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lean surge under boost

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  • Fuel System: lean surge under boost

    R2 Albert Ross is shaping up finally. I do notice that under boost, it seems to lean out, and once I get back down to 0 PSI, it actually pulls harder. Mind you, I've only about 20 miles on the engine, so I am not pushing it yet.

    Ideas?
    Ron Dame
    '63 Champ

  • #2
    Obvious question: is the pressure reference line from the supercharger to the top of the fuel pump present, and not leaking?
    Gord Richmond, within Weasel range of the Alberta Badlands

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    • #3
      FWIW, wideband O2 sensors and meters are so affordable today, I wouldn't attempt to tune or diagnose A/F ratio problems without one and definitely not where a mistake is fatal, as on a supercharged build..

      jack vines
      PackardV8

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      • #4
        Pretty much the obvious stuff -

        Jetting
        Air bleeds
        Fuel pressure
        Float level
        Intake leak (MANY different locations)

        What Jack said.

        Mike

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        • #5
          Originally posted by gordr View Post
          Obvious question: is the pressure reference line from the supercharger to the top of the fuel pump present, and not leaking?
          well, it is in place. Leaking? I'll pop a new one on to see.
          Ron Dame
          '63 Champ

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          • #6
            Originally posted by PackardV8 View Post
            FWIW, wideband O2 sensors and meters are so affordable today, I wouldn't attempt to tune or diagnose A/F ratio problems without one and definitely not where a mistake is fatal, as on a supercharged build..

            jack vines
            I'm only 20 miles in in this build, so before I go that far, I want to see if I've missed something first.
            Ron Dame
            '63 Champ

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            • #7
              OK, the fuel pump pressure reference hose was replaced, no change. The problem did not exist prior to engine rebuild, and it's the same carb, fuel pump, and supercharger. None were touched.
              Ron Dame
              '63 Champ

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              • #8
                I drive a turbo car. It was bone stock when I put the first few miles on it. I have since modified it several ways. I have permanently installed a Wide Band O2 sensor, a fuel pressure gauge and a vac/boost gauge (as well as an oil temp gauge). It now has over 320,000 miles on it.

                When I install the 57 Golden Hawk SC engine into my 53 Commander, I plan on installing a Wide Band O2 sensor, a fuel pressure gauge and a vac/boost gauge.

                I would not wait until I am farther into it than 20 miles before going "that far". There is no other way to know exactly what is going on. In fact, you don't know for certain that it is even lean. It just "feels" lean.

                With those three gauges, you will know exactly what is going on. With a boosted engine, if it really is going lean, you could be only 30 miles into it when you melt something down. I understand that isn't likely, but just being possible is enough to invest in some gauges.

                Could be something else entirely (like timing that changes drastically under boost) but you won't know without gauges.

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                • #9
                  Originally posted by Lynn View Post
                  I drive a turbo car. It was bone stock when I put the first few miles on it. I have since modified it several ways. I have permanently installed a Wide Band O2 sensor, a fuel pressure gauge and a vac/boost gauge (as well as an oil temp gauge). It now has over 320,000 miles on it.

                  When I install the 57 Golden Hawk SC engine into my 53 Commander, I plan on installing a Wide Band O2 sensor, a fuel pressure gauge and a vac/boost gauge.

                  I would not wait until I am farther into it than 20 miles before going "that far". There is no other way to know exactly what is going on. In fact, you don't know for certain that it is even lean. It just "feels" lean.

                  With those three gauges, you will know exactly what is going on. With a boosted engine, if it really is going lean, you could be only 30 miles into it when you melt something down. I understand that isn't likely, but just being possible is enough to invest in some gauges.

                  Could be something else entirely (like timing that changes drastically under boost) but you won't know without gauges.
                  I get that, but It ran great before. The engine was rebuilt due to oil pressure issues. Nothing is significantly different than before except the oil pressure, and now it feels crappy under boost. It's not like I changed cam specs, fueling, ignition... No the only difference is several months and more oil pressure ... And... What?
                  Ron Dame
                  '63 Champ

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                  • #10
                    OK, the fuel pump pressure reference hose was replaced, no change. The problem did not exist prior to engine rebuild, and it's the same carb, fuel pump, and supercharger. None were touched.
                    Ron Dame
                    '63 Champ

                    Comment


                    • #11
                      I understand you didn't do anything different, but SOMETHING has changed, albeit unintentionally.

                      Do you have a Mighty Mite vac pump? Reason I ask, is that it is one of the few that you can reverse; i.e. you can turn it into a pressure pump. With the car idling, pressurize the vac advance cannister and see how it affects timing. Next, put vac to the cannister and see how much it affects timing.

                      At the risk of beating a dead horse, the WB A/F ratio gauge is such a worthwhile investment, if it were me (and it isn't) I would go ahead and install one now to see what is going on with A/F ratio.
                      Attached Files
                      Last edited by Lynn; 05-20-2019, 06:01 AM.

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                      • #12
                        Agreed, something changed. I'm hoping someone will point out something I can quickly find and address. I'll check the vac advance, even though the whole dizzy has under 500 miles since a Dave Tbolt rebuild.
                        Ron Dame
                        '63 Champ

                        Comment


                        • #13
                          Just a thought on a/f gauges. After doing a modicum of study, buy a wide ratio unit with the Bosch 4.9 sensor. The older style and sensors require adjusting and resetting. The 4.9 apparently will work out of the box.

                          Here's some thoughts - https://10carbest.com/best-wideband-gauges

                          Here's the one I bought a couple years back for the 74 Avanti. https://www.amazon.com/dp/B00N3VGPYS...32e3e886432b45

                          Posting this more for general info than anything.

                          Bob

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                          • #14
                            Good choice Bob.

                            Wish I had the AEM. I have an Innovate. Although it uses the Bosch 4.9 sensor, it still needs to be calibrated from time to time.

                            Still, way better then nothing.

                            If I have the car torn up one more time, you can bet I will swap it out for an AEM. Also when I get the 53 up and running with the 57 SC GH motor, I will be using an AEM.

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