Inverted throttle response ? [Archive] - SaabCentral Forums

: Inverted throttle response ?


hildebird
11th March 2004, 12:24 PM
Why does my 9-5 Aero accelerate quicker when you lift off from full throttle?

I thought it might be down on power when under maximum load, but at a recent rolling road power run, it showed a figure slightly above spec. at full throttle.

However, on a second run at 3/4 throttle the power and torque were higher and on a third run at about 1/2 throttle, it was higher still (peaking at 247bhp and 272lbft)

Why can't it go like this when it is at full throttle, it isn't natural to have to remember to lift off when you need more go.

kamalk
14th March 2004, 04:14 PM
What year is your 9-5 and how many miles are on it?

hildebird
15th March 2004, 06:59 AM
It is a year 2000 and it has now done 83000 miles.

kamalk
17th March 2004, 02:08 AM
Please advise if the car has been checked by a mechanic and what exactly they checked. I would not overlook all the obvious things like, dirty fuel filter, old spark plugs, failing DI cassette, failing mass airflow sensor. Also check O2 sensor/s, throttle body & full throttle switch, is your car an auto or a 5sp? if it's an auto dose the problem happen in any particular gear?

hildebird
17th March 2004, 05:27 AM
Yes it has been checked over, repeatedly. I have owned the car for 14 months now and it has always had this odd behaviour. It has been serviced by the saab dealer twice and also been in to them to be 'sorted out' for this peculiarity on two occasions. It has had new platinum plugs (by the dealer). They can't find anything wrong and claim that it has all the power it should have. I can't dispute it isn't short of go, it's just odd.

On the rolling road day, before me, a 900 specified at 175bhp came out at 173bhp and after me, a 9-5 specified at 150bhp came out at 151.6bhp. This suggests to me that the rolling road was giving reasonably accurate and consistent readings. My car is specified as 230bhp. It measured 239bhp at full throttle, but was better at less throttle, giving a best reading of 247bhp on the third run with plenty of heat soak inbetween.

It is a 5 speed manual and doesn't seem to have any other failings, it starts instantly every time, runs really smoothly, never misfires or misbehaves, gives really good fuel economy and peforms well.

TW_95
17th March 2004, 08:44 AM
This behaviour has also been noted on "other popular UK-based Saab 9-5 forums".

kamalk
19th March 2004, 01:06 AM
Has the dealer checked or changed the "mass airflow sensor" and the "full throttle switch"? (if equipped)

hildebird
22nd March 2004, 11:55 AM
I didn't think that 9-5's had a full throttle switch? Isn't it just the potentiometer on the fly-by-wire throttle body?

As for the air mass meter, I don't know if the dealer checked it or not. How do you check it, so long as it's not broken, doesn't it just work?

I could try cleaning the AMM internals with some spray solvent, in case it is oil contaminated. If it was oil contaminated, doesn't this fool the ECU into running lean, due to the insulating effect of the dirt on the outside of the wire?
When on the rolling road, the owner/operator said that the lamda control looked absolutely the perfect shape of curve, richening up towards the top end slightly.

I'm convinced that it is the trionic limiting the torque output for whatever reason it thinks necessary? I can't find out yet if they all do it or is it just mine?
If I were to fit a stage?? ECU do they do it as well, or would that be one possible cure?

Mattlach
23rd March 2004, 06:10 PM
This may be a silly thought but...

Is it possible the TCS is lowering power at full throttle? Have you tried doign the run with TCS turned off?

kamalk
24th March 2004, 01:00 AM
Yes indeed, I think your right about the "full throttle switch" it is incorporated within the fly-by-wire throttle body. (which could be bad) I would clean the air mass meter as it could do no harm. If you have access to another ECU swapping it might leed you in the right direction.

hildebird
25th March 2004, 05:17 AM
This may be a silly thought but...

Is it possible the TCS is lowering power at full throttle? Have you tried doign the run with TCS turned off?

TCS, this is all in with the electronic throttle/torque limiting - it isn't a separate system.
If it is TCS it shouldn't be cutting back as there is no trace of wheelspin or of lack of grip, it even does it in 5th gear.
When you say 'doing the run' it suggests I'm trying a deliberate acceleration run (1/4 mile?) The car does this 'pick-up when you back off' ALL THE TIME.
Should I turn the TCS off every time I drive the car?
(it defaults to being ON)

I'll give it a try it anyway, thanks Mattlach :cheesy:

Mattlach
25th March 2004, 08:20 AM
TCS, this is all in with the electronic throttle/torque limiting - it isn't a separate system.
If it is TCS it shouldn't be cutting back as there is no trace of wheelspin or of lack of grip, it even does it in 5th gear.
When you say 'doing the run' it suggests I'm trying a deliberate acceleration run (1/4 mile?) The car does this 'pick-up when you back off' ALL THE TIME.
Should I turn the TCS off every time I drive the car?
(it defaults to being ON)

Haha I must admit I know very little about what I am talking about.

I've just noticed that on my 2001 9-5 Aero the TCS tends to jump the gun a lot, even if there is no risk of wheelspin.

Is this different in power at different throttle levels apparent? I'd like to test if mine is like that as well, but I dont have the equipment to measure it.

hildebird
25th March 2004, 10:52 AM
YES!

I can very much feel it, it was just that when it was on the rolling road, I asked them to try it and see if they could measure it.

The RR operator said he could feel it too, when he was driving, even before the computer came up with the figures.

To get the effect you need to give it some boot (but not necessarily full throttle) and then partially lift off. It seems to pull quicker the more you lift, so long as it is still making full boost. If the boost drops off, you've lifted too far. If you get it right, the torque rush is brilliant :cheesy:

Mattlach
31st March 2004, 05:15 PM
YES!

I can very much feel it, it was just that when it was on the rolling road, I asked them to try it and see if they could measure it.

I tried reproducing this in my 2001 Aero with 34k miles but my throttle response seems to be linear.

I tried, as you mentioned, flooring it, and then lifitng off, but I noticed reduced acceleration, not increased.

So apparently this does not affect all Aeros.

--Matt

ma1rk
20th July 2009, 11:18 AM
Could this have anything to do with the vacuum hoses involved with controlling wastegate etc? (Id like to rule that problem out as Ive replaced the short engine and turbo due to sludging about 20k miles ago (courtesy of Saab GB-thankfully).and have since replace the vacuum hoses. I have had the same problem on my 2.0lpt 1998 where I have no TCS system. Pulsing the throttle produces quite agressive accelleration when I come off the gas. I find that the response varies which makes me think that the effect is due to some kind of random noise in the system rather than a programmed response, but I could be way off track. I'm running a stage 2 abbott ECU upgrade.