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so I have this A8 with bank 1 and bank 2 lean condition codes.
fuel pump, injectors and o-rings, PCV valves, MAF sensor, vacuum hoses, all checked and/or replaced thoroughly. o2 sensors are all replaced withy genuine audi parts
what happens now is;
I reset the CEL, do a set readiness test through VCDS, all systems pass flawlessly.
I did a roadtest while observing group 32 Long term Fuel trim, Bank 1-2 partial adaptation values rise above 15% in about 10 km/6 miles, and after 3 stop and starts or 50 miles-80km’s, CEL comes back on.
when CEL comes back on, engine runs rough and vibrates between 2000-3000rpm.
driving around 50-60mph/80–100kmh; throttle is irresponsive until it is floored, engine vibrates and it doesnt want to rev. but as it goes past 2800 rpm, it feels like a big giant turbo kicks in (which doesnt exist in this car) and the engine revs and goes like it should be.
so long journeys are a pain in the **** in this car right now.
whats your take on this? what happens at 2800rpm on this engine?
The system is designed so the RHS (passenger side for USA) works all the time and the left pump comes on under load, or to move fuel over, as well as coming on for exactly 30 seconds on start up.
The easy way (and a great way to get home once the pump actually fails) is to pull the left fuel pump relay, then use a bridge wire to force it to work constantly. The fuel pump relay is directly above the battery.
Clear your codes and see if it drives better.
If it does, replace the main pump.
The left pump only does about 30% of the work of the main one which is why your engine comes good when the RPM turns it on.
The system is designed so the RHS (passenger side for USA) works all the time and the left pump comes on under load, or to move fuel over, as well as coming on for exactly 30 seconds on start up.
The easy way (and a great way to get home once the pump actually fails) is to pull the left fuel pump relay, then use a bridge wire to force it to work constantly. The fuel pump relay is directly above the battery.
Clear your codes and see if it drives better.
If it does, replace the main pump.
The left pump only does about 30% of the work of the main one which is why your engine comes good when the RPM turns it on.
Mike
that seriously makes great sense. they said they checked the fuel pump and it worked well, but I’ll look into it and I’ll let you know.
it definitely drives better when I erase the codes, and when the CEL comes back on, the car suddenly feels like it’s running on 6 or 7 cylinders despite having misfire codes, and a significant yet slight tremor/shaking at between 1600-2800 rpm, as it goes past 2800-3000rpm, it performs great, business as usual.
The system is designed so the RHS (passenger side for USA) works all the time and the left pump comes on under load, or to move fuel over, as well as coming on for exactly 30 seconds on start up.
The easy way (and a great way to get home once the pump actually fails) is to pull the left fuel pump relay, then use a bridge wire to force it to work constantly. The fuel pump relay is directly above the battery.
Clear your codes and see if it drives better.
If it does, replace the main pump.
The left pump only does about 30% of the work of the main one which is why your engine comes good when the RPM turns it on.
Mike
forgot to add;
with many other repairs, fuel pump has also been examined. the shop told me that it had dirt and mud-like things in it, but they had it cleaned and tested the fuel pump pressure and it was alright.
but they never mentioned there were 2 of it, and what kind of a pressure test they did and the result of that test.
How old is the fuel filter? It's easy, cheap and will need to be done anyway. Solved my similar lean codes problem (I think; it's only been ~100 miles).
-Tom
with many other repairs, fuel pump has also been examined. the shop told me that it had dirt and mud-like things in it, but they had it cleaned and tested the fuel pump pressure and it was alright.
but they never mentioned there were 2 of it, and what kind of a pressure test they did and the result of that test.
The VDO pumps in these cars are quite impressive and will give you warnings before failing.
In my case, I had a misfire and engine lacking power after about 3 hours of highway. Then the main pump would give low pressure. a couple of weeks later, I sent the car to Audi who tested the pumps and told me they were fine.
The next weekend, the main one failed completely after I was about 4 hours from home.
These pumps give you about a month to change them before giving up completely. Heed the warning.
The system is designed so the RHS (passenger side for USA) works all the time and the left pump comes on under load, or to move fuel over, as well as coming on for exactly 30 seconds on start up.
The easy way (and a great way to get home once the pump actually fails) is to pull the left fuel pump relay, then use a bridge wire to force it to work constantly. The fuel pump relay is directly above the battery.
Clear your codes and see if it drives better.
If it does, replace the main pump.
The left pump only does about 30% of the work of the main one which is why your engine comes good when the RPM turns it on.
Mike
I owe you a beer mate.. seriously..
I plugged the car to VCDS yesterday, Group 106, went on for a drive..
transmission manual mode, 4th gear, gentle (%10-15) throttle.. start at 2000rpm.. the car accelerates and revs up to 3200 without incident, Electric Fuel Pump 3/4 remains OFF..
transmission manual mode, 4th gear, hard (%40-50) throttle.. start at 2000rpm, car revs to 2800 and as soon as it reachs that rev, it's like something kicks in inside engine and the acceleration is more rapid, that's the exact moment when Electric Fuel Pump 3/4 kicks in
...so the erratic acceleration curve and LEAN Code is because of that I guess.. I'll look into it and let you guys know.. thanks a lot guys..
I bought a new genuine fuel pump from the states and had it posted to me (including the crap currency exchange) for less than half of what the dealers wanted for one.
I changed the pump myself. The procedure is actually pretty simple and completely outlined in the tech manual. PM me for a link of it f you need.
thank you sir. car is in the shop right now, first it’ll go to a highly experienced ecu guy.. I’ll keep this post updated for future use of people with same problems.
do you think I should change both pumps? I was quoted USD500 for each one. and I’m pm’ing you for details right now.
Originally Posted by mcs
No worries.
I bought a new genuine fuel pump from the states and had it posted to me (including the crap currency exchange) for less than half of what the dealers wanted for one.
I changed the pump myself. The procedure is actually pretty simple and completely outlined in the tech manual. PM me for a link of it f you need.
10-04-2019, 08:24 PM
What happens at 2800rpm? (D3 4.2 40V Engine)
