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how to test a injector?

B

baybilly

NAXJA Forum User
Location
eastern shore maryland
on the wifes 92 4.0 cherokee. it was running fine, she said she hit a big pot hole and it started running rough. it was time for a tune up anyway so, plugs, wires, dist cap and rotor. still ran bad. i checked all vac lines, OK. started pulling plug wires when running and found # 3 cyl dead. i pulled the new plug and it has fire. went to the compression test and fine. so I'm thicking bad injector ???? Thanks for any help.
 
Engine running, listen for the injector to "click". Use a thin wood dowel pressed against the injector body or a mech's stethoscope.

You can use a voltmeter to test for power to the injector from the harness. You need a GOOD DVOM to test for the firing impulse from the PCM, and no, you can't borrow my Fluke; your next best option is a NOID light, about $3-$10 at most parts stores:

This:
61911a.jpg


Not this:
imagesqtbnANd9GcSuAwW0PbuZogLLKPKOI7gmJSaK3X4KIYHGLtLy0dBSOFIdldza.jpg
 
Fuel injectors can be tested (electrically ONLY) for resistance values with a meter.

Check out some of the others, then check the suspect cylinder. Only takes a few minutes. Can't remember what the spec is but somewhere around the 13 ohm area?
 
joe_peters said:
Engine running, listen for the injector to "click". Use a thin wood dowel pressed against the injector body or a mech's stethoscope.

You can use a voltmeter to test for power to the injector from the harness. You need a GOOD DVOM to test for the firing impulse from the PCM, and no, you can't borrow my Fluke; your next best option is a NOID light, about $3-$10 at most parts stores:

This:
61911a.jpg


Not this:
imagesqtbnANd9GcSuAwW0PbuZogLLKPKOI7gmJSaK3X4KIYHGLtLy0dBSOFIdldza.jpg
Click to expand...

HAHAHA, Got ya, Thanks for the help. i do have some injectors from the 88 i could try. but that wood stix thing, I'm to dame old to try and do the can you here that thing HAHAHA
 
birchlakeXJ said:
Fuel injectors can be tested (electrically ONLY) for resistance values with a meter.

Check out some of the others, then check the suspect cylinder. Only takes a few minutes. Can't remember what the spec is but somewhere around the 13 ohm area?
Click to expand...


Thanks for the help,just did the ohm test and same as the others around 14 at RX 1 could it just be plugged up? the fuel rail and injectors are out. i pulled it when this test was done.
 
i'm constructing a fuel injector cleaner with a connector I got for a buck at pick a part... basically hook the positive of the connector up one side of a switch, then the negative and the other side of the positive up to a 9-v battery connector....

use a 5cc syringe to plug into the injector (should fit snug) and the other side you insert the red tube from a bottle of carb cleaner and use the carb cleaner bottle connected for the pressure and click the button down to open the injector

http://www.youtube.com/watch?v=VFJlTfHyrUk

i'll let you know tomorrow if it works or not

edit: can't spell
 
Last edited:
LOL avoid the noid!

Anyway check for voltage to all the injectors, ohms across all the injectors should be around 14.

Is it clogged? It not likely but possible. There is so much detergents in the gas no a days injectors dont get clogged like they used to.

I would try the noid light, you can make one, google it, or buy one cheap.

I'm still wondering why it started running rough after hitting a pot hole...hummmmm
 
seigeXJ90 said:
i'm constructing a fuel injector cleaner with a connert I got for a buck at pick a part... basically hook the positive of the connector up one side of a switch, then the negative and the other side of the positive up to a 9-v battery connector....

use a 5cc syringe to plug into the injector (should fit snug) and the other side you insert the red tube from a bottle of carb cleaner and use the carb cleaner bottle connected for the pressure and click the button down to open the injector

http://www.youtube.com/watch?v=VFJlTfHyrUk

i'll let you know tomorrow if it works or not
Click to expand...

interesting, let me know how it works out. Thanks
 
maybe when she hit the pothole she mixed up the contents of the gas tank and some dirt from the bottom got into the fuel line and hit an injector even though the filter shoulda taken care of that *shrug*

or did she by chance run out of gas at the same time? :) could do the same thing
 
seigeXJ90 said:
maybe when she hit the pothole she mixed up the contents of the gas tank and some dirt from the bottom got into the fuel line and hit an injector even though the filter shoulda taken care of that *shrug*

or did she by chance run out of gas at the same time? :) could do the same thing
Click to expand...

I love her but that info will never come my way if you know what i mean. The fuel rail looks clean from what i can see/ no rust in that injector hole/ I haven't pulled the rest yet. I'll get the tester mon to see if i have a input problem on #3 and go from their. Thanks for all the help!!
 
Skreed said:
What does the oil look like when you pull the dip stick? Pull the oil filler cap turn in over and look at whats in side...do you have while smoke?
Click to expand...

i changed the oil last week when it went down with the tune up. after pulling the stick today i can see the same rusty looking stuff on the very tip of the dip stick. under the cap looked good. when i start it in the shop i can smell unburnt fuel in the EX no smoke?????
 
Well the oil on the filter indicates excessive blow by, oil getting past the rings and passing back thru the CCV orifice and into your filter.

As far as the goop, I cant say I have ever seen that before, maybe someone else has, but it looks like oil and coolant mix. I have not seen goop like that in the filter tho.

Would you be comfortable pull the valve cover? I'd be itching to see what under there.
 
Skreed said:
Well the oil on the filter indicates excessive blow by, oil getting past the rings and passing back thru the CCV orifice and into your filter.

As far as the goop, I cant say I have ever seen that before, maybe someone else has, but it looks like oil and coolant mix. I have not seen goop like that in the filter tho.

Would you be comfortable pull the valve cover? I'd be itching to see what under there.
Click to expand...

First check the small vacuum lines, mine was plugged for more than a year, I checked that last :-(

I thought I had too much blowby, but the vacuum line was plugged solid.
 
Skreed said:
Well the oil on the filter indicates excessive blow by, oil getting past the rings and passing back thru the CCV orifice and into your filter.

As far as the goop, I cant say I have ever seen that before, maybe someone else has, but it looks like oil and coolant mix. I have not seen goop like that in the filter tho.

Would you be comfortable pull the valve cover? I'd be itching to see what under there.
Click to expand...

Ya, i'll pull it this weekend to take a look see but i think she is gone. good thing i picked up a clean 89 as a spare a few weeks ago.
 
i watched a video on youtube about the air reintroduction setup .. the hoses that come out of the top of the valve cover.. if they are clogged bad it could cause oil to make its way to the filter ... the guy had oil on his because of the rubber grommet being destroyed on the rear of the valve cover (nearest the vehicle cab).. i'll see if i can find it for you


also if you want to check if your rings are leaking I believe the test needed would be the leak down test
 
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