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I have an Audi A4 Quattro 3.0L. Previously I had P0171 and…

Hello I have an Audi A4...
Hello
I have an Audi A4 Quattro 3.0L.
Previously I had P0171 and P0174.
I was told I should check for vacuum leaks.
I purchased a smoke machine and check for leaks.
No leaks.
After I put everything back together I drove to store and fast food (about 5 miles).
No difference in how it ran.
I erased the codes.
After erasing codes and driving it the car ran really rough at idle and stalled a few times.
I checked the codes when I got back,
I know have p0300, p0301, p0302, p0303, p0304, p0305, and p0306.
I checked my work since I disconnected the air intakes and the MAF to see if it needed cleaning.
I did find one air connection underneath the intake and re-connected that.
Everything looks good to me and I still have these codes.
I understand these are random cylinder misfires.
But I don't know where to start.
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Answered in 7 hours by:
10/2/2017
Matt
Matt, Engineer
Category: Audi
Satisfied Customers: 23,069
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello

to get the lean mixture codes and then a persistent misfire I'd say its possibly a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

And one other thing to try is to loosen off the fuel filler cap, as there’s a 1 way valve built into the cap to let air into the tank and so prevent a vacuum from being created as the fuel leaves the tank to the engine
If this helps then replace the cap with a new item

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Customer reply replied 7 months ago
How do I check that its relay switches in and out? Will there be a sound?
Can I measure voltage with a meter?

Hello

you can usually 'feel' the relay click by holding onto the top whilst your assistant flicks on the ignition

or you can measure for voltage at the pump - which is the better route

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Customer reply replied 7 months ago
Hello
I took the rear seat out and had my son flick the ignition. I hear the pump buzz.
I can hear the click of a relay.
I also rode down the road and can hear the hump of the fuel pump get louder as I go faster.
Feels to me like fuel is getting there.
But maybe a test of pressure at injector rail?

Hello

yes thats the best method

as even though the pump is running it may not be delivering enough pressure due to a blocked filter or a faulty regulator, or even just plain old worn out

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Customer reply replied 7 months ago
I have google'd and physically looked for the place to hook a Fuel Pressure Tester Kit.
They say it should be at the end of my injector rails but I don't see a schrader valve.
Some say I may need to splice in the rubber hose?
I've attached what I think is the feed line in to the rail.

hello

that certainly looks like the feed point, if you were to remove the plastic engine cover you should be able to confirm this by checking the metal pipe forms the injector rail

some models had the schrader valve some did not

if you don't then yes you have to add the gauge with a Tee piece on the feed pipe

Matt
Matt, Engineer
Category: Audi
Satisfied Customers: 23,069
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Customer reply replied 7 months ago
I think it's more likely that I found my issue.
And it's not fuel supply related.
I changed my plugs Saturday and found oil in most all the spark plug wells.
I'm planning on replacing the valve cover gasket this weekend.
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Matt, Engineer
Category: Audi
Satisfied Customers: 23,069
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Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing

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