hjeff

2002 Audi A4 1.8T Quattro

Just recently, I ran into a problem with the Audi and would like to have some advice.

Symptoms:
The car accelerate slowly and gradually if the gas pedal is pressed lazily and will maintain any speed, however, if the gas pedal is pressed in a hurry, the engine vibrates, and the car hesitate. The engine and EPC light is also on.

Therefore, I got the car on the scanner and received those two diagnostic errors:

P0304 Cylinder 4 Misfire Detected
P0688 ECM/PCM Power Relay Sense Circuit

So far, I have cleaned the throttle body, checked the MAF and tested each spark-plug to ensure that they all fire up when the engine is cranked – (Coil pack seems ok). I still have the same Symptoms.

What should be verified next?

(I’m trying to avoid brining the car to the dealership, as everyone else, the money is a bit tight, and would rather fix it at home).

Pete@ECSTuning

How many miles are on your plugs. I was getting the same P0304 error until I changed plugs. Also, check your wires for premature arching, IE: melted or worn through wiring.

hjeff

The plugs are 1 year old, but the wires are older. Thanks for the input, i'll give that a shot.

AudiDriver

Hey ECS Tuning - Sales, when you say "/wires", are you talking about the wiring harness assembly inter-connecting all ignition coils? If so, my local Audi dealer (ya, I know) informed me this was a one piece entire harness assembly that connects all the way to the control module; expensive. Any other alternatives to resolving a wire issue if this is the case for hjeff?

The reason I chime in is because a week ago, after getting my 2002 A4 1.8T Quatrro (114K MI) back from a minor rear-quarter panel dent repair, I started getting rough starts during the 1st minute of idle. Now I know my Audi will do this for the catalytic convertor, however, this time it felt like a misfire. Vag-Com pulled codes:

16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - Implausible Signal - MIL ON
16687 - Cylinder 3: Misfire Detected
P0303 - 008 - Implausible Signal - MIL ON
16688 - Cylinder 4: Misfire Detected
P0304 - 008 - Implausible Signal - MIL ON
16686 - Cylinder 2: Misfire Detected
P0302 - 008 - Implausible Signal - MIL ON

But after 10 seconds of abnormal rough idle, my car idled normally. I keep up on my 02 pretty well (new plugs, new ignition coils, etc) so it took me back a sec. Then I noticed that the wiring harness on coil 2 was touching the valve cover and had exposed the harness wiring (the black insulation cover had pealed or pulled back from the harness exposing the inner insulated wire pairs which still kept their insulation). No actual bare copper or silver wiring had touch the valve cover but I wrapped the wires pairs with black electrical tape as the harness cover should. Started the next morning and consecutive mornings aftewards with no misfires.

Long story short, 1) this may be the case for hjeff and his ignition wire harness (meaning opens or shorts), and 2) any other cost effective PM aside from replacing the entire harness assembly? I'd actually love to replace several harnesses and remove any variables that have built up over 7 years and engine/turbo heat under the hood, but man that gets costly...

2004_audi_a4_1.8t

p0304-cylinder 4 misfire
p0688-motronic ecm power supply relay-j271

hjeff

I opened the e-box plenum chamber, there is nothing suggesting J271, however, as per the ebox diagram, the voltage supply relay is at position 3, and this relay switch has number 219 on it...

The relay switch is $75.00 – Before I go purchase one, how do you test if it is indeed the root of the problem??? It doesn’t look burnt or damaged?!..!

Turtle Power

If you haven't already - double check the coil by moving it to another cylinder and see if the misfire moves with it.

Potentially it could just be the coil causing the probs and leading to other indicated problems.

If the misfire does not move with the coil then you will definately know the problem lies else where!

Pete@ECSTuning

No we don't sell wires separately. Your dealer informed you properly. BUT, I'd check for the exact issue you've already mentioned. If the wires (wiring harness) has been seating wrong and rubbing/melting on something hot for a while you may have some arcing issues, just like you've had.

Sorry for the confusion, I'll edit that.

AudiDriver

Cool. Thank you ECS.

hjeff

In the ODB codes, it also says that it could be a faulty exhaust valve. So after a bit of reading, some suggested to use the Seafoam to clear the engine ...

What are your thoughts?