jeff jackson

I have recently acquired a beautiful black late 1986 (86.5)... 928S, and have been reading and trying to absorb as much of the available information about this car as possible. I have found this forum, to be one of the most reliable and consistent sources of info going....Now my question, I have been told that there is some sort of a "Low Octane Fuel Selector Switch" on my car....which impedes ignition advance to prevent detonation on poor grade fuel. But...I don't know anything more than this...not where this "switch" is located....or what position it should be in for someone like myself, (who only uses 93 octane premium fuel in my car). If any of you "enlightened" owners could toss me a clue as to the validity of this...or useful info...I'd be most grateful.
Regards..
Jeff Jackson

mspiegle

on the passenger side of the car, there is a small compartment with a little strap. Unbutton the strap and open the compartment, you'll see the fuel and ignition computers. Coming off one of the wiring harneses, theres 2 wires with connectors on the end that should probably be disconnected. If you connect these 2 wires, you'll get some ignition retard.

Mark

It's more of a plug then a switch.

In the pass footwell - behind the carpet - is a BUNCH of electrical stuff. The main elec panel is behind that board.
To the right are the computers, and there should be 2 single wires with connectors on them, down around the bottom. When plugged together, they accomplish the 'limp home' mode.

Welcome to the asylum!

jeff jackson

Thanks fellas ....guess I better have a look in there, not sure why anyone would want to deter the available performance on tap with this car....but I'll feel better knowing for sure I'm getting all of it. Any other issues you guys know of that I need to have a look at ??? I am considering doing the rear muffler bypass / cat converter bypass, and a set of Autothority performance chips for my car...you guys think this will be a noticeable power adder...or would I be better off with a set of exhaust headers, and new set of injectors and O2 sensor....(almost 100K on my car, but it seems very healthy for 2:20 rear axle ratio).... thanks for the advice. PS....I LOVE THIS CAR !!!

IcemanG17

The Autothority chiped dyno numbers I have seen are very impressive for the 85-86 cars, a nice gain! The gains for later cars are much smaller. I think the chip + RMB would make a noticeable improvement, the cat bypass would help too, but then you won't pass smog? Add headers and a rising fuel pressure regulator with the chip and exhaust...you should have a nice gain....probably 30-40 whp!

jeff jackson

No problem with the smog test....its only once a year, I have a "loaded" garage ..., and look for any excuse to work on the car anyway....so, I think I'm going RMB, and Cat bypass pipes, along with the Autothority ECU and ignition upgrade chips, and see what that does for my "***-dyno" ... if more is required....I'll probably go for a recently recommended "piggyback" fuel computer setup, I'm pretty familiar with these, from my days with the 3000GT VR4.... adjustable fuel pressure regulators, and a fuel pump upgrade, and hopefully that will "safely" give me a high level of the available "street driven" performance, I am sure is beneath the surface of this car. Its already a blast to drive, I just have never grown up from my days in the early 70s driving Mopar muscle cars.... (I'm 48) ...
Regards ...

Kevin Michael

jeff, how does the 928 compared to the 3000gt stack up performance wise?

Kevin Michael

is there such a "switch" on 87 cars as well?

John Speake

Hi Kevin,
Yes, there is a "switch" for low octane fuels on the ECU coding plug that lives on the mounting plate for the LH and EZK ECUs on your '87 S4.

If you look in the W/S manuals Page 24-221 you will see coding option "Australia" this is for 91 octane fuel. Your US car won't be coded like that, of course.

Kevin Michael

john,
how to disable or enable this "switch"?
thanks, kevin

Shane

Kevin the only octane coding you have to worry about is activated through your knock sensors.

John Speake

Kevin, the "switch" is a series of soldered links to pins in the part of the plug that is on the mounting plate.

If your car was not fisrt regirstered in Australia, then it is most unlikely anyone would have gone to the trouble of re-coding it for 91 Otane

jeff jackson

In my view these cars each have their own particular advantages. With a "Sport Turbo" upgrade and "cat converter bypass"... my VR4 ran 12.40 at 112 mph 1/4 miles, with a very "mild" launch technique. The car had the stock clutch, and at 3800# ... the stock clutch would not have lasted long to aggressive launching , but the AWD mad it very, very quick out of the gate. WithHKSelectronic boost controller, and a supplemental "piggyback" fuel computer called an SAFC, along with 550cc fuel injectors. These mods were unobtrusive, and did not in any way detract from the daily driveability of the car . It was a very, very nice car, and I do miss it. But...that being said, the more I learn about my 928, the more I take things apart and put them back together, I see alot of potential with this platform. I am still trying to sort out lots of electrical system issues...(PO was a security nut apparently and theres all sorts of alarm system wiring and relays and stuff I am trying to sort out), and the German engineering philosophy is very evident with this car. Thats one reason I like it so much even though it is a rather old car (1986.5)