_Thomas_

Hi

has anybody got any results from installing a resistor (potentiostat) in parallel with the temperature sensor II to be able to change the air - fuel mixture?

Cheers Thomas

John Speake

Your chance to be first on this idea, Thomas !
(it will work.....)

Jim bailey - 928 International

You might exercise some caution as temp sensor two also advances ignition timing when the engine is cold .

John Speake

Hi Jim,
The idea was just to modify the sensor in Temp 2 that goes to the LH, to weaken the mixture. And leave the EZK one as standard.

_Thomas_

Hi John and Jim

today I stole :-) a potentiostat (0-10 k Ohm) at work so I am ready to solder it tomorrow ... But thinking about it if I wanted to change the mixture uniformly at all temperatures I should have another temperature dependent resistor (basically another temp sensor II) in parallel, because intsalling a constant resistor in parallel with the temp sensor II could help the performance at normal operating temperature but would mostly upset the mixture for the engine being cold ... that is why I ask whether anybody has got some experience.

Cheers Thomas

PS: John recalibrated my MAF and he did a very good job, since the car runs very well, and this 'idea' just came up because in Switzerland we have got some quite strict emission laws, and I might have to weaken the mixture to pass it (1 % of CO with the air pump disconnected).
There was a special version of the 928 (code 277) for Switzerland, apart from that on the control unit which has a vacuum connection for the ignition advance I guess (it is 5° BTDC @ idle speed) there is a handwritten label S, A, CH (meaning Sweden, Austria Switzerland) - anybody knows of the exact meaning of 'version for Switzerland'?


Apart from that today I soldered the cable to the temp sensor II and the cable to the WOT/idle microswitches, so maybe the problem was there anyway. I haven't come round to do another CO test, maybe it is sorted out anyway.

John Speake

Good luck ! I suggest you set the idle mixture pot on the MAF to 250 ohms, then start tweaking the "new" pot. You should hear a change of engine rpm at idle when you start going from rich to weak.

As far as I can tell, only the ignition unit changed on the Swiss/Swedish/Aust S2s, the power rating was down to 275bhp, but I don't think cams or pistons changed, because it is still called a M28.21/22 motor.

_Thomas_

Installed a pot parallel to temp sensor II so the pot allows you to gradually change the resistance of temp sensor II from its normal value to 0. With the engine warmed up the resistance of the temp sensor II was 230 Ohms) and the effect of the pot was nil. Changing from 230 to 0 Ohms had no effect on the idle speed at all. Also I didn't notice any change when driving the car.

Where did you get the figure 275 bhp from? because in my driver's handbook it says 310 hp. If 275 bhp is true I would start to investigate what is different with the Swiss S2 and 'undo' that :-) ...

Cheers Thomas

John Speake

I took the information from "Service Technical Information" for 1985 (I thought you car was that year.

This is where I found the info on the different ignition controller, and less ignition advance It also confirms max power as 310bhp.

When I quoted 288bhp today, this was from the small pocket book "Technical Specifications" - again for 1985 MY.

I've just looked at PET, and it only shows a special version for the Swiss, Swedish and Aus. markets from MY 1986 ! Even more confusion.

If your car is indeed a standard Euro S2, then you could well have a problem meeting CO of 1%. It is difficulet to get them much below 1.5% consistantly.

I suppose you could check the part number of the EZK. -----------I've just looked on PET, and this is just totally confusing. It shows two EZK numbers for 1983, M28.21/21 engine. the 928.618.124.03 is standard. and a .04 is shown for option code M154 which is not shown on PET ! An option code is shown for M151 for Switzerland.

This appears to be confirmed that it is the Swiss market by page 28.36 of the Workshop manual - some sense at last ! Although this says for 1984 modles onwards.........

perhaps you might want to check the number on the ECU ?

_Thomas_

My car is the WPO ZZZ 92 ZES 840.327 which is late 1983, already model year 1984 (S2). I also asked on the German message board whether anybody knew the exact differences between the Swiss and e.g. German model, and one of the most knowledgeable forumers told me he only knew that the ignition control was different.
The number of the ignition control is 928.618.124.02 and of the injection control 928.618.123.02.

ViribusUnits

For a CO tester, you can get a three wire O2 sensor, and a clamp for your tail pipe. Get an exaust shop to weld a nut on to the fitting for the end of the tai pipe. Get a good quality analog voltmeter. Not one of the non powered type, but one of the ones with it's own internal battery, and a high impedence. You can then hook the heater wires up to a plain old 12V source, and use the volt meter to get a reasonable reading.

To make this work, you'll need to make sure the O2 pump isn't working, as it'll throw the reading off. You'll have to use the heated type O2 sensor, as the sensor will be to far away from the engine for it to work. I belive you'll want to adjust the mixture till the voltage from the sensor lead is around .5-.6V.

Good luck.

_Thomas_

This would be a good idea, but it is not very useful for me since I will have to do the annual emission test anyway, and there is a fixed price for it which includes setting the ignition, idle speed and the CO mixture screw which is normally all that should be necessary to get a proper reading once you have your vehicle properly serviced (air filter, motor oil, spark plugs would of course cost extra).


Actually I already wanted to buy/diy a wideband oxygen monitor (needs a 5 wire sensor), but ... "The NTK sensors skyrocketed in price once they became popular with wideband manufacturers" (quote from ebay seller), it looks there is no way under approx 300-400 $ for a complete instrument including monitor. And once I will have paid this much, I will just start to fiddle around unnecessarily with everything in reach of the said device ...

Z

There's supposed to be one available soon that uses a Bosch 5 wire sensor. That's the one I'm waiting for. I believe the Bosch sensor is cheaper and lasts longer too.

_Thomas_

Which one is it you are waiting for? there are two Bosch 5-wire oxygen sensors already on the market:

-The Bosch 5-wire sensor (Bosch 13246) which is equivalent to the original NTK L1H1 oxygen sensor is just as expensive.


-Beware: The other Bosch 5-wire sensor (e. g. currently on ebay for 41 $ see link below and seller's comment) will not work with the DIY circuits published e. g. at
http://www.tragacs.com/wbo2.html
"Pls also be aware that there is a widely avaiable Bosch wide band sensor (the LSU4 sensor), but it won't work with these kits"








http://cgi.ebay.com/ebaymotors/ws/eB...tem=2429150527

This is a brand new, un-used Bosch LSU4 5 wire wideband (UEGO) sensor. It can be used to make your own air fuel ratio (AFR) meter. It is currently used on some of the top quality commercial units available (recommended by AEM, Motec, Lambdaboy, FJO, and others). From 10.5 to 25.0 AFR it will read accurately within 0.1 AFR. Most of the available Air Fuel Ratio meters allow you to buy the controller without the sensor and add your own. Either way, it allows you to tune your engine with the same accuracy that the dyno does!! Using one of these will keep you in tune for peak horsepower at all times!
I will include technical information regarding LSU4 sensor wiring pinouts and the part number for mating connector with purchase. Accuracy is comparable to the currently overpriced NTK L1H1 and L2H2 (according to most actual dyno comparisons). The main difference is the LSU4 is much more immune to exhaust pulses and therefore provides a much more stable reading (which makes it much easier to read in real world use). The NTK sensors skyrocketed in price once they became popular with wideband manufacturers. Get it at a good price before these go up too!!

Normy

John-

As per your post above... You say that it is difficult to get an S2 below 1.5% CO? This means that these cars need to run a little rich- something that I've believed for years.

A few years ago, I had a mechanic at a reputable garage set my CO to 0.5%, and I had no end of missing afterwards. I richened it up myself later, but the problem has slowly gotten worse...though your chip has helped.

I drove to Michigan today. A section of road south of Ann Arbor is under construction, with only one lane open. They have a concrete barrier up to protect the road workers, and of course....this reflects the delicious sound of my Borla exhaust, so I dropped it to 4th gear and wound it out for a few seconds at a time. I found that when I lifted off the throttle, then got back into it quickly, I got a rather LOUD backfire! It was pretty cool, and I did it several times. I guess this means that I'm running a bit rich...

And then on one segment today, with speeds of around 75-80 mph, I managed to get 20 mpg over a 280 mile distance. That's right in the ballpark....

Hmm. I think your chip may have solved some problems, but my missing might be the result of something else.

Is a 1.5% CO enough to cause a visible cloud of black smoke with a simple throttle blip?

Normy?
'85 S2 5 Speed

Z

The one I was talking about was the one at:
http://wbo2.com/

Looks like that kit is available now.