Mis-fire

[mcandmar]

For an ABY i would have said dodgy POS units, as far as i know there is still a single POS unit to trigger the coil on 7A/3B setups.

[AndyP]

To answer all the questions:-
-The car has run this exact set up since it was mapped, without an issue. Something has gone wrong to cause the misfire, it’s not a case of wrong/unsuitable parts being used.

-Not checked the knock sensors, but they were both brand new when the engine was built so they’ve done about 9k. I’ll check the torque on the bolts to be sure though.

-Spark plugs, I’ve tried F5DPOR, FR5DP and NGK BKR87EIX, all set to stock gap. I’ve thought about closing the gap a bit to give the ignition system an easier time. If that works, at least it might point me in the right direction.

-Oil consumption is high, always have been, I put this down to the JE pistons. The plugs never really look fouled, I thought this might be an issue, that’s why I replaced the VSOS but it’s not made any difference.

-Ignition system is pretty much stock, I’ve tried 2 different distributors and a new cap and rotor arm, both Bosch. I’ve also tried 2 different sets of aftermarket leads and 1 set of OE Beru leads.

-The POS is built onto the same bracket as the coil on a 3B, so that’s also been changed.

I was also thinking wiring fault this weekend as when I swapped the injectors I noticed 2 of the injector plugs were broken, so I changed all 5 connectors and also cleaned the contacts, I still want to check continuity of the wiring back to the ECU. I’ve also been round all the electrical connectors under the bonnet and cleaned them with fine wet and dry paper and electrical contact cleaner.

I’ve ordered some parts today to make a fuel pressure tester, so I’ll report back at the weekend.

[prj]

What is the AFR reading on WOT at 1 bar, what is the AFR reading at WOT at 1.2 bar? And what about 1.5 bar?

Knock sensors won't cause your car to misfire, it'll just feel slow if something is wrong with them.

Try a third coil... swapping 20 year old parts with 20 year old parts and you can run into the same issue on both. Bad grounding could also be an issue.

[tajgreidotu]

I´ve seen something similar in my 3B caused by a faulty battery....worth a try!

[AndyP]

I'll make a note of the AFR's next time I'm out in it. I'll also try and get another coil.

Battery is almost new, Bosch S5, alternator also checked and is kicking out 14.2volts from memory.

[macspring]

Given the grief you're having, and the friction it's causing, what's your PayPal details, and I'll chip in for a new coil !

Is a new Bosch coil / POS, not from the Audi dealer, killer money, or not too bad ?

Hope you get to the bottom of it.

Post when you do.

Kind regards.

[AndyP]

Got another coil to try on Wednesday

[4WheelDrifter]

What's the condition of your knock sensors?
Is your MTFS acting up?
Have you taken the wastegate off and checked for play in the valve?

Sorry, Brian. But I am with Dmitri here.
A misfire that appears under high boost only, especially not on all cylinders is pretty much always down to a spark problem.

Changing every component on the car is not the best way to fix it IMHO.

[Tonks4x4]

I never suggested change everything just test or inspect where necessary.

I agree that it sounds ignition related but can't fathom what it can be as he has changed it all before several times.

I didn't initially reply with any attitude I was merely quoting Shelock Holmes lol.

[Rocco]

Andy...

is high time you did 3B to ABY/AAN Motronic conversion¡¡ new ignition + new mapping
and keep only your distributor for the hall signal


about your problem... i had simillar problems before with stock turbo and K26/27 turbo and was spark plugs first and faulty TFSI coils later becaue they tended to unplug itselfs from the spark plugs because i did not know about the cam cover mods needed to plug the coils


with one bar 0 problems and above it cuts...

[4WheelDrifter]

I never suggested change everything just test or inspect where necessary.

I agree that it sounds ignition related but can't fathom what it can be as he has changed it all before several times.

I didn't initially reply with any attitude I was merely quoting Shelock Holmes lol.

Well we all know about Dmitri and his people skills. But he does have the knowledge to back it up.
And of course no one can doubt your mechanical skills. But in this case I think it's a waste of time replacing unrelated parts.

I remember I had trouble with the 1.8T misfiring above 1.3 bar a couple of times. They are well known for coil pack problems. But in one case it was a loose connector, and the other a loose spark plug. Both happened before I took on the servicing I might add, but led me to further mistrust Audi 'specialists' and main dealers.

I had troubles on my 7A with a damaged injector connector and series resistors. But both resulted in pretty constant misfires, not load related.

[AndyP]

It's fixed!!

I broke my own rule of only changing one thing at once, so I can't be certian of what it was but I think it was the electrical connectors to the fuel injectors. I changed those on sunday afternoon but didn't test drive it as the F1 GP and MotoGP were on Then on Monday I pulled the plugs to check the gap, and it was 0.6mm. I decided to gap the NGK plugs to 0.5mm and fit them. A test drive resulted in full boost and no mis-fire, BUT the AFR gauge was showing some funny readings, sometime too lean on boost, sometimes really rich off boost.

I took it down to Brian Tonks last night and when I went to take him for a test drive it wouldn't start, loads of power in the battery, just wouldn't turn over. Brian hooked a jump lead from the battery earth to the engine and it started up. So we took off the earth strap, cleaned up the connections and Brian fitted a second earth lead from the gearbox bellhousing to the battery earth. Now the car runs brilliantly, turning over noticably quicker during starting so perhaps I've had a dodgy earth for a while.

Anyway I'm just glad it's back to full and extremely rude health

Big thanks to Brian too

[UrS4boy]

The good news: Yay!! It runs and boosts!!

The bad news: We don't know what the issue is/was. Injector wires, plugs or bad ground. Oh well. It runs.

[A80Avant]

My bet is the injector connectors just because I mentioned it

Also your afr readings are correct. When you lift off boost the gauge will momentarily show too rich as the velocity of TB closure is always faster than the injectors stopping their overflow of fuel while your were on boost.

The fact that its lean on boost though means you may need a map or a check of your fuel pump if the fuel used to be rich.

So shall I bring the performance box finally next time I'm at Brian's?

[AndyP]

The strange AFR readings were also caused by the bad earth. I use a 4 wire Bosch lambda sensor rather than the 3 wire std one. The fourth wire is an earth that I have connected to the chassis where the battery earth leads connects. Once we had sorted the earth points the AFR's are back to normal.

@Vas, yes bring the Performance box!