High wastegate duty cycle

[Alan_C]

I've posted here as this is more related to an ElanScan, so sorry about the double post.

The SE is now running Elysium V5.3, K&N filter in standard dustbin, Piper 2 1/4 exhaust, timing is spot on, no dump valve, but boost won't go above 0.79 BAR. Checked most things, can't find a fault. I've attached a short ElanScan in case I've missed anything, if someone could have a look?

Looking closer, I notice that the wastegate duty cycle is very high when on boost, at about 80%, other cars seems to be about 40%? Looking at my previous ElanScan results http://forum.lotuselancentral.com/viewtopic.php?f=34&t=15816 when running standard PROM it's also high at 80%, but with standard boost. I can't get my head round what this means, does a higher wastegate duty cycle mean the ECU is trying to reduce the boost and for some reason it can't? If so, why would it be trying to reduce the boost when it hadn't reached the max limit set by the Elysium PROM?

Alan C

[Alan_C]

Any comments? Someone? Anyone?!!

[Blue_Bullet]

Did you ever sort this out?

I still have the same problem running a Everest Peco with Watgate Ported!

Maybe its just the gauge but it seemed accurate with stock chip!

[tigerdog]

As I understand, "wastegate duty cycle" represents the percentage of time the boost solenoid valve (BSV) is held open.

If there was no BSV, the wastegate would open as soon as the boost pressure in the actuator can overcome the spring holding the wastegate shut. There's a pipe connecting the actuator to the pressure side of the turbo.

The BSV introduces a leak in this pipe. when it's open, pressure bleeds off instead of opening the wastegate. The longer the BSV is open, the bigger the leak. The bigger the leak, the longer the wastegate stays closed and the higher the boost gets.

in your case, the duty cycle is long but the pressure is still low. This could mean any number of things:
- the wastegate may not be closing fully
- the pipe circuit from turbo to BSV to air cleaner might be blocked or crimped (test by energising the solenoid and blowing through the pipe)
- the BSV may be broken (but probably not if you can boost above the minimum even a little)
- there could be a leak somewhere in the intake path from turbo output to plenum input, bleeding off pressure
- loose clamps at junctions. Don't just look - tighten!
- split rubber pipework/elbows
- leaky dump valve (if fitted)
- your gauge might be broken

It's easy to tell if you're boosting higher than stock - the car feels LOTS quicker. I couldn't believe how slow the car felt when i went back to stock boost. If the car feels the same as with the stock chip, then you're losing boost somewhere because the duty cycle is higher but the boost isn't there. Diagnosis is mostly process of elimination at this point. best of luck with it!

EDIT: found your other thread Looks like the first point called it right. Glad it's fixed, Alan! Hopefully this treatise (typed on my mobile phone, by gosh!) will help Blue Bullet or some other lost soul understand the mysteries of boost control.

[Alan_C]

Hi Tigerdog,

I'd pretty much exhausted (ha ha, there's a pun!) all other options regarding the high duty cycle, and deduced that my only option was to examine the turbo, which I didn't want to do unless I had a spare to bolt on, which turned out was exactly what I needed. I've not yet done another Elanscan as the car is off the road for more repairs, but seeing as the waste gate valve was being held open about 2mm off it's seat I'm pretty sure this was the cause, and also partly due to the leaking hoses too.

[rip]

seeing as the waste gate valve was being held open about 2mm off it's seat I'm pretty sure this was the cause.

Sounds reasonable. Unusual fault though.
Hopefully it will work properly once everything is back together. That should please you as its been bugging you for a while now.

[Alan_C]

The car is currently up on jack stands for a front and rear HiSpec brake upgrade, and while it's up, new front dampers, new driveshaft gaitors (once they arrive from S J's, out of stock ) and a clean up and coat of POR15 to the bones. A nice new set of horns to replace the feeble squeek of the originals, and probably a few other minor things. I've booked a week off work, so my wife has been saying I'm having a car-cation (American holiday = vacation, stay-at-home holiday = staycation, car tinkering holiday.......). Managed to bleed the air out the cooling system today, don't try it with it up on just front jack stands, nose in the air, it just stayed air locked.