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Thread: 93 Mustang Cobra 347 w/ powerdyne

  1. #1
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    93 Mustang Cobra 347 w/ powerdyne

    Hello, I think I talked to Tony about this but I can't remember.

    I have a Coupe with a 68 302, bored and stroked to a 347. I have a mild cam, low compression pistons, and AFR heads. I'm running the EEC-IV computer with the RJM harness. I have a stock distributor and 42lb injectors, pro-m racing 80mm MAF, BBK 75mm throttle body and of course the powerdyne supercharger. Timing is set at about 10 degrees base.

    I have a couple of problems. First and foremost I can't get this thing to idle, it keeps hunting/surging. I have set the base idle several times adjusting the tps to get it nice and smooth at .930 volts, but after I shut it down and restart , it goes back to the same hunting idle.

    My buddy has a Snapon MT2500 and I can't pull codes out of it, and I can't get live data from the ECU. It seems some wires are missing from the connector.

    I'm wondering a couple of things. First with these engine mods do I need a custom tune? Will I be able to pull data from the ecu? Who does factory five recommend for a tuning shop? I think the one I heard about was in the Worster area.

    Thanks,

    ScottyC

  2. #2
    Director of R&D, FFR Jim Schenck's Avatar
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    We have had very good luck running the stock ECU with no tune on similar combinations, I had almost the same thing, stroker small block, 9lb Powerdyne, aftermarket heads and a decent size cam and ran it all with the stock A9L. If you are having issues every time you turn the car off and restart then it seems possible that your keep alive memory circuit is being disconnected by the key. I would double check that first, also make sure that if you have a battery key that you use often then that power source should be on the live side of the cutoff.

    Secondly at idle with the blower kits, most of them re-route the PCV system but sometimes I have seen the whole thing get left disconnected. If you are pulling air in from the crankcase with the PCV valve and the air getting into the engine is coming through a valve cover filter or catch can then it hasn't been metered by the mass air and that will throw off your idle especially. The two options are to either make sure the valve covers draw air from the intake system between the mass air meter and the blower, or route the valve covers and PCV both to a catch can so the intake isn't drawing any extra air from the crankcase.

    As far as tuning, you can get software that allows you to tune with the factory ECU however if you have a wide band O2 sensor you can get a good running car by just adjusting the timing and fuel pressure and making sure you are always in a safe zone. With that size injector you shouldn't need a boost controlled fuel pressure regulator, however you do want to make sure your standard regulator has a vacuum signal just to compensate for the boost pressure effectively lowering the relative fuel pressure at the injector nozzle. Also when I was running 9 lbs of boost I would start at 6 degrees of timing just to be safe.
    Jim Schenck
    Factory Five Racing

  3. #3
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    Quote Originally Posted by Jim Schenck View Post
    We have had very good luck running the stock ECU with no tune on similar combinations, I had almost the same thing, stroker small block, 9lb Powerdyne, aftermarket heads and a decent size cam and ran it all with the stock A9L. If you are having issues every time you turn the car off and restart then it seems possible that your keep alive memory circuit is being disconnected by the key. I would double check that first, also make sure that if you have a battery key that you use often then that power source should be on the live side of the cutoff.

    Secondly at idle with the blower kits, most of them re-route the PCV system but sometimes I have seen the whole thing get left disconnected. If you are pulling air in from the crankcase with the PCV valve and the air getting into the engine is coming through a valve cover filter or catch can then it hasn't been metered by the mass air and that will throw off your idle especially. The two options are to either make sure the valve covers draw air from the intake system between the mass air meter and the blower, or route the valve covers and PCV both to a catch can so the intake isn't drawing any extra air from the crankcase.

    As far as tuning, you can get software that allows you to tune with the factory ECU however if you have a wide band O2 sensor you can get a good running car by just adjusting the timing and fuel pressure and making sure you are always in a safe zone. With that size injector you shouldn't need a boost controlled fuel pressure regulator, however you do want to make sure your standard regulator has a vacuum signal just to compensate for the boost pressure effectively lowering the relative fuel pressure at the injector nozzle. Also when I was running 9 lbs of boost I would start at 6 degrees of timing just to be safe.
    Ok I will try and take this in order.

    Let's start with the keep alive circuit. Where on my engine harness can I find that wire? Also I do disconnect the battery often, actually every time the car is off. I can put a jumper in across the shutoff if needed but I will always be disconnecting the battery on a regular basis. Also if nothing changes with the vehicle other than the battery being disconnected, then this may be problematic for me.

    The second point you bring up about the PCV may be the problem. The PCV valve is venting to the intake therefore there is unmetered air in the plenum. I will disconnect the PCV and block that port off and see what happens there.

    As for the timing, I think I am good where I'm at. I'm running 100ll aviation fuel rated at 98 octane. I have an aftermarket aeromotive fuel pressure regulator with a vac/boost reference. Fuel pressure is set for 45lbs right now. I do notice when the idle starts surging, that the fuel pressure drops to around 38 ~ 40lbs when the engine is at the low point.

    For further reference I have -6 to 3/8" fuel lines both supply and return with aeromotive fuel rails. The fuel pump is a walbro 255 in tank pump in the factory five fuel cell. I also have a boost timing retard box from vortec.

    ScottyC

  4. #4
    Director of R&D, FFR Jim Schenck's Avatar
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    Scotty,

    I couldn't find a wiring diagram for the RJM harness, although Ron Francis sells that harness now and they may have a diagram. The way the harness is built they assume that you have the main power hooked up at the starter solenoid and that never becomes disconnected from the battery, so if that main power loop gets switched off you will lose the keep alive memory. If you do not want to have any circuits powered while the car is sitting or stored then you can just live with the rougher start up by bumping the idle up a little, but first I would get the PCV and fuel pressures set to where it runs the best. And, if you do adjust the idle at the throttle body then you want to re adjust the TPS voltage as it will likely bump up above 1.0 with even a fairly small adjustment.
    Jim Schenck
    Factory Five Racing

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    Quote Originally Posted by Jim Schenck View Post
    Scotty,

    I couldn't find a wiring diagram for the RJM harness, although Ron Francis sells that harness now and they may have a diagram. The way the harness is built they assume that you have the main power hooked up at the starter solenoid and that never becomes disconnected from the battery, so if that main power loop gets switched off you will lose the keep alive memory. If you do not want to have any circuits powered while the car is sitting or stored then you can just live with the rougher start up by bumping the idle up a little, but first I would get the PCV and fuel pressures set to where it runs the best. And, if you do adjust the idle at the throttle body then you want to re adjust the TPS voltage as it will likely bump up above 1.0 with even a fairly small adjustment.
    Sorry for the delayed response; my work schedule sometimes gets a little hectic. I tried to no avail, removing the PCV valve from the system and plugged the port on the intake. There was initally a change for the better: https://www.youtube.com/watch?v=7j1mQ-tnbk4 but shorty after this video was taken, it started hunting again.

    I did some research on why the check engine light does not work. Apparently there are 3 capacitors in the ECU that sometimes fail, and when they do it can effect the CEL. I took my A9L apart and found that 2 of the three capacitors have been replaced already. With this info, I was able to source a new ECU that should be here Wednesday. The only small issue is that I could only find an A9P. I doubt there will be much of a problem though. I will try that and see what happens. If its not fixed I will try and get a video of it hunting.

    ScottyC

  6. #6

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    Just a basic question ... have you tried moving the Mass Air further from the intake to the Powerdyne supercharger? I found that I needed to have them about 12" apart to allow the Mass air to work well otherwise I also had problems with the idle. Just a thought.
    Ralph Button
    FFR 1436 (PROUD Owner of an Original Mark I)
    400,013 miles as of 11/1/2009
    417,840 miles as of 8/12/2010
    435,021 miles as of 12/19/2011
    Now a well broken in 347 engine
    523,145 miles as of 7/29/2014
    601,165 miles as of 6/1/2018
    615,215 miles as of 4/23/2022

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