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high injector resistance at ECU harness
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wareiter
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PostPosted: Thu Jul 19, 2012 6:47 pm    Post subject: high injector resistance at ECU harness Reply with quote

1985 1.9 digijet van starts but runs rough, hesitates, slow throttle response. new cap, rotor, plugs. TPS works, Temp II to spec, coil to spec. Polished the engine and left side of enging bay grounds. the only test so far out of spec is resistance at the ECU plug for all 4 injectors is about 19.8ohms. pulled injector plugs off and measured resistance of injectors. All injectors have resistance between 16.1 and 16.4 (w/in spec) I have about 3.9 ohms resistance from each left side injector plug contact to terminal 7 of the harness plug. Shouldn't this be close to 0 ohms? Where do I look for the source of this resistance? could this be cause of rough running?
Thanks
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Vanagon Nut
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PostPosted: Fri Jul 20, 2012 10:56 am    Post subject: Re: high injector resistance at ECU harness Reply with quote

wareiter wrote:
1985 1.9 digijet van ..... the only test so far out of spec is resistance at the ECU plug for all 4 injectors is about 19.8ohms. pulled injector plugs off and measured resistance of injectors. All injectors have resistance between 16.1 and 16.4 (w/in spec) I have about 3.9 ohms resistance from each left side injector plug contact to terminal 7 of the harness plug. Shouldn't this be close to 0 ohms? Where do I look for the source of this resistance? .....
Thanks


I don't see it noted pages 24.20 and 24.21 but does Digijet FI & wire test require that all FI plugs be disconnected then each tested one by one? (plug one in, test, unplug etc.) From what you wrote, sounds like you did this.

In Bentley I see an "aux air reg." positive connects at junction where FI positive also connects. I'm not sure of this but...

If "left side" of injector plug you're measuring at is positive, then maybe the aux. air reg. is the point of resistance? If "left side" of injector plug is negative ......

Put one VOM probe directly to frame and other to negative connection of each FI plug. If 0, then maybe ground wire "left at cyl. head" to 7 ECU is faulty? (corroded or corrosion at wire end and its terminal etc.) I recently found a ground wire that was corroded (brown) at least half way up wire.

Is FI spray pattern ok?

Neil.

couple words edited for clarity.
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wareiter
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PostPosted: Fri Jul 20, 2012 12:09 pm    Post subject: Reply with quote

I tested resistance with all injector plugs plugged in and then all unplugged tested continuity from one side of plug to 7 on ECU plug. It does look like the ground for FI's goes through the AAR and to 87 of the fuel pump relay. Could the extra resistance be from the AAR?
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Vanagon Nut
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PostPosted: Fri Jul 20, 2012 2:01 pm    Post subject: Reply with quote

wareiter wrote:
and then all unplugged tested continuity from one side of plug to 7 on ECU plug. .....Could the extra resistance be from the AAR?


Maybe. I inferred that if you ended up measuring resistance between FI plug + contact (your term "left side") and ECU 7 (constant ground) the AAR could be the added 3.9 Ohms resistance. This could also be due to the wire between "18" and ECU 7 (and looking again, poss. the Yellow wire from "18" to - of AAR) but my guess is that either wire would have to be in pretty rough shape to create that resistance, albeit a low value. The 3.9 Ohms may not be causing your running issues. Checking spray pattern will help confirm. If they all look weak, or some aren't opening, then maybe the added 3.9 Ohms is causing FI's not to get enough power. But that's a rough guess.

JSYK, I'm not a Digijet owner/operator so am only using Bentley as reference. Smile

"left side" of FI plug was a term you wrote so was quoting that. I have no idea which side is + or - Smile

Here's some info on the AAR. As usual, Tencent provides a really well written post:

http://www.thesamba.com/vw/forum/viewtopic.php?t=347362&highlight=aar

wareiter wrote:
I tested resistance with all injector plugs plugged in


At ECU connector, maybe test only one FI plugged in at a time? This is the procedure for the 2.1 but that may be due to somewhat different wiring scheme.

wareiter wrote:
It does look like the ground for FI's goes through the AAR and to 87 of the fuel pump relay.



Nope. Smile To my eye....

FI grounds are NOT connected to the AAR. Engine cranking or running, each FI is actually supplied a ground by the ECU. (hence test requirement of Ign. On: you are testing the resistance of the FI, FI plugs, all concerned wires, quality of grounds, via two "ground points" at ECU connector)

Every VW relay I've seen shows 87 as + power out. So.... once energized by the Digijet relay, power from 87 of FP relay goes to + of all FI's and + of the AAR.


Neil.
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asiab3
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PostPosted: Tue Mar 28, 2017 9:19 am    Post subject: Re: high injector resistance at ECU harness Reply with quote

Hey folks, I thought I would piggyback on this thread, since the title is perfect and there's great info here already.

A borderline no-start, this 84 Digijet Vanagon will struggle starting and run, but if it's shut off, it won't catch during cranking until it cools. Every electrical test checks out except the injector resistance from terminal 7 to 11/12/23/24 on the ECU plug. We're looking for 14-18 ohms, according to the VW ProTraining manual, but we measured 60 ohms yesterday. We cleaned and polished the five brown ground wires on the left side of the engine, and that brought the resistance down to 45 ohms. The injectors themselves measure 16 ohms exactly.

Am I looking at a new wiring harness? (I read something above about having the ignition on, but I did not remember reading that in a manual. Can someone elaborate on that?)

Thanks!
Robbie
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MarkWard
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PostPosted: Tue Mar 28, 2017 11:24 am    Post subject: Re: high injector resistance at ECU harness Reply with quote

Hello, Pin 7 is a ground for the ECU. With the ECU unplugged, I would measure the resistance between pin 7 in the ECU plug and to a point on the chassis. It should be close to zero resistance. That will verify the ground is good.

Next, With the ECU still unplugged, I would unplug the injectors and then check between the injector pin that goes to the ECU plug and the ECU plug. It sounds like you are using your manual. Again you should have close to zero resistance on each lead back to the ECU.

Last test is done with the fuel pump relay unplugged. You will check the other pin in the injector plug to pin 87 of the fuel pump relay. Again, you should have about zero resistance.

If all those tests pass, you have effectively tested the injector wire harness and you need to look elsewhere.

If the test between the injectors and the fuel pump relay fails or varies from injector to injector, there is a hard connection that connects all 4 injectors for power from the fuel pump relay and the auxiliary air regulator. Only go looking for that if you fail the last test on some injectors or see a variance. I am looking at page 97.55 in the Bentley manual.
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