3B Misfire & Boost Cut

[vagrallye]

update misfire gone was deffo leads now revs nice and free
but there is another problem it does the lurchy thing people are talking about , boosts to 20psi sometimes and sometimes only stock

it doesnt go massively rich at this point tho on the wideband afr guage which i would expect ?

gonna double check the pipe to ecu to make sure all is sealed... any other obvious vacume leak places? its interesting that the guage is t d into ecu pipe and reads the correct vacum and correct boost there fore ecu is getting good reading?...

ps after the leads were fitted i just slackened of the wastegate spring another couple of turns ... could this be related to my problem?
i still havent set it to stock boost as im unsure what spring it has(haven checked yet)
anyone got a stock spring??

any other ideas?
jim

[newsh]

Stock spring. This is my spare one. If you give MRC a call they've probably got a bunch of them knocking about.. In the meantime just undo it as far as it goes, easy to whip the top off the WG and check the spring is fully unloaded and go for a spin, see if the lurching stops.

[vagrallye]

Stock spring. This is my spare one. If you give MRC a call they've probably got a bunch of them knocking about.. In the meantime just undo it as far as it goes, easy to whip the top off the WG and check the spring is fully unloaded and go for a spin, see if the lurching stops.

now thinking about it the more i undo it the more it lurches?....

ill go and check it after tea

[newsh]

Thats just plain weird..

Make sure your MAF connector is clean and the pins are making good contact, do a search for "that pesky MAF connector" or something similar

[vagrallye]

the "fault" is not wastgate relevant, it still did it with the wgv disconnected
i now have the spring adjusted to 0.4bar mechanical boost
reconnected plug and all works fine
but i still got the intermitted problem
its like hitting a brick wall then going again litterally like some one has switched the engine off and then back on again ,
but no dip in lighting or battery light etc so it cant be to do with the charging system
It doesnt do it at higher speeds / more boost/ more revs/wot etc

my thoughts are;

throttle position sensor, slight flat spot in signal??
a harness plug , maybe water in it?
distributor/ hall sensor just not giving off signal momenterily?
crank/ fly wheel sensor as above
dodgy ignition switch?
mafs?
boost leak? this i dont understand its relevance



gonna try and check as many as i can if one of the engine sensors did any of the above surely it would register a fault? cause i have none!

[Davidsinclair05]

Boost Leak, trust me i checked exactly the same things, check the boost pipe under the back seat as well!

[vagrallye]

Boost Leak, trust me i checked exactly the same things, check the boost pipe under the back seat as well!

where was your leak ? im gonna check over the next few days gonna renew all the vissable cotton coloured joiners and re clip every thing...
may try and get hold of one of those hand pump style testers, they can test pressure and vacum

[newsh]

Its known as a MAF cutout and is usually a boost leak but can be the MAF connector or wiring, you need to plug the system and pressurize it and make sure it holds at least a Bar of pressure.
As I understand it, engine draws in air which is metered by the MAF, ECU supplies enough fuel to go with metered air but some of the air leaks out so lamda tells ECU to lean it off, lamda cannot compensate enough as the reqired value is off the edge of the fuel map and ECU cuts the fuel pump. You should have a code which says "mixture adaptation exceeded" or something like that. Same thing happens if the WG or WGFV is leaking and the boost rises too high, ECU cuts fuel pump off. I'd also suspect the brown ground wires on the side of the IM but as you've not been showing any codes I think its probably boost leak or MAF connector. Did you find the thread I mentioned? Pull the MAF connector off and give it a squirt with contact cleaner and a good wiggle on and off and then take it for another run, see if its any different. Also reset the ECU (2 "motor 2 fuses at the front of the fuse box , and see if that changes things.

[newsh]

I can lend you a boost test kit, or someone can, I don't know if you're local to me but I have a compressor too, you need a lot of air quickly to do a decent test..

Classic place for a leak is where the intercooler connects to the crossmember, there's an O ring there which perishes. There's a mod called the Mark H Mod which is to use a cut-down silicon reducer pipe over this joint to seal it, worth doing

[vagrallye]

Its known as a MAF cutout and is usually a boost leak but can be the MAF connector or wiring, you need to plug the system and pressurize it and make sure it holds at least a Bar of pressure.
As I understand it, engine draws in air which is metered by the MAF, ECU supplies enough fuel to go with metered air but some of the air leaks out so lamda tells ECU to lean it off, lamda cannot compensate enough as the reqired value is off the edge of the fuel map and ECU cuts the fuel pump. You should have a code which says "mixture adaptation exceeded" or something like that. Same thing happens if the WG or WGFV is leaking and the boost rises too high, ECU cuts fuel pump off. I'd also suspect the brown ground wires on the side of the IM but as you've not been showing any codes I think its probably boost leak or MAF connector. Did you find the thread I mentioned? Pull the MAF connector off and give it a squirt with contact cleaner and a good wiggle on and off and then take it for another run, see if its any different. Also reset the ECU (2 "motor 2 fuses at the front of the fuse box , and see if that changes things.

good answer/ research , you have just confirmed a thought of mine , it only does it when running "lambda" ie up to the point the "map" is used and the lambda is ignored

and yes it does now seem like its just cutting fuel , would it only be a split second fault ?
ps
didn find the thread

[vagrallye]

I can lend you a boost test kit, or someone can, I don't know if you're local to me but I have a compressor too, you need a lot of air quickly to do a decent test..

Classic place for a leak is where the intercooler connects to the crossmember, there's an O ring there which perishes. There's a mod called the Mark H Mod which is to use a cut-down silicon reducer pipe over this joint to seal it, worth doing

yea i saw that join looks a bit pathetic for a turbod car lol there could be a leak there , i can hear a slight whistle from under the bonnet , but i put that down to the spool up of a "worn" non ball bearing old school turbo

also thought about the "boost leak" option , its also doing the "brick wall" thing just under part throttle with no/very very little boost possibly not even up to -5 psi

[newsh]

I'd say you have a leak somewhere and they can be a PITA to find without a leak test kit.

http://www.s2forum.com/forum/showthread.php?t=24544&highlight=maf+connector

http://www.s2forum.com/forum/showthread.php?t=17820&highlight=boost+leak

[newsh]

And yes it just cuts the fuel for a split second. Mine is doing it occasionally at the moment, its because I'm running a GT3071 and full 3" exhaust on a chipset mapped for an RS2 turbo and stock DP with the WG spring unscrewed all the way, sometimes if I give it too much throttle at too low revs it overboosts and cuts out. Bloody annoying but I need it properly remapped for the turbo.

As I understand it though your car is not actually overboosting just acting as if it was, so almost certainly a boost leak.

[vagrallye]

And yes it just cuts the fuel for a split second. Mine is doing it occasionally at the moment, its because I'm running a GT3071 and full 3" exhaust on a chipset mapped for an RS2 turbo and stock DP with the WG spring unscrewed all the way, sometimes if I give it too much throttle at too low revs it overboosts and cuts out. Bloody annoying but I need it properly remapped for the turbo.

As I understand it though your car is not actually overboosting just acting as if it was, so almost certainly a boost leak.

yes its just cutting ....something , more than likely fuel!
BUT, its doing it under vacum and not boost, on lambda not once lambda is ignored
i read that topic that you put a link for, that seems more like its happening when on boost,
the reason my origonal thoughts were throttle position sensor was because this fault only occured under light throttle, it may do it up to the 0 mark on the boost gauge but i would say once over half throttle and on boost (even low figures) it doesnt do it
or its hall sender related ,which is rev related

[Davidsinclair05]

http://www.s2forum.com/forum/showthread.php?t=11748&highlight=Vacuum+Tree