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Code 41: Injector circuit

My car was stumbling recently and the CEL came on. I was able to pull it today and got code 41: Injector circuit. Can I use the injector feature of MMCD to help me narrow down which injector has the problem? If so, please explain. The car died yesterday and then wouldn't start for 15 mins. Any help with this is appreciated.
 

Eureka! Injector #4's clip wasn't on all the way. Not sure what happened as I haven't worked on the injectors myself. The car pulls hard again.
 

If this happens again, the easiest way to figure out which injector is open is with a voltmeter. Just unplug the connector from the ECU, and check the resistance to ground on each of the 4 injector wires. The one that ISN't very low, like 20 ohms, is the open one. I had that happen once, from taking ECU's in and out of my car so many times. /ubbthreads/images//graemlins/frown.gif
 
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stevep

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Oct 23, 2004
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416
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St. Charles, IL USA
You can just trigger the MPI relay and look for 12v on each injector wire at the ECU.
I wouldn't expect you to be able to measure the resistance to ground from the injector pins. The resistance is about right for the resistance to the MPI relay but there isn't a path to ground in the injector circuit unless there is an undocumented connection in the MPI relay when it deactivated.

Steve
 

Sorry to disagree with you Steve, but the same 12 volts that feeds the injectors feeds a ton of other stuff under the hood, creating parallel paths to ground. Granted, most, if not all of those paths must go through the ECU to get to ground, but I just repeated the test on my GVR-4, and I read 20 ohms on each injector wire at the ECU when measured to ground. Pin #102/107, which is the MFI voltage that feeds the injector resistors, ISC, solenoids, MAS, etc shows only 12 ohms to ground with no power turned on to the car whatsoever. Maybe my car is just weird, but that's what I read. /ubbthreads/images//graemlins/dunno.gif
 

CP

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Aug 30, 2004
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West Simsbury, CT
My code 41 was caused by a bad trace on the ECU board. Jeff was able to figure it out for me /ubbthreads/images//graemlins/grin.gif Search for my screen name and "code 41" for details.
 

stevep

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Oct 23, 2004
Messages
416
Location
St. Charles, IL USA
Quote:
Sorry to disagree with you Steve, but the same 12 volts that feeds the injectors feeds a ton of other stuff under the hood, creating parallel paths to ground.



No problem. I didn't go out in the garage and double check and forgot about the ground path through the other things connected to MPI power.

People just have to understand that measuring the resistance that way is testing more than the injector circuit and a problem elsewhere could mislead you.
 

Yes, but the point of my post is that if you have a Code 41, the majority of the time that means that you have an open in one of the injectors/injector wiring. Since all the injectors share a common positive path thru the resistor pack, the one that shows a higher resistance to ground than the other three must be the culprit. I think you will find that to remain true no matter what the resistance actually is. You are simply reading the DIFFERENCE in resistance in the wiring between the ECU and the injector, the injector itself, the wiring from the injector to the resistor pack, and the resistor pack itself. The four paths *should* always test within a couple tenths of an ohm of each other to ground.
 

14u2nV

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Jul 22, 2004
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Agency/St. Joe, MO
FWIW; a failiing resistor pack can throw this code too. Took me a while to find that problem.
 
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