S3 8l issues.

[Gavin S3]

Hi, so this is my first post on here. I’ve done a lot of reading and have learned a lot from peoples experiences on here regarding the 1.8t 20v
So here goes…

I have owned my s3 8l for around 5 years now. When I bought it it had had the following done engine wise;
Full engine rebuild,
Forged rods,
K04 hybrid,
Large TIP,
FMIC and pipes,
Forge recirc,
All new seals, rings, etc,
N249 del,
Tubular mani,
Decat,
3” to tip,


It was running a soft map to bed in the rings for around 1k miles then mapped to around 280 which has been a beauty to drive for some time.
recently I’ve been having a misfire on cylinder 1.
I’ve swapped coils from 1 to 2 and no change. I’ve swapped injectors and still no change. Im getting low compression on that cylinder so assuming it’s top end. Valve maybe.
I’ve started a head build on a another head and have all the parts to uprate the head with the intention to eventually swap it out and cure the issue. Also fixing the damn mani-turbo gasket that I can’t get to stop blowing.
I have noticed recently that if I red line (I know this can be dangerous with a miss-fire to the engine) that my idle becomes rough as. Dropping almost to stall, then blipping to 1300, dropping and blipping.
Sometimes it does stall. If I cut the ignition and restart it’s fine and idles perfect.
The misfire live count doesn’t register while connected on obd but once cleared the engine light comes back on in 30 mins of driving or so with misfire on cylinder 1 code.
Does anyone know if this could be any other problem I’ve maybe overlooked?
I’m hoping I’m on the right path.
I don’t know a great deal about car mechanics so go easy on me.
Thanks in advance

 

[whizz371]

I would check the compression on each cylinder , if you have determined that its not electrical. A compression tester is not expensive, and very easy to use.

 

[whizz371]

Just spotted that you have said you have low compression on that cylinder, so assume you have checked it. Could be any number of top end issues, although in my case recently it was a broken ring.

 

[Gavin S3]

Hi whizz371,
Yes I checked compression and cylinder 1 was low. I have almost finished head build and I’m hopeful that it’s a top end issue. If it is a ring then at least the head has been up rated.
I have done the following for my
head build.
Full port (gas flow) and polish,
Head skim,
Super tech single groove valves, stem seals, double springs,
INA hydro lifters ( I have solid too but think it’s too much maintenan
ARP bearing cap bolts,
Street/race exhaust and intake cams,
Adjustable cam gear,

if there’s any advice or recommendation at this stage id appreciate it.

 

[desertstorm]

How low is the compression on cylinder 1 compared to the rest?. My 90K mile 225 TT did around 170-175 psi on all 4 cylinders . Low compression is either on the rings / cylinder or valves. It's not uncommon to have issues with the standard exhaust valves on tuned engines. I certainly wouldn't be red lining the engine and the issues you have with idling after you have are not unexpected and to me say that the issue you have may be more cylinder / bore related than valve.
One of the ways to tell if it's valves or cylinder is to do a compression test and then squirt some engine oil in the cylinder. This will help seal the bore and increase the compression but won't make any difference to a leaking valve.
The head build you have is well OTT for a k04 car , You certainly don't need solid lifters stock hydro is good for well over 8K rpm. Cams don't make that much difference with a K04 as unless it's something like an AET380 they just don't produce enough boost at high RPM to really make use of the extra flow given by the cams. Who is setting up the adjustable cam timing?
My 510bhp TT has an unported 125bhp N/A head with N/A cams , stock inlets with supertech exhaust valves and Ross tech uprated springs, and stock valve timing.
Are you planning on going big turbo at some point in the future?.

 

[Gavin S3]

How low is the compression on cylinder 1 compared to the rest?. My 90K mile 225 TT did around 170-175 psi on all 4 cylinders . Low compression is either on the rings / cylinder or valves. It's not uncommon to have issues with the standard exhaust valves on tuned engines. I certainly wouldn't be red lining the engine and the issues you have with idling after you have are not unexpected and to me say that the issue you have may be more cylinder / bore related than valve.
One of the ways to tell if it's valves or cylinder is to do a compression test and then squirt some engine oil in the cylinder. This will help seal the bore and increase the compression but won't make any difference to a leaking valve.
The head build you have is well OTT for a k04 car , You certainly don't need solid lifters stock hydro is good for well over 8K rpm. Cams don't make that much difference with a K04 as unless it's something like an AET380 they just don't produce enough boost at high RPM to really make use of the extra flow given by the cams. Who is setting up the adjustable cam timing?
My 510bhp TT has an unported 125bhp N/A head with N/A cams , stock inlets with supertech exhaust valves and Ross tech uprated springs, and stock valve timing.
Are you planning on going big turbo at some point in the future?.

Thanks for the advice! Seems to make sense with testing the compression with oil on the piston. I don’t know what the compression is as I didn’t see. My friend at the garage tested. I’ll skip testing as I’m hopefully taking the engine out soon. I’m hopeful it’s top end but as engine will be out anyway if it’s bottom I will look at boring and stroking possibly.
I probably should have mentioned that the plan is to go big turbo (which turbo I am unsure at this stage), twin plate clutch.
Plan is a stable 500hp setup, strip seats and interior, roll cage and a occasional track car road legal

 

[Gavin S3]

Thanks for the advice! Seems to make sense with testing the compression with oil on the piston. I don’t know what the compression is as I didn’t see. My friend at the garage tested. I’ll skip testing as I’m hopefully taking the engine out soon. I’m hopeful it’s top end but as engine will be out anyway if it’s bottom I will look at boring and stroking possibly.
I probably should have mentioned that the plan is to go big turbo (which turbo I am unsure at this stage), twin plate clutch.
Plan is a stable 500hp setup, strip seats and interior, roll cage and a occasional track car road legal

Oh and once built I hope to get custom map at R-Tech

 

[Gavin S3]

So I think I will be looking at the garret g25 660 turbo with matched manifold and external wastegate down pipe from badger5. Looks to be the best option for me at this stage. If anyone has any info on other mods required it would help. I know I’ll need secondary inline fuel pump, 1000cc injectors and possibly a high flow inlet mani. Meth? Bigger maf?

 

[<tuffty/>]

I would suggest getting an Ignitron Ecu if going for a G25 660... You can ditch the MAF and tune it properly then

<tuffty/>

 

[Gavin S3]

I would suggest getting an Ignitron Ecu if going for a G25 660... You can ditch the MAF and tune it properly then

<tuffty/>

Yup that’s what I’m doing. Bill is going to sort me out with a basic map after the build and then I’ll book a proper map day. Also like you said, no more MAF.

 

[Stuart B]

If you do a leakdown test, you should have a better idea of the cause or low compression.