I have recently successfully connected up an SDS system to my 1988 Porsche 911 (3.5L). The car was dyno'ed last week and makes 271bhp (flywheel). I am overall pleased with the results except a couple of minor querks.

The idle is not very constant, the rpm's hunt slightly between 800rpm and 1000rpm.

When driving at very small throttle openings, in traffic, the car can surge slightly like it is saying "give me more gas".

Lastly, during the dyno session the signal from the MAP locked up at -15 and wouldn't more dispite changes in throttle or rpm. I had to switch off and re-start. Software crash ?

Anyone any ideas ?

cheers Pete,

thanks SDS a great system

For the idle is sounds like it is running to lean...make all the MAP values around 500-1250 the same. If you have a wideband set it at around 11.5 to 12.1 at idle and see if it smoothes out. You can also tune idle by ear, use the mixture knob and twist it richer or leaner until the idle is smooth.

Dax

I would definitely get a wideband to monitor AFR. Also try ti keep the rpm-fuel values the same for that idle rpm ranges (750-1000), and another idea is keep ignition timing same at 750rpm as 1000rpm. But like last poster, sounds more like lean condition. The tuning knob is really great in cases like this.

Bought a WMS mixture meter from SDS at the same time as I bought the system. Very un-impressed, the meter reading jumps up and down all over the place so I never really could tell what it was say'in.

Anyhow, Yes you are both right, thanks.
It was running a bit lean. I increased the fuel in the RPM/Fuel first to see I was going the right way and this worked. But as this made for a significant bump in my otherwise fairly smooth RPM/Fuel graph I made a change in the MAP where the engine was hunting. This sorted it completely and fixed the idle at the same time.

cheers

Pete

Just what to share this nugget of information I was given when the car was on the rollers.

If you make your ignition advance much greater below your idle RPM it stops the engine ever cutting out when you lift off.

e.g. if your idle is 1000 RPM then set up like this.

500 = 20 deg advance
750 = 20 deg advance
1000 = 10 deg advance
1250 = 14 deg advance
1500 = 17 deg advance
1750 = etc

works like a charm, now I never stall.


cheers.....