Injector resistance question - Diesel Forum - TheDieselStop.com
Power Strokes 1994-1997 General Technical discussion of topics related to vehicles powered by the Power Stroke engine in 1994 through 1997 models.

 
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post #1 of 6 (permalink) Old 12-03-2018, 04:54 PM Thread Starter
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Injector resistance question

Truck has been displaying some intermittent issues that are analogous to a gas motor running on partial choke; stuttering, skipping...feels like its running on 6 or 7 cylinders when hot...at times. I checked the external UVC GP/injector connections and the rear one under the intake to the turbo revealed frayed/cracked/missing insulation; basically 4/5 wires revealed various degrees of being bare. Soldered in a new pigtail connection but still seem to have an issue.

Checked the resistance of the injectors and was seeing 3.2 - 3.6 ohms on all but one injector. One injector was 9.1 ohms...obviously high. Is this a surefire sign I have a bad injector? I do not have the scanners or apparatus to do any detailed tests?


Any help would be appreciated...


Burgie

1996 F-350 4x4, PSD, E4OD (Ford reman installed at 185K miles), 218,000 miles, WD downpipe, BFG 295/75R-16's, 28K Tru-Cool, Magnafine, Tricum Springs, Diablo Accumulator Valve, Hollow Cat, Tymar Intake and HX Mod, Rancho Add-A-Leaf, Lund Visor & Running Boards, Deflecta-Shield, Dee-Zee Brite-Tread Bed caps, Husky Diamond Plate Tool Box, Reese Class IV hitch...and more to come..


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post #2 of 6 (permalink) Old 12-03-2018, 06:24 PM
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You could always swap the solenoids between the 9.1 injector and another and see if the miss follows. Cheers!

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post #3 of 6 (permalink) Old 12-04-2018, 02:22 PM Thread Starter
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Good morning Patrick,
Thanks for the response. Forgive my ignorance as I only have a satellite view understanding of injectors.

So, if the injector pulse from the IDM is 110V – 120V and a normal solenoid resistance is ~3.5 ohms the current would equate to ~31-32 amps. Given that current is inversely proportional to resistance, a solenoid coil with 3x the resistance would mean ~1/3 the current, or around 12 amps. I’ll assume for a minute that that would generate a magnetic field that is insufficient to properly pull the poppet valve off its seat (or perhaps for the proper duration). I don’t know if that is true or not because I don’t know what the injector specs indicate…just using simple Ohms Law stuff…

I understand the logic behind swapping solenoids to another cylinder IF I had other data, like a CCT or Buzz test or some other running test, to see if the problem moves…but not sure the intent otherwise?

I know I can buy just a solenoid…so is replacing just the solenoid acceptable? Or ore the injectors “matched” to a solenoid? I don’t see how they would be but again, not sure…

Any additional insight would be appreciated!!

1996 F-350 4x4, PSD, E4OD (Ford reman installed at 185K miles), 218,000 miles, WD downpipe, BFG 295/75R-16's, 28K Tru-Cool, Magnafine, Tricum Springs, Diablo Accumulator Valve, Hollow Cat, Tymar Intake and HX Mod, Rancho Add-A-Leaf, Lund Visor & Running Boards, Deflecta-Shield, Dee-Zee Brite-Tread Bed caps, Husky Diamond Plate Tool Box, Reese Class IV hitch...and more to come..


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post #4 of 6 (permalink) Old 12-04-2018, 05:30 PM
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I don't believe that the injector coils will be drawing that kind of amps but only what is needed to activate them. If they pulled that many amps the wiring harness would be the size of a large pencil.

I would pull the valve cover and test them directly instead of through the harness. Then if you find the same readings you can replace just that solenoid, they are not matched to a injector but just a coil that causes the valve to open and close on the injector.

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post #5 of 6 (permalink) Old 12-04-2018, 05:38 PM Thread Starter
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Hi bugman,

Totally agree...which is why I'm asking. The wire size when I replaced the outside-the-UVC 5-pin connector appeared to be 14ga. -16ga. or so...but electronics is electronics and 110V with 3.5 ohms resistance = 30+ amps (I=E/R). I agree it is probably less but some YouTube vids I've seen show people using a scope to see the trigger pulses with the Y-scale set to current and it's showing 18-20 amps...

Agree...I'll pull the valve cover and test directly after disconnecting the connector. Best place to buy a new solenoid? Any suggestions??

Thanks

1996 F-350 4x4, PSD, E4OD (Ford reman installed at 185K miles), 218,000 miles, WD downpipe, BFG 295/75R-16's, 28K Tru-Cool, Magnafine, Tricum Springs, Diablo Accumulator Valve, Hollow Cat, Tymar Intake and HX Mod, Rancho Add-A-Leaf, Lund Visor & Running Boards, Deflecta-Shield, Dee-Zee Brite-Tread Bed caps, Husky Diamond Plate Tool Box, Reese Class IV hitch...and more to come..


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post #6 of 6 (permalink) Old 12-04-2018, 06:54 PM
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I think that if I was you I would talk with some injector rebuilders and see what they think about your problem. It is hard to say if that difference in resistance would cause the problems that you are experiencing.

As for where to buy one, I did a quick Google search and came up with a supplier that sells them for $60. You might be able to find a cheaper one on fleabay or elsewhere.

https://www.accuratediesel.com/shop/170.html

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
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