mega_stream

Suffered it on the motorway flooring it in 3rd, the car just "died" for a second then the power came back on fine.

Peak was 1.175 on the Defi reading (around 16.7psi)

Whats happening!
Kinda got me worried now, wasn't that cold, didn't reach the 1.2 it normally peaks at (with no problems reaching 1.2 on previous runs)

Kinda got me worried.

John

john banks

You are running too near to fuel cut. Turn it back. Fuel cut can be unpredictable, and a threshold needs to be exceeded for a few seconds. I think you are being too greedy for the std ECU. Also your gauge may not be accurate no matter how posh it is. A lot do under-read and you may be running more than you think. I think you need to be running at least 1 PSI (in 5th gear under full load) below where you got the fuel cut in third gear today.

Whatever, turning the Dawes down will not kill your top end power.

ScoobyJawa

Exact same thing happened to me when I added a SS BB, turned it down and seemed ok - could be hitting the boost cut Bob Rawle talked about.

I since started getting it all the time after stretching the spring and increasing the bleed to 2.0mm (in an attempt to cure fluctuation and peak). Sorting out some decent pipework (not what comes with the dawes), remounting and using a 1.5mm bleed instead cured it - goes like a train now, MY99 car.

16.7 is very high to be running, as the cut is only around .8 more than that......

john banks

The flexible walls may result in peaks with the grey hose? Most hose including the factory stuff is more rigid.

nom

Now that's something that I have noticed - after a 'hack', fuel-cut comes on more easily (well, it does come on, which it doesn't usually )
Well, yes, obvious, but then leaping under the bonnet to whirl the Dawes back half a turn (recently went through the spring-stretching stage ), I noticed that the hose was seriously more flexible 'cos of the heat from this sort of driving. Again, obvious, but it seems quite likely that the new flexi-hosing is causing the fuel-cut to come on.
When cruising on the motorway with ocassional foot-to-the-floor moments in 5th it was fine at the same setting as caused the cut above. Presumably because of the cruisin' the innards wouldn't be as hot - certainly the turbo wasn't up to anything most of the time.
I have 'held' boost (well, there's virtually no peaking) set to 15psi (gauge reading) at WOT, 5th, 3k5ish RPM, so unless the gauge is quite do-lally, it should be fine. I wasn't paying too much attention to the boost gauge whilest driving like a maniac to see what the gauge was up to before I adjusted it though, which really wasn't very helpful Probably waggling around all over the place
Time to look into better tubes, I think!

john banks

Any boost control method becomes more peaky after a thrash. Trout mentioned the phenomena during a discussion on bleed valves, and then I posted about it after a recent thrash. Hence the recommendation for lower settings on track!

PING

Are we suggesting then that the standard tubing with the Dawes isn't rigid enough to cope with the temperature rise as you drive?

Steve

babber

Well my crap boost gauge peaks at 1.2 bar and holds around 1.1 bar, with no issues. Did thrash it the other day and in fifth on acceleration did reach fuel cut but was luckily on the motorway. Wouldn't like that to happen around town, so I'll drop it down a little.

What about a PE remap Could hold more bosst then

Cheers Phill C

nom

John -
Well, yup, but the thing is, why? Never quite got to the bottom of that one It seems to be that different control methods will have difference reasons to be peaky - if on the Dawes it's because the device & its hosing gets hot, surely some cunning way of keeping it cooler could be found? Wrapping it in kitchen foil springs to mind Probably not a good fix for track days, though

john banks

For all methods the turbo seems to spool up quicker when it is hot - not necessarily the Dawes getting hot I suppose? Otherwise electronic methods should not be similarly afflicted but they are.

How about running 17.5 PSI and running a fuel cut 2 PSI higher and having some DISCIPLINE to stay away from fuel cut?

I have never unintentionally or unexpectedly hit fuel cut, but then mine is over 19 PSI, so I am not a disciplined saint far from it. I have three times deliberately.

nom

Oh yes.
The turbo spool-up time depending on heat.
That's quite important, that one.

Stiffer spring? A day spring & a thrash spring? Well, it could work! Certainly easier to change than the diameter of the hole. Possibly one that's modulus changes depending on temperature, only the other way round to usual... hmmm, maybe not

nom

I think at this point I shall give up
My brain is starting to det - I need to go & put some beer in it to cool it down

L555BAT

WHAT IS "Dawes" MY CAR MY CAR HAS THE SAME PROBLEM BUT AS FAR AS I KNOW IT HAS A RDA CHIP AND A MONGOOSE SYSTEM

Fosters

...Also, what boost does a PPP run?

john banks

It was running 17 on my car originally.

mega_stream

Ok thanks, just aswell its only really the 2nd time I've pushed her with this setting (1st time was fine..)
I'll take it off tonight until I get time at the weekend to set it up properly.
I am using proper turbo piping that came with the Defi's for the Dawes, must admit I wasn't impressed with that grey stuff that it comes with.

John


[Edited by mega_stream - 3/12/2002 3:34:40 PM]

john banks

Or self adapting PID code? IE measure overshoot and increase D and reduce P until it doesn't happen. Use the final duty cycle as the new base duty cycle. It is possible. But then if PID is correctly setup it should adapt anyway to some degree as the D term will be higher the quicker the boost rises.

[Edited by john banks - 3/12/2002 5:56:40 PM]