Engine Management - Very Odd Behaviour

Here's an interesting 'issue' (or is it?) relating to Porsche's Bosch Engine Management systems on the 996. Simply, resetting your engine's control computer results in VERY marked improvements in the car's performance that 'goes off' again over a few hundred miles. I'm now on my second 996 - the first was a 3.4, this one a 3.6. This 'phenomenon' can be repeated time after time on the 3.6 and was just as marked on the 3.4. You can try it yourself - it's totally harmless to your car. Either disconnect the negative termnal to the car's battery for a couple of minutes (remember to have the ignition - but not the engine - switched on when you do this or the damned alarm goes off!) or alternatively remove fuses B8, C1 and C2 for a couple of minutes and replace. (Check your car's fuse allocations first to make sure they're the same as mine. You should remove those relating to Engine Electronics and Fuel Injection). Either method resets the car's engine management computer. I suggest you do this when your engine is hot so you can go for a drive immediately after you've replaced the battery lead or fuses. After about 2 minutes running you will be astounded at how much torquier and accelerative the car is and how much better it sounds. If this turns out to be repeatable in many owners cars then we are possibly looking at a design or programing issue in the engine management. I believe it stems from the unit's ability to 'learn' your engine (it stores modifed ignition retard values and mixture correction values for each engine that it 'learns' over a few miles). I believe it is programmed to back the settings off too far and is ruining the performance of our cars. I will be very interested to hear from anyone who fancies trying this 5-minute exercise, especially as it has been repeatable for me on 2 cars. Looking forward to your experiences and replies Ian W

I will give it whirl for you...But not till Saturday as I am going for a large hoon to the rainy city (Manchester). I will report back!

This is true. When the car is serviced they have disconnected my battery. The performance is always much better. The throttle response is sharper and I get more boost more easily. However, I do not think it is much quicker and if you push the throttle to the floor, then the same maximum power is available. It is just harder to get maximum power. It is just that at part throttle openings it learns to be more conservative, since normal road driving in this country does not allow hard driving very often. It is a deliberate feature, not a bug. It is intended to reduce fuel consumption.

Hi, I think the cure is to give the car a good caning every time you take it out so that it doesn't "learn" the economy settings. We have a Volvo V70R with an auto gearbox that adapts in the same way to your driving style, Apparently is is to save having to push a sports button (or economy button -whatever that is) as on the older gearboxs! I always find the car a bit lethargic when I first go out in it after my wife has driven it. Iain 996 C4 GT3 aerokit/wheels/sports suspension

Or is it a clever ruse so that every time your OPC services your car you think Wow! - but all they really did was disconnect the battery and have a cup o' tea and a fag[ ]

I've often wondered whether people get fooled when they rechip the control unit and redyno into believing that they've got more improvement than they really have got. If ever I did anything that involved a before/after dyno run I'd want to do exactly the same procedure on the before run, i.e. disconnect anything that's going to be disconnected for the second run (hope that makes sense, Dan).

Is there a chip or something similar you can fit to over ride this? Ant.

I don't think you can keep the default settings. The best way to get round it would be to replace the chip (or get it reprogrammed) by one of the tuning companies. Howeve this causes warranty concerns. I suppose you could disconnect the battery every few days, although the bolts on the terminals will wear since they are not designed for such frequent action. Alternatively, I suppose you could fit a battery isolation switch and then just flick it off every now and then. Next time I'm in the OPC I might ask what they think.

People like Revo and Milford Micros offer a device which you can plug in to the diagnostic port and load a 'performance' map, or revert to the standard map when you want to take it to the dealer. Nice idea, but extremely expensive for a 15bhp increase.

Thanks for all the comments. This change in performance is definitely not just at part throttle (on the Carrera at least - I have no experience of the Turbo). There is a very marked increase in full throttle acceleration and - more tellingly - the car sounds totally different. Much 'sweeter' sound and particularly noticeable with the PSE's fitted. Once the performance (and the sound) eventually goes off again, no amount of caning the car brings it back - this is a one way street and only reversible by resetting the Engine Management computer as described. Has anyone else tried this yet? It really does work - you will be quite amazed by the difference. Ian W

I haven't tried it yet as I had the garage door opener fitted in Manchester on sat as planned but then I felt a bit crap so didn't go out again. I will defiantly try it this weekend though and report back.. Phil

Interesting. I have heard this mentioned before, where cars seem much better having been to the dealer for a service. I will try this at the weekend if the weather is nice and report back accordingly. What happened to the good old days when cars weren't so damn clever - apart from bending valves when you missed a gear of course!

You are effectively resettign the ecu, and losing all the faults that the ecu has been working around for the previous months. I did this every month with one of my BMWs, it was the quickest way to get rid of all the electrical glitches

Agree with the above. Used to do exactly the same with my old subarus when i filled them with SUL (wasn't always available up here in the sticks a few years back!). If no reset was done they just gradually change timing etc to make most of the higher octane rating whereas reset was virtually instant eg brand new datum point. Used to make a fair difference but that was on turbo charged cars don't know if it would make a huge difference on N/A's

Did it last night, but forgot to take the advice of leaving the ignition on before disconnecting the battery - oh my God the alarm is loud!!! My ears were nearly bleeding. Seems a bit more responsive - but then again it doesn't do very many miles.

You're not kidding about the alarm - it's a mistake you only make once!!! The car will need to be warmed through thoroughly and then driven hard for a mile or two (pref accelerating throught the gears) then you will feel the full benefit. Much more mid range and noticeably quicker at high revs / full throttle. Ian W

It works!! Very noticeable. Its got smoother acceleration but best of all when you are in the higher revs it pulls harder. Only problem is that now I have no radio...and the code in the car is not for that stereo [ ]. Its going to be a long journey next week with no sounds unless anyone has an idea. Spoken to OPC but we are talking a couple of weeks to get a new code...

Had the same problem in my last 996 - missing radio code - got it from the previous owner! Ian W PS. Really pleased you have noticed a substantial difference. Driven hard from 4500rpm to the limiter, it's like having a new engine!

It is good...I have been out 3 more times since!! Staying in now or I might find myself on police Camera Action...[ ]

If you are a member of www.renntech.org try posting a message there. I believe someone there has a program for getting the code if they know the serial number.

Ian w, What petrol are you using ? Depending on your answer, this maybe a reason, I only ever run on optimax and the odd 100ron Tesco. Thanks Andy

Andy Same as you - always Optimax - so in theory the DME should not be backing the timing off very much if at all. It is my intention to delve into this whole issue much further. Last time my car was running 'badly' (about 300 miles after I'd reset the engine mangement and it had 'adapted' again) I took the car off to my local Porsche specialist who confirmed that there were no fault codes whatsoever. (They have the proper Porsche / Bosch tester). Yet resetting the DME once again brought about the usual perfomance increase. So it's not the electronics working around faults. Next on my list is to get the car dyno'd before and after the reset and see if we can detect differences in lambda (mixture) values and recorded ignition timing. Once we know what is being altered it may be possible to track down why. As I said at the beginning of the thread, it's not just my car; my last one did exactly the same! Just to clarify too, we're not talking about a small difference - I'd put money on there being a 20BHP increase after the reset. The difference in top end performace is not in any way subtle!!! Are there any more owners out there who are willing to try this 2 minute reset? You'll be surprised (if not amazed) and it will confirm that it happens the same way across a number of vehicles. Meantime, I'll try to get a dyno session sorted and report back. Ian W

I have not tried this yet and it would be intersting to see a dyno of my car now. Especially since it has only really been run on optimax, then reset and dyno again to confirm your results. I have never noticed any change after a service, or after a number of RMS chnages, which I assume the battery would be disconnected. I also note your car is a 3.6, mine is 3.4, was the other person's car also a 3.6.? Has anybody tried this on a 3.4 car ? Oh, my car is a fly by wire version on the throtle. Thanks Andy

ooopps just read your first post, 3.4, the same..

Mine is a 3.4 too and as posted the difference was amazing. (Still no radio....I have to listen her indoors now!)

I know this thread was from a long time ago, but was the dyno test ever done? Did anyone ever confirm it? I only ask as I have a friend temping in an OPC and she's offered to ask about it....

The DME (engine control unit) adapts itself over a period of time to adjust the fuelling settings, based on the conditions, fuel quality, etc. By disconnecting the battery, it resets these adaption values to the factory default. Therefore, if it hasn't been done for a while, it can make a perceptible difference to the performance. On cars with electronic throttle (eGas) it is not necessary to disconnect the battery. All you have to do is switch on the ignition, but don't start the car or touch the pedals, for 60 seconds. Then switch it off for at least 10 seconds. This resets the adaption values. MY1998 and MY1999 C2's (up to August 1999 build date) and Mk1 GT3's have mechanical throttle, so you have to disconnect the battery. Everything else has eGas. To be sure, check the options sticker - M620=eGas. If you have to disconnect the battery, put the key in the ignition and switch it on, but don't start the car. Switch off all loads, such as aircon, radio, etc. Leave the key in this position and disconnect the negative terminal. If you don't, the alarm siren will sound, as it has a backup battery inside. Have fun!

I followed the directions with the fuses last night....so it wasn't my imagination that it felt a bit perkier glad there's a way to do it not using the battery/fuses, they were a right fiddle! is there anything similar on boxsters or even 993s? i have a couple of friends who might be interested to know! Cheers, Marco

Same process can be used for eGas Boxsters. I'm not 100% sure about 993s. IIRC there is a system adaption option on the PST2/PIWIS tester to reset the adaption values, so I don't know if a simple battery disconnect will do the job. UK 993 Carreras used Motronic v3.x DMEs, whereas early 996's used Motronic 5.2.2. It should work on a 993 Turbo, as that used Motronic 5.2.

I did this by accident at the weekend as I went out to programme the satnav then had to wait as she who must be obeyed still wasn't ready. Car felt particularly fine. Glad it wasn't just my imagination!

thanks for the info! Marco