Boost issue

8bit · Nov 18, 2010

Did have a search but not the easiest thing to search for - "boost problem" just returns stacks of threads and none seem to describe my issue so here goes...

Noticed lately that sometimes if I floor it in 2nd or 3rd then boost doesn't seem to appear until betweek 3k and 3.5k rpm, then when it does it's very sudden, like someone just switched the turbo from 0 to 100%. Seems to be more likely to happen when the weather is colder and usually once the car has been warmed up a bit it starts behaving normally again, i.e. it builds from about 2500rpm or thereabouts up to around 3000 rather than just appearing in one big surge.

Car had new spark plugs and fuel filter about 1500 miles ago, no EML light showing but haven't had a chance to get it scanned for codes yet. Only recent mod was Jabba heatshield, Jetex cone has been on there for ages. Car seems to idle fine.

Worth changing the coilpacks? Any other ideas?

doug2001leon · Nov 18, 2010

dont think its the coilpacks, i would imagine its the throttle possitioning sensor, only as i saw this about 6 months ago on an ibiza.

Just clean it and spray it up with some wd40 ect to try and keep moisture out that is what it seems like, if its not that then i can only imagine your recirc valve or n75 valve is playing up a little.

Let me know how you get on bud

sambryant · Nov 18, 2010

sounds to me like a bad turbo lagg problem, is your dump valve ok?

8bit · Nov 18, 2010

Recirc valve is a Forge 007p fitted in reverse, it was brand new bought about 7 or 8 months ago.

When you say clean the throttle position sensor, do you mean the throttle body? Been meaning to do that for a while, had a code "19534 - Throttle Control: Airflow at idle too low" come up a couple of times in the past which suggests throttle body needs cleaned and aligned...

sambryant · Nov 18, 2010

8bit said:
Recirc valve is a Forge 007p fitted in reverse, it was brand new bought about 7 or 8 months ago.

When you say clean the throttle position sensor, do you mean the throttle body? Been meaning to do that for a while, had a code "19534 - Throttle Control: Airflow at idle too low" come up a couple of times in the past which suggests throttle body needs cleaned and aligned...

could be your maf. i kept having a boost leak code due to a dead maf. new maf and problem solved.

doug2001leon · Nov 18, 2010

yes mate that is what i meant, sorry have been up since 4am with my little ones ear aches lol

Once cleaned up just spray some water repellent like wb40 ect around the sensor though incase the seal has perished over time and letting the moisture in and could be throwing the readings off.

doug2001leon · Nov 18, 2010

good thinking sambryant could be the MAF i hear that it can throw it off too!

8bit · Nov 18, 2010

Last time I had the car logged I tried my MAF and another one which was known to be fine as I had another issue that MAF was suspected, both MAFs showed pretty much the same numbers but cool, I'll get that logged next time I get a chance.

EDIT - actually, if it was the MAF then wouldn't it be like this all the time? It's only intermittent...

doug2001leon · Nov 18, 2010

Did you find that it was idling irratically when your MAF went though? or even cutting out when pulling up to light ect....?

sambryant · Nov 18, 2010

i fitted 2 brand new mafs and still had the problem, i the bought my third, oem one and job done

sambryant · Nov 18, 2010

doug2001leon said:
Did you find that it was idling irratically when your MAF went though? or even cutting out when pulling up to light ect....?

car ran fine, just went into limp mode after a few mins

8bit · Nov 18, 2010

doug2001leon said:
Did you find that it was idling irratically when your MAF went though? or even cutting out when pulling up to light ect....?

Not sure if you were asking that to me or Sam but my MAF never went, that wasn't the problem.

Last time my car was logged was 4th Sept so just over 2 months ago, my OEM MAF logged a peak of 183g/s, another OEM made the same.

@sam - I'm not poo-poo'ing your suggestion but if the MAF was dead/dying then would it cause this problem intermittently or just all the time?

sambryant · Nov 18, 2010

intermittently id say. i could drive the car for 15mins with no problem, then my next trip being only a few mins and i would go into limp mode. the best thing to try is, unplug your maf for a while and see if this stops the problem. if it does, your maf is dead or you have a boost leak

8bit · Nov 18, 2010

ok, i'll get the car checked and logged when i can and if it gets any worse then I'll try disconnecting the MAF, thing is cos it only happens occasionally then I'd have to drive around for about a week with the MAF disconnected, which will eventually put the car in limp mode won't it?

sambryant · Nov 18, 2010

heres the difference i had on the rolling road with a dead maf, we then unpluged the maf and got much better results

sambryant · Nov 18, 2010

8bit said:
ok, i'll get the car checked and logged when i can and if it gets any worse then I'll try disconnecting the MAF, thing is cos it only happens occasionally then I'd have to drive around for about a week with the MAF disconnected, which will eventually put the car in limp mode won't it?

yes it will after 50 miles or so, you will have to erase the code after.

8bit · Nov 18, 2010

This log was done back in late August, similar figures to your "MAF unplugged" ones but I guess that was a few months back so maybe it has started heading south since then...

jamie1 · Nov 18, 2010

Could it be an intermittent fault with the n75? Just a stab in the dark?

8bit · Nov 18, 2010

Could be I guess, just read this thread i found in another one on boost problems which would suggest that's a possibility. It mentions adjusting the N75 valve as well, must look into that. Would a faulty N75 give an error code?

Pyro · Nov 18, 2010

8bit said:
Could be I guess, just read this thread i found in another one on boost problems which would suggest that's a possibility. It mentions adjusting the N75 valve as well, must look into that. Would a faulty N75 give an error code?

Never adjust the N75 from what I've Hurd it's factory set and needs to stay like it

a faulty N75 will cause boost problem as it helps contol boost

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