vrs boost issues

[rbertnitro]

hi ive been chasing an intermitent hesitation/soft limp issue for a while.decided to try changing n75 see if that helped first off tried a mates f valve that he had 'modded' basicaly hed turned the end screw in whatever direction to give better boost onset or whatever wasnt much diffrence same on/off hesitation when pedal floored,also tried a controversial j valve he had laying around....worse spiking and limping all over the place.next got a new one online standard f valve this time.has reduced the previous hesitation altho im left with even wierder boosting now.normal up to 10 (going by my gauge) then bouncing down to 5-6 and bouncing around there.at the same time ever since i tried his modded f valve ive heard the turbo whooshing a lot more checked for leaks and none to the eye anyway.its really loud.also when accelerating i have to kinda go carefully and gradualy on the throttle up to full.if i stomp on it for example in 3rd at 2000rpm the boost will start rising up to max with the loud whoosh but the car just doesnt move itl increase speed slightly up until the revs get higher (almost 4k) then itl boost and accelerate away,before all this the throttle was a hair trigger and would pounce forward and accelerate nicely and smooth doing the same.i know i have max boost at the mani by my gauge its almost like its not putting fuel in until my revs are up to 4k just blowing air.ive checked for any major leaks and all vac connections etc nothing major found.ive also swapped out the dv for a new std one. could anyone offer any help please.

thanks

rob

[rbertnitro]

forgot to add no codes on handheld scanner apart from boost limit exceeded that happend when i disconected the n75 wg feed briefly to make sure i could achieve full boost

[YellowCar]

Have you tried a run with the maf unplugged? Apparently n75 issues aren't that common as long as the right one is fitted, symptoms sound like it though. When you say up to 10 you mean 10 psi? Is it not remapped?

Try unplugging maf as I say, it's a free check, if it runs better the sensor is messing things up. Coolant temp sensor can also do weird things...

[rbertnitro]

thanks yellowcar no ive not tried mafless i will give it a try in the morning.yes thats right up to about 10psi on my gauge altho id assume it would have a bit of an error margin as its a £10 gauge.not been mapped that i know of prev owner didnt say.i got the gauge after all this started but when i got it was very quick quite a bit faster under 100 than my mk3 vr6 so could have been mapped and now its running crap but i doubt it as its refusing to go over 10psi. would unpluggi g coolant sensor prove anything?

[YellowCar]

No don't unplug that. Only thing to trial and error the temp sensor with is fitting a new genuine one. Try unplugging the maf first and get it scanned with vcds if you can.

[rbertnitro]

right i will certainly try the maf off anyway.only other things i could think of were it might need a throttle alignment as the battery was off for some time while i was fixing door control module wires.also when is boost supposed to start as i can be light on throttle and itl be in vacumm or 0psi rite up to high revs and a decent speed its only when i take a chunk of pedal like 1/2 throttle or more the psi starts to climb above 0

[YellowCar]

Should be requesting boost from just over 2000 (I think, forgive the lack of accuracy) with boost really coming to peak from 3000 ish. Sounds like aligning the throttle body after a clean wouldn't do any harm. Only align a clean one though, you'll need a replacement gasket as well. If the throttle body is dirty and/or out of line unplugging the maf won't prove much, so I'd be tempted to make sure the throttle body is right first as it goes.

[rbertnitro]

right thanks.il have to find someone local with a copy of vagcom then.eliminate the tb at least

[YellowCar]

Let us know how you get on, see what codes have popped up as well

[rbertnitro]

quick update.tried unplugging maf this morning on way to work= inconclusive. only a 3mile drive but id say it ran a little worse with it off.struggled to start initialy and idle was all over the place not as much punch performance wise and just seemed generaly worse.i did notice the boost was slightly lower but it was still doing its odd ramping up way high,hesitating and then dropping like a rock down to about 3psi. with the maf in it accelerates and boosts fine if im carefull with the throttle and gentle with it going on smooth and slow.but a slight 1mm more pedal on high gear high load (hills) situatuons and its whooshing like a leaf blower and going nowwhere.boost spikes up then throws a wobbly and plummets to 3 or 4psi. closer inspection earlier i did notice i had a small split in a oil breather,its the one that comes off the y camcover piece and goes down i to the block its split just before it goes into the connection lower in the block. would this split cause such crazy running and boost probs i thought these breathers didnt see boost in them?gona get it temp fixed up for now while i order the replacement. and find someone to vagcom my car

[YellowCar]

I had a split in that one where it connects as well, I didn't really have running issues because of it though. Bit of roughness on idle, a bit of noise but nothing major. Hence I didn't really know until I was removing it for a catch can install.

Yes boost would have been lower unplugging maf as the ecu then uses a baseline reading, however it removes the confusion of a potentially dodgy sensor. But like you say it seems inconclusive. Was worth a try though. I think a scan should be the next step before you start throwing parts at it chasing a problem, oh and it's still worth trying a throttle body clean and alignment in the meantime.

I'm still wondering if the coolant temp sensor could be responsible for such erratic running...Try a scan mate, could save a lot of time.

[rbertnitro]

yeah thats my next port of call as i believe vagcom is better at finding all the codes than these generic obd scanners.in fact at only 99dollars (65pound near enuf) for the full registration of the older version i may just get it myself. Could be worth a shot but is it possible that the coolant temp sensor from my mk3 vr6 is the same and would fit this engine? ive got loads of spares laying around for the vr6 and if anything is compatible between the two i could shove it in right away as my mk3 has the engine out just now so not needing them immediately

[YellowCar]

That's a good question, worth looking into. Is the part number visible on it? I'm not sure how far across the range they spread but I do know some stuff in the bay looks suspiciously similar to the V5 Seat I had. If I'd have known the airbox was the same I wouldn't have had to get another pipercross panel when I bought this one, still that's another story.

[YellowCar]

059 919 501 is the part number for the green sensor for ours, see if it matches.

[YellowCar]

Just had a quick look on ebay and they look completely different.

[rbertnitro]

oh well worth a try.i may order one anyway as going by the vag cars ive had in past im no stranger to having to fit new coolant sensors to them

[YellowCar]

Just make sure it's a genuine one

[rbertnitro]

so im waiting for my vcds cable to arrive.decided this weekend to clean the maf see what that done since its free.anyway cleaned it as best i could with a can of maf cleaner then put it back in.however forgot to connect the plug took it for a run and now it actualy runs better with the maf unplugged.im puzzled as before it ran crap with it unplugged.post clean its still **** with it plugged in but now whenever its unplugged it running better and smoother albeit with reduced power and midrange.im more and more thinking of just ordering a maf even though i havent vagcom logged it yet.anyone chime in with thoughts?

[YellowCar]

Strange one, certainly sounds like it's worth crossing a gen/bosch new one off the checklist. Weird how unplugged before made no difference. When you were getting the issues is it every time you drive or sometimes not so bad?

[rbertnitro]

before.when i unplugged it to test it started and idled rough drove alright but still did its strange boost all over the place thing,it calmed down a bit once i got to work that day but still unsettled at idle.havent drove it at all most of weekend.then when i have the plug off again its smooth and better psi is only peaking at 8 or so,lower power but no mad spiking and surging like before.i can only assume its possibly adapted a little to having the maf unplugged. it still goes ape when i plug it in tho. didnt do anything else apart from a scan with torque android app and the blutooth dongle

[YellowCar]

You'll have lower boost and power as unplugging means the ecu will run from a baseline. Lumpy idle often points towards an air leak, have you checked pipework? With the heat of the engine and expansion/softening of material the effects aren't always consistent, you found one split, how is idle now? Could there be more?

[rbertnitro]

my idle wasnt the problem originaly.it was only when i initialy unplugged the maf that idle was rough.when the maf is plugged in and its surging and limping it idles great infact it drives perfectly in the vacuum to 0psi range.only when boost starts to come it goes nuts. now when i unplug my maf a second time it idles great and drives thru the whole range inc boost perfect just slower.i think i may need to rig up some kind off pressure tester using a bike pump or small compressor to check for further leaks cause theres not much to see just by eyeballing it tbh

[YellowCar]

Think that's a good idea getting a pressure or smoke test done, try your luck with a scan as well. My concern would be after shelling out on the maf it will happen again, but I suppose a new one won't hurt

[rbertnitro]

is there any sort of guide to testing the mafs values with a multimeter id like to be more sure.

[YellowCar]

You can log it in vcds,can't remember the block number or what the numbers mean lol, someone I know on here interpreted mine for me. As for meter testing I don't know, sorry