[Shalmaneser]

Hi All,

I've always been fascinated by ECUs and I think it's time I got stuck in. This will hopefully be a build log/reference for developing an ECU for my Porsche 996.

As standard the car has a Bosch Motronic 5.2.2 - it's a very early car with a cable throttle so has a slightly simpler ECU than a later 'e-gas' car.

I've like to make this ECU plug and play as much as I can - so that means using the standard 'dumb' coils so from what I've seen I'll need ignitors to run them.

As the engine is a flat 6 it has two completely separate exhaust systems to the two tailpipes so two wideband sensors will be required which is a bit annoying. I think the best solution here is to combine the information from both sensors to give an average reading? This will clearly also need an external controller. I would like for the wiring for these to be the only external wiring required.

Flywheel is 60-2 which is good, hall effect sensor.

There is one cam sensor, which I also think is hall effect. Need to check this.

The motor has single stage variable valve timing on the inlet cam which is triggered by a relay, should be easy enough. There is also a resonance flap in the intake which opens from 2500-5000 rpm roughly, vacuum actuated again via relay.

An oil pressure gauge connects directly to the dash, it would be great to be able to log this data too as it's currently 'dumb'

I think it looks likely that I'll run wasted spark ignition and will start off batch firing the injectors although I would like to go sequential - looking at pizi88's work on the BMW speeduinos this looks doable if I can copy his homework. I guess an adaptor board is the best way to go about this.

First port of call finding a decent pinout of the Motronic ECU and joining the dots.

I'm a design engineer by day but have been looking to expand my electronic skills so I'll need all the help I can get. Luckily my buddy is an electronic engineer so I'll be running a lot of stuff past him too.

[jonbill]

do you expect the o2 levels in the two exhaust banks to be different? wondering why you need a wb in each, especially if you're prepared to average them anyway - they can't be very different.

[Shalmaneser]

It's a fair point - maybe I can start off using one WB and swap it back and forth to confirm nothing bad is going on. I'm just concerned a bad injector could be ruining my engine on the unmonitored side and really ruin my day... maybe I could use the existing NB sensor as a sanity check?

Found an excellent pinout here on page 15:

http://arma.free.fr/porsche/996/GT3/996 ... 9-2000.pdf

Need to get it into excel.

will download in case it goes missing!

EDIT: that's actually for a rather unusual 5.2 '.2' which has an air pump for emissions and post-cat o2 sensors unlike mine, hopefully the pins are the same!

[jonbill]

I've not done it myself, but I believe speeduino supports a 2nd wideband purely for logging and gauges - none of the ego type stuff can use it but sounds like it would do what you need.

[Shalmaneser]

That's interesting have you seen any documentation for that second wideband logging? The Bosch ECU trims each bank separately which is a shame to lose but I don't think the speeduino is able to do that.

I've noticed with a lot of aftermarket v8 kits out of the states they only monitor one bank but leaving one bank completely unwatched feels a little risky to me!

[PSIG]

It's a fair point - maybe I can start off using one WB and swap it back and forth to confirm nothing bad is going on. I'm just concerned a bad injector could be ruining my engine on the unmonitored side and really ruin my day...

It's good to be curious or somewhat paranoid, but I'd say you are approaching it obliquely. You would not want to find an issue by bank if you had a choice, and you do. Read your spark plugs, check your manifold port temperatures, check your Lambda for skewed values without cause, 'scope your injectors, etc. Watch for clues, and test specific components for specific issues.

The problem here is averaging by bank. If you had one injector 5% lean and one 10% rich on one bank, the ECM would lean it. Monitor your engine without relying on a tiny brain with limited programming and no knowledge to protect it, and monitoring batched or banked injectors is not a good job for it.

The Bosch ECU trims each bank separately which is a shame to lose but I don't think the speeduino is able to do that.

I've noticed with a lot of aftermarket v8 kits out of the states they only monitor one bank but leaving one bank completely unwatched feels a little risky to me!

You don't lose it. In-fact, you can gain individual-cylinder trims to balance them perfectly if in a mode that supports it, or group them for "bank" corrections (not). If only paired injectors or bank-fire, you only get to balance as an average. As outlined above, you don't want to rely on bank-to-bank. Pay attention to it, read the signs, and tell the ECM what to do that's in the engine's best interest. That is minimum risk.

[dazq]

I've not done it myself, but I believe speeduino supports a 2nd wideband purely for logging and gauges - none of the ego type stuff can use it but sounds like it would do what you need.

Yes this is completely correct, the pin for the second O2 is board specific so check in the pinlist for the chosen board to see where to connect

[Shalmaneser]

It's a fair point - maybe I can start off using one WB and swap it back and forth to confirm nothing bad is going on. I'm just concerned a bad injector could be ruining my engine on the unmonitored side and really ruin my day...

It's good to be curious or somewhat paranoid, but I'd say you are approaching it obliquely. You would not want to find an issue by bank if you had a choice, and you do. Read your spark plugs, check your manifold port temperatures, check your Lambda for skewed values without cause, 'scope your injectors, etc. Watch for clues, and test specific components for specific issues.

The problem here is averaging by bank. If you had one injector 5% lean and one 10% rich on one bank, the ECM would lean it. Monitor your engine without relying on a tiny brain with limited programming and no knowledge to protect it, and monitoring batched or banked injectors is not a good job for it.

The Bosch ECU trims each bank separately which is a shame to lose but I don't think the speeduino is able to do that.

I've noticed with a lot of aftermarket v8 kits out of the states they only monitor one bank but leaving one bank completely unwatched feels a little risky to me!

You don't lose it. In-fact, you can gain individual-cylinder trims to balance them perfectly if in a mode that supports it, or group them for "bank" corrections (not). If only paired injectors or bank-fire, you only get to balance as an average. As outlined above, you don't want to rely on bank-to-bank. Pay attention to it, read the signs, and tell the ECM what to do that's in the engine's best interest. That is minimum risk.

Thanks for this post, that's really interesting information. Obviously sequential injection allows me to trim injectors individually, that is a good reason to focus on that injection method.

I'm a little nervous of setting up the speediuno two run with 6x sequential injection but I can cross that bridge when I come to it.

[PSIG]

Bluntly - don't lose the point that sequential or per-cylinder fuel trims are for small performance benefits in specific ranges, not auto-detecting or solving random problems. Averaged bank or after-merge Lambda data is fine for general tuning. The ECM is not AI and should not be babysitting the engine; that's your job as the tuner/operator. Be aware, gather and read your data. You can't avoid everything that could potentially go mechanically wrong, but you can see most of it before it happens—if you're paying attention. My advice: Relax and have fun!

[Shalmaneser]

Understood, I'm going to be making a custom interface board anyway so this is futureproofing really.

Can anyone point me to some information about 'dumb' coil ignitors? Is one dumb coil the same as the next, or do the values need tweaking based on specific coil types and what's the best way to find out what I have?