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HELP!! Car won't start! Cranks fine.. I'm seriously baffled now!

Discussion in 'A6/S6/Allroad forum (C5 Chassis)' started by v12bug, Sep 23, 2012.

  1. v12bug
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    v12bug Audi A6 Avant SE V6

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    Hi

    My 2000 Audi A6 2.8 30v APR engine will crank fine, but is just not starting. The main issue is the 'fuel pump' does NOT prime / turn on when you turn on the ignition key. The car has been running absolutely fine previously, but this happened after I replaced all the vacuum lines (they were seriously brittle / broken) don't think that's related though?

    Anyway things I've done thus far :

    1. Replaced Fuel Pump Relay (although original tested fine)
    2. Replaced Fuel Pump fuse # 28 (although tested fine)
    3. Tested 12v power at the relay panel - fine
    4. Measured voltage at fuel pump connector (across pins 1 & 4) - 12v ok
    5. Bypassed Fuel Pump Relay to provide 12v directly to Fuel Pump (Fuel Pump activates just fine!)
    6. VagCom engine output tests carried out - can hear fuel pump, fuel injectors spray, solenoids etc.. - all seem ok.
    7. Replaced Crankshaft Sensor (although original tested fine with Vagcom) - Get ~ 160/200 Engine RPM when cranking engine
    8. Removed Throttle Body, cleaned, re-installed and did adaptation with Vag-com.
    9. Added 10L of fuel as car was low on fuel (always put in high Ron fuel - Momentum 99)
    10. Tested all other fuses in side panel - all ok.
    11. Tried cold-booting the car. Remove both battery cables from the battery, shorted the battery cables together (away from the battery) for about 20 secs

    12. NO vag-com engine error codes displayed at all.


    For some bizarre reason the fuel pump relay is just NOT activating the fuel pump when turning on the ignition key.

    I've read when some of these cars are started the ECU/ECM looks for a signal from the crankshaft sensor. If it missing it will not activate the fuel pump relay - preventing it from pumping fuel in case of an accident where a fuel line gets ruptured - but I've already replaced the Crankshaft sensor, and tested it with Vag-Com to no avail.

    Next, I thought it might be the ECU relay, but could not locate it in the ECU Box Plenum Chamber under the windscreen, in fact nothing there other than the ECU itself - then phoned Audi who confirmed my particular engine does not have one!

    Things it could be? -

    1. Ignition switch - although all electrics work fine, windows etc
    2. Starter relay - although can't locate it
    2. Air lock in fuel delivery - accidently opened a fuel line when removing the throttle body, spilt a little fuel, but put the hose back on..
    3. Should I try spraying some 'easy start' ....?
    3. Fuel pressure regulator
    4. MAF

    But I don't think any of the above would prevent the fuel pump relay from turning on when the ignition key is turned on? There is NO sound at all emanating from the fuel pump when the ignition is turned on...

    Any advice much appreciated!


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  2. v12bug
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    v12bug Audi A6 Avant SE V6

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    thought I'd just try something. Disconnected battery. Removed ECU, cleaned connectors with electrical cleaner and refitted - then reconnected battery, and did a TBA (throttle body adaptation)


    Now, the fuel pump primes when turning on ignition!


    Fuel pump Fuse #28 went on then off, with ignition key, and now stays on whilst cranking. Fuses 29 & 34 (engine management) give +12v with cranking also. (tested with test light)


    Still - no joy, cranks but doesn't turn over..


    thinking the engine 'might' be flooded - I tried pulling the pump fuse and cranked the engine with a wide open throttle for ~15 seconds, then replaced fuse and waited for a mo. I then tried and it fired up!


    BUT, it is idling very badly / engine popping / misfiring... - without putting your foot on the gas, it cuts out. Still no engine errors codes reported in vagcom, which seems a little strange.


    wondering if when i replaced the vac lines, I put the vac line from the fuel pressure regulator back on wrongly - at the mo it goes straight to the EGR Vacuum Solenoid Valve via a t-piece. Should the vac-line from the fuel pressure regulator go via the non-return check valve, then onto the vacuum solenoid?

    Can anyone quickly check theirs please..?


    Although, I don't think this has a bearing on why the engine is mis-firing - but nothing else other than the vac lines has changed, since it ran last ok..


    Thinking now I could have faulty fuel injectors and / or ignition HT leads...?
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  3. v12bug
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    v12bug Audi A6 Avant SE V6

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    So, as above just require some confirmation on the vacuum lines on my Audi A6 2.8 30v.

    Should the vac-line from the fuel pressure regulator go via the non-return check valve (part # 433 862 117) blue/black valve, then onto the vacuum solenoid? ..
    wondering if when i replaced the vac lines, I put the vac line from the fuel pressure regulator back on wrongly - at the mo it goes straight to the EGR Vacuum Solenoid Valve (part # 026 906 283 H) via a t-piece - gold colour solenoid in pic.

    After doing the vac lines it is idling very badly / engine popping / misfiring... - without putting your foot on the gas, it cuts out.
    No engine errors codes reported in vagcom, which seems a little strange.. Could someone quickly please check their vac lines for me.. many thanks

    Audi EGR Vacuum Solenoid Valve - 026 906 283 H (gold colour solenoid)
    Audi Non-Return Vacuum Check valve - 433 862 117 (blue/black check valve)

    vacuum lines.jpg
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  4. warren_S5
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    warren_S5 Moderator Staff Member Moderator

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    Plugs? Coilpacks? Air leak on induction side (check all hose connections and pipes)

    When were plugs changed last?
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  5. v12bug
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    v12bug Audi A6 Avant SE V6

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    thanks guys for the replys - finally sorted out the issue with the rough idling / mis-firing etc.


    I had taken off the throttle-body for a good clean, and failed to screw it back on properly with the gasket - doh!


    I sprayed some intake cleaner around the engine to see if they were any vacuum leaks, and there was a significant leak around the throttle body!


    Many thanks for all the tips, but just a heads up -


    If you ever encounter any rough idling . mis-firing, please first check your vac pipes (replace with silicone, very cheap) and then clean and 'carefully' put back your throttle-body and do a TBA.


    Engine is now running better than ever. :)
    #5

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