Not boosting

[Paulm]

Replaced my thermostat today along with all the small bore rubber tube for DV, wastegate solenoid. Replaced all the jubilee clips on the boost hoses. Also did the O ring mod with reducer silicone hose. Pressure tested the whole thing and no boost leaks but still no boost.

Here is what my car is doing.

It has Homefry now so should be boosting to 21psi


30mph in 4th WOT 17psi boost by 2600rpm ish, then drops back to 12psi from 3 to 4 k then 15psi.

It feels like it wants to go. it is not missing but feels like it is holding back going a wee bit then holding again. by 4k it clears its self.
If i thrash it 1st & 2nd 15psi all the way

3rd & 4th 17psi all the way

5th 21psi all the way it starts dropping again about 5k ish

any ideas

cheers

Paul

[Mihnea]

Sounds to me a bit like Lee's plugged fuel filter... might be worth a shot to replace it, I bet it's never been done before, as most of the S2 avants out there...

HTH,

Mihnea, knackered after a day at the Nürburgring mapping a friend's RS2-ed S4 mit plugged fuel filter (ran awfully lean, now ok until he replaces the fuel filter and he gets black clouds of smoke from the exhaust).

[OZzzt]

Re: Not boosting

Originally posted by Paulm
any ideas

cheers

Paul

You have'nt by any chance reassembled the boost control solenoid the wrong way?

Any fault codes?


OZzzt

[Pete_RS2]

This sounds exactly like mine and does seem to affect all Avants with homefries. What petrol are you using ? Mine is better with Optimax but still noticeable.

Hopefully changing my fuel filter this week which is easier said than done on the Avant. If you haven't seen where it's located on the Avant the bracket which holds it in place by the fuel tank is impossible to get to without dropping the fuel tank. I'm going to try using the coupe filter (which is bigger than the Avant one) as piloted by Lee:

http://www.s2forum.com/forum/showthread.php?s=&threadid=1669&highlight=fuel+filter

If that doesn't work I'll try the barometric pressure sensor which fixed Jim's (blu_S2) similar problem:

http://www.s2forum.com/forum/showthread.php?s=&threadid=2899

[Dr H]

Also sounds very similar to mine but I am convinced mine is a leak.

I have had the problem for months (after getting a home fry) and changing my fuel filter made no difference. I'm waiting for the samcos for an excuse to remove every hose and check eveything properly.

[S2central.net]

@Avant S2 - This problem is NOT because of 'homefries' on Avants. There are plenty of healthy ones running about with 1.4bar in overboost.

PaulM's car had similar behaviour on 'Superchips'.

Your car doesn't develop max overboost because the ECU never sees full throttle. I shall send you instructions on how to test your Altitude sensor - as this was the root cause of identical behaviour in Jims Coupe - now fixed.
I'll spare you the boring detail, but the altitude sensor is wired in such a way that a faulty one (doesn't show a code) can alter the signal coming friom the throttle body - hence the ECU doesn't see the ~2.5k resistance path needed to detect full throttle. Could actually be the same thing in PaulM's car.

Have you got a fuel pressure test done yet - that is the only way to know that your pump, filter and regulator are upto scratch ?

Its all too easy to point fingers at chips when problems appear, but neither your nor Jims car went into overboost with stock chips.

Yes of course, chipped cars develop more boost and will always put a little more stress on the metres of ageing hoses around the engine, but that doesn't mean that 'chips' are the root cause of air leaks and other faults !

VAG-COM doesn't find every fault on these cars - truth is, the MOtronic diagnostics only detect sensor faults when they are open or short circuit.



Cheers,

Paul

[Dr H]

My car runs a first genersation homefry and always gets to full boost (1.4 - 1.5 bar) it just doesn't hold it hence my suspicions of a leak.

You could argue that the homefry has caused the leak but it is doing what it is supposed to do - increasing boost. It's just my crappy hoses that gave up when they were asked to perform under more stringent conditions

[blu_s2]

Paul(M),

From all the small niggles I've had with my car over 4 years of ownership the behaviour you describe really does sound like a leak.

I had a similar problem (which I confused with my WOT fault for a while) that was caused by an intermittent leak from the ID4mm vacuum tubing to the ECU.

Just my $0.02

[Paulm]

PLEASE NOTE THIS IS IN NO WAY A HOME FRY FAULT. SUPERCHIP DID THE VERY SAME.

I am very happy with Home fry as when i get 21psi in 5th it really fly's

Thanks for the info every1.

Mihnea, I will repalce the filter and pump as they have both done 96k now.

OZzzt, yeah boost control solenoid on as it came off, dont know how to check for fault code yet.

Avant S2, always use Optimax, cheers for the links

PaulN, dont know how to check for ecu code yet, need to read more on here to find out. I may well change the Altitude sensor as a precation. No time to check for fuel pressure as i go away again Wed so will have to wait till i come home

LPHUK2002, yeah but mine never gets to 1.4bar till 5th gear and holds boost very well from there. mine is just about the exact opposite of yours can't get it but when i do it holds well. strange.


blu_s2, I read your post re WOT so may well be that , I will be testing again today for boost leaks as I tested everything individually as I removed them so may have missed something.

thanks again, the search goes on

Paul

[Pete_RS2]

No offence Paul N - I wasn't having a go at the homefries. I was just pointing out that there have been more problems with Avants

The fault on mine is only apparent under load in 4th gear and because I know it's there I tend to look for it more. If I drive it 'normally', i.e. not putting in 4th gear early you wouldn't know it was there.

Anyway hopefully the Altitude sensor or fuel filter will fix mine this week. I plan to try Alistair's Altitude sensor on mine before he sells his Coupe.

[S2central.net]

Initially there were some chip related niggles that affected some (not all) ABY Avants, as the extra weight implied higher load and therefore less advance that could be sustained on the generic ABY chips. This was resolved many months ago by reducing the timing a 'tad' at WOT.

@Leigh - I had forgotten you still needed an upgrade, so as soon as I get my spare ECU back from PaulM, I shall get you sorted. That won't fix your air leak, but you will at least then be up to spec when the Samcos arrive.

I will post details on the altitude sensor tests here or on S2 Central later this week. It took about four or five days in total (over a year maybe) getting this resolved on Jim's car, so nobody (except Jim maybe) was happier than me to see a resolution after all that time. Just goes to show you can't always trust the fault codes.

Couldn't have solved this without the schematics and VAG breakout box for the ECU. I'll bet there's a few other cars carrying this fault around.



Cheers,

Paul

[blu_s2]

Couldn't have solved this without the schematics and VAG breakout box for the ECU. I'll bet there's a few other cars carrying this fault around.

Good point.... without a boost guage to show low boost levels at WOT and logging throttle switch values with Vag-Com this would just appear as slightly lower performance than expected.

If I had never had the car working 100% I wouldn't have even known it was at fault.

[Paulm]

Checked everything again, put on a diff DV cleaned the MAF with carb cleaner. still no better.

I can get plenty boost high the revs. In 6th it @4k 12psi slowly climbs to 24psi:eek2: maybe a wee bit high. it can hold 22psi upto 5600rpm then drops off agian.

I can feel the car being held back from 3 to 4 k. I can feel the ecu retarding ignition and/or reducing boost, prob both not to sure. then @ 4k it all settles down and off we go. I dont get full boost @ 4k in any gear but it builds as the revs rise.

what sort of symptoms does a hole in the Wastegate diaphram give?

cant do any more testing for 2 weeks now,

thanks for your help so far

Paul

[Mihnea]

Originally posted by Paulm


I can get plenty boost high the revs. In 6th it @4k 12psi slowly climbs to 24psi:eek2: maybe a wee bit high. it can hold 22psi upto 5600rpm then drops off agian.

I can feel the car being held back from 3 to 4 k. I can feel the ecu retarding ignition and/or reducing boost, prob both not to sure. then @ 4k it all settles down and off we go. I dont get full boost @ 4k in any gear but it builds as the revs rise.
Paul

All this sounds very very very similar to what I had been experiencing while mapping Lee's car in real time the first time in December, no boost, timing got retarded and no way to get power at low RPMs. High RPMs were just fine, the engine was kicking *** above 4k RPM.


If you have a digital multimeter, you can hook up the red lead to the lambda sensor output and the black one to the ground, then try to read the sensor's output at full throttle, it wouldn't surprise me much if you saw readings below .6 Volts, which definitely means too lean at WOT.

I might be wrong but if you have a DMM and some leads, it would be worth testing this...

Cheers,

Mihnea

[audiman]

Having aslightly blocked fuel can cause all sorts of problems that are hard to find. As the blocking process is so slow, many ppl dont notice it, but on cars like the S2, it needs as much fuel as possible. Knowing main dealer servicing, i bet PaulM's filter is the original. The interval for it is something stupid like 80k!!!!