what does the 1989 325i E30 'remember' as regards fueling?

[orangecurry]

I went on holiday (without the car!), so I took the battery out (made sure it was fully charged whilst I was at it - it was).

A week later, I put the battery back in, and as usual I have to play the stalling-at-junctions game as the fueling 'brain' tries to decide what to do.

BUT the car SEEMS faster; definately more responsive; more urgency...

Not stupid amounts, but noticable.

I've been driving a faster car all week, so it ISN'T that I've gotten used to a slow car....

So my question is please

...what does the E30 brain 'remember' from being driven?
and why is it quicker when it has been forced to 'forget'?

[E30BeemerLad]

I didn't think the ECu on these were a "learning" ECU, so a reset would make no difference, but that doesn't explain the antics you experience at junctions etc.

maybe Ant can shed some light on this one...

[orangecurry]

I didn't think the ECu on these were a "learning" ECU, so a reset would make no difference, but that doesn't explain the antics you experience at junctions etc.

exactly what I thought

but it ALWAYS has a problem for quite a few junctions if I disconnect the battery for any length of time, and I thought (from posts on the 'zone) that it was a common experience?

[E30BeemerLad]

what u been driving on holiday fella?

[orangecurry]

no no no there's a school of thought on my 'family' car, and it doesn't sit comfortably on the 'zone

[Morat]

Its a saab???i? ;)

[orangecurry]

I've always wanted a Saab

900 turbo - from before Vauxhall took over - mid-to-late 1980s

vertical windscreen
turbo-lag like waiting for christmas

one never turned up when I was looking

[E30BeemerLad]

classic shape 900 is a very durable old beastie, the 8V has monster lag put pulls good n proper once it spools up, never been in a T16

would have one like a shot though

a mate of mine had a 90 years ago, odd combination of 99 front end and 900 saloon rear end, slow n thirsty but it held on in the corners surprisingly well.

[MikeeMiracle]

If you have not changed anything else like the type of fuel your using then it should feel the same. All ECU's tend to "learn" a bit which is why you can put 95 or 97/98 ron fuel and it will adjust to them. I know on the civic type-r we used to reset the ECU after starting to use Optimax fuel so we didn't have to wait a few tanks for the ECU to adjust.

The junction antics you refer to.......is that the engine revs dropping when you first press the throttle? I thought all E30's did that?

[orangecurry]

hmm not sure about that Mike - the old fashioned E30 ECU doesn't have a 'knock sensor' or whatever it is called - it doesn't alter anything for different fuel grades... it doesn't know they exist!

Modern ECUs do I agree totally

throttle antics = car dies as you coast to the junction; throttle not being touched at all

[MikeeMiracle]

I hear where you are coming from mate, it will need to be checked. Im sure the inside of my 318is filler cap sais "Minimum 91RON" indicating that it could adjust. I also believe they can tell from the content of the exhaust gasses if the fuel has fully burned so you do not necesarily need a knock sensor. Im not sure if thet feature would be on an older car though.

A good question to ask would be does anyone use 97RON fuel and do they feel a difference. If they do feel it slightly quicker then it must be adjusting, if not then you are taking power away by using 97 RON on a engine/ecu that cannot adjust.

What do people normally use on their 325's?

[E30BeemerLad]

i used whatever shite was going and personally have never noticed a difference when switching between the "super" fuels and normal 95 ron.

I can't notice any difference in my jap wagon either and the ECU does learn on that

[orangecurry]

I hear where you are coming from mate, it will need to be checked. Im sure the inside of my 318is filler cap sais "Minimum 91RON" indicating that it could adjust. I also believe they can tell from the content of the exhaust gasses if the fuel has fully burned so you do not necesarily need a knock sensor. Im not sure if thet feature would be on an older car though.

ah no I think that means you need a certain grade of fuel so as not to damage the engine; but the engine management does not adjust anything on the E30 regarding fuel grade.

Top Gear did a test I think on fuel grade and type of car - if you have an older or lower spec car, the increase in RON made no difference to the BHP, but something in the middle (modern GTi IIRC) showed an increase of 10 BHP, and a Jap wagon (Impreza something or other) showed 30 BHP on the rollers.... but you DO have to reset the ECU (disconnect the battery for long enough for the capacitors to drain) to see any differences, because these ECUs do learn, and they use average readings to set the fuelling

so if you do 100 miles on 95RON, then fill up on 97RON, there will be no difference, then very very gradually it will get better and better..... but if the previous owner has used 95RON for the past ten years, you'll never see any improvement, until the ECU is reset....

........allegedly....

[Simon13]

they take about a 100 miles to sort themselves out after the battery is disconnected.

should be back to normal after that. All my facelift M20 cars do it when that battery is disconnected

[Brianmoooore]

I agree with Simon13's approx 100 miles.
All the ECU is learning is the idle settings, as the only feedback sensor is the engine RPM (crank position sensor).
There is no knock sensor on any E30 or exhaust gas analyser (lambda sensor) on most E30s, so there are no feedback loops for the ECU to be able to learn from.
Using a fuel with a RON any higher than that needed for detonation prevention on an E30 will have no other effect than that on your wallet.

[orangecurry]

thank you Mr Moooore sir - 'it is only learning the idle settings'.

So the more eager feel to the car was just my imagination... shame.

[Brianmoooore]

Not necessarily, it may overfuel slightly throughout the range while it's doing so.

[georob]

i notice a considerable difference in my 89 320 when i use optimax and the like.

its running a viper2 chip, would this make a diff with the fuel/ ecu issue spoken about?

[orangecurry]

Not necessarily, it may overfuel slightly throughout the range while it's doing so.

right - that's it; I'm going to fit a battery isolation switch under the dash, pull the plug every night, and put-up with the constant stalling in order to reap the extra 25 BHP that Brianmoooore states is now available

And watch out for my Ebay entry - 'Extra 25 BHP for every BMW E30' and the 12v electrical switch, 6p from Maplins I'll be selling for 48 quid.

What should I call it? 'BMW Hyperspace technology from Japan'?

[MikeeMiracle]

i notice a considerable difference in my 89 320 when i use optimax and the like.

its running a viper2 chip, would this make a diff with the fuel/ ecu issue spoken about?

Chips normally play with the timing to produce a cleaner burn so yes most definately, especially if you have other mods also. They also try and draw in more air/fuel than usual so if you have other mods like air intake and exhaust you will get more bhp percentage wise when using higher octane fuel than you would in a standard setup.

I thought all E30's ovefuel at the top end anyway so I assume you could get good gains from sorting out the mixture properly regardless.

[Gwynleym10]

If the chip has been set up to run on 98octain fuel, car will run better with that.

However most "plug in" chips are set up on normal fuel, so the gains your getting are probably in your head. Its amazing what modern advertising can do to the performance of your car!

Someone did a test on the zone over a large amount of miles and found no difference with high octain fuels

[MikeeMiracle]

I would say you'd be hard pressed to notice any difference although a rolling road should be able to highlight any differences. The more highly strung an engine, the more the gains would be from using higher octane fuel.

Taking my previous car into account, a Civic Type-R, this could adjust the ECU and even then under half those on the forum said they could feel a difference. If you can just about tell on that motor which is very highly strung, I would imagine its almost impossible to detect any difference on a E30 engine.

[Brianmoooore]

Using a fuel with a RON any higher than that needed for detonation prevention on an E30 will have no other effect than that on your wallet.

[orangecurry]

I think that's snappy enough to add to your signature, Brian ....

[ric325i]

oh common guys there must be a difference!

is my wallet getting punished for nothing!

i use 97 oct and would use a higher oct but its not as easy to get to the stations that let me have it.

last week i planned a trip down the motorway, so i was being tight and thought i would burn the cheap 95 oct as i didnt need any performance extras to cruise and save petrol.

in choosing this lower oct the car ran like a dog! from cold the car can hardly stay alive. lunging, jerky (not just my pour clutch control) and was a general pain in the be-hind tp drive. maybe the zone chip has adjusted?

with a higher oct the old smoker runs much smoother on the short journeys and defiantly runs better from cold.

as for performance i believe you can tell a slight difference in the power delivery through the revs.

-for an example the 97 oct has a slight dead area just after the 4k kick, until you get to high revs.

-as for the optimax (amazing stuff) i do believe the power delivery is more consistent, eliminates the flat spot and runs smoother still.

as for extra Bhp? who knows but i think the power delivery is different and there must be gains.

i have a degree in car design not engines but i would like to think it helps.?.

[MikeeMiracle]

Well on that testimony im just gonna have to try it

[Brianmoooore]

but i would like to think it helps.?.

The advertising guys like you to think this as well.
Too low an octane, and you will fataly damage your engine. Too high, no advantage at all.
If your car is chipped, then maybe the timing is advanced so that it needs a higher octane.