Lbcavant

Hi guys, I have a 2008 A4 manual that I bought from the East Coast (wanted a manual, willing to budge for some rust). Im in California and I have replaced all Coil packs, spark plugs, PCV, and the car still has very rough idle. Could this be the injectors due to it being an East Coast car? The HPFP has not been changed. My buddy who is an Audi tech says its most probably the injectors. Im thinking the HPFP. If there is low fuel pressure, wouldnt it cause occasional misfires? Alway comes in Cyl. #2 as well. There are no codes for the fuel pump. I VCDS it. Should I replace fuel pump first or the injectors? Any help is appreciated. Oh car has 144k miles on it, exhaust and DP, not that that would matter.

mitnworb

I have a constant random misfire on cyl 4 in my 3.2L I have replaced my plugs, coils, injectors and just put on a new HPFP. Still there. I did have a mechanic tell me that I have a stuck or burnt valve in cyl 4 so I am debating whether to take the head off or not. It might be worth your time if the new injectors don't fix it to see if you might have the same problem. Also, the easiest way of determining if the injectors are the problem is to just move the injectors around and see if the misfire follows.

lloydieb8

Are you getting any fault codes at all? May I suggest you carry out a compression test wet and dry on each cylinder, this will therefore give you an idea whether it is valve or piston related.

vce1232000

carbon cleaning ?

toitle

Low fuel pressure on either the low or high side will trigger a fault code of it's own, you can also check the duty cycle of each in VCDS. It's easy to check the follower especially on an 08 without that annoying banjo bolt. It seems that you're throwing parts at a car with a potentially unknown issue. More testing, less spending.

Lbcavant

Good advice. Im gonna get carbon cleaning done this weekend coming up, will tell my tech to check the cylinders (compression test). I would hate to put all these parts in the car and end up with the same issue. thanks all!

lloydieb8

Just a thought, when you say carbon cleaning, are you on about an additive that is injected into the cylinders? I personally do not recommend these and they do not clean off as much carbon as you may think, it's just a marketing ploy from my point of view. Just get your tech., to carry out compression tests and work from there as if head has to come off then it's time to do a full De-coke, remove valves clean and RE-seat valves and s rape out and clean ports, maybe even get a reputable machine shop to RE-port the head and pressure test head, hope this helps, all the best.

vce1232000

The type of carbon cleaning Im referring to you have to remove the intake manifold to get to the back of the intake valves and blast with either walnut or soda blasting materials. Or use chemicals and pick tools. The 2.0T engines in this platform are Direct Injection. So using additives has no benefits as it does not see fuel to dissolve the carbon behind that valves. The carbon deposits are from the PCV recirculating oil and moisture back into the combustion process.

lloydieb8

OK that understood, are you doing this yourself? Your Gna need a good vacuum cleaner and make sure those valves are shut tight, hence why if you have any deposits sneaking into combustion chamber it could cause piston/ ring or even bore damage, I would never take this route personally! Just be careful dude and good luck. If you have a badly seated inlet valve and you get debris in the combustion chamber??? You see where I'm coming from? Just get Como., test done prior to any other work, it could be worth it.

vce1232000

When I preform the carbon cleaning I always bring that particular cylinder to top dead center. I usually also have the valve cover off doing other maintenance work. So you can see that it is by the position of both cam lobes on the camshaft. Audi and VW also carbon clean the valves with the same method. But they use walnut shells for the blasting solution