TheSamba.com :: View topic - Low Resistance In Wiring Harness to Fuel Injectors

Sun Oct 09, 2016 5:19 pm

Hello Samba Community!

In the Digijet Pro Training Manual, there is a procedure where you can check the condition of your injectors, which includes spray pattern tests, volume tests, leak checks, and resistance checks. Upon checking all of these things on my van, the only part of the test that failed was the resistance check in the wiring harness. Here's what you do:

With the ignition turned on (at least, that is what I did), connect your multimeter to pins number 12 and 7 (Fuel injector to cylinder 1), then 24 and 7 (fuel injector to cylinder 2), then 11 and 7 (Fuel injector to cylinder 3), and finally to pins 23 and 7 (fuel injector to cylinder 4). With your multimeter on the Ohm setting, you should be getting anywhere between 14 and 18 ohms (preferably 16), to all injectors.

My problem is that I'm only getting between 12.2 and 12.5 Ohms to all injectors at the ECU multipin connector. What could this mean? The test subject is a 1983 1/2 watercooled vanagon with a digijet fuel injection system.

Any thoughts?

Sun Oct 09, 2016 8:26 pm

you should not have power on a circuit when you are measuring resistance.

Mon Oct 10, 2016 6:01 am

You should also be testing resistance directly at the injector terminal, and not at the harness. The harness test can be a check of overall resistance drop to the ECU, to help isolate wiring issues.

Tue Oct 11, 2016 2:12 pm

Upon running the resistance test again at the wiring harness, this time with the ignition off, this is what I got:

28 ohms to injector 1
28 ohms to injector 2
27.8 ohms to injector 3
28 ohms to injector 4

I also tested the resistance at the terminal heads to the injector as well (thank you a1fa) and got 16 ohms across every injector

Fri Nov 04, 2016 8:25 am

Update: I replaced the #7 wire at the ECU connector, which is the common ground between all the fuel injectors, and it reduced my resistance from 28 Ohms to 19 ohms, which is definitely a lot closer, but still not in spec...

How should I proceed? Should I just go ahead and buy a new wiring harness? KYLE Automotive Specialities out of Ohio makes brand new harnesses for all years Vanagon for around $600.

Fri Nov 04, 2016 8:57 am

if the van is running fine, Id ignore the slight ohm deviation. also consider your ohm meter, how accurate is it? have you calibrated it? why not buy a percision resister of simular ohm value and test it with your meter? that would help determine your calibration. note the tolerances on the resister you use.

also run the ohm test to the ecu connector pins, then to the wire new the pins, the difference will tell you if you got wrong resistance at the pin to wire connection.

also make sure the contact between the meter probe and the pin is good. best to use an aligator clip so that you have consistant force rather than using hand pressure to hold the probe.

also note that the ohm meter may not be temperature compensated, so it will read different depending on ambient temperature of the meter. also note that the ohm meter will be off accuracy if the battery in it is low.

good luck

ps something is wrong with the ohm meter and or measurement technique. you got a higher resistance on the injectors than you did on the injectors and the wire harness, that is opposite of what is expected. thus id not believe the readings

and no, dont bust out for a 600 buck new harness based on this!!!!!!!

Fri Nov 04, 2016 12:08 pm

Hello, I am not looking at the pro training, but am looking at the Bentley Manual. The injectors connect to the ECU in this order.

#1 connects to pin 12 of the ECU
#2 connects to pin 11 of the ECU
#3 connects to pin 24 of the ECU
#4 connects to pin 23 of the ECU

With the injectors unplugged as well as the ECU plug, you should be able to ohm out each lead individually. Resistance should be extremely low and should be almost identical. This tests the wire between the injector and the ECU. You'll need to figure out which pin runs to the ECU, but it should be in the same location of the injector plug for all 4. If you test and it's open, you got the wrong connector in the injector connector. Use the other pin. If it is also open, there is a problem. I just don't recall the order. The other pin of the injector plug is connected to the auxiliary air regulator and pin 87 of the fuel pump relay. So once you are done checking the wires to the ECU you can then test the wire resistance back to the fuel pump relay from the other pin in the injector plug. Again, resistance should be minimal on this power circuit of the injector leads.

Next with the injectors unplugged, I would meter across the injector pins. Again, resistance should be similar for all 4 injector plugs.

Good luck. Sorry my explanation might be a little hard to follow. Fuel pump relay supplies power to the injectors. ECU supplies on/off grounds to the injectors to spray them.