Hi guys.My VRS has been boosting all over the place even with a constant throttle! At say 70mph with 1/2 throttle it will boost from 5psi to 10 psi all by itself? Ive done searches on this and some people say n75's so i changed it and it made no difference.Also suffers from flat spots all over the place and the mpg is around 21/23mpg!!!

When you boot it it will spike at 20psi then drop to 10psi then rise to around 14psi and then tail off according to the boost gauge.The car has a forge intercooler,remap and cai with a high flow cat.Yesterday the management light came on saying lamba bank one/cat below threshold.Could this be a sign of a dying MAF?

Sorry if your all sick of "surging" posts but with poor mpg i felt this was a bit different. P.S please be gentle as ive only had it a day

Think this is in the wrong forum?

Think this is in the wrong forum?

Sorry as i said new to this :p where should it go and can it be moved or do i need to repost?

Oh i just realised it says i have a fabia.That was my last one this is an octavia

Edited 30 June, 201016 yr by wagonwheels

Got me wondering there!

What was the actual fault code it gave you?

If the lambda is giving the ECU a dodgy reading then it may be overfueling (in which case new lambda), or if the lambda is detecting too much oxygen in the exhaust then it indicates an exhaust leak somewhere, possibly the downpipe. That may explain why your turbo boost is all over the place, if the exhaust gases are escaping the turbo will be spooling up quicker and the ECU is cutting the boost

Edited 30 June, 201016 yr by chicken_eyebrow

I think the fault code is 16804 - Catalyst System: Bank 1: Efficiency Below Threshold but i cleared it and it stayed off.Would it be worth changing my bailey DV for the standard one? Ive checked the visible hoses for splits and bad connections but nothing,so not pointing towards MAF then? I only mention it as my subaru did a similar thing.

Funny question but is your cat ok? No rattling noises from it?

If the cat has disintegrated then your fuel consumption will skyrocket because theres not much to restrict the exhaust flow and the turbo will be affected because of the change in backpressure.

Mate of mine with a Mk4 Golf 2 litre blew the innards of his cat out on the M25 in the Spring, he hardly uses the car so is only getting it sorted out later this year when its up for it's MOT but since he lost the cat the mpg went from 32 down to 22

Its got a blue flame 100 cel cat.

CEL light came back on tonight.Probably the same code.The post about the lambda being knackered could be right .I changed the dv to standard and no difference then the n75 and no change.Been checking the hoses to no avail and tightened all the jubilee clips.Ill give it a few more days of tinkering then it will have to go to Star performance to find out whats going on.

One final thought is could a knackered maf cause a secondary fault of the lambda?

Got the fault code 17704 now.I know what it means but would it cause the symptoms above?

Yeah 17704 error can cause poor mpg. When my coolant temp sensor and thermostat went my mpg dropped but nowhere near as much as yours has, mine went from about 34-35mpg to 31mpg. I've not heard of it affecting boost etc but it's possible if the ECU thinks the engine is colder than it really is it could be doing funny things with the boost and fueling.

Yeah 17704 error can cause poor mpg. When my coolant temp sensor and thermostat went my mpg dropped but nowhere near as much as yours has, mine went from about 34-35mpg to 31mpg. I've not heard of it affecting boost etc but it's possible if the ECU thinks the engine is colder than it really is it could be doing funny things with the boost and fueling.

Thanks for you help on this chicken eyebrow.Fitted a new temp sensor today and cleared the code.Nothing changed in terms of boosting problems and it wasn't a long enough run to check mpg.

Dropping it off at Star Performance tonight and just leaving it with them.

Let us know what the verdict is from them

Let us know what the verdict is from them

Well i just picked it up and its certainly better after a faulty n75 was diag'ed along with a slight boost leak.I changed the n75 myself and it made no difference? :wonder: but i guess it could have been the wrong one or a faulty one.The car still holds back at about 3-4k with the boost dropping to 10psi then going back to 15psi.Its really doing my head in now

Hi there wagon,do you have vagcom?if so do a boost log specified boost against actual,what the ecu is seeing,had a 1.8t bora at my work,had a burst breather pipe under the inlet manifold,a fairly common pipe for splitting,this pipe is notorious for boost leaks.

If there's no other fault codes and your tuner has checked all the pipework and valves (and replaced the N75) then have you considered having the remap taken off? Or even just checked on a rolling road by whoever remapped it in the first place?

Edited 9 July, 201015 yr by chicken_eyebrow

If there's no other fault codes and your tuner has checked all the pipework and valves (and replaced the N75) then have you considered having the remap taken off? Or even just checked on a rolling road by whoever remapped it in the first place?

It was custom mapped down near newcastle and im too far away to go down.The map was checked at star and it seems good but he did say there a bit of an over shoot in boost when you floor it suddenly.I wasn't really happy with the attitude and service so ill look for someone else to look at it.Ive got vagcom but not the cable yet If im smooth with the throttle its not as bad.Tried a new maf today to and no difference! It must be a boost leak somewhere?

Fitted new plugs yesterday but still no joy.Running out of ideas now.No fault codes and feels like its getting worse Anything else it could be?

What you said about it being ok if you're careful on the throttle seems to support the point Star performance made about it boosting too much if you floor it suddenly. It sounds like the map is making the car boost too much too early (possibly also explains why it is using massive amounts of fuel) then the ECU is trying to cut the boost, possibly by using the N75 to partly open the wastegate or using the N249 valve to open the DV and vent boost that way. If you have a boost gauge fitted try accelerating very gently until the boost reaches 15psi and hold it around there and see if there's any juddering.

If it is an overboosting problem then I'm not sure how you can get round it short of having the map taken off. It sounds like you've already replaced all the components that could possibly have been to blame and had all the hoses etc checked. Might be worth finding out who remapped it originally and asking some questions.

Hi wagon.are you up in scotland?i presume so that you took your car to star performance,im down near dunfermline,i could take a look at your car if your struggling,im off work just now with a broken jaw,would probably be next week before im up to it,if you can log block 115 in vagcom,if it does turn out to be your map,i know a guy who can tweak it.first thing to do is a boost log though.

Hi wagon.are you up in scotland?i presume so that you took your car to star performance,im down near dunfermline,i could take a look at your car if your struggling,im off work just now with a broken jaw,would probably be next week before im up to it,if you can log block 115 in vagcom,if it does turn out to be your map,i know a guy who can tweak it.first thing to do is a boost log though.

That would be great yea. ill pm you my details

Funny question but is your cat ok? No rattling noises from it?

If the cat has disintegrated then your fuel consumption will skyrocket because theres not much to restrict the exhaust flow and the turbo will be affected because of the change in backpressure.

Mate of mine with a Mk4 Golf 2 litre blew the innards of his cat out on the M25 in the Spring, he hardly uses the car so is only getting it sorted out later this year when its up for it's MOT but since he lost the cat the mpg went from 32 down to 22

really????

p.s the only way you wil know how to solve the problem is to get vag com on your car and do some live logging then you will be able to pin point the fault

all the other things said and parts changed is pointless untill you know what the fault is.

are cars have computers on them that do 90% of the hard work in fault finding you just have to remove the data and get someone who knows what there looking at and 99% of the time it will pin poin the exact fault

hth

The cat is a blue flame high flow cat and fairly recent.Ive had a cat implode on me before and i dont think its that cos there's loads of gases out the back

stop speculating do some logs and it will tell you the prob !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

do you want me to say itt agin lol

stop speculating do some logs and it will tell you the prob !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

do you want me to say itt agin lol

The only logs ill be doing are in th little boys room As said earlier in the post i dont have a vag com cable and even if i did i wouldn't know how to understand what was displayed.

Help seems to be on hand to ge it sorted.