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fuel injector tests


scrapper

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I was testing the fuel injectors with an ohm meter and got a reading of 2? I read it should be 11-18? I'm not sure I'm reading the ohm meter correctly it goes from 1 to about twenty. All four of them are right on the 2. The last cylinder doesn't make a difference when I pull the wire off the injector. I read that when testing the wires it should move the needle around even at idle. I used the meter set on dc volts and it stayed in the same place on 3 of them. I didnt check one as the rest were doing the same thing. Am I doing something wrong? I have been having rough idle for awhile but just got around to checking the problem out. It would seem the very back cylinder isnt working though.I'm going to get a compression tester this week, maybe a fuel pressure gauge also. Any ideas?
 


scrapper

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I just tested the tps and it was good and the spark was okay on the last cylinder.
 

RonD

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Set OHM meter to 200 or lowest setting it has.

Then remove injector connector and test OHMs, yes, 11-18ohms is OK, they should all measure about the same so your "2" probably means they are OK and the meter is the issue.

You can test voltage at injectors with key on/engine off.
Set volt meter to DC Volts, 20vDC if it has that setting.
Ground the black probe of the meter to engine or battery negative.
Test each wire on each injector, each should show Battery voltage, 12.5v or so, test battery voltage first to see what that is.

You can't get any useful information from an injector with volt or OHM meter while engine is running.
The Ground pulse width is only milliseconds long so volt meter doesn't have enough resolution to show anything of value.
You use a Noid Light to test injector pulses.

Another simple test is to unhook the coil packs, so no spark, then crank the engine a few times.
Now pull 1 spark plug from each cylinder and see if it is wet with fuel, should be, dry spark plug tip would mean no fuel/no injector
 

scrapper

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33/12.50/15
I will check the plugs to see if they are wet tomorrow after work. I am thinking it would have to be an injector problem but you never know.
 

tomw

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The failure rate for injectors on FoMoCo products is low. Before buying a replacement, you could try swapping a pair. If the problem persisted and followed the injector, that's a good clue. If the problem remained in the #4 cylinder (last on a 4), it is something else, and a compression test would be a good step to take.
The injectors have 'boots' and are a press fit(you push in or pull out with a twist & squirm) into the head aperatures. Lube them before trying to install, ditto the O-rings on the fuel rail.
For sure one of the wires to the injector will /should/ have 12v with the key ON, but the other wire would be connected to the driver transistor in the computer that provides ground to complete the circuit. I do not know what voltage it would be when not firing, but know it would not be at ground... So for sure one wire should have the 12v.
tom
 

scrapper

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Location
central IL
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1994
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ford
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V8
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1975 302
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Automatic
2WD / 4WD
2WD
Total Lift
6+3
Tire Size
33/12.50/15
I tested the fuel pressure and it was about 40 key on and running it was 33.
 

scrapper

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Location
central IL
Vehicle Year
1994
Make / Model
ford
Engine Type
V8
Engine Size
1975 302
Transmission
Automatic
2WD / 4WD
2WD
Total Lift
6+3
Tire Size
33/12.50/15
The starter just went out, not sure if it was causing any other problems? It froze up after not wanting to start for about a week.
 

scrapper

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central IL
Vehicle Year
1994
Make / Model
ford
Engine Type
V8
Engine Size
1975 302
Transmission
Automatic
2WD / 4WD
2WD
Total Lift
6+3
Tire Size
33/12.50/15
I replaced the injectors and the misfire went away. I'm still working through other problems but for right now its running ok.
 

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