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  • Aan engine hard to start when cold

    Gents has anyone ever had any issues with hard to start problem when cold. AAN engine in type 85 chassis, all has been well for many years but in the cold weather car just refuses to start but eventually fires up after persistent cranking. Once started all is fine ,drives well no other problems, no fault codes,no problems when engine warms up. Hopefully someone has had similar issues,many thanks in advance Paul.

  • #2
    If it's only hard to start when cold and runs fine once it's going then it has to be something to do with the cold start fuel enrichment cycle which I believe is governed by the MFTS on the water manifold as well as perhaps the MAF. I'm not an expert on how the Motronic engine management system works but I have pretty good idea of the basics, perhaps someone with better understanding could chime in?. Fuel pump priming issues can also cause the engine to be difficult to start, but then I'd expect it to have the problem all the time regardless of ambient temperature .
    1992 C4 100 2.8 Avant quattro, daily driver.
    1995 RS2, MTM K26/7, 380 BHP conversion.
    1996 C4 2.8 30V quattro, future project car...

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    • #3
      Many thanks for reply,I would say replacing the MFTS probably would be a good start. Will get one ordered and take it from there.

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      • #4
        No worries, happy to try and help. Have a good look at the connection to the MFTS before ordering a new one, as the fault could easily be here, as opposed to with the sender itself. I can't recall if AAN's suffer from the same problem as 3B's and ABY/ADU's where the boot for the connection fill's with water causing the connector block to disintegrate and the terminals to heavily corrode.
        1992 C4 100 2.8 Avant quattro, daily driver.
        1995 RS2, MTM K26/7, 380 BHP conversion.
        1996 C4 2.8 30V quattro, future project car...

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        • #5
          No not the MFTS

          As far as Motronic is concerned, coolant temp is measured by the small white temp sensor at the back of the head. That’s the one the ECU uses for the warm up cycle.
          MFTS just drives the temp gauge and temp warning on the autocheck as well as reducing max boost if the engine is over temp.
          Good news is the little white sensor is cheap and easily available! I’ve seen dzz as made at the wiring plug for this sensor too, worth a look.

          Check or replace the vacuum hoses relating to the fuel pressure reg.

          Clean the maf connector.

          S2 Coupe 3B Project


          Ur quattro restoration

          S2 Avant

          Boost is the new rock and roll!
          sigpic

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          • #6
            Thanks for clearing that up John! I did say I wasn't a Motronic expert.
            1992 C4 100 2.8 Avant quattro, daily driver.
            1995 RS2, MTM K26/7, 380 BHP conversion.
            1996 C4 2.8 30V quattro, future project car...

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            • #7
              No worries mate

              S2 Coupe 3B Project


              Ur quattro restoration

              S2 Avant

              Boost is the new rock and roll!
              sigpic

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              • #8
                Have replaced the white sensor a while back for that reason,but didn’t cure the problem. Will check fuel pressure regulator and hose as well.
                Tryed restarting it after 24 hours again impossible on cold ,eventually starting after a huge backfire .

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                • #9
                  Ok.
                  Just a thought..
                  It’s not old fuel is it? Or been filled with E10 and left for a month or two? Ethanol absorbs water and grows bacteria.

                  Or fuel pump starting to fail?

                  S2 Coupe 3B Project


                  Ur quattro restoration

                  S2 Avant

                  Boost is the new rock and roll!
                  sigpic

                  Comment


                  • #10
                    The huge back fire will be unburnt fuel in the exhaust, so it's getting fuel, whether it's getting a rich enough mixture to fire when cold is another matter... A tiered fuel pump can cause starting problems but as I said I'd expect the fault be more consistent. What pump is the car running, is it still on the old B2 one?
                    1992 C4 100 2.8 Avant quattro, daily driver.
                    1995 RS2, MTM K26/7, 380 BHP conversion.
                    1996 C4 2.8 30V quattro, future project car...

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                    • #11
                      IIRC, if the head temp sender fails it goes full rich, so actually more likely to start when colder... it's a fail safe essentially. It will generate a code, however.

                      As above though, quite possible the fuel pump is failing, or the filter is getting blocked?



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                      • #12
                        Here's an old post of Dave's that if run through like a check-list (he has prioritized items for the AAN). may be of use:

                        https://www.s2forum.com/forum/genera...35#post1077635

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                        • #13
                          That’s a very comprehensive post there from Dave, I’d expect nothing less, as he says a quick squirt of easy start into the throttle body hose would help narrow it down to a fuel supply issue.
                          1992 C4 100 2.8 Avant quattro, daily driver.
                          1995 RS2, MTM K26/7, 380 BHP conversion.
                          1996 C4 2.8 30V quattro, future project car...

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