ralphr1780

Hi,
Have scrolled with the search function into the numerous posts on the octane subject, but without finding the clear guidance, hence this post.
I have a 85 Euro (16V - M28.21 - manual), and would like to adapt the LH unit to lower octane (RON95 instead of RON98).
Can anyone illustrate to me how to proceed with the octane loop on the LH unit?
Thanks in advance!
Ralph
'85 S2 Euro

Mrmerlin

see post 19 but read through this whole thread
https://rennlist.com/forums/928-foru...t=porken+chips

ralphr1780

Thanks Stan for the very interesting link, shall probe this over the w-e!

Ralph
'85 S2 Euro

PorKen

AFAIK, there are no 'octane loop' plugs on the 16V LH wire harness. There are plugs on the 16V EZF harness.

Connecting the EZF plugs (w/green wires) shorts the air temp sensor input, making the EZF think the airbox temp is very high, whereupon it retards 3° at higher loads.


With the stock chips, connecting the 32V LH plugs (w/brown wires) only changes the O2 loop pattern slightly (less time spent richer than stoic).

32V plugs:

John Speake

Confusingly the EZ-F retard on the Euros is called the "octane loop link" although it doesn't make any change to the LH ECU.

It just retards the igntion so that it is safe to use low octane fuel.

hacker-pschorr

Simply disconnecting the intake air temp sensor in the airbox also "activates" the low octane loop.

A bit easier than taking the LH connector apart.

PorKen

Easy to disconnect (on the dyno) with a long screwdriver, hard to reconnect.

The 'octane loop' plugs are factory taped to the EZF and LH (32V) wire harness.

16V don't have the plugs on the LH.

hacker-pschorr

Sounds like ralphr1780 wants to leave the low loop on for long term use.

Just pointing out another way to accomplish the same thing. Never found disconnecting a two pin Bosch plug to be all that difficult and reconnecting even easier.......

Also a good time to actually test the sensor. When we had Shane's car it came with a bad sensor and two used ones sitting in spare engines were also bad. If the sensor is toast he's already running the low octane loop, makes me wonder how many 85/86 & EuroS cars are running around with the ignition loss due to this.

Z

You've got it backwards. Just disconnecting the air temperature sensor wouldn't activate the low octane loop. You'd need to put a jumper across the pins of the plug to activate the low octane loop.

The system is intended to reduce ignition timing if the intake air temperature gets too high. The resistance of the sensor goes down as the temperature goes up, so shorting the plug pins would have the effect of the air temperature sensor being at high temperature. Jumping the pins of the air temperature sensor plug would be the same as connecting the two low octane loop wires that are down by the EZF computer together. If you just removed the plug from the air temperature sensor and did nothing else, the timing would be the same as what it is normally, and wouldn't get retarded, even if the air temperature was high.

hacker-pschorr

I'm afraid it's more complicated then that, had a moment of clarity.

With no sensor it defaults to "full cold" in the temp compensation map in the EZK which reduces timing. How much I cannot remember but I'm 99.9% sure the high end of the scale, which is the same as the low octane loop, takes out even more.

Need to see a photo of the stock BIN file temp comp. map screen...........anyone, anyone.....

Should call that the "mid-grade" octane loop

PorKen

Connecting the airbox plug requires removing the airbox...


Disconnecting is the same as connecting the octane loop (with the stock chips).

Temp I
127F -3
105F 0
28 F 0
-26F 0
-37F -3

Z

That makes sense. Connecting the low octane loop wires at the EZF retards the timing. If the low octane loop wires are not connected, the air temperature going high causes the resistance of the sensor to drop, effectively doing the same thing as connecting the low octane loop wires, and retarding the timng. If the low octane loop wires are not connected and the air temperature goes high, but the sensor has failed, accidentally come unplugged, or a wire has broken, the resistance would be infinite, and the timing is retarded as a fail safe type mode. It's sort of like the later cars having their timing retarded as a fail safe mode if a knock sensor or the hall sensor fails.

You guys with cars that have one of those air temperature sensors in your airbox really might want to check and make sure that sensor's working. If it's not, you may very well be down on power to some extent.

ralphr1780

Thanks to all for chiming!
Well I have taken a close look at both LH and EZF connectors.
Indeed, there is a black tape around just ahead of the connectors with some plugs, but not exactly as expected: my car is equipped with a G-Cat. An original equipment since it was delivered by the dealer (have traced all this on the documentation and official registration), the fix is very neatly done.
The Green wire is cut on both LH and EZF, and goes into a small black box which was hidden behind the CE panel. See the pics, sorry if a bit unclear as difficult to snap better given the crawling position.
Indeed, I am concerned by a long term cure for low octane.
How did Porsche workshops re-tune these S2 cars in markets where only low octane was available?
I am all ears for your good suggestions!
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Ralph
'85 S2 Euro

John Speake

That looks like an add on O2 loop system for use with the cats that I suspect were fitted to comply with US state emmissions. They usually are not very successful...

If you need to retain cats/O2 loop, the best solution would be to fit an 85/86 US LH ECU with the maps adjusted for the Euro motor. This would give a proper O2 loop function.

What emmissions regs apply to your state ?

ralphr1780

John, this car was not at all meant for export to US, but solely for the German market. I have all the history in this respect.
The CO (%vol) is measured:
1. between 2500 and 3000 rpm and should read <0.3 (mine reads 0.007 at 2770)
2. between 900 and 1200 rpm and should read <0.5 (mine reads 0.019 at 960)
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Ralph
'85 S2 Euro