Rob Edwards

Y'know, John, funny you menition it, since I finished adjusting the TPS, the revs drop much more rapidly during upshifts, so that I've got to blip it right before engaging the clutch in order to avoid some jerkiness. The car also registers 90 mpg very (1-2 sec) rapidly after letting off the gas on level ground. Does this sound related to this 'cut off restore rpm' parameter. I need to get my spanner back from Bill Swift- will running the idle adaptation help, or shall I enlist the services of a ST?

BrianG

I have the opposite situation to Rob's. While my GT does idle at a nice even 825 rpm, and it does show 99mpg on throttle let-off, there seems to be little engine braking when I lift the throttle. I cannot feel the lift-throttle injector cut-off like I can in my non-928 car, and I'd like to see better engine braking. Is something off with this too?

Bill Ball

[Edit after post: Ooops! Misread the above - you're switch IS working if you see 99, so the following is NA]....This would indicate the idle switch is not working. One possibility is the throttle cable is too snug and not allowing the plate to close against the stop or the switch to engage. With the engine off and the hood up, move the throttle cable. You should here a faint but definite click within a few degrees off-idle position. If there is no click, make sure there is a tiny bit of slack in the cable. If you now hear the click, see how the car runs and if the "99 MPG" now appears when you are engine braking.

John Speake

Hello Bill and Brian
The LH ECU has to reeceive the closed idle throttle switch signal before the injectors will be shut off on the overrun (rpm above abt 2000rpm from memory). Then the digidash indicates the 99mpg.

So in both your cases it does appear that the closed throttle switches are working OK. But of course the time it takes for the switch to operate may be dependant on friction in the throttle cable/pulley system....

This may explain the improvement that Bill noticed after adjusting his throttle switch.

It is surprising that Brian doesn't feel any obvious engine braking effect on the overrun. I suggest that you use your SharkTuner and make some data runs under these conditions.

Note carefully the time it takes for the closed throttle signal to respond.

You could also experiment with the fuel restore to come in at a much lower rpm.

Bill Ball

Oops! I misread Brian's post immediately prior to mine. Somehow I saw the word "not" before "show 99". Wishful thinking. Nevermind.

AO

If there is little engine braking, then I would presume that some fuel is still getting into the/a combustion chamber. Just becasue the MPG says 99, does not mean that no fuel is being delivered via a leaky injector. The 99MPG just indicates that the computer has shut off the injectors and your car is moving.

However, I seriously doubt a single leaky injector would make that significant of a difference, let alone allow the car to rev to 3k.

What if the code on the chips is slightly corrupted or being misread? Not sure if that's possible, but since Brian is running custom chips via his STer, I would pop the chips out and verify the code still matches the .bin file. Or maybe just burn a new set and re-install. BTW, don't forget to cover the little glass window. The chips are UV sensitive.

John Speake

I don't think Brian has SharkTuned his GT yet......

BrianG

Correct... I have not... I'm still messing with the AutoRotor'd S4.

John... what is the OEM fuel-restore rpm value? How low is reasonable?

John Speake

Ooops ! I was wrong, it is the high rpm fuel cutoff and respore that is editable with the SharkTuner.

You can only turn the trhrottle shut fuel restore on or off with the SharkTuner........

I thinkl the fuel restore on closed throttle is 2200rpm, but you can measure that with the SharkTuner...

BrianG

OK...I'll bet that's the issue.

On my V-10 Dodge, you can feel the closed-throttle fuel-restore kick in at about 1200 RPM. I just enjoy the extra engine braking through the lower 1000 rpm I guess.......

the flyin' scotsman

As we are talking about initial start up issue why would the closed throttle restore be active? Would this not only engage when lifting the foot from the go pedal from a 'high' rpm/road speed?

John Speake

Hello Malcolm,
Yes the thread has diverted a little, about over run closed throttle....

High idle speed with foot off throttle as high as 3000rpm must be an air leak. The idle speed when cold is somewhat higher.

We have been doing some work on the SahrkTuner to make the idle speed adjustable. In doing this we have discovered that idle spped is set somewhat higher when the temp is colder. e.g. at -10degC the idle spped is set to 950rpm, against the normal 675rpm when at normal temp.

BrianG

Well that about points to a vacuum leak or ISV issue, indeed! My GT idles a needle width above 800 (825?) rpm.