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View Full Version : 3.0T Missfire debacle...



grmnmusl
05-03-2024, 03:54 PM
So I have a 15' A7 Prestige 3.0T and car has 179K had since 85K car been rock solid.

That said 2 weeks ago Sunday I switched out of comfort and stepped down...... puff and Check engine/EPC follows.
I get home 2/4/5 cylinders misfire. Change and gap 6 new plugs, cylinder 5 misfire remains. I swap coil from cylinder #1 to #5 and the inverse and misfire remains....I know I know.
Car does not burn any oil more than usual (no smoking), didn't do compression test at this point.

I pull charger, intercooler cores not leaking visually inspected plus never had to add coolant and intake clean valves not much carbon as previous done as part of PPI. However upon further inspecting I see that Audi tech who did carbon cleaning failed to see one o-ring stuck in the rail and installed a 2nd on the injector itself. At this point I remove the remnants which has since been dislodged and most likely parts forced into injector. This being the culprit cylinder I assumed I dodged the bullet as it was sideways blocking fuel path and put her back together

....Once again cylinder #5 misfire remains. I tear her down again down put a good non misfiring #6 injector into #5 cylinder and I got a spare injector from a friend and put into #6 cylinder.

Fire her up and #5 cylinder still has a misfire upon startup. I am doing compression test tomorrow 5/4.
VCG good and not leaking.
Intake valves all seat as I had cleaning agents in there for 2-3 hours while cleaning carbon which wasn't much.
I have no other codes besides secondary are which we all know what that is. Could it be related to one cylinder?

ALL, comments guidance and or advice is welcome. Fuel trim on bank 2 look a bit off based on down stream but again no codes!

HELP PLEASE!

If post is in wrong area please move!

Mister Mike
05-04-2024, 09:09 AM
Possibly a broken valve spring in cylinder #5?

grmnmusl
06-19-2024, 03:11 PM
Update.... Cylinder 5 exhaust valves springs damaged/bent. Mister Mike called it!

- - - Updated - - -

You called it bro!

WittyWookiee
06-20-2024, 11:29 AM
Update.... Cylinder 5 exhaust valves springs damaged/bent. Mister Mike called it!

- - - Updated - - -

You called it bro!

The dreaded cylinder 5 misfire…

Botbasher
06-20-2024, 01:32 PM
The dreaded cylinder 5 misfire…

Interesting video on spring breakage from Steve Morris. When you said you changed out of Comfort and stepped on it, it sparked the connection.

TL-DW: Springs have a resonant frequency that when they stay at for extended periods it can destroy them.

Makes you never want to use cruise control again!! [o_o]

Cheers,

KS

Mister Mike
06-20-2024, 02:27 PM
Glad you figured it out! I wonder if that was the problem with my S6 too, as I couldn't get the Cylinder 5 misfire addressed with coil packs/plugs either. With the 4.0TT it's an engine out scenario just like injectors, I wasn't willing to go there and unloaded the car instead, just posted that update.

Botbasher
06-23-2024, 06:20 AM
Glad you figured it out! I wonder if that was the problem with my S6 too, as I couldn't get the Cylinder 5 misfire addressed with coil packs/plugs either. With the 4.0TT it's an engine out scenario just like injectors, I wasn't willing to go there and unloaded the car instead, just posted that update.4.0tt Cyl 5 misfire is a well documented issue relating to turbo back pressure and valve float.

An upgraded exhaust manifold and/or work to the valve springs is about the only fixes for it.

Check out Klassen's 4.0 single turbo build for some very detailed explanations of it on YT!!

Cheers,

KS

Sent from space..