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Thread: It's been a while and I really need this fixed.

  1. #1
    Rice Patrol verified Feedback Score 0 Mean Green's Avatar
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    It's been a while and I really need this fixed.

    I've made many threads on 3si with not a single one leading to a solution.

    The car is a 1993 VR4 in all stock condition. The engine is fresh also.

    The car drives fine out of boost but once you hit boost I can hear it backfiring through the intake from time to time and very loud backfires through the exhaust when the throttle is pressed 100%.

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    The data logger says the TPS is set at around 12.5% when the switch has continuity. The TPS also has a nice path on the data logger with no interruptions so it is not the TPS.

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    Me and Echo419 tested the ECU today in his car and my ecu ran better in his car than his own...lol...

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    The fuel pump is the only upgraded mod on the car right now. It is a walbro 255 but the pressure is perfect at idle and changes when the vacuum line is removed from the FPR so that is not the issue but was part of the issue before.

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    I changed out the MAF with another one I had laying around and now the car will rev past 4000rpm but still has the stumbling issue.

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    I replaced both front and rear O2 sensors with brand new units and they are both reading correctly according to the datalogger.

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    The engine temp sensor is a brand new unit also. I tested it in accordance to the FSM just to be sure.

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    I replaced the injector resistor pack with a brand new OEM unit as the old unit was reading an abnormally high ohm level but it is now correct.

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    I swapped the injectors out with known to be working OEM 360cc from another VR4 and no change at all.

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    The mechanical timing is spot on and the electronic timing is perfect according to the datalogger.

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    The car does not read any knock, only catches a few counts in the mid RPM range but it appears to only be hiccups once in a blue moon.

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    The compression is perfect with not a single pound of variance between cylinders which to me, is badass.

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    I boost leak tested all the intercooler piping to 30psi with just a car air compressor and it held 30psi...yea I wanted something to blow and expose a weak point but no success.

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    I took the K&N air filter off and cleaned it and noticed a small difference but nothing that changed how well it drives.

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    Now, the car has no power at all if I give it more than about 30% throttle. If I go to 80+% the car will backfire really bad. The rear turbo will be visibly glowing when I get done driving it but that's only after I boost it.

    Gimme some more idea's as I only have 250$ to throw around.


    EDIT: Also, all updates to reply's will be posted here and a bump added.

    The pump is hot wired and getting around 13 volts.

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    The car also has no cats what so ever and full egr delete.

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    The spark plugs are new NGK platinum's and they are gapped at 35 already. I did have them at the OEM gap and the car did run worse. Closing the gap to 35 did make it alot more drivable out of boost and it idled better.

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    It goes to 7 pounds of boost and will hold that but it pushes and pulls as if it wants to go but something is holding it back. The car is running on wastegate pressure as in the vac line goes from the intercooler piping to the wastegate actuators.

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    When I took the plenum off to replace the plugs again, I noticed alot of soot / carbon build up and its all new. The old plugs looked great with an identical pattern on all 6 and no carbon build up what so ever.

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    Last edited by Mean Green; 09-20-2010 at 11:01 PM.

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    Try testing the voltage at the pump itself. You will have to pull the fuel pump assembly to do this. I had a bad in-tank ground wire and I was getting low voltage to the pump.

  3. #3
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    Spark plugs? Maybe your having a dramatically worse version of what I was having: I couldn't rev past 5000 rpm w/o misfire (no knocking though) at greater than 12 psi boost solely due to spark plug gap. I got some new plugs in at .035 gap now and she'll rev as far as I need at whatever boost I want. Good Luck

  4. #4
    VR-3747 :D Not Verified Feedback Score 1 (100%) futurevr4man's Avatar
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    yeah, plugs are my question as well.
    rise and rise again until lambs become lions

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    Rice Patrol verified Feedback Score 0 Mean Green's Avatar
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    bump....added more info

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    Did I miss it or did you say anything about the coil pack. You might want to test it. or try swapping with a known good one.

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    Quote Originally Posted by vr3.9 View Post
    Did I miss it or did you say anything about the coil pack. You might want to test it. or try swapping with a known good one.
    That or the PTU is what I'm thinking..

    anyone have a video of what bad coil packs do on these cars?


    I was going to order a set from IPS but I have seen to many horror stories on shipping so I am hesitant to order from them as they are the cheapest.
    Last edited by Mean Green; 09-20-2010 at 11:12 PM.

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    Yep, agreed with above. Coil packs, spark wires, and I think ptu(?)
    The fact that closing the gap improves the situation makes me think its ignition power related even more than before.

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    Bad coil pack would do the same thing as having too high of a gap on 2 of 6 spark plugs (at least, but in multiples of 2)
    Eventually it would stop firing altogether in multiples of 2 I believe.

    P.S. you ninja posted... -.- lol

  10. #10
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    Quote Originally Posted by Midnight92Vr4 View Post
    Bad coil pack would do the same thing as having too high of a gap on 2 of 6 spark plugs (at least, but in multiples of 2)
    Eventually it would stop firing altogether in multiples of 2 I believe.

    P.S. you ninja posted... -.- lol
    LOL... I'm quick with that shit huh?...lol

    I just want to be 100% sure it's that. Like I said, I only have 250$ to play with as I have no more spare funds for the next 2 months. I've already wasted over 3k in the past 3 rebuilds.

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