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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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1988 Westy To Be Named! :^)

Vanagon VAG GAS engine swap Google Group:
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My Air Cooled Vanagon to 15 Jetta ABA swap pages:
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