Limiter type hesitation on boost
 

Hey guys, it's been a long time since I've been here, but I've got another Scooby since I love them so much :D

Picked up a 4 door MY99 U7 ECU with an amazing amount of service history and it genuinely appears to have been looked after well part from the last owner who had it for a year and did nothing to it. he also ran it on cheap fuel which is annoying for a great car like this.

It's been to Scooby Clinic a few times and recently had a new MAF, Lambda and o2 sensor, The map seems great and it pulls very smoothly apart from the occasional limiter like hesitation on hard acceleration. I was wondering whether the hesitation could be the fuel filter as it had been run on crap fuel? The HT leads look less than 2 years old but I have new plugs to go in as soon as I can get it on a ramp. It's not burning/leaking oil and isn't smoking at all and I've had no warning lights or limp modes.

It's also just had a reconditioned TD04 which looks like new.

Despite having 120k UK miles, it's lovely compared to the MY93 WRX jap import I had previously which ran like a dog and cost me a fortune trying to trouble shoot. I've searched a lot of threads regarding hesitation issues but don't know enough to pin it down to anything specifically. Any help would be greatly appreciated as I wanna save this one and enjoy it for the summer.

MY99 UK 260bhp @ wheels on last dyno
CAT
After market exhaust and manifold
Aftermarket Air intake, Pipercross I think. Standard recirc.
External waste gate (Previous TD05 I was told)
3-5k engine oil changes, no smoke or leaks and doesn't sound like it's knocking or misfiring. All hoses are good and have been thoroughly checked, although it hasn't been leak tested with me yet. I was planning to have a Diag and Dyno to confirm..

Could be a number of things, I would look at the fuel pump and possibly still be an issue with one of the sensors starting to fail on you (camshaft sensor or the likes).

Tony:)

Thank you Tony, I was wondering about fuel cut, fuel pump feels right, would the diag show this?

Yes it does sound like fuel cut, is it mapped for the mods?

Thanks Richard, I can't confirm this, I was hoping to get a better idea of the problem and potential cost before booking it in for a diag. The rear arches need doing which is gonna be about £300 altogether and I was planning to get to a decent induction kit after the service parts. Just done the oil and oil filter and changed the coolant yesterday, got the plugs and was gonna do the fuel filter next although it looks relatively new. If I book it in for a diag will it show the problem relating to the map if it is that? No point having a remap with the current air filter as it's on it's last legs I think, but I'm pretty sure it's been mapped with the exhaust and manifold. I bet it was mapped with the decat that came with it, that might cause an issue? Also debating the cam belt, tensioner and water pump lol the list goes on doesn't it :D

An aftermarket exhaust will cause overboost & fuel cut if not mapped for as will an uprated turbo. What does it boost to? You need to find out if it's been mapped as fuel cut can be one stage before engine failure.

Thank you, Boost gauge says 1.5 in 3rd gear, although I don't know how reliable it is. I'm not a foot to the floor kind of driver so not sure about 4th and 5th. I never rev above 5k either. Guess I'd better get it looked at sooner rather than later eh?

Here's the last dyno.

https://www.facebook.com/photo.php?f...type=1&theater

The problem has become progressively worse this week, it's cutting at low speed and minimal boost which I'm trying to stay out of. The prev owner confirmed it's been mapped with the exhaust and manifold and it's certainly driving very differently. I noticed I can smell fuel on cold start but I checked for leaks today and didn't come up with anything. Hope it's not coil packs :( I still haven't been able to do the plugs, could it be something simple like that? I got a Golf TDI today to ensure it's not driven and doesn't do damage. Thanks in advance.