Hi all, so my VRS has a weird issue and im at my wits end with it.

 

Between 2 and 3k rpm if i floor it, the power comes and goes a few times, then when it clears the car picks up and pulls hard to redline. If i roll onto the throttle, there are no power dips and it just pulls hard.

 

Mostly evident in 3rd and above. if im over 3k and floor it, the car picks up like it should.

 

i have done various "tests" and replaced some parts to try to diagnose, I've also got limited info from live data using the torque app.

 

I've replaced : -

 

Diverter valve - now has Rev G fitted. Previously had a Rev C piston type, made no difference

Coil packs and spark plugs - Had a misfire under load on one cylinder. Replaced coil pack, no misfires since

Evap purge valve - came up with a Po441 fault code. Probably unrelated to the "main fault", replaced valve and code hasnt come back

 

I have tested a few bits : -

 

MAF reading - Peaks at around 204 on average on a 3rd gear pull. Sometimes a few up, sometimes a few down but its similar every time. Due to this, i dont think its a garden variety boost leak, especially as its making that kind of power higher up the rev band than the dips.

Uplugged MAF sensor - Less pronounced, but dips still there.

 

Can't see any evidence of oil seepage around boost pipes.

 

Any ideas? im thinking i might need a copy of VCDS to log data, but if it could be something simple ill try that before laying out £200 without fixing it

 

 

Air filter?

Air filter is only a few months old, ramair foam one 

Try the original.

It did this before I replaced the air filter so I’m reasonably sure it’s nothing to do with it. Plus it’s making very good peak power above 3k

How many miles. Have you cleaned inlet ports and valves? Checked In jectors? 

its on 95k. Thats the second recommendation for cleaning inlet valves, i havent checked the injectors but i have checked rail pressure after i switch the engine off. it goes up slightly as i would expect. The fuel pressure does not drop off as if an injector was leaking but ill check first thing tomorrow. If pressure is zero ill know theres a leak.

 

I would have thought i would get a misfire if either were that far gone tbh, but idle is rock steady and it really takes off later in the rev band.

If carbon clean has never been done. I'd do that as a start. It disturbs the air flow, can cause misfires and lack of response.  I'll link to my thread that shows you mine at 60 something miles. 

 

 

Edited 14 September, 20223 yr by TheClient

On the injectors  there is also the spray pattern and flow rate which you can't check without pulling them and getting checked on ansu machine or similar. If you do carbon cleaning I'd send your 4 injectors off for cleaning at testing at same time. They cone off with the intake manifold. 

Edited 14 September, 20223 yr by TheClient

I’ve done some live data this evening, fuel rail pressure holds rock steady around 2100 psi which is just under 145 bar. Not sure if this is too high? 
 

when the power dips, boost and MAF values drop which I would expect. I can hear the DV activate when the power dips. Overall MAF reading hit 200 so I’m convinced whatever the issue is it isn’t serious. 

10 hours ago, PopeyeVRS said:

I’ve done some live data this evening, fuel rail pressure holds rock steady around 2100 psi which is just under 145 bar. Not sure if this is too high? 
 

when the power dips, boost and MAF values drop which I would expect. I can hear the DV activate when the power dips. Overall MAF reading hit 200 so I’m convinced whatever the issue is it isn’t serious. 

I never did any logging with HPFP. From what I've heard 40-50 bar at idle.  And up to 120bar in operation is good. Yours maybe a touch high, maybe. Would it cause a problem though. No check engine light, so it is not flagging it as out of range.  The DV operating is because the ECM thinks you are backing off I suppose and yes that will lower boost for sure.

Edited 15 September, 20223 yr by TheClient

@PopeyeVRS What's your engine code?

It’s a ccza.

 

That’s what is strange about the whole issue. If I get it over 3k before flooring in any gear you’d never know there was an issue. I’ve even tried cable tying the actuator for the runner flaps in case they were causing an obstruction.

 

you can watch the boost drop slightly and return strong. il l try to get a video later if i can find a way to mount my phone

just to update this, ive been looking into getting a copy of VCDS.

 

In the meantime, the N75 valve could be the culprit. For the sake of £30 its worth a go

 

looks a bit of a sod to get to!!

 

Edit : Correction, it IS a sod to get to!!!

 

Changed N75 and the small hoses, what an absolute pain on a job if you dont have small hands.

 

Anyway, first drive out and the power held strong right through the rev range. Looks promising.

 

Edited 17 September, 20223 yr by PopeyeVRS

Sounds promising, finger crossed. I guarantee you'll be cleaning intake ports and valves in the near future if you hold onto the car!😬

no doubt i will, just wanted it running right. Its about due a service so ill do it then

 

Edit : Just to update, it hasnt stuttered once since i changed the N75 valve, smooth power all the way through.

 

Thanks to all for the suggestions!!

Edited 20 September, 20223 yr by PopeyeVRS