2002 A6 Avant 3.0 Starting Issues
05-03-2018, 09:33 AM
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2002 A6 Avant 3.0 Starting Issues
have a ‘02 A6 that doesn’t want to start on the first crank. It will always start right up on the second try but never on the first. This is a new issues in the last week or so. I am planning on looking at the injectors, maybe there is a leaky one that if flooding the manifold? Anyone have any ideas of what I should look at next?
05-03-2018, 02:50 PM
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Thank you for your suggestion! The starter cranks the engine quickly, consistently, smoothly and has never failed to engage when the key is turned so I am a little skeptical about the starter being the issue. The car will turn over no problem when I try to start it but will not actually fire until I crank it over a second time. Interestingly, I can crank it for 10 seconds and it will make no attempt to fire but if I blip the starter for one revolution, turn the key all the way to the off position then try again it will immediately start. It is almost as is the ECU is not turning on the ignition until it has failed to start once.
05-03-2018, 03:07 PM
#4
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Probably NOT the starter. Could be a failing check valve in the fuel pump, that maintains an amount of pressure in the fuel system to supply the injectors at restart. What happens if you try a restart after a short amount of time? Like if you turn the car off, go into the coffee shop and come out five minutes later and try a start? Will it fire on the first try or do you have to go a second try. Or does it only do this after being shut down for a few hours? Also it would be helpful to pull fault codes.
05-03-2018, 03:52 PM
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Probably NOT the starter. Could be a failing check valve in the fuel pump, that maintains an amount of pressure in the fuel system to supply the injectors at restart. What happens if you try a restart after a short amount of time? Like if you turn the car off, go into the coffee shop and come out five minutes later and try a start? Will it fire on the first try or do you have to go a second try. Or does it only do this after being shut down for a few hours? Also it would be helpful to pull fault codes.
05-04-2018, 06:53 AM
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The 15 minute deal is another strong indicator of a bad check valve. Takes a while for the fuel pressure to bleed off. I am thinking you are due for a new pump.
05-04-2018, 07:25 AM
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05-07-2018, 06:23 AM
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So I measured the fuel pressure at the rail tia weekend and made some interesting discoveries. First, the pump does not turn on when the ignition is turned on! With the key at “run” the fuel pressure was 0 psi. Tried cranking once and the pressure went up to 10 psi and stayed there. Tried cranking again and the pressure jumped to 55 psi and the car started. When I turned the car off the pressure dropped to 44 psi and slowly lowered to 36 over the next 30 minutes. I performed the test with a hot engine and was told to expect the pressure jump to ~65 psi as the residual heat warmed the fuel in the lines. This app leads me to think that you are right about the fuel pump/check valve being bad. I am very confused so to why the pump isn’t turning on when the ignition is on, wondering if it might be a solenoid issue? Thanks for all your help as advice!
05-07-2018, 06:54 AM
#9
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I believe that you should hear the fuel pump buzzing when you turn the key to the run position but not 100% sure. If you aren't sure and can't contact someone who knows for sure you could always try changing the relay first. They cost around $28-$30 depending on where you buy. I am still thinking fuel pump but it is relatively expensive and if you aren't sure it could be worth changing the relay first. Anyone else here want to jump in on this, georgeb944 maybe?
05-07-2018, 06:58 AM
#10
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hey Harleyguy,
So I measured the fuel pressure at the rail tia weekend and made some interesting discoveries. First, the pump does not turn on when the ignition is turned on! With the key at “run” the fuel pressure was 0 psi. Tried cranking once and the pressure went up to 10 psi and stayed there. Tried cranking again and the pressure jumped to 55 psi and the car started. When I turned the car off the pressure dropped to 44 psi and slowly lowered to 36 over the next 30 minutes. I performed the test with a hot engine and was told to expect the pressure jump to ~65 psi as the residual heat warmed the fuel in the lines. This app leads me to think that you are right about the fuel pump/check valve being bad. I am very confused so to why the pump isn’t turning on when the ignition is on, wondering if it might be a solenoid issue? Thanks for all your help as advice!
The reason for all of this weirdness is simple, if the pump runs when the ignition is on and the engine is not running, a break in the fuel supply lines or an injector that is stuck open will lead to, at worst, a fire on a hot engine, or, at least, a cylinder filled with fuel, leading to a bent connecting rod, or a ruined catalytic converter.
That's why the fuel pump doesn't turn on when you turn the ignition switch to on and no further.