Part load surge

[bigmig95]

Hi Folks,  seem to have a issue with the car at the moment that seems to be coming more prominent as time goes on particularly in higher gears such as 5th and 6th.  When cruising at around 2000 with light throttle I open the throttle a few percent more and as the car gently comes on boost the engine seems to surge and come on and off boost until it hits over 4000 rpm where all feels OK.  I have no problems at WOT only at part load.

Car details, K03 GTi, 2005 with Revo stage 1 map and ITG enclosed canister and a recently changed DV to a revision G from revision D.  I've an SPS switch as well and have switched from my usual V-power map over to a 95RON map and the issue remains.  I can drive around this "surge" but my lazy driving likes part of the map.

Anyone any experience with this issue ?

[56OctyVRS]

Have had the ecu scanned for any fault codes. I would also get some datalogging done, as that will show you why the engine is surging.

[bigmig95]

No access to VCDS at the moment unfortunately and I realise it's the most logical route forward.  I've an ex colleague with the kit but it's just getting across to him at the moment thats an issue. I've read threads about WOT surging but none about on/off surging on part load when coming on boost.  It's possibly happening throughout the gears but is definitely more noticeable in higher gears.

[R-tech-Nick]

ARMD (Torque-Based Anti-Jerk Function) can cause your issue, ask your tuner to switch ARMD off to see if it sort it out. I am 99% sure it will.
Nick

[graeme]

coil pack misfiring under load ?

[GrayMK5GTI]

This sounds almost exactly like my issue. I've tried plugs & coil packs, cleaned the MAF and now put it down to a fuelling issue. Annoying thing is it doesn't do it on the dyno 

Keep us informed of any more updates 

[bigmig95]

Thought it might be the map but just put it back to the stock map and still got the same issue.  Tried another map which the Revo guys have labelled V-V Power in my SPS settings book and it didn't do it on the way home tonight.  I'll keep this map on for a day or so and see if it does it. 

I'll look into what R-Tech Nick has suggested as Revo HQ is only down the road from where I work next week.  If they draw a blank I'll pop and see Nick and have an excuse to discuss more grunt once this is sorted.   

I would have thought it unlikely to be misfire, it doesn't feel like it, it feels more like a boost control issue and the boost surging noise heard through the ITG  (boost megaphone) kind of backs this up, the frequency of the surge is a lot less than you'd get from a coil pack misfire ???  I'll not rule anything out yet though.


If you have any joy in the meantime Gray let us know please 

[GrayMK5GTI]

My clutch is past it's best now so I can't dyno it  will have to save for a clutch before I can investigate further 

[PDT]

A dyno won't help much in finding a part throttle surge tbh.

[rtechniki]

A dyno won't help much in finding a part throttle surge tbh.

It will do if its the Anti jerk routine cutting torque via timing reduction.   Set your ramp rate on lowest load and do a 5th gear sweep then watch the engine pulsate.