power loss at 4800 rpm ?

[GIXXERUK 0]

today i went to awesome gti and had about 20 runs on the rolling road for 3 hours to try and discover why my car hits a wall at 4800 rpm

it drives fine but will not reach peak bhp because it tails off at 4800

 

the things changed which made no difference

 

3 maf's

ecu

fuel pressure regulator

distributor

run with the air filter on and off

 

all maps were identical , the only thing they can suggest now is that its the aftermarket cat strangling the power at 4800 rpm

 

overlayed the map with a 2.8 golf and its up until it gets to 4800

 

do i get another cat or de cat it ??

 

cheers

 

paul

 

anyone ever heard of this ?

 

vag com was totally clear

[veeDuB_Rado 0]

Maybe the leads are naff?

[ben16v 0]

not anything like fuel filter (limits of my knowledge) is it?

 

de-cat and keep your old one if it needs it for MOT

 

 

good luck mate

 

ben

[Supercharged 2]

I'd say the fuel pump is a likely candidate...

[GIXXERUK 0]

the rolling road maps the air /fuel and it was perfect , no spikes or sudden drops

the guy was at a total loss and really p!$$ed he could'nt find the fault, he remembered the car as he rebuilt the bottom end and fitted the koni's and magnex exhaust

 

i asked about the leads/plugs and he said they were fine and there is no problem elsewhere in the rev range, driving it you can't feel it , it doesn't hesitate, miss ,idle rough - nothing

i wouldn't have known if i hadn't had it RR , thats how subtle it is but i know there are horses out there somewhere so i'm not happy

 

16v, i only noticed the other day that i have a book with loads of pics of your car in it (press car)

[GIXXERUK 0]

Supercharged, maybe mate i'm at loss now but you would think it would hesitate or miss or at least not be exactly the same revs every time ?

 

it will lose power at 4800 rpm in any gear , he ran it in different gears

[Supercharged 2]

Rebuilt bottom end rings alarm bells - have you had the timing checked, the cam could be a tooth out causing this problem....

[GIXXERUK 0]

Supercharged, it was rebuilt by awesome 2 years ago, it was a 2.8 block rebored to 2.9, i've got the receipt , i'll check the timing though cheers

[NickVR6 0]

I have my cat off at the mo (until the next mot) if you can think of a way to get it to you reasonably then your welcome to borrow it mate, for as long as it takes to test fit and test it. My mots not until Sept 2006!? It ran 200 at stealth with it on and came off two days later. Also have a spare lambda probe if you wanna try that, peanuts to post.

[NickVR6 0]

Or you could book it into VAG, and see if its the air freshner!

[GIXXERUK 0]

NickVR6, much appreciated mate but i think i may go the decat route , where did you get yours ? they quoted me £80 + vat for a supersprint

 

(disc hasn't arrived yet )

[NickVR6 0]

Disc should have been with you today bud, tommorrow morning latest! If its not there tommorrow let me know and ill send another.

 

pm'd re the de-cat

[GIXXERUK 0]

NickVR6, nice one cheers nick , £176 i spent at awesome today but at least i know the ecu, dizzy, maf and fuel regulator are all ok

[NickVR6 0]

Looks like you have narrowed the field mate. Cant be many things left to try. At least the de-cat is worth doing even if it isnt that. I noticed no difference at the top end, but it definately picked up the low down torque quite noticeably imo. Much more that the cat back and bmc when they went on.

[NickVR6 0]

Fuel filter? Thats a cheap easy check.

[GIXXERUK 0]

NickVR6, he mapped the air /fuel and there was nothing that linked it at those revs, you would have seen it drop he said :-(

 

the 4wd RR at awesome was only fitted in february and its the dogs , all the whistles and bells but the car is let down by the prehistoric obd1

 

lets say obd1 doesnt tell you the wheel nut is loose , it tells you when the wheel has fell off , if that makes sense

 

and iirc the lambda is ignored at wot

[GIXXERUK 0]

no more ideas ?

[dr_mat 0]

How does it run above 4800rpm then? Rough? Smooth? Not at all? Noisy? Pinking? What did the A/F gauge say up there? Any engine temp weirdness? Valve timing is still primary concern ...

 

How long has it been doing this? What happened when it started ..? Have you tried a standard ECU and map?

[GIXXERUK 0]

dr_mat, it runs perfect above 4800 rpm without the rolling road i would never have known, maybe its been this way since i've had it ? if you drove it you would never know there was a loss

i've tried a standard replacement ecu and it ran exactly the same

[dr_mat 0]

And you're sure it's not just the rolling road?

I mean, when you say "performance drops off" how is the torque curve? What's your torque figure at 5500 rpm, say?

[ben16v 0]

dr_mat, its not the RR cos it was spotted at stealth and awesome have just had the same readings

 

heres the graphs

 

ben

[dr_mat 0]

Oh yeah, remember talking about that now. Weird...

[GIXXERUK 0]

dr_mat, as ben16v, says it was the same at awesome and stealth , both power and torque drop off at 4800 rpm

 

as i said before awesome suggest it could be the aftermarket cat strangling the power at those revs as there could be too much gas trying to escape causing it to bog down , do you think this is possible ?

 

tried

 

3 mafs

new dizzy (hall sender)

fuel pressure regulator

a different ecu

air filter on and off

 

all gave virtually the same result within 2 bhp

[Kevin Bacon 5]

I've only ever heard of Cats causing that kind of brick wall when the cells collapse, impeding flow. There was a Golf VR6 on the VR6OC forum that had the same problem, only his wouldn't rev past 5K at all......and it was the cat.

 

My old Supersprint Decat is at Stealth if you want to try it.

 

Only other thing I can think of is the fuel pump as already mentioned. It might be tired and not quite delivering enough juice from 4800rpm....which won't cause any problems lower down the rev range since the fuelling requirements are significantly less. I've seen a VR hooked up to a pressure guage on the rollers.....sat there at 4 bar fine all day long at idle, but when the injectors opened to full duty cycle at high rpms, the pressure dropped to about 3.2 bar, which kept the engine running, but with no further acceleration.

 

Since there is no 'Gospel according to Saint Haywire' in new and old VR6 Testaments, don't take that as read. I'm just airing thoughts from previous experiences.....

[GIXXERUK 0]

i'll take any advice on board mate , it revs round the clock but loses power at 4800 , although you cant actually feel it as such, the car doesn't decellerate or hesitate and does continue to drive normally

 

odd thing is , nothing made any difference on the rollers but the car does feel more lively now and instead of 22 mpg at 70 - 80 mph its showing and the guage verifies 30- 32 mpg which is a boon :-)

 

did the VR with the dodgy fuel pump show any signs at WOT ? such as hesitating or unable to hit the rev limiter ?

 

mine will red line no problem without a miss or hesitation

 

cheers

 

(ps . not easy but i might drop the cat to see what condition its in, the engine had a short engine due to excessive oil consumption , rings iirc, so i'm wondering if its all claggy in there ? )