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

[Andy Cotton]

Gents,

please please help.

I have a 20v 1.8T in a Lotus elise with GT28RS turbo fitted.

The car is running Emerald ECU and Mr Emerald himself tuned it on the rollers.

TSR also live mapped the car on the road - the car's a total animal.

BUT - I have a rattle under load , above 1 Bar boost, occassionally you car hear a rattle, if you lift off, the rattle goes.

I have had this problem ever since fitting the engine, it was the same with the K04 and the GT28RS.

I was convinced the problem was pinking ! however Dave Walker tells me that it can't be............so what is it them.

The only other sound i can think it's simular to is the Cam Chain. The engine was stood for 4 years in a garage before I found it. The sound only comes on under load over 1 Bar boost - and it sounds like a chain rattling in the head.

If you throttle off the sound goes, when the rattle does come on the car's still pulling like a train. The emission connector thinghy on the other side of the cam is not connected.

PLEASE HELP !

The local Audi specialist recon the had a TT in with exactly the same problem (rattle under high load) , they replaced the cam chain and tensioner and it was fixed !!

 

[ibizacupra]

your last sentance sounds like you have your own answer perhaps.
not come across it myself

 

[devonmikeyboy]

Sorry i cannot help you mate but i would love a ride in your car.

 

[Andy Cotton]

Yeah no problem - I live nr Yeovil in Somerset.

 

[h17och]

what turbo kit did you go for? or is it custom

im currently looking at gt28rs

cheers

Hooch

 

[stoneyfordNI]

local fella had a loose wastegate "door" if you get me , made a funny noise as prescribed on a ko3?

 

[Andy Cotton]

The Car is mostly be-spoke, the Turbo and manifold are the only off the shelf items I bought everything else is custom fabricated.

Back to the Rattle - I took a man from Audi out in it and guess what, it didn't rattle !!

But I did notice that the turbo didn't produce any more than 1.2 Bar - when it rattles the rate of acceleration of the boost gauge is crazy and often it goes to 1.6 Bar very very quickly.

Could this be the problem ? maybe it is Pinking due to the massive boost spike !

Does this mean the N75 Valve is giving me too much boost - is this possible ?

When the car was rolling roaded it produced 1.3 Bar max - now it's going to 1.5 /6 bar.

Reading up on the N75 valve (VW Vortex) it can give boost spike problems, making the car overboost and go into limp mode (not applicable on my car)

I'm wondering if this is my problem ?? anyone else had overboost problems with their N75 ?

 

[Feel]

Most of the limp mode stuff you've read will apply to the standard ECU - I don't know if your ECU does this or not? Limp mode on standard ECU is 0.8bar IIRC.

It might help if you described the rattle -metallic/tinny, solid thump, cho-cho-cho? You're going to have to get aural

Is the Emerald load based? That mnight explain the lower boost on the RR? Not enough load/different gear?

You mention boost gauge - I remember reading some people had rattly boost gauges??

 

[Andy Cotton]

Emerald does not have limp mode.

The Rattle only occurs if the boost shoots up over 1 bar to 1.5 or 1.6 Bar.
If the boost goes to 1.2 or 1.3 you don't get it.

The rattle is consistent with 75-100% throttle and you want the car to accelerate as fast as possible.

It's defo not the gauge - cos the gauge is in the dash and the engine is in the back - the sounds from the back.

the car was Rolling roaded in 5th cos any other gear it smoked the tyres.

The rattle sounds like a rattling cam chain, tinckel sound not a knock knock sound or heavy thump. Like a few marbles in a can rattling around.

I can rev the car to the red line without alot of boost and it doesn't do it.

Only a boot full of boost will make it do it - and usually if the gauge goes to 1.5Bar it will do it.

What I don't understand is why the varyation in boost - the map is fully boost controllable and this has not changed so what has the N75 ?

 

[h17och]

possibly the n75! can you log duty cycle on emerald ecu's?

Hooch

 

[Andy Cotton]

You can log Boost pressure and boost PWM

 

[Feel]

engine is in the back

I knew that

Like Bill said before, if it rattles like a cam chain and it quacks like a cam chain...

Does it do it all the way up the revs once you've hit 1.3-1.5 bar, so from 3,500 rpm all the way up, or just while it's over 1.3 bar?

Have you spoken to Mr Emerald to ask what it should boost to? 1.5/1.6 doesn't so THAT high compared to K04'd cars on here.

 

[Andy Cotton]

When boost falls off so does the noise - but yes I could happen all the way through the rev range from about 3.5k to 6K.

Dave said categorically it's not pinking ! he told me to reduce the ign timing by 4 degs on load site 14 and 15.

I did it and it made no difference. That's why he said it can't be pinking, but I'm not 100% convinced.

My thoughts on the cam chain is that "why is it boost dependant" ? It shouldn't make any difference - but it does.

 

[WeeJase]

Back to the Rattle - I took a man from Audi out in it and guess what, it didn't rattle !!

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

 

[h17och]

lol good idea

 

[cupra_matt]

I have had a few worn cam chain tensioners, which cause a rattle, but it normally rattles on idle,

But replaced the tensioner on my just to be safe. Its worth changing i think, even if it doesn't cure the rattle its one thing less to worry about.

I would also replace the cambelt tensioner damper, as i have seen many of these fail resulting in a scrap engine.

Hope you sort it, sounds like a fabulous car.

 

[Andy Cotton]

Right a bit more info needed I think.

The cam belt has been changed 10K ago along witht the tensioner, water pump etc...

The head has been overhauled with new valve guide seals and re-lapped valves - and therefore the old tensioner and chain were also off, but assessed as serviceable and therefore re-fitted.

I re-built the engine so I know a bit about it - the sound is DEFO engine related.

Would a large rise in boost (up to 1.6Bar) cause pinking ? the cars running 630cc injectors ?

Is there anyone an expert out there on PINKING - I would even drice the car to you if I thought you would know - it's driving me mad !

What if I put octane boost in it and try that - I do run 97 at the mo.

 

[Saul]

if its pinking, why not buy some a tanks worth of race fuel and see if it still does it

could it be the wastegate/spring?

 

[-=Rob=-]

You have to be careful with pinking, too much and a valve can go. About 10 years ago a friend had a seriously modded RS Turbo, it had a bad pinking problem which came about on med-full throttle, especially up long steep hills. The cause was too much boost and the custom ECU map not set to expect this boost. I believe it was an issue with the turbo actuator causing over boost. I went out in the car several times when it happened and it sounded like a type writer going really fast. I know the cars are totally different, but the symptoms sound similar. He drove it like this without getting it looked at and a valve went and also a piston, so be careful...

Higher octane fuel or addative would help slightly, but it's not a permament fix (Thats if it is a pinking problem).... Hope you get it sorted as the car sounds awesome!

 

[Feel]

I was wondering if it might be the DV - I'm not sure that you'd hear it as a rattle though, more likely to hear it dumping boost.

Not sure what you're running, but if it's servicable it might be worth having a look? Which way round is the DV is it "normal" or "reversed", depnds on your definition, but to me "normal" means boost coming in from the side.

TBH I think I'd get it on a rolling road and have a listen...