Motronic Octane Switch Resistor Values.

[JoshGti 8]

Anyone know any? Ive been reading up on it and I've found a few values for it and values from different motronic ecus, wondering if anyone on here had any difinitive values.

 

I tried a few resistors I had lying around today and one of them I put in (around 250ohms iirc) made the idle so smooth!

 

I'd just like to know as from reading the resistance value either retards or advances the timing for different fuels, soi don't want to be retarding the timing with resistors on higher octane fuels.

[Ryan 99]

There's a pretty good explanation in this document. The chart at the end shows the different types of effects that can happen (idle speed raised, timing retarded, fuel increased, etc.) but it's only about Vauxhalls and varies from one model of ECU to another, so without testing I've no idea if the Pug ECU is programmed the same. You'd have to try a few different resistor values and compare results.

 

My Mi16 loom had a 4.7K resistor fitted when I got it, which according to the charts is for 97/98RON. When I removed it and left the terminals unconnected (95RON according to the chart) then the idle speed went up a tiny bit and it seems to chug less at idle.

[KRISKARRERA 2 1 Cars]

I thought Mi16 looms didn't have this feature. Whereabouts on the loom is it?

[welshpug 1,626]

my MP3.1 loom has the plugs iirc.

[Ryan 99]

I thought Mi16 looms didn't have this feature. Whereabouts on the loom is it?

 

Mine is a 2-row loom from a BX. There are a couple of wires with spade terminals near the ECU plug. One is the 12V feed for the fuel pump, and the other two are for the octane resistor.

[petert 554]

As you see from the attached 3 row schematic, there is no additional resistor, or opportunity for one, other than the 1200Ω resistor which can be substituted for the canister purge valve. The 3 row doesn't need one as it has a knock sensor to automatically adjust the timing. As for 2 row, I was under the impression that the fitting a resistor only retarded the timing from maximum. ie cars from markets with high octane fuel didn't have one fitted. Maximum is not necessarily optimal however, and if you have a modified engine you may well find retarding the ignition improves top end hp. However, the retarding will be across the entire range, so it's possible to loose low-mid range torque. I have seen the table of resistance vrs advance retard on the net somewhere. Keep looking!

[JoshGti 8]

Cheers Ryan/petert

 

I have found a number of articles with quite a few saying that the resistor values should be applicable to all motronic 3 series ecu's but I've not yet seen a table? I'll keep looking for that. I'm under the assumption that as the cars the ecu comes from doesn't have a resistor fitted already that it would be setup fine for normal 95 RON fuel, but as I intend to run 98 RON I'd like to get the most out of it without a remapped ecu.

 

Edit; as above, mine is a 2 row 8v ecu

Edited November 26, 2011 by JoshGti

[petert 554]

Wasting your time with an 8V ECU. The mapping is so far wrong. Too much advance, not enough fuel. Buy either a 2 row or 3 row ECU, and I'll sell you a chip for $45 inc postage which is mapped for D6C running 98. A 3 row is better as it has the knock sensor.

[JoshGti 8]

But I have an 8v engine

[petert 554]

But I have an 8v engine

 

Oh! What ECU?

[welshpug 1,626]

by the sounds of it, a motronic one

 

0 261 200 160 or the 162.

 

spotted this link but haven't had chance to read through

 

http://www.205gti.com/bosch/index.htm

Edited November 28, 2011 by welshpug

[JoshGti 8]

Mp3.1, ecu number 0 261 200 212 zx volcane ecu.

[welshpug 1,626]

DOH!!

 

same as mine then.

 

has mixture pot + MAP sensor + wasted spark coilpack, but no knock.

Edited November 28, 2011 by welshpug

[JoshGti 8]

Exactly that, I've tried it with a lambda loom and the ecu doesn't like it at all, and I've played around with the mixture pot to get it running right, but as soon as I popped in a resistor the idle just smoothed out!

 

Don't know if you've played around with the octane facility at all or have you had your ecu mapped by chipwizards?

[pug_ham 241 3 Cars]

Have you both the mix pot & lambda sensor at the same time?

 

I haven't on mine, just lambda & it's fine.

 

My ecu was originally remapped at chipwizards but that was when I still had the mix pot fitted.

 

I'll be taking it back sometime with the new engine to see if the changes have made much difference, it feels better now anyway.

 

g

[JoshGti 8]

Nope, I used a loom with just the lambda function not both (I have 2 looms) and the lambda just caused idle to hunt a lot more, whereas the mixture pot seems to work at controlling idle fuel very well after I rebuilt it with new components.

[welshpug 1,626]

sounds like that lambda was a bit tired then.

[pug_ham 241 3 Cars]

As above, sounds like a duff lambda or other fault within the loom / ecu.

 

Mine idles so much better now its got the lambda instead of the (admittedly) old mix pot & emissions are well down.

 

Not that it was bad to start with though.

 

g

[feb 47]

Graham, do you have some emission results from yours?

Do you have a catalyst or just using a Motronic management?

[pug_ham 241 3 Cars]

Feb,

 

I have the emissions slip from the MOT I did jsut after I got it all running but the hc's were high due to the valve clearances being way out (at least twice recommended) & the c/o was 0.23% where previously with the mix pot getting it under 3% was a struggle.

 

I think it would've benefitted from a revamped mix pot but I couldn't find them anywhere & didn't fancy trying to build a new one without the full info of whats inside.

 

g

[JoshGti 8]

I've rebuilt my mix pot with the same components that were in it originally, will be interesting to see what my co results are when I take it for mot in Jan to see if new components make a difference. My mixture pot does seem to make quite an impact on the idle fuelling, being able to make it lean right out up to way over fuelling.

[welshpug 1,626]

I think I need to do similar with mine at some point, I did look into the components required and found them on the RS website after popping the cover off a spare pot, which also happened to display the same strange readings as the one fitted to the car, i.e not doing a great deal!

 

maybe fitting the wires for a lambda may be worthwhile.

[JoshGti 8]

Feel free to give me a pm with your address welshpug, more than happy to chuck a potentiometer and resistor in the outgoing post at work if you want.

 

I couldn't get the lambda working on mine as is obvious from previous posts, it wasn't overfuelling, just hunting alot at idle.

[welshpug 1,626]

that'll be the lambda not being able to give a steady reading, what was it giving on the emissions?

 

I'll PM you my address shortly

Edited December 6, 2011 by welshpug

[pug_ham 241 3 Cars]

Could I also beg a set of the resistors etc for rebuilding the original mix pot?

 

I've got a couple that hardly change resistance across the range & they never gave me near the book figure for the co levels when fitted, this is the main reason I swapped to a lambda.

 

Did the lamdba test OK & give the correct resistance?

 

g