Too much voltage to fuel injector

adam24r

adam24r

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Feb 11, 2021
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Orange County, CA
Hello,

been trying to fix an open circuit in fuel injector 1 for awhile now.

replaced coils, spark plugs, fuel injector, pigtail to fuel injector, ecm etc

mechanic wants me to do all new wiring harness from mopar for like 500 bucks...

I went and checked the voltage for all the fuel injectors. 2-6 were at around 3ish while 1 was at like 12-14!!!

something tells me that’s my problem. But usually the issues are that u don’t get enough power to the fuel injector...

anyone know how to fix? A resistor? A relay?

Thanks! 🙏
 
Aren’t they all powered constantly by the ASD relay when the key is on? And then the ECM just grounds them each at proper timing when it needs fuel to the engine? I’m under the impression that you need to have 12V at all of them when the key is on...
 
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Check the fuel injector's wiring harness where makes its bend around the threaded stud near the rear of the valve cover. The stud commonly rubs the insulation away shorting the wiring together and to ground which commonly causes fuel injector problems.
 
machoheadgames said:
Aren’t they all powered constantly by the ASD relay when the key is on? And then the ECM just grounds them each at proper timing when it needs fuel to the engine? I’m under the impression that you need to have 12V at all of them when the key is on...
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Yes.

You should have a steady 12 Volts while running at all times. The PCM provides a ground based on it's calculated Pulse Width Modulation required after translating inputs from multiple sensors (IAT, MAF, CKPS, CPS, etc.)

I'm just spit-balling here because I've never seen low voltage on a power feed to an injector. I've seen a lot of opens (broken wires, and popped fuses) but never this. But from a trouble-shooting standpoint, couldn't you backprobe the suspected low voltage injectors and run a jumper wire directly from battery? Essentially "be the computer" and give those injectors 12 Volts while it's running and see if your problem goes away?
 
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adam24r said:
Hello,

been trying to fix an open circuit in fuel injector 1 for awhile now.

replaced coils, spark plugs, fuel injector, pigtail to fuel injector, ecm etc

mechanic wants me to do all new wiring harness from mopar for like 500 bucks...

I went and checked the voltage for all the fuel injectors. 2-6 were at around 3ish while 1 was at like 12-14!!!

something tells me that’s my problem. But usually the issues are that u don’t get enough power to the fuel injector...

anyone know how to fix? A resistor? A relay?

Thanks! 🙏
Click to expand...
Are you back probing the injector while reading 3V on 2 and 6? Or are you unplugging the sensor and reading it like that? Whenever I run into issues like this, I like to get all of my readings on a "loaded circuit". I also like to back up whatever multimeter readings I get with a confirmation from an incandescent test light. One strand of wire will show 12 Volts on a multimeter, but won't light a test light.
 
ItchyDong said:
Are you back probing the injector while reading 3V on 2 and 6? Or are you unplugging the sensor and reading it like that? Whenever I run into issues like this, I like to get all of my readings on a "loaded circuit". I also like to back up whatever multimeter readings I get with a confirmation from an incandescent test light. One strand of wire will show 12 Volts on a multimeter, but won't light a test light.
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Yeah this was the issue, when I grounded it to the battery they all had like 14 volts. Idk what there is left to check, maybe the ground to the battery is causing an open circuit? Or I could try a whole new pcm
 
adam24r said:
Yeah this was the issue, when I grounded it to the battery they all had like 14 volts. Idk what there is left to check, maybe the ground to the battery is causing an open circuit? Or I could try a whole new pcm
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When you grounded it to the battery, they ALL had 14 volts? What happened to the "3ish" volts you were originally reporting?? How exactly were your probes oriented when you were getting 3ish volts? The red lead was going to power, and the black lead was going where?
 
adam24r said:
Yeah this was the issue, when I grounded it to the battery they all had like 14 volts. Idk what there is left to check, maybe the ground to the battery is causing an open circuit? Or I could try a whole new pcm
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Btw... relax with the PCM talk. IF your issue is truly low supply power to a few injectors, Your PCM is fine. All of your injectors are powered from a single wire from the ASD relay which spiders off to a supply to each injector (not the PCM). As said before your PCM is ONLY providing an intermittent ground to each injector when it determines it's time to fire a specific injector. The fact that you have 12 volts on SOME of the injectors proves that the power feed is somewhat in tact. Follow Jerry's advice at inspecting the wire harness for points of contact. If you don't see anything out of the ordinary, I'd be happy to walk you through some isolation procedures, but that's going to require you to admit when you don't understand something, and also provide consistent symptoms. What you replied with above doesn't jive with what you first reported.

Also, a battery ground causing an open circuit in a fuel injector, is also beyond unreasonable.
 
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adam24r said:
Lol my bad, I just checked for continuity for the ground and it’s good so maybe the dude that checked the pcm was just wrong idk

sorry sorry 😤
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Continuity to ground on the ground coming from the injector pig tail? Or just continuity to the PCM?
 
I'm about to bow out of this one, being that your purported symptoms are all over the place, plus your trouble sticking to a narrative, but I can't help but add one more thing...

IF you tested positive for continuity to GROUND from the pig tail with the key off, you most certainly have a short to ground which will cause that injector to fire all the time. I.E. Jerry's advice was probably spot on. Good luck man.
 
ItchyDong said:
Continuity to ground on the ground coming from the injector pig tail?
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Ok lemme clarify,

I checked voltage by connecting the red and black to each fuel injector pigtail. 2-6 read about 3v while injector 1 read about 13v

But I read about using a running ground, so instead I checked each fuel injector by connecting the red to the fuel injector pigtail and the black to the battery ground and they were all about the same 13-14v
 
Jerry Bransford said:
Have you not yet actually checked your wiring harness next to the stud for damage as suggested?
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You are talking about these connections, right?

I’m a bit confused because the ground for the fuel injector goes to the middle harness of the pcm. The middle harness wires appear to go behind the engine and not through these two harnesses.
5588F466-FC30-477C-88D5-38FEA6978D5B.jpeg
 
adam24r said:
Ok lemme clarify,

I checked voltage by connecting the red and black to each fuel injector pigtail. 2-6 read about 3v while injector 1 read about 13v

But I read about using a running ground, so instead I checked each fuel injector by connecting the red to the fuel injector pigtail and the black to the battery ground and they were all about the same 13-14v
Click to expand...
Jeepers. Follow Jerry's instructions. You're getting 3-4 volts when you're inserting both leads into the pigtail BECAUSE YOUR PCM PROVIDES AN ITERMITTENT GROUND. You're not going to see a steady12 volts this way. This is why you hook a noid light or a test light up to the ground to watch the PCM pulse the injector. When you connect up to the power wire of the pigtail, and the battery or known good ground, you're seeing the constant 12 volt supply provided by the ASD because you're not using an intermittent ground. This is perfectly normal. FOLLOW Jerry's advice.
 
ItchyDong said:
Jeepers. Follow Jerry's instructions. You're getting 3-4 volts when you're inserting both leads into the pigtail BECAUSE YOUR PCM PROVIDES AN ITERMITTENT GROUND. You're not going to see a steady12 volts this way. This is why you hook a noid light or a test light up to the ground to watch the PCM pulse the injector. When you connect up to the power wire of the pigtail, and the battery or known good ground, you're seeing the constant 12 volt supply provided by the ASD because you're not using an intermittent ground. This is perfectly normal. FOLLOW Jerry's advice.
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Ok but I still think it’s weird that the 1st fuel injector gave me a much higher voltage than the rest when I was attaching both prongs to the pigtails no?
 
adam24r said:
You are talking about these connections, right?

I’m a bit confused because the ground for the fuel injector goes to the middle harness of the pcm. The middle harness wires appear to go behind the engine and not through these two harnesses.
View attachment 246766
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No. I said the fuel injector wiring harness (the wires that lead to the fuel injectors) and where it bends around the stud at the rear of the valve cover.

Find one of the six pairs of wires connected to any of your fuel injectors. Follow that wiring toward the rear where all of the injector wires collect together and then bend around that threaded thing sticking up from the rear of the valve cover area. That threaded thing, the stud, has sharp threads on it and it can wear through the wiring that is passed too closely to it. That threaded thing, aka stud, is also grounded so any bare wires it creates by wearing through the insulation get shorted to ground and possibly to each other.
 
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adam24r said:
Ok but I still think it’s weird that the 1st fuel injector gave me a much higher voltage than the rest when I was attaching both prongs to the pigtails no?
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IF YOU HAVE A SHORT TO GROUND (WHICH IS WHAT JERRY WANTS YOU TO CHECK FOR BY THE STUD) THEN YOU'LL READ A CONSTANT 12VOLTS WHICH MEANS THE INJECTOR IS FIRING ALL THE TIME. THE PCM CAN NO LONGER COMMAND AN INTERMITTENT GROUND TO FIRE THE INJECTOR IF YOUR ENGINE BLOCK IS PROVIDING A CONSTANT GROUND.

Stab your multimeter lead in the ground wire of the first injector with the key off and multimeter in continuity. Take your other lead and go to battery. As stated before, if you have continuity in this case, you have a short to ground.
 
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