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Can a cylinder head flow more than the exhaust can handle?

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  • #76
    That's interesting. I think I have heard similar for the 7a. The lambda isn't used on cold starts or at idle, it takes a few minutes of driving (and heater circuit) to get the lambda up to operating temp then it is working. But yes, on w.o.t it makes sense for the probe not to be bringing the afr back to 14.7. I will have a close look at my spare to see if there is any potential that the sensor part of the TPS has any potential for rotation. My throttle butterflies are fully opening but if the TPS sensor is rotated round the wrong way, it will never reach its maximum stroke.

    Good idea.
    Last edited by steve briance; 27th November 2018, 20:44.

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    • #77
      Now, there is something to be checked. Full throttle and see what the signal voltage says, adjust it one way or the other and see if the signal changes. Now, what it 'should' be is to be found out but it is a good idea for sure. Cheers!
      Attached Files

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      • #78
        Originally posted by steve briance
        Now, there is something to be checked. Full throttle and see what the signal voltage says, adjust it one way or the other and see if the signal changes. Now, what it 'should' be is to be found out but it is a good idea for sure. Cheers!
        There will be a correct procedure in the manual somewhere!

        S2 Coupe 3B Project


        Ur quattro restoration

        S2 Avant

        Boost is the new rock and roll!
        sigpic

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        • #79
          The interweb knows.

          This will have to wait till the weekend to do but i noticed that the spare in the photo has paint seals in place on the screws which secure the sensor to the body. They haven't been disturbed so this one should be in the correct position. It is a delicate balance to strike as there is a micro switch built into it which is the idle switch. If any adjustment is made, this has to click on closed throttle....

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          • #80
            found it.

            Attached Files

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            • #81
              Update time.

              The parts turned up to make a gauge to measure back pressure and a wind speed meter to measure gas flow.

              The pressure gauge was simple to do - lambda probe boss, tapped to take a threaded boss with pipe brazed on, silicone hose to the dial which reads 0-15psi. Sadly, this read pretty much nothing so no figures from that. I am not sure why, you might think it was because back pressure was so low however holding hand over tail pipe certainly built up enough pressure to move my hand yet still nothing on the dial.

              The exhaust gas speed was more successful. Anemometer from ebay for £8, mounted in a plastic tube to direct flow and protect from ambient wind. The meter can be switched between mph/kph/knots and usefully - peak speed...

              I also made a bung to close off one of the tail pipes as when testing the flow without back box I was going to be measuring off one pipe so it seemed right to do so when the back was on. and yes, that is gaffer tape holding the tube in place - it kept popping off otherwise. Low tech is sometimes the best tech.

              I measured at idle, 2000, 3000, 4000 and 5000rpm and did 3 runs at each to get an average just in case i stopped either slightly short or slightly over the target rpm.

              I drove to a quiet spot out in the countryside to measure with no back box, it was unsurprisingly VERY noisy and i have to live next door to my neighbours!

              Results in meters per second:

              back box on.
              idle 2.36
              2000 4.33
              3000 6.56
              4000 9.16
              5000 14.4

              no back box.
              idle 3.6
              2000 6.1
              3000 9.6
              4000 14.2
              5000 19.4

              Interesting reading! Whether or not the exhaust is causing the issue with the maps i don't know but it looks like there is some benefit to be had from changing the back box to one without any baffles in the flow. Once this is sorted i shall be on my way back for a revisit....


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              • #82
                Errrr....... Where is the video of the unsilenced 7A?
                Panthero Coupé quattro 20vt
                Indigo ABY coupé
                Imola B6 S4 Avant

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                • #83


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                  • #84
                    There is only one thing for it - back you go, try again
                    Panthero Coupé quattro 20vt
                    Indigo ABY coupé
                    Imola B6 S4 Avant

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                    • #85
                      Originally posted by Error404 View Post
                      There is only one thing for it - back you go, try again
                      Looking forward to these 20 valves at full chat.
                      96 URS6 plus speck saloon
                      96 URS6 plus speck estate
                      94 2.6 80 Avant
                      99 2.8 final edition Cabriolet

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                      • #86
                        I reckon my original 7A exhaust has zero baffles in it by now, they do sound lovely

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                        • #87
                          New rear silencer being made on 18th December and while waiting for that, im doing some electrical testing today...

                          Resistance values from TPS are within spec so I went on to check voltages. Book says pin 1-2 should be 4.5-5.5volts, pin 1-3should be same. I wasn't getting anything testing pin 1-2 but was between 1 and 3 as well as 2 and 3 so I dug deeper...

                          It seems before my ownership someone had cause to repair the wiring to the TPS right up by the bulk head. Wondering if there was a possibility that they could have got the wires the wrong way round I consulted a spare TPS to ge the pin number order.

                          What do you think? Bear in mind the pic of the plug is 'reversed' when it plugs onto the TPS. Do. You think my wires have been the wrong way round ever since I have had the car?

                          !
                          Last edited by steve briance; 9th December 2018, 12:56.

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                          • #88
                            Steve,

                            If you suspect the wiring positions may have been altered, can you confirm your current arrangement against the Bentley's schematic wire colour-codes?

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                            • #89
                              Not easily unfortunately. The factory diagram tells me that connected to G69 (tps) there is brown and green to pin 2 (I have this in the correct place) but then black to each of the other two pins from the ECU. In the car I have a black wire and a black with brown tracer. If the diagram mentioned the black/brown wire then it would be a lot easier to resolve...

                              There is a test procedure for checking wire continuity from plug back to ECU but this might have to wait until I go back to the tuner. The ECU has to be dug out from the dashboard anyway.

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                              • #90
                                Hunting for ghosts...

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