DME help needed

I have a Koni Challenge 996 racecar that just got a new engine, ran great during break-in and now simply will not start. It turns over, but the DME seems to be telling the car not to start (lots of reasons, unbelievable flywheel sensor, bad injectors, etc, etc), all of those components are new and test good, so I believe it is the DME. As I bought the car from RPM Motorsports who raced it, but have since gone out of business, I don't know how to change the DME as it has to be customized to allow the car to run without airbags, alarm, etc. Does anyone out there with more experience with 996 electronics have ANY suggestions. We are really at a loss here.... THANKS.

The 996 used 3 different DME's. DME 5.2.2, DME 7.2, or DME 7.8 - which do you have? or did they use a GT3 racing Motronic?

I would check for the obvious, the plug going into the DME and all the surrounding grounds. Grounds can drive you in circles, with all the things that it is saying is wrong.

Disconnect battery for 10 min and reconnect. Check fuses and DME relay at back if your car is similar to component locations as stock 996.

Not sure how to tell which version it is, but it has the same serial number 996.618.604.00 as my 03 Targa, and was/is running a normal (non-GT3) 3.6 engine. It has been in and out numerous times for checking and the power is killed via the kill switch whenever the car is off for any length of time. All fuses are good, car cranks, but will not fire with the DME codes implying the DME does not want it to start for a host of reasons.

Way outta my league here, but did you try the DME from your Targa in this car, or visa versa to see if you got the same error messages?

DME's are a one time programming per car serial number per my understanding. The Targas will not work in the racecar as the airbags and alarm are missing and thus would not start. As a long shot, I did put the race DME in the Targa, but as expected, it wouldn't even turn over as it recognized the car, or alarm or something was wrong. (The racecar turns over, but won't start). Thanks, keep the ideas coming....

Have you reseated connectors X59/1 and /2 (round connectors in the engine compartment, sort of under the right rear quarter panel) as well as all the connectors on the DME?

Quotes source post: 5520328

Can you explain this alittle better.

We have removed most of the wiring harness trying to find any shorts or frayed wire and when the car is left overnight, the power is off at the kill switch to save the small racing battery. It was working fine until I went to start the car to load onto the trailer after a test and tune day with the new crate engine. The power was never cut between when it worked fine and when it decided not to start, just sat in the pits for an hour or so.

Quotes source posts: 5520639, 5520552

These would all have been removed and reinstalled while testing and looking for shorts.

Is the alarm system (black box under seat) in or out of the car? If in it has a fuse a external fuse.

I'm not sure if the DME is like most of these units in other german cars, but if so you may need to actually clear the internal fault codes using a device which can directly access the eeprom or static memory in that specific module (assuming PST2, paging Loren?). I've had to do this on AMG before, even though the wiring fault detected was corrected it wouldn't restart until specific subsystem modules were cleared on a real SPS. That may be way off, but if you are losing practice/about to miss an event or something, is there a reason not to go from the motronic to another 3rd party unit?

Quotes source post: 5520781

The car still has the black box, but it has been defeated in some unknown way when the car was original converted to a race car. The DME is not giving an alarm system error, so I don't think that is the problem. Does anyone know specifically how these systems are bypassed for a racecar? Ironically, we ended up buying this car instead of building a similar car from scratch in order to avoid this DME mess

Quotes source post: 5520811

The fault codes have ALL painfully been checked and cleared on the official Porsche fault reader without any success after many hours of following flow charts, but new and different faults just appear.

Is the car actually pumping fuel during cranking?

It has a fuel pressure gauge showing good pressure (just replaced the pump after a dual pump at the track fix during the test and tune) I do not believe the injectors are firing, that is one of the DME error codes, but I have assumed it is related to a DME problem.

I assume you have checked the fuses, particularly for the fuel pump and dme? There is also an injector relay under the carpet behind the back driver's side seat.

Quotes source post: 5521184

Not sure of your kill switch setup and what it is killing, the battery, fuel, etc. That is why I was asking. Just curious what are you using to read these error codes?

Using the Porsche PS2 tester I think it is called. The work is being done by a shop that knows street Porsches very well. The issue seems to be related to the customization of the DME, or simply a bad DME, but we don't know how to test or even replace the DME as we don't understand how the street features can be bypassed. The kill switch cuts off the battery completely shutting down all systems.

I had a problem with my kill switch in my 964. We looked at all normal things (DME relay, fuel pump, fuses...). We ended up just juggling the kill switch itself, turning it off and on. It finally cranked right up. I swore to replace that kill switch. That was 2 years ago. Switch is still in the car an it's never done it again. Hope you get it solved soon. That car's too nice to not be on the track!

Good thought on the kill switch, but we have a quick connect for a second battery going directly to the engine/starter in case the small battery dies, and have hooked it into the system making the car crank very quickly, but still not want to start The Porsche tester is showing that the DME is telling the car not to start, we just can't figure out why or more importantly what to do to make it start the car. I have a very good mechanic who has wasted a ton of time and effort and is very frustrated trying to get the DME corrected. If we knew how all the racing bypasses worked, we would be great, but I can't find anyone who understands the inner workings of the mystery black box. I think I am going to send the DME to GMG Motorsports today to see if they can figure anything out

PS. Big thanks for all the help and suggestions. I was on this forum a lot about 10-15 years ago, but have moved to a local PCA forum. Nice to see so many helpful people out there lending a hand to a stranger!!!

Quotes source post: 5522748

FVD USA is tuning (via wifi connection) my custom setup SC and have cracked the Black Box Gnome I simply tell them what is installed (headers, gas etc) and how I am using the car they send me tuned DME maps to suit my needs. I think it would be nice even if you got your car to fire up that you still would not be in control not knowing how to tweak your engine for the future. Can't remember if you tried another stock DME to see if it fires up? Anyway if you need FVD-USA maybe they have some suggestions. FVD-USA Mark Hatfield Toll Free: [phone removed] ext. 27 Local: [phone removed] ext. 27 Fax: [phone removed]

"The car still has the black box, but it has been defeated in some unknown way when the car was original converted to a race car." Why then is the immobilizer still in the car if that function has been disabled in the DME ECM? "Can't remember if you tried another stock DME to see if it fires up?" It's not that easy without all the coding info, i.e. one can't just plug in another unit. "I think I am going to send the DME to GMG Motorsports today to see if they can figure anything out" Why would you do this without fully testing all inputs/outputs, e.g. all power inputs (#30s & #15s), the engine speed sensor, and relay output drives?

I do not know how they defeated the immobilizer, but I guessed they jumpered something at the immobilizer, not internal to the DME, which is why it is in the car, but I do not know this for sure. It WAS on the list of things to remove for weight, but reliability issues have kept me busy in other areas. I do not know how to fully test all inputs/outputs of a DME which is what I hope GMG can do for $250. We have read the PS2 fault codes and worked through the flow charts related to diagnosing those faults coming to the conclusion of a bad DME, but we doubt a new DME will work because of unknown solutions to the various alarm and airbag issues. So we currently have a large, expensive paperweight and don't know how to move forward.

A stock DME should not work, but we have not tried it as the DME must be programmed to match the chassis and once you do that, it can't be reprogrammed for another car per my understanding. Thus it would be a very expensive experiment considering chances are very good it won't work. I did try the race DME in the targa as a long shot, and it appeared to recognize the car was wrong and would not even engage the starter.

Quotes source post: 5523129

Sounds like a good price and if they due tuning then works for the future. My airbags are out and still starts but have the idiot light and error code. Not to be a total pain but you may want to take a look at that immobilizer box and fuse. Frustrating I know but one thing for sure is in the big picture it will be working sooner or later and you will know allot more about your car....that's what keeps me going.

The first step to figure this out is understanding how the immobilizer system works. In brief, there is a small 'pill' in the ignition key that transmits a signal picked up by a transponder mounted to the ignition switch assembly. This device transmits a signal to the immobilizer, if the 'pill' is correct for the car, the immobilizer releases the starter relay etc and allows the motor to start. If not nothing happens when you turn the key to start. The DME and immobilizer are also matched. The immobilizer can only be programmed with a code once and this code must match the expected code in the dme. The immobilizer code in the dme can be changed to work with a differently coded immobilizer. If the immobilizer code in the immobilizer and dme don't match, again the starter relay is not released. The fact that the car turns over suggests to me that this system isn't the problem and you should be looking elsewhere. As stated, if the immobilizer functionality has been removed, there is no need for the 'black' box to remain, so I doubt it has been removed. -Todd

Do you know how to remove the immobilizer from the loop? If we do that, couldn't we use any DME or would there still be other DME programming custom to the chassis?

"I do not know how they defeated the immobilizer, but I guessed they jumpered something at the immobilizer, " NOT POSSIBLE!!!!!! "The fact that the car turns over suggests to me that this system isn't the problem and you should be looking elsewhere." Actually, it's very simple to bypass the immobilizer to get the engine to crank. The key is to bypass the communication between the DME ECM and the immobilizer ECU, i.e. the code checking/sync between them. If that doesn't occur, then the DME ECM will not enter the "run" mode and generate spark and injection. "but we have not tried it as the DME must be programmed to match the chassis and once you do that, it can't be reprogrammed for another car per my understanding" Actually, the DME ECM can be recoded (reprogrammed) for another after coded for the initial VIN. Bottom line: Without fully checking all necessary inputs, then the troubleshooting effort amounts to a "dart game". Maybe time to find a very knowledgeable Porsche shop.

I think this is something that the company who modified the DME needs to be asked and them only. If they made the custom mods to the DME, they should know of the possible issues this causes.

3 months later, and the DME is still causing problems. It was sent to GIAC who "fixed" the DME, but after repeated calls have never been able to tell me what they fixed. Put the fixed DME in and it generally starts, though a 75% success rate is not what I am looking for. I just want to buy a STOCK DME that can be programmed to start a racecar (ie no airbags and bypassed immobilizer). I have not been able to get an answer from anyone as to whether this is possible. Can anyone build me a completely stock unit, so all the Porsche test equipment can be hooked up, that will work? Seems like a simple question, but no one has answered. Please help if you can.