Boost lost!!!!!!!

**lesurfman** · 05-20-2013 09:06 AM

Last night I was on the highway cruising at 60 in 6th gear. Mash the gas pedal the boost gauge went to 20psi as usual but 2 second later the boost went down to 15 psi than 5 second later it went down to 1-2 psi.

I let go of the gas pedal and try again only getting 2psi of boost, took it easy and full boost came back maybe 15 seconds later. ( is this what's called limp mode ?)

Tried this 5-6 times and got the same result every time.

I will pulled the codes tonight.

I changed the cam follower 2 weeks ago so that is not the problem.

I haven't done the recall for the fuel pressure sensor and the pcv yet.

I suspect the fuel pressure(g401) or the N75 to be the problem.

What are you guys thinking it could be?

TIA

**mec** · 05-20-2013 09:48 AM

Possible fuel cut or dv failure

**kerfuffle** · 05-20-2013 02:15 PM

I am currently experiencing similar if not exact issues with my 08 A4 S-Line with 45000 miles. How can I go about diagnosing what the cause is? How can I "pull" the codes? Vagcom?

Thanks

**CorneliusRox** · 05-20-2013 02:18 PM

Lost? Where did it go?!

**pule333** · 05-20-2013 04:46 PM

Same thing here! Replaced cam follower, n75, checked n249, checked pcv, all the piping, replaced fuel pressure sensor on HPFP.... No luck so far. Waiting for upgrade kit from hpfpupgrade.com to rebuild HPFP.

**pule333** · 05-20-2013 04:51 PM

Ps. Managed this on Saturday with

**jimrobbington** · 05-21-2013 08:18 AM

Sounds like a fuel cut. Limp mode doesn't just go away a few seconds later.

Sent from my porcelain throne.

**BenMTL** · 05-21-2013 12:15 PM

PM if you need vag com cable to pull errors. You are probably close to me.

**1975audi** · 05-21-2013 12:46 PM

Same here.
Only I never go as low as 2psi.
One day 20psi the next only 15.
Changed my spring on the dv to yellow. Same thing happens
On Uni stage 2
Any thoughts

**mr shickadance** · 05-25-2013 10:20 AM

Originally Posted by lesurfman

Last night I was on the highway cruising at 60 in 6th gear. Mash the gas pedal the boost gauge went to 20psi as usual but 2 second later the boost went down to 15 psi Normal than 5 second later it went down to 1-2 psi. not normal

I let go of the gas pedal and try again only getting 2psi of boost, took it easy and full boost came back maybe 15 seconds later. ( is this what's called limp mode ?)

Tried this 5-6 times and got the same result every time.

I will pulled the codes tonight.

I changed the cam follower 2 weeks ago so that is not the problem.

I haven't done the recall for the fuel pressure sensor and the pcv yet.

I suspect the fuel pressure(g401) or the N75 to be the problem.

What are you guys thinking it could be?

TIA

i would do a boost leak before anything else. the taper from 20-15 is typical, but not hitting above 2psi routinely indicates a potential boost leak

Originally Posted by kerfuffle

I am currently experiencing similar if not exact issues with my 08 A4 S-Line with 45000 miles. How can I go about diagnosing what the cause is? How can I "pull" the codes? Vagcom?

Thanks

because of the mileage listed, i would 1st check cam follower, then check boost leak

Originally Posted by 1975audi

Same here.
Only I never go as low as 2psi.
One day 20psi the next only 15.
Changed my spring on the dv to yellow. Same thing happens
On Uni stage 2
Any thoughts

unitronics software adjusts to how you play around.... you need to essentially 'wake up' your software. you can do this two ways, throttle reset (google search) or you can go WOT a few times and watch your boost go from 15 spike to 17 spike to 19 spike to 22 spike.

source - i ran uni stage 2

uni is a very good software, but not a lot of places tell you that their software essentially adjusts to your driving, if you baby the car, it is not going to go balls to walls for you, pretty innovative imo because it steps back the performance when you do not want it potentially increasing the life of a tune engine ya dig?

**jimrobbington** · 05-21-2013 08:16 PM

Originally Posted by 1975audi

Same here.
Only I never go as low as 2psi.
One day 20psi the next only 15.
Changed my spring on the dv to yellow. Same thing happens
On Uni stage 2
Any thoughts

That sounds more like a wastegate adjustment might benefit you.

Sent from my porcelain throne.

**1975audi** · 05-22-2013 02:30 AM

I'll look into it.
Thanks.
I emailed uni but still no response.
Could it be the n75 valve?

**jimrobbington** · 05-22-2013 07:54 AM

Originally Posted by 1975audi

I'll look into it.
Thanks.
I emailed uni but still no response.
Could it be the n75 valve?

it's possible. But I guess it's also possible it could be a fuel issue. Again, boost and fuel logs would help.

Sent from my porcelain throne.

**lesurfman** · 05-22-2013 06:50 PM

I vag-commed my ECU and there was 2 codes

P0087 Fuel Rail/System Pressure: Too Low
(have seen this code twice in the last 3 years)

P000A Camshaft A (Bank 1 Intake): Positioner Slow Response
(first time I see this code)

I will have the G410 recall done and see what happens after that

**jimrobbington** · 05-22-2013 10:11 PM

Yep, still leaning towards fuel cuts.

Sent from my porcelain throne.

**lesurfman** · 05-23-2013 07:31 PM

What do you think could be the cause of those fuel cuts

What should I log?

thx

Originally Posted by jimrobbington

Yep, still leaning towards fuel cuts.

Sent from my porcelain throne.

**jimrobbington** · 05-24-2013 06:39 PM

I don't know the blocks off the top of my head, but I would do boost requested vs actual, fuel rail pressure req vs act, and lpfp req vs act.

Sent from my porcelain throne.

**mec** · 05-24-2013 08:55 PM

Originally Posted by lesurfman

What do you think could be the cause of those fuel cuts

What should I log?

thx

Too much fuel requested when the hpfp can't produce that amount. If you have a friend near you with an upgraded pump I would check that out, otherwise order a hpfp upgrade and put those fuel cuts to sleep!