320BHP GT28RS 1.8T Elise - Rattle under Boost ! HELP

[Andy Cotton]

The Turbo and actuator are brand new - so I'm pretty sure it's not that and so are all the interconnecting pipes and hoses.

Anyway it was exactly the same with the K04 setup, which is a bit strange.

The DV valve is new (ish) and is a piston one - you can hear it dumping back into the intake so I'm sure it's not that - and anyway it's a totally different sound. Boost comes in from the bottom on my one and exits at the side - the opposite way round to the std bosch one.

Over the last few days a strange thing has happened - the car has been acting normally - boosting to only 1.3Bar (as expected and as mapped on the RR) and no chinking from the back - the boost has appeared to be linear - this has been the case ever since (coincidentally) the Audi man went for a spin in it.

I went out last night in the car and I was getting boost spikes which I controlled with the throttle to 1.6Bar (very very rapid increase in boost) if I had not of controlled it with the throttle I'm sure it would have gone a bit more 1.7 Bar ????

Anyway - the chinking was back - completely consistent with this rapid increase in Boost (boost spike !!)

I've ordered a New N75 and I'll let you know the results - should be here next week

 

[minimivic]

just curious but do you need the n75 when running SEM? surly the boost is controlled by the SEM.
Probably wrong.
Or drive to me and I'll have a listen for you and give a second opinion.

 

[Andy Cotton]

What's SEM ? and where do you live ?

 

[minimivic]

SEM = Stand alone Engine Management (emerald in your case?)

I live near Shaftesbury so just up the A30 from you.

 

[ibizacupra]

just curious but do you need the n75 when running SEM? surly the boost is controlled by the SEM.
Probably wrong.
Or drive to me and I'll have a listen for you and give a second opinion.

an n75 or equivalent other control valve is not just for bosch ecu's, it a frequency valve for bleeding out boost to actuator, as controlled by any ecu, be it stand alone or ME7 bosch.

that or crude bleed valves which are just a constant leak, and a little more laggy than an n75 valved car

 

[Andy Cotton]

The Emerald has a page for Boost Control within the Software - the table is filled in depending on how much boost you want.

Shaftsbury hey - I'm moving to Sherborne this wednesday so I'll give you a shout when I'm settled.

I'm going to change the N75 for starters (£42) and then see how I get on.

 

[max_torque]

Sounds to me like you have a boost calibration issue. I can't remember much about how the emerald ecu is cal'd (i had the first "turbo" M3d of Daves shelves way back in '95!) but you need to get the boost control cal looked at.
i suspect that the "rattle" is detonation occuring, especially as it seems to be worse on sudden tip in situations with a rapid rise of boost. (what you find here is that your ignition values at lower load are agressive, this starts the det as the load builds, then once you have started the det you need a very retarded ignition to remove it)

if it is det, then as mentioned before, be careful, or it will be cream crackered very soon!

Go through the boost control system with a fine tooth comb, check the wastegate for jamming, hoses for leaks, the condition of the N24 boost control valve etc. Then look (or get looked at!) the boost control system, check what the valve drive frequency is (should probably be round about 25 to 35Hz depending on valve type), check what the "open loop pre-position" table values are set to (if this table exists) then look at the PID terms for overall gain and response.

One simple test to check the systems hardware is to leave the valve electrically disconnected, this should give you the "min boost line" across the rev range, check with some steady state tip in that the boost does not surge or flare and that it settles to a steady value (use a high gear, or hold car back against brakes in 3rd for example). If it is all over the place at this point there is something wrong with the hardware on the car, i.e. wastegate sticking etc)

Hope that is some help!

 

[ibizacupra]

some great advise as always Paul

 

[simch]

now i may sound demented,but could it possibly be the passenger seat?

Maybe the missus needs some oil on her earings.......?!! LOL

Thrust washers on the crank maybe.........? Givign too much endfolat, maybe noisy under load...?


Otherwise, depending on the engine you have, it could be a top end noise, camchain / VVC system if it has it? But maybe it is the compresser wheel complaining if the boost is spikinig for some reason...? Check you hoses to the N75? Sticking wastegate...?

 

[Andy Cotton]

Paul,

thanks for the advice.
The Turbo and wastegate are brand new so I'm sure it's not sticking. We also had our head in the engine during some of the RR runs and we saw the waste gate opening every time.

If I disconnect the N75 the car doesn't go over 0.5 Bar so again not the wastegate area.

I have changed the N75 valve for a new one and a funny thing has happened.
I drove the car and waited for the coolant temp to get to 90 Deg C (about 15mins of driving) then I gave it some welly.
again the rate of rise in boost/acceleration was very aggressive and tinckling was heard over 1 bar - so obviously a waste of money for the valve.

The next day I drove the car for about 30 mins before i started to give it some welly and guess what - the car didn't go over 1.1 Bar and i saw 1.2 in 5th uphill but no more.
I've driven it for the last two days and the same thing has happened -nothing over 1.1Bar also the rise in boost is quite linear and not as agressive as before.

So is this an temperature related thing ? The charge temp sensor on the intake is my next point of call.

Looking at the Emerald map and depending on the temp it's detecting it adjusts the ignition and injectors so this could also be the problem.
At £22 delivered I have decided to change it anyway.

If the car behaves itself I will have to go back into the map and turn the boost back up to 1.3 Bar as mapped on the rollers by Emerald.

 

[Backdraft]

Hi Andy,

Why are you running such large injectors. What make are they? There are only a few available that give the same spray pattern as standard.
On a different note, I have lost your contact details and found you on here. I have solde a turbo kit to another customer that is putting the 1.8T in his Lotus and would like to talk to you about drive shafts and gearbox adapters. If you are happy to talk to him, please give me a call and I will give you his number?
Regards,
Mark Hosken. 01908 676140.

 

[f1btn]

Hello Andy

I run an emerald in one of my vw's its a v6 turbo not a 4 pot but i have had similar issues it turned out to be the map sensor cocking about,but having said that i didnt have the boost fluctuations that your having but it was detonating in a similar fashion when under load!
I would say that it has to be a boost leak as the emerald wont shut anything down if it overboosts, is it temperture orientated, i.e does it occur more in certain conditions (hot weather etc).
Thinking about it though the map sensor should cut the ignition if it overboosts so dave must have mapped it into the map if you see what i mean!

 

[Andy Cotton]

I'm running those injectors because you can't get 320BHP from Std ones - it's physics at the end of the day and you can't change the laws. Dave at Emerald tuned the car on the rollers he said they were fine - so there's nothing wrong with them.


Anyway - I've found out what was happening - basically the N75 valve was connected with cheapo blue fancy hose (Not Samco !) and what was happening was, the weight of the N75 vlave was pulling the hose such that it was kinking the charge line. When the pipe was cold the restriction (kink) in the pipe was basically not opening the waste gate quick enough and I was getting this boost spike which was causing the pinking.
When the car and pipe heated up - the pipe went soft and basically would move and react to charge pressure quicker, push the actuator quicker and hence no pinking.
When the car was left overnight the charge pipe to the N75 went cold and stiff and would cause a restriction to the actuator and hence wouldn't open the wastegate quick enough - hence rapid boost = pinking.

I have secured the N75 valve so it doesn't move and changed the cheapo pipe for some descent stuff .

The car goes like stink now with no associated pinking !

Since doing this I have modded the car to run a separate oil breather system and catch tank so hopefully I won't get any issues with oil fouling up the N75, Charge temp sensor and MAP sensor. When racing on the track the car was breathing heavy through the intake - so I've separated the breather system out and I'm running a baffled sump.

I'll let you know how I get on.

Andy C