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fun173 09-01-2016 09:47 PM

Stumbling at higher RPMs under load - modded 8V
Hello all,

I'm having some driveability issues with my 8V 900T that I would like to start addressing.

The car has been tweaked by one of the owners prior to me and I have a list of what he gave the PO in terms of mods:

High voltage coil, performance plug wires
3'' exhaust system from the turbo back with a Magnaflow muffler
Bosch mechanical injection
New Garrett T-3 turbo High performance wastegaste
Brand new clutch with short throw shifter
Extensive custom work and much more performance parts
Battery relocated to the trunk

The car boosts to 13psi which I know is significantly higher than stock.

Here is my issue: The car will break up and stumble under hard acceleration once it nears 5k rpm. It mostly exhibits this behavior when it's in 2nd or higher. It will usually run to redline in first without much issue. Additionally, when at WOT on the highway. It feels like it's missing and not making as much power as it should and I can feel it struggling to accelerate even though it will eventually reach higher speeds.

I'm wondering where to begin looking to remedy the issue. I'm assuming it's either a fuel delivery issue or it's not getting enough air. I have pulled the injectors and will be looking at how they spray tomorrow. I have read that these could be the issue.

The car has 218k if that helps. The valves also make a decent amount of noise but I have read conflicting opinions on whether that could be the cause of my issue. What can I check besides injectors to get the car running as it should. It also dies upon startup unless I hold the gas pedal down for 20 seconds where it will then idle perfect for the duration of it being on. The exhaust header is also cracked in multiple places but it looks like repairs were attempted.

The car has an a/f autometer guage that's connected to the O2 sensor and the guage always gives me highly erratic readings, springboarding from lean to rich. It stays constantly lean at idle and under wot it actually stays in the middle between lean and rich.

Sorry for the lengthy thread but I al not knowledgeable about these things and would really appreciate assistance in getting the car running as I know it should. I'm not opposed to taking it to a shop but I want to eliminate as much as I can myself before spending shop prices.

I put a new air filter in and saw the assembly where the Bosch CIS conencts to the airbox only had 2/6 screws. I got more screws and re-assembled it. The car seemed to run a little better but I fiddled with the IC piping and now it will only boost to 10psi sometimes but it actually felt faster at WOT at 10psi because it wasn't breaking up as much.

I ordered OEM Bougi leads and 4 new injectors to put in, hopefully that makes a difference.

fun173 05-29-2018 09:44 PM

Just a quick bump for anyone who happens to come across the same issue, it ended up being a horribly cracked exhaust manifold. Once I put an un-cracked one in, it ran much better!

Saabeh 05-30-2018 06:32 AM

True MVP, updating a post that is two years old!

DrewP 05-31-2018 10:38 AM

Seriously weird, I have never seen that happen, thank you for sharing!

mike d 06-01-2018 03:26 PM

must have been bad enouph to throw lambda reading off, Bet it was pretty loud!

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