Just Did Motor Swap.. Car Falls Flat On Power

Discussion in 'SN95 4.6L Mustang Tech' started by Back in Black, Jul 29, 2013.


  1. Back in Black

    Back in Black Don't feel bad. Almost 3 years on here and the onl Founding Member

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    It's been a while since I've been on here. I had a nice engine build (550 lift cams , new pistons the works). And to male a long story short I paid the shop to fly cut my pistons and they didn't do it. Valves hit, pistons broke, cylinder walls were sliced and 7 grand went away like that.
    Anyways , I picked up a 99 cobra motor, computer, gauges and all the wiring for $1,500. Only has 51,000 miles on it. Everything works fine and all except the car has no power like it should. It falls flat on its face. Now I know the guy that had the motor before had a supercharger on it. He took it when they sold the motor. My question is if the computer is still programmed for the supercharger, would that cause it to have that large of a power loss ?
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  2. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    take the chip out of the computer
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  3. Three50won

    Three50won Member

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    Sorry about the blown engine. It always pays to inspect everything going into your engine before and after it is installed. There are very few shops I trust. And even those shops know that I will stop by and look things over every day my car is there. You have to be like that.

    And yes, tuning can cause power losses like you described. Or you could be having internal engine problems, trans problems, etc. Start with looking everything over to make absolutely sure everything is connected. Check your plugs and coils. Check for vacuum leaks as well. After that you can check for the ECU tune. The quickest and easiest way is if you have a tuner...try to flash a tune onto the ECU. If the tune flashes, then try driving it again. If it doesn't flash, then there is a tune inside there and you will need assistance getting it cleared. If after you flash it there is still power loss, then you will need to check for codes as well as a compression check, leak down test, etc. Other things to check are fuel pressure, spark, exhaust leaks, etc. Hopefully the engine is solid and the problem is minor.

    While you are at it you may want to check all your sensors (MAF, IAC, TPS, O2, etc) and make sure they are all intact and operating properly
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  4. Back in Black

    Back in Black Don't feel bad. Almost 3 years on here and the onl Founding Member

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    There is no chip in the computer. And yeah I checked and said " the pistons will need fly cut" and I was right. They did. I payed for it but it never was done.

    But yeah I checked for leaks, plugs, and what not. I do not have a tuner but the dealership I work at can hopefully flash it to factory and it'll all be good. The CEL is off so the engine seems to think everything is cool.
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  5. trinity_gt

    trinity_gt Advanced Member

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    Is the Cobra motor stock internally or was it built for the blower? If it was, maybe it's got lower compression pistons and is soft because of that.

    If the motor is stock internally, you might do a compression check and a leakdown. Maybe it's tired (or broken) from the blower use.
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  6. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    i would also pull codes even though the CEL is not on, many codes do not trigger the light but may help diagnose your problem
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  7. Back in Black

    Back in Black Don't feel bad. Almost 3 years on here and the onl Founding Member

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    It was running lean and showed that code madspeed. But I also had two year old gas in it. As far as the motor being built for the blower it was completely stock internally. It's at my dealership now and I'm hoping they can figure it out. Oh with the car idling I unplugged the vacuum line on the egr valve and nothing changed. Could that have something to do with it?
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  8. trinity_gt

    trinity_gt Advanced Member

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    No. At idle the EGR valve is supposed to be closed and there will be no vacuum present at its line.
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