Not an expert, but having thought about this for a bit I don't think so.

The main issues with an overlean condition are detonation and overlimit EGTs killing your cat.

At idle, there is no load on the motor so detonation is unlikely and a) while the EGT is high the actual heat flow rate (Q dot) is low and b) umm... probably there's no cat on a race car.

ToSi's response seems very astute. Does the lean condition continue into the operating realm? For obvious reasons that *would* be an issue (like, duh.)

 

The ECU MAY be set up for alpha-n operation (i.e. taking into account engine RPM and throttle position as the only variable inputs), but there is an O2 sensor still in the system. I don't understand Motronic 100%, but shouldn't that go into closed loop operation at idle if the throttle position switch idle microswitch is depressed? How do you know if the ECU is operating in closed-loop mode and paying attention to the O2 sensor, or if it is open loop and looking at the throttle/rpm map to deliver fuel? Do I basically need a OBD1 tool?

Do note that the engine is not lean over 1.5-2k RPMs. It looks happy on my AFR gauge.

I've got no cat so not worried about killing that, as you suggested.

In any case, I doubt the ECU was modified to operate for Colorado. The chip in there is still the one from 1999 when the car was set up for German GT series operation. The seller of the car to me did not modify the ECU in any way.

That said, I haven't checked fuel rail pressure, and I haven't checked the calibration of the throttle position sensor. I will check both of those before I mess with the throttles.

 

^^ ah, didn't notice the o2 sensor in your photos. Its probably NFG by now if covered in white / lead residue. Could try unplugging it but I doubt that'll help the warm-up issue.

Does it have a MAP sensor buried in there somewhere? You mentioned the FPR was the only thing connected to vacuum. if no MAFS & no MAP, then alpha-n is the only option.. M3 evo's were like this & I assume this, being of similar vintage, also.

Don't over think the lean / EGT @ idle. Its a racecar so no need to keep a catalyst happy. It might very well just be setup that way to keep the plugs clean.

Thanks FC - I've tinkered w/ a PCM or two ;-)

 

ToSi: Oxygen sensor was just replaced, so it is brand new. Yes, I know Motronic operates open loop without the O2 sensor for 90 secs or so until O2 sensor is up to speed. At least, "normal" Motronic.

There is no MAP sensor or MAF sensor.

 

Well,

Adjusting the air bypass screws in a turn each didn't help anything. It made it idle even worse.

I ordered a Durametric.

At this point, I think I definitely need to get in touch with someone who knows their Motronic tuning who can help aim me in the proper direction, step by step. Anyone have suggestions?

No, I am not intending to convert this whole system to Motec without getting the Motronic at least baseline operational again first. After all, it ran that way for 10+ years already...

 

The Durametric arrived today. Here's what it says about my ECU:

Block 0 (ECU Type) M04MOTRONIC
Block 1 (Porsche Part Number) RS-TUNING
Block 2 (Vendor Part Number) SC95000718
Block 3 (Software Number) .02.97

I'm excited about the prospect of live data logging. Will be working on getting some values tomorrow.

 

RS-Tuning means Reinhold Schmirler:

http://www.rs-tuning.de/

One of the best and well known adresses in Germany for excellent motor tuning and big experience especially regarding the "old" air-cooled stuff.

I would try to establish a direct contact to RS-tuning, maybe they have files about the car and can give you advice.

Stefan

 

Just so people following along don't think this project is totally stalled:

I am currently trying to figure out how the chip in the Motronic DME unit is mapped. I've got some good assistance from people in the know. I'll give an update when we know more.

 

What a cool car, good luck getting it all sorted out.

 

Just found this thread... great story! Good luck with the car... & enjoy her the track when finished!

 

Well, the RS Tuning chip kind of sucks. At least it sure looks like it sucks for this motor.

I've been working with someone who knows Motronic very very well. We have deciphered several of the maps on the chip, including the idle and part throttle Ignition and Fuel Injection maps. I'm using TunerPro RT, an Ostrich EEPROM emulator, and my AEM wideband 02 sensor to see what's going on. I can trace where the DME is looking up values in the chip in real time on my laptop, and make changes accordingly on the fly.

The car is indeed running Alpha/N mode, via tuning the "limp home" mode that the 993 is capable of when the MAF is dead or malfunctioning -- it just relies on the Throttle Position Sensor (TPS).

The chip was set up to run VERY lean at idle. As soon as I brought up the fuel getting dumped in at idle, things got much much better. It idles just fine now, and the muffler doesn't start roasting your leg hair off.

The part throttle maps need some work too. Not enough gas down low. I need to do some more basic adjustments in my garage and then book some dyno time to do the real tuning. There is quite possibly a BUNCH of power left in this motor that has probably never really been unlocked. At least at part throttle. And improved drivability too...

I took it for a spin down my street last night. Naughty, I know, but I had to do it. Either these old race tires need to seriously heat up or my alignment needs work pretty soon too -- the car wanted to dart left and right a bunch, and I wasn't going very fast at all.

Feeling good about how things are going at last! And I'm happy I am going to be able to get the Motronic ignition working properly and not have to toss everything out the window and go with Motec or some other system, at least at this point.

 

bump for update.. how's the race car resuscitation going?

 

Unfortunately, I've had some issues in my personal life that have put the racecar rescue project temporarily on hold. Not dead, but definitely on hold for a little while. I am in the midst of trying out a MegaSquirt ECU conversion after getting pretty upset with the Motronic, despite my tuning aids. I'm about halfway wired up at this point.

I will be back to update, but it may be a few months. Life is complicated.

 

Just read the whole thread!

Very interesting project, past history etc inc the links to Adrian streather and his knowledge on these cars too.

Do you have any updates to share?

 

Just a quick update. I know it has been awhile.

The project is rolling again. I spent the last month or so getting a MegaSquirt 3X (MS3X) ECU working with what is left of the stock Motronic wiring harness. I had to run my own wires for an Inlet Air Temp. sensor because those were missing from my harness. Other than that the harness was intact enough for me to build a "connector" between the 55 pin Bosch motronic connector and the DB25 connects that a MegaSquirt uses by default.

I have now begun tuning the MegaSquirt to run the car. I am using a wideband O2 sensor, my TPS sensor, an Inlet Air Temp. sensor, the Cylinder Head Temp sensor, and a MAP sensor as my inputs. I got the car started again on the new computer (rough idle) for the first time the other night. A few nights of tuning and tweaking and then hopefully its off to the dyno for some real tuning.

When that's done, I'm going to try to get the car to VIR this fall for some testing and to see how the suspension setup is as it currently stands.

I'm very excited to be working on the car again! It's a real survivor of a rather difficult period for Porsche and there aren't many cars like it. I found something special.