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I believe I may have inadvertly destroyed my DME; I turned the key to ON with the bellhousing ground disconnected.
Porsche literature warns that this will 'destroy' it. Immediately. What does that actually mean?
The car won't start... and after performing all the steps I could without an osciliscope and checking my (new) reference sensors, everything passed, except Step 14. See pic.
I imagine that, like the reference sensors, I should see some voltage while doing this. I don't.
If I open up the DME, is there a way to tell what may be up?
There cannot be fuse as it affects all inputs and outputs! All ECU's are basically programmable ground switches and having a solid ground is essential for it to work.
Before declaring a destroyed DME or KLR, you must perform a few more tests.
If you are not getting a proper speed/ref signals the car will not run. Have you reversed the sensors plugs by mistake? Have you checked or bypassed the DME relay?
The more info you give us and listng the tests performed will allow us to assist you better.
I appreciate the glimmer of hope. Okay, here's what I've done:
In December, I began to work on The Clutch (and all that entails, including a few extras like slave cylinder, catalytic).
The reasons I feel DME is "destroyed":
1. Broke both ref & speed sensors on removal; bought new ones. Took considerable amount of time with bracket setup, using washer method
2. Before removing old sensors, I decided to change the heater valve. I began to drain the coolan.. then realized that the hvac control is on "cold"; being very ignorant at the time (all this work is first time new to me), I thought I should turn the ignition ON, move the hvac to full warm, and continue draining fluid. Unfortunately, I'm pretty sure I had removed at least the smaller ground wire from the bellhousing before doing this.
Yes, even now this sounds ridiculas
3. After installing everything--yep, just finished this job up--the car won't start
Using the DME / KLR Test Procedure that I downloaded (offical Porsche document, got it from this site http://www.arnnworx.com/dme-data.htm ), I began with all the steps I could do without an osciliscope:
TEST POINT 1. Physical checks of connections -- checked them all
2. Checked power supply for DME via pins indicated in procedure (didn't check KLR). I even checked pin 3 in the 14 pin connection (voltage there was lower, like 8volts, until I grounded on the intake manifold instead of shock tower; still learning!). Checked voltage in DME Relay socket 30 & 87, 12 volts. Checked fuel injector connection voltage, good. All this with key ON position
3. Checked fuel pump by removing the return line and jumping the DME Relay socket. Fuel squirted all over except in the container I set up
Everything measured properly and the DME Relay clicked at certain tests
4. To test the ref & speed sensors, I measured the voltages while turning key to START (car turns over fine, and the battery has been trickle charging this whole time). Took me a while to figure out the multimeter needs to be on AC, not DC. I got 5-something volts on the speed and almost 2volts on the reference. I also checked the resistances both at the DME plug and the ends of the sensors themselves: each sensor measured 800-something ohms (BTW, why does the multimeter read with a decimal in front, as in .800?) They are new FAE sensors.
5. I did no tests for this test point--Ignition system. The first one requires an osciliscope, and I don't know how to measure the "primary resistance, secondary resistance" (whatever that is), the spark plug "shielded resistance", or the distributer "shielded resistance". I also didn't test ignition timing as the car won't run. I did confirm that the distributer is installed correctly; I even lightly cleaned the contact points with emery cloth. Car did run fine In December when I parked it.
6. I tested the AFM while waiting for parts. All the values seemed okay. NTC I coolant sensor test measured fine.
7. I didn't test fuel pressure
8. The idle control valve is new--installed in September and running fine till I parked (I did AOS seals then too)
9. I did not test the Throttle switch. According to the chart, it's not a symptom of no-start. I skipped the whole part about KLR and DME checking with ignition timing and car running, for obvious reasons
10. I installed a brand new NTC II coolant sensor. Did not actually test it. Old one was working fine--I checked it in boiling water; figure I should change it anyway (note: car did fail emissions with high CO2 in November; pulled cat definitely bad, crumbling stuff coming out of it, and I've put a new one in).
11. Did not test injectors specifically as this step indicates. They were tested & cleaned professionally back in September
12. Skipped test point 12; it appears to be all about turbo charging pressures etc
13. I did extensive intake system leak tests in September and changed a whole bunch of vacuum lines at the time. I am confident this is all good
14. This test point is what is "confirming" for me the DME destruction: though I have no oscilloscope, I assume that I should at least see something on the voltmeter while starting and touching 9 & ground (10) on the KLR plug (DME plugged in, of course). Both AC and DC show nothing. The test point clearly states if no signal (on oscilloscope), replace DME
I skipped the rest for obvious reasons (idle speed, running conditions). FYI I did these in September.
Oh, there is no tach bounce.
What do you think? Should I pull the plugs and confirm visually if there's no spark? I can't think of anything else to test...........
Sad Dan
Last edited by Dan Martinic; 03-17-2018 at 04:10 PM.
Reason: clarification
I'd give a finger for a good DME to plug in and see if it starts. Anyone in the Toronto area feel like ripping theirs out and dropping by? Case of beer? Bottle of Brandy? Cohibas from Cuba??
I am thinking of getting one.. but I have not a clue how to use them or what to buy. A quick search revealed some complicated-looking equipmemt that cost a lot more than 30!
Can you recommend a specific one to look for? Are they all pretty similar in operation, at least for stock 951 needs?
Tonight, I went out and performed every test on the following chart, gleaned from a post by John_AZ; everything passed except for Full Throttle Switch where I didn't get continuity at full throttle and Tachometer/upshift light (no continuity)... I didn't check O2 or AC (O2 new in Sept):
Look for "Assembled DS0138" and get the case for it. Both around $30. No PC is needed, you need a 9Vdc power source.
For what you need, they are fine. And if it gets damaged, not much $.
Lots of online tutorials on how to use a scope.
Look for "Assembled DS0138" and get the case for it. Both around $30. No PC is needed, you need a 9Vdc power source.
For what you need, they are fine. And if it gets damaged, not much $.
Lots of online tutorials on how to use a scope.
I managed to borrow this crazy scope! But... it only has one lead with a clip. I don't want to make assumtions, and unbelievably, I'm having a hard time finding how to simply hook it up.
All the online videos show the screen—not the connection!
Black wire wire alligator clip goes to ground, probe pin (or hook) goes to pin you want to measure/view the signal.
Ground in you case may be the chassis or other good electrical ground, try to keep the lead as short as possible, but not critical.
Ok.. but... the ref & speed sensors have two pins each?
Only one pin is the signal, the other is the shielding, try one with the probe then the other with the probe, one will give a signal the other won’t. As PaulD_944S2 said ground the scope clip, you never use that to measure (or probe) as you need it as a baseline measurement for the scope which in this case is ground.
There are lots of videos on YouTube on how to use a multimeter and oscilloscope correctly.
03-16-2018, 10:52 PM
DME destroyed?
