2001 A4 Avant Quattro V6 2.8L

This is boggling me.

Car idles fine and runs fine at low rpm but I can tell its hurting for power.

Freeway driving and I stomp on the throttle and the car bogs down (like a jake brake) and you can hear pinging. I have to pull off the throttle and then ease it back again for fear of trashing the engine and the car just dying.

So I've chased this thing and replaced:
Fuel Filter
Vac Lines
Temp Sensor
New Plugs
Cleaned MAF with proper cleaner

I thought maybe injectors or fuel pump may be suspect since this issue seems to be from running lean, but after reading codes which are mostly cylinder misfires, I clear the codes and the car comes back to life and runs great...until the issue comes back a few hours later.

No codes in relations to cats or o2 sensors

What am I missing?

Is this an electrical issue?

 

Damn! I had cylinder misfire issues too, but I can't remember the fix.

If you're not getting specific codes, I would continue chasing down the basics: Fuel, Air, Spark, Cats/O2 Sensors.

You're getting restriction somewhere. Check all of the intake piping and the air filter. See if you find anything there. If that's fine, check the plugs and coil packs.

I'd also Seafoam everything, just for good measure.

G/L

 

What cylinders are misfiring? Always the same ones? If so, move your spark plug wires around and see if it follows the wires, or stays with the cylinders. If it follows the wires (you didn't say you swapped them), get new wires, if it stays on the cylinders, post back and I'll tell you where Togo from there.

Also, is it always the same side (bank)?

 

Hi,

I had a similar problem albeit on a a4 1.8, but I'm sure I read some where that the v6 motors had/have the same problems,

like mine it had lack of power when putting your foot down, no faults shown on diagnostic scanner.

I never had it but apparently it can give you a misfire if I remember correctly depending on severity,

and on mine i found that it was the intake manifold change over valve....the connecting plastic push rod from the motor to the connecting plastic cam that moves the cylindrical tube 90 degrees inside the inlet manifold half of the bottom end of the rod snaps off, causing the vehicle to bog down as it does not get full air flow when putting your foot down, and on mine it caused a vibration through out the car/engine bay.

 

and Im sure i have seen some replacement rods for the v6 models (if it is this that this is your problem),

apparently the rods snap/break some people say due to a defect in the material and or there has been a misfire on the vehicle and some carbon build up occurs on the cylindrical inlet tube seizing it up so to speak unable to move when the motor it trying to move it and the rod snaps. apparently you can strip and clean them but i have not done this yet.

 

Plug wires are fine, swapped around and misfires continue on cylinders 1,2 and 3. I even checked the coil by swapping wires to opposite side. Same same, misfires continue on cylinders 1,2 and 3.

So to date, I've replaced:
fuel filter
vac lines
temp sensor
cleaned MAF
New Spark Plugs
Checked plug wires
Checked coil
Ran fuel line cleaner a couple of times.

Right after I posted this thread a couple of weeks back, while chasing this issue, I cleared the codes and the car sprang back to life for a close to a week. I thought I fixed it. However, it's now back to the same issue with no power and crap gas mileage.

It's been suggested that it might be a worn cam tensioner since the issue is on Bank 1, but I have a feeling that is not the case. No noise at all to indicate sloppy tensioner and it wouldn't correct itself from code clearing for a week.

I'd submitted to bringing the car into a German Car specialist and they will run a diagnostics on the engine since my cheapo POS code reader will not tell me whats really up. I sure hope its a knock sensor or something.

 

It's definitely not the cam chain tensioner. If it was you would HEAR it. I just had mine replaced. It sounded like a tractor. lol

If it runs good after clearing the codes, it has to be a sensor. Have you replaced your vehicle speed sensor or cam speed sensor?

 

No I haven't.

Got so frustrated I went to a shop and they ran diagnostics on a high end diagnostic unit.

Came up with these codes:
PO300 random misfire
PO301 cyl 1 misfire
PO302 cyl 2 misfire
PO303 cyl 3 misfire
P1476 Evap detection
P1143 Load calculation crosscheck upper limit exceeded (intermittent)
P1429 Brake boost vacuum system mechanical malfunction

Now to narrow it down to what is actually going on. Could be a vac leak but where? Brake booster has vacuum. Suggested a head gasket leak, but I think we'd see coolant in the oil as well as oil and coolant leak on the side on passenger side of engine.

Evap leak is probably gas cap or canister, but that shouldn't cause the loss of power issue I think.

P1143 seems like a result of whatever the problem is...I think.

 

If you have vacuum to the brake booster, then it's not a vacuum leak.

Like I said before: It has to be a sensor.

Whatever is throwing the P1143 is definitely the culprit, because it says "intermittent" and you said it runs fine when you clear the codes. That has to be a sensor somewhere.

Check your Throttle Pedal Position Sensor and your Throttle Pedal Position Sensor 2

If it's not those, try your Check Angle Sensor 1 for Throttle Actuator and Angle Sensor 2 for Throttle Actuator.

If those don't solve your problem, then you more than likely have a bad ECU.

I'd try finding a ECU that you can use to test with before you go diving into the other stuff.

G/L

 

Cool...will do, but I do have to say that I think I mislead on the code clearing and running fine thing. I've cleared the codes many times with no change in performance. It just seems that when I'd performed a couple of things like Fuel filter and temp sensor changes, then cleared the codes, that is when the car ran fine for a period of time.


Which now that I say it out loud, maybe I'm on to something. If I make some kind of change to the running performance of the engine, seems like the computer or a sensor is picking up on the change and correcting whatever it is that is hindering the performance. Then, it somehow reverts back to limp mode in time. hmmmmmmm