DME bad or Immobilizer

After an engine fire in my 2002 Targa, I replaced every burned item and reinstalled the engine. I did not own the car before the fire, so no experience with starting it. Now it turns over and fires up, but immediately dies. Took it to Porsche dealer for one hour of service and the very knowledgeable tech said the DME recognized the key, and that it might be the used engine and interior wiring harnesses (from donor 2002 Targa) I installed. Porsche dealer did not solve the issue. I checked EVERY single wire on the engine harness to the round connectors, front and back, and all colors match up. I have replaced the DME fuse with 4 spares (#53 type) and it is the same result with all of them. The pill in the fob is not the issue, because the engine turns over and fires. I opened up and inspected the immobilizer under a magnifying glass, and it is in perfect condition. I have not done that to the DME. Should I try that next? Do you guys think that the fire (about 24" from the DME) could have shorted the DME? The carpet above it was not scorched. Another puzzling issue is that the SAP runs constantly when connected, on battery power alone, no key in the ignition. I have it unplugged, and yes, I replaced the relay for the SAP as well, to no avail. Ideas?

Sounds like you have a massive vacuum leak to me. Engine fires up on start program then leans out and dies due to excessive air (lean stall). Try disconnecting the MAF sensor and adding some extra fuel via a propane torch to see if it continues to run. NOTE OF CAUTION : Be prepared to shut down the engine is case of engine high RPM or run-away...

Just throwing out suggestions because I know nothing about a 2002 Targa and how it relates to a 996 - a lot of times it comes down to a faulty/bad ignition switch. In our 996 world, the electrical part of the ignition switch is more often than not the culprit. Questions, what caused the fire...shorted wires or something else? Since the secondary air pump is running even without the key in the ignition, could it be that either something is still shorted out electrically, or again, back to the ignition switch electrical part. Good luck!

Thanks for the replies. The 2002 Targa is mechanically the same as any other Carrera built from 2002-2004, so it shares the same wear items. I can try electrically checking the ignition switch. The no start is an instantaneous shut down about one second after it turns over and fires up. All small vacuum hoses are brand new. I double checked every air passage to be sure it was tight when I recently dropped the engine a second time. The shut down happens with or without the MAF connected. I could try spraying starting fluid in the TB before cranking to see if it runs longer. Oh, and the fire was located on the right side of the engine, so I suspect either a leaking p/s line, or a leaking o-ring in one of the injectors on that side. I did not own the car at the time of the fire. The Porsche tech is convinced it's the immobilizer, but it was pristine inside. I think it's worth an internal inspection of the DME.

If it's starting for at least one second, I would be shocked if it's the DME or immobilizer. What if you start the car and push the gas pedal 3/4 of the way down? Also, how old is the gas? On my BMWs, when I they had issues running for 2 seconds or less, one time was a bad MAFS and the other was a clogged idle air control valve.

Also just guessing, when you turn the key to ON (not start) can you hear the fuel pump running? Have you checked and double checked all of the fuses? It could be a faulty fuel pump relay. Also, do an e-gas calibration...turn ignition to ON, wait 60 seconds then OFF...then try to start it up. During that 60 seconds you should hear some whining and clicking from the engine bay.

I appreciate all your responses. Prelude Guy - all gas is premium and brand new as of two weeks ago. The symptoms were exactly the same with old gas. I'll try starting with 3/4 pedal. The MAF is used and came from a moderate mileage 02 Carrera. DBJoe996 - fuel pump is new, and so is FP relay. Even the old pump produced correct fuel volume in a test bottle. All fuses ohm out in the correct range. I have done the e-gas calibration several times, but I never do hear the reported whining or clicking from the throttle body. Does that indicate a bad TB? I have removed current one and cleaned it twice. I actually replaced the TB with a known working one and it did not change the symptom.

Im assuming u dont show any codes? It really sounds like a wiring issue. R u sure the cam sensors are pluged into the correct sensors. Apperently its easy to swap them on the engine. Not sure if this would cause a start/stop like u have. Also another vote for the ignition switch as these can cause weird issues when they fail.

I show the following codes: P1120 P1139 - O2S B2 P2135 - TPPS switch A voltage correlation P0122 - TPPS switch A low input P1141 P0117 - Coolant temp sensor low input P0418 - SAP low voltage P0348 - Cam pos. sensor low input B1. Cam sensor and crank sensor are brand new. Secondary Air Pump is disconnected, so that may be throwing the P0418. Coolant temp sensor is used, but from a known working motor. Not sure of age of O2 sensors. On this vehicle the throttle position sensor is inside the throttle body. I changed it out and still got the same codes. I agree that it could be the ignition switch, and perhaps several of these codes are cascading after the apparent break in the "run" circuit. When it fires up (for as long as it takes to say "vroom") I noticed the tach gently rises from off the scale to zero position, but no higher.

I would be concentrating on the cam sensor and then the tpps sensir codes. These r gonna keep the engine from running. Triple check u have the correct harness plugs connected to the correct cam sensors. This mix up happens often.

I'll check the cam sensor plugs. Since the TPPS is inside the Bosch throttle body, how do I check that?

Quotes source post: 16495572

You got a lot Sh*t going on there. I'm seeing a lot of "low input" messages. I would be checking for the 5v reference voltage from the DME to sensors, also the DME ground.

Just a question - what engine harness did you use? Same year, model and transmission or different?

I used the same year harness from a Targa, for both the interior and engine harnesses. They match perfectly with each other and all of the components each connection was designed for. I can't see all of the bank one connections, but I check the four terminals coming off of the front section, and each terminal is unique to its component. However, I realized today that the CPS on bank 1 that is throwing the code P0342 is the original one from before the engine fire. It was not scorched but must have been damaged. So, I bought a new one and will install it as soon as I figure out how to reach the screw. It's in a tight space behind the engine brace, and my socket wrench will not fit, with the 5mm Allen socket. Anyone else solve this problem? Maybe removing the engine mount screws and carefully lowering the engine is the only way to get access to that screw.

Very good on the harness As for the cps screw - no engine moving required just take off the left rear wheel and use a long extension socket it's a 5mm hex (size is from memory)

Dan, you are referring to the Crankshaft Position Sensor, mounted near the flywheel. I replaced that, as I mentioned above. The sensor I need to replace is the Camshaft Position Sensor at the rear of bank 1, to the right of the green cam timing plug. The engine brace blocks sockets from reaching the screw. I think I can reach it with a 90-degree hex wrench, but the space is so tight my hand can't fit in there to get a good pull on the wrench.

Quotes source post: 16499319

Ah yes sorry, got my sensors confused

No worries, as they say down under! I've determined that the only way I can get to this little 5mm screw for the cam position sensor is to remove the cats and the engine cross brace. I tried to use a wrench to grab a 5mm allen socket from the side and turn it, but it started to strip the socket of the screw head. Now I'm almost done moving the brace out of the way after over an hour to remove all nuts and bolts. With the brace moved I should have a straight shot at the screw with my ratchet.

I don�t to derail this thread, but if you want to rule out the ECU and Immobilizer, ECU Doctors in Florida is the way to go. They have the tools to verify a good or bad ECU, and can repair it.

I think you have found your problem by what you posted in your other thread. Having two different types cam position sensors in the same motor will surely confuse the DME..

LOL, I'm such a goof! I should have just posted that here instead of starting another thread. But yes, I do agree, and put that thought in my reply to the other thread. I bench tested both sensors and got 12.5V on the multimeter, but even connected to power, when I switched it to Ohms, I could not get any resistance on either one of them. If that means they are both bad, then I only have one new sensor on the way (the Bosch 040). Do you have a sure fire way to bench test the resistance of the sensor, not just the terminal?

Now that we have a bit more time on our hands I thought I would update progress on the no-start. I have found the source of all the low input codes: yup, it's a fried DME! I took it apart and found evidence of a hot spot with smoke tracks and a burned area, right behind connector III. That connector also has melted plastic at the base of several pins, which are now very loose. I just bought a used Bosch DME that matches mine on all of the Porsche and Bosch part numbers. The next step is a trip to my local Porsche dealer to have it programmed to the car. I may get a new key fob while I'm there. I'll keep you all posted. Hopefully I'll get to hear it running real soon.

The car runs!!! What a great sound after 11 months of work to bring it back to life after the engine fire. A huge shout out to High Tech Mobile and the owner, Dustie in Escondido, CA. I decided to send him both the damaged and donor DMEs (with VINs) instead of towing the car up to Porsche. He reprogrammed the new one and sent it back to me in one day! After reinstalling the DME, it fired up the first time. In my excitement I forgot to do the e-gas calibration, so it idled loud and high at first. I shut it down and did the calibration. Then it started up and purred at 750 rpm. I took it out for it's inaugural drive around the neighborhood and it ran perfectly and shifted smoothly, thanks to new clutch and resurfaced flywheel. All of the old codes are gone, but a couple of new ones popped up for the upstream 02 sensor on Bank 2. Bench DMM tests for resistance and voltage (using my propane torch to heat the element) showed that the sensor has no signal - just like the DME reported. So, it needs replacing. I'll get that installed tomorrow. Anyhow, that's minor as things go. I'll let you guys know if it has any more nagging issues as it gets back to working condition. Thanks for all the great feedback over the last several months. You guys helped me more than you know, and believe me I researched way more posts than I posted questions to the group. That is the best way to learn about the well-engineered systems of our fantastic cars.

Congratulations! Good job bringing it back to life!

Awesome job!

[Image-only post; no author-written text. Original image references:] https://rennlist.com/forums/graemlins/thumbup.gif

Comgrats! Pics of the car, before and after?