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Thread: Fuel Air ratio changes.

  1. #1
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Fuel Air ratio changes.

    I dynoed at 18 psi and came up with very good fuel air rates. I noticed that at 24 psi they had gotten richer. Is this a function of the mptune program accomodating the increase in boost? I imagined it would stay the same throughout the rpm and boost range.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Fuel Air ratio changes.

    My fueling has gone bonkers. I just turned it down to 17 psi and it's 10:1 @ full throttle and boost. At the dyno it was mid to upper 11's. Checked all the vac lines/OK. Fuel pressure 55 psi rises to 72-74 psi. I dont know where to look next. Tune is the same as at dyno.
    Last edited by jeff1234; 04-29-2021 at 07:50 PM.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Fuel Air ratio changes.

    Today I burned a chip to use in the lm instead of the Ostrich in case it was screwing up. The car ran the same, going instantly to 10:1 as soon as boost started to build. It seems unlikely that the fuel pressure regulator has a problem, it got a new diaphragm and spring last summer. The car idles at 14:5_15.3 to 1 and looks normal at part throttle. I also changed out the TPS, no change. Can anyone tell me what else might cause this over fueling?
    Last edited by jeff1234; 04-30-2021 at 11:28 AM.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Fuel Air ratio changes.

    Perhaps an obstruction in the return somewhere? Could the MAP be bad? No codes, I presume?

  5. #5
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Fuel Air ratio changes.

    I took the Accufab FPR apart yesterday and could find no obstruction or even some little piece of junk that might be keeping the disk off of the seat, no problem there. Concerning the map sensor, the pressure is being reported on MPScan so it seems unlikely. Is it possible for MPScan to report the pressure even with a bad map sensor? I wouldn't think so but maybe you have heard of this happening. No codes, goes straight to 55.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Fuel Air ratio changes.

    Well, I solved the problem today. As I adjusted the FPR this morning I thought the engine just didn't sound right so I decided to check timing. I disconnected the waterbox sensor and put the light to it. To my great surprise, the timing mark was barely visible at the left edge of the timing window. That was also a little disconcerting because I think the timing belt jumped a tooth. This, inspite of the fact that I went to great lengths to be certain the marks were all aligned, used the factory tool on the belt tension and turned the engine through a couple of turns to be sure. This happened during my oil pump replacement. I re-timed the engine and took it out for a test. Voila, it goes like hell somemore . Now, I need to take the front dress off the engine and do the process again if for no other purpose than to check things over. I had to turn the distributor counter clockwise to time it and the position of the distributor doesn't look normal. Does this mean that the cam is advanced or retarded.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  7. #7
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Fuel Air ratio changes.

    Quote Originally Posted by jeff1234 View Post
    Well, I solved the problem today. As I adjusted the FPR this morning I thought the engine just didn't sound right so I decided to check timing. I disconnected the waterbox sensor and put the light to it. To my great surprise, the timing mark was barely visible at the left edge of the timing window. That was also a little disconcerting because I think the timing belt jumped a tooth. This, inspite of the fact that I went to great lengths to be certain the marks were all aligned, used the factory tool on the belt tension and turned the engine through a couple of turns to be sure. This happened during my oil pump replacement. I re-timed the engine and took it out for a test. Voila, it goes like hell somemore . Now, I need to take the front dress off the engine and do the process again if for no other purpose than to check things over. I had to turn the distributor counter clockwise to time it and the position of the distributor doesn't look normal. Does this mean that the cam is advanced or retarded.
    It all depends. One could just be off on the intermediate shaft, while the cam and crank are lined up properly. I never used the marks on the crank and int. shaft sprockets. I just use the timing mark on the flywheel and the arrows on the cam gear with the seam in the cam caps. I make sure the rotor is pointed at cyl. #1 and I'm off to the races.

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    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Fuel Air ratio changes.

    That seems alot simpler therefore less prone to error. Thanks for your assistance.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  9. #9
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    Re: Fuel Air ratio changes.

    Yup, if the intent is to simply get the distributor in a good spot for setting timing, having the rotor point at the 10:30 position is perfect. I've found if the rotor points at the #1 spark plug the distributor body is canted more than I care to have it.
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