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Thread: MAF voltage error, car running rich

  1. #1
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    MAF voltage error, car running rich

    This particular issue is solved, but I thought I'd share it with the forum, might save someone some time/agro in the future.

    I've wired in a fuel piggyback, that adjusts the voltage from the MAF, thereby causing the ECU to adjust the mixture. Anyway, I couldn't get the mixture to do what I wanted, it was all over the place, but generally too rich. We had it out at the track last weekend, and couldn't solve it, so disconnected the MAF entirely. The car actually ran pretty well, albeit a bit rich, and both me and Junior new lap PRs. New tyres helped.

    Long story short, I had bunched the new wiring into the adjacent injector wiring, and the MAF signal wire was getting interference from the injector wires, and signalling roughly an 0.2 volts more than it should have to the ECU, about 1.5 volts at idle where it should be around 1.2 volts. The ECU was responding by adding more fuel. It appears that the interference may have been through the heat shrink where I spliced in the new wires running to the piggyback. I didn't manage to figure all this out until last night, but once the new wiring and the splices were clear of the injector wires, it ran fine.

    Once it was sorted, it was cool watching the ECU retrim the fuel on the wide band, took about 3 minutes at idle for it to be corrected back to 1 lambda.

  2. #2
    Purist, whats that? Jason Broadhurst's Avatar
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    Good pickup bro.

    Do you mean the injectors, or ignition leads? Injectors run about 1 A max each, more briefly but not a heap. Induction from 1 A adjacent to a MAF/MAP signal would be very difficult to achieve. A high resistance fault via a stray strand or pointy solder blob would have a huge impact though.

    It's not common practice to shield MAP or MAF signals so it's an interesting problem you had!
    Jason Broadhurst

    Someone once asked me if they could use my mower. I said "sure, so long as it doesn't leave my yard"

  3. #3
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    Quote Originally Posted by Jason Broadhurst View Post
    Good pickup bro.

    Do you mean the injectors, or ignition leads? Injectors run about 1 A max each, more briefly but not a heap. Induction from 1 A adjacent to a MAF/MAP signal would be very difficult to achieve. A high resistance fault via a stray strand or pointy solder blob would have a huge impact though.

    It's not common practice to shield MAP or MAF signals so it's an interesting problem you had!
    Well, I thought it was the injector wires, but now that you mention it, the junction of the ignition wires (It's coil on plug) was close by too, I'll have a closer look and report back. And thanks for the pointer about crappy soldering, I thought it was OK but I'll double check that too.

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    Here's a pic of the splices and adjacent area. The black goes from the MAF (which is out of shot above) to the piggy, and blue from the piggy to the ECU. They were taped to the existing bundle on the left side, which has the injector wires plus some others such as MAP, possibly crank angle, plus maybe a couple more. The ignition coil wires branch off below out of shot, so they were maybe 80mm away from the splices.



    And here's a close up of the splice from the MAF side. Not sure if the soldering is up to standard, it's a bit lumpy, but solid and I couldn't feel any wires hanging out of it. If you have a close look at the bracket you can see some blue residue, I think this has rubbed off from the heat shrink, which may have created a weak spot in the insulation.

    Last edited by Sprinkles; 18-05-17 at 08:29 AM.

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