expand...

That may not tell you a lot. You also need to be able to measure the duty cycle or "pulse width" of the injector. Theoretically you could have similar voltage at the plug but have it not fire properly. When an injector fires it applies voltage for a certain amount of time (Miliseconds) to open it (basically a solenoid) and removes the voltage for a certain amount of time. You could have full voltage, but it might not be firing the injector for the proper amount of time. Plus voltage needs to be measured while connected, otherwise you could have the proper voltage but no amperage causing a false reading.
 
joe_peters said:
Hell, never mind. I was having a senior moment.:twak:

Ok, try this (Plan B)--pull the harness from a known good firing cylinder and measure the voltage for that connector at idle. Then repeat for a known poor cylinder connector and compare.
Click to expand...
I already tried that..Voltage is so sporadic you can really get a correct reading on any cylinder
 
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