vr6 turbo misfire

[jims13 6]

hi guys, right car runs fine..but occasionally im getting a cut in power..now its not fuel as we kept a good eye on that at the recent rr day.. but i did notice (although its hard), that the boost gauge peeks at 12 psi..now im running a external wastegate..and was reluctant to run a bleed valve/dawes device..but i now think its the only way to run a constant boost pressure.. i take it that the standard maf will reach it 5v cap at around 11 psi??? if so i reckon its this causing the cut.

any sugestions..apart from capping the boost at 10 psi..

btw, i dont have the money for c2 software , and tbh id prefer standalone, i now regret selling a megasquirt system i had.

[UnitedMotorsport 55]

MAF is topping out, and knock sensors are pulling timing.

[jims13 6]

thought so..thanks for the reply

[FishWick 21]

The MAF peaks out a bit lower mate.

My old GT3071R turbo running 8psi used to smash the MAF into it's upper limit by 2800rpm, so the momentary cut is more to do with air mass drawn in and how quickly, rather than boost pressure.

Are you running the BEGI fuel riser? Can't remember how you're fuelling yours, sorry!

I've got a MAF clamp you can try if you want? It will stop the MAF exceeding 5V.

It's not an elegant solution, but it'll get you by.

[jims13 6]

that'd be good kev. yep im using a begi fmu , on a t4 hybrid. its a bit weird as, if i keep my foot planted from the word go, it'll be fine and pull like a train. but if so as yesterday, im on the a12, and go to increase my speed from say 70mph, ill more than likely get a quite sudden and voilent cut. ive not yet had the car on vag com to confirm it , but my idea was the maf.. not to keen on going 4" maf at the mo, as it entails a whole load of other stuff , which at the mo i dont want..plus theres more than enough power as it is.

[thegoth 5]

plus theres more than enough power as it is.

what have you done with the real Jim Potter? ;-)

[jims13 6]

still here nig, but the things near on dangerous , with the way it gathers speed

[FishWick 21]

that'd be good kev. yep im using a begi fmu ' date=' on a t4 hybrid. its a bit weird as, if i keep my foot planted from the word go, it'll be fine and pull like a train. but if so as yesterday, im on the a12, and go to increase my speed from say 70mph, ill more than likely get a quite sudden and voilent cut. [/quote']

That is classic MAF clipping mate.

You can drive through it as you say, by keeping your foot in, which forces the ECU into open loop. When you part throttle boost it, the lambda is trying to maintain 14.7 AF and gets confused by the huge air flow the MAF is seeing......then panics and switches off the injectors, hence the violent shunt. It's a bit like that "Fuel cut defender" in the Jap tuning world.

ive not yet had the car on vag com to confirm it ' date=' but my idea was the maf.. [/quote']

Yep. Scan it on VAG-COM and I'll put money on there being a "MAF - Short to ground" or "Short to B+" error in there :-)

not to keen on going 4" maf at the mo' date=' as it entails a whole load of other stuff , which at the mo i dont want..plus theres more than enough power as it is.

[/quote']

It does indeed involve some changes. The 4" MAF clips out aswell, but it's "worked around" in the software that C2 or Stealth provide.

The MAF clamp will work, but I don't like them. All the air mass drawn in beyond the point of peaking the sensor to 5V (i.e 8 psi) is unaccounted for.

But you're welcome to try it :-)

Are you OBD2? If so, you really need VAG-COM.......stick the laptop on the passenger seat and monitor the knock regulation.....I think you will be horrified by what you see :-)

Tell you what, I have VAG-COM actually, so we can do some tests when you pop round for the clamp if you like?

[jims13 6]

er, yeah that'd be cool..you said you wanted a ride in it when it was done. i do have vagcom, but trying to watch a laptop and drive, just aint clever.

id would like to try the maf clamp, if only to see what it gonna fo like without the stutter..

im on nights at the mo, but can do any time during the day. or perhaps sat morning..or the bank holiday monday

[jims13 6]

ill pm you later, and we sort a time out

cheers jim

[FishWick 21]

OK mate. Saturday I think I'm free.

You can run the log in VAG-COM and export it to MS Excel when you get back from the test run.

You can then cross reference MAF, Throttle position, injector duty, knock and then build up a picture of what's happening.

[jims13 6]

sat morning if its all right with you kev as, i have 2 partys in the afternoon

[FishWick 21]

Yeah, not too early though!

[jims13 6]

no probs mate. im on nights anyways.. ive still got your number, so ill bell you when im up.

[FishWick 21]

OK dude, see you soon....

[jims13 6]

thanks for yesterday kev, ill let you know how the cars goes once ive fitted the maf clamp.

and would you believe it on the way home, the cut was worse and much more voilent.......

look forward to seeing the graphs..

jim

[FishWick 21]

PM your email address mate and i'll forward you the Excel graphs. I've seen much worse timing pull, so yours is pretty good.

Good effort with the turbo install, drives very well :-)