1991 4.0 injector coil resistance question

[Klitch]

I'm tearing down my parent's 1991 4.0, I've got the injectors out on the bench and I'm having a hard time finding a good spec for the injector coil resistance. I have found one source saying for 1992 its 14-17 ohms, and 1993-1994 its 12-19 ohms.

I found mine to be hanging around (2) 17 ohms and (4) 22 ohms.

Cause for tear down is intermittent misfires, discovered a litany of other minor issues coming up too.

 

[decipha]

that wouldn't be too concerning to me usually if the solenoid goes bad it will be dead shorted 0 ohms or wide open > 1k ohms

now keep in mind checking ohms will not tell you the condition of the injector itself, you can power them up and blow them out from the bottom with 125psi of compressed air. Usually a bunch of funk comes out of them if they have any appreciable mileage on them.

 

[Klitch]

Will try that, they could have 175k on them as far as we know. #6 may have been sticking open and fuel washing, #6 was 150psi and the rest of the cylinders were 175-180. unless its the valve, need to rig up a way to to a bleed down test.

 

[RonD]

OHM range, when its under 100 ohms, is specific to the OHM meter, low ohms are just hard to read accurately
Ignition coils are like that, low ohms, under 2 ohms

17-22 ohms should be OK

4.0l OHV engine runs 9.0:1 compression ratio, multiplier for sea level compression test is 18
18 X 9 = 162
So 162 PSI on compression test should be expected on lower mile COLD engine
18 is from 15 psi air pressure at sea level(14.7psi), + 3 for mechanical action of engine compressing the air

So your readings are high, but again this is probably from the pressure gauge you are using, test equipment deviations
Which is why you test all cylinders at the same time so engine temp, battery condition(start motor speed) and gauge used are all the same
You can then get an average

If your gauge reads 15psi high then #6 is at 135psi, so yes a problem there
You can do another Dry test and then do a WET test on #6, add a teaspoon of oil to cylinder
WET test number will always go up, if it was 150psi dry then it might go up to 155-160 WET which would indicate Valve issue
If it jumped up to 170 then Rings are whats leaking
So similar to Leak Down test

1991 4.0l probably uses Batch Fire fuel injection not sequential
Look at the injector wiring
Each connector will have 1 Red wire, that's the 12v wire just daisy chained from one injector to the other
Computer Grounds an injector to open it
In sequential injection each connector will have a different colored 2nd wire, so computer can open each injector separately
Batch Fire will just have 2 wire colors, computer opens 3 injectors at the same time, 1 on one side and 2 on the other side
This keeps lower intake full of air/fuel mix so any cylinder on that bank can suck in what it needs
Very much like a carburetor setup

An injector could stick open, from debris in its needle valve, but wouldn't be a wiring issue with Batch Fire or 2 other injectors would also be stuck open
Sequential injection can get a shorted to ground injector wire which would cause single injector to stay open with key on