[nevilmi]

hey guys... i have the problem of my battery dieing overnight. i found that my dme relay is drawing 1.5 amps as soon as i put the positive terminal on. i tried a different dme relay and get the same result. also my car exhibits little to no power under a load but will rev just fine under a no load scenario. ive inspected to entire vario cam mechanics and all looks good. im starting to suspect a bad dme. does anyone have any ideas on how to test the dme? id hate to spend the money on this dme if its not the problem. any help is appreciated. does anyone have a spare dme that i could swap and see if thats the problem. at least id know that way. [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img] [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img]

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[94SilverCab]

This is one of those occasions where a location in your profile might prove useful. Another 968er could be induced to lending you one to test...

Jay

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[nevilmi]

<!--quoteo(post=70490:date=Apr 17 2009, 12:14 PM:name=94SilverCab)-->QUOTE (94SilverCab @ Apr 17 2009, 12:14 PM) <{POST_SNAPBACK}><!--quotec-->This is one of those occasions where a location in your profile might prove useful. Another 968er could be induced to lending you one to test...

Jay<!--QuoteEnd--><!--QuoteEEnd-->


Great point... i'll update my profile... my location is Logan, Ohio which is about 1 hour southeast of Columbus, Ohio.

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[Darryl]

<!--quoteo(post=70489:date=Apr 17 2009, 11:36 AM:name=nevilmi)-->QUOTE (nevilmi @ Apr 17 2009, 11:36 AM) <{POST_SNAPBACK}><!--quotec-->id hate to spend the money on this dme if its not the problem. any help is appreciated.<!--QuoteEnd--><!--QuoteEEnd-->

I'd go ahead and purchase one anyway, as it's good insurance to have in your glovebox...I haven't priced them recently, but aren't we talking 50 bucks or so?

Good luck finding your problem and hopefully it's as simple as replacing the DME. Welcome to the board...you'll find lots of valuable stuff here when it comes to troubleshoot stuff like this.

- Darryl

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[Ryan]

I think he is talking about the brain-box and not a relay. This could be a big expense. Has a blink test been done to test for codes?

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[DaveN]

One wonder if your fuel pump (controlled by that relay) is working properly - low fuel pressure so no go underload? A new relay can be had for 40.00 CDN (32ish USD) or 20.00 (used) from nineapart.com.

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[nevilmi]

Well, first off.. thanks for all of the replies so far. First off, I am talking about the main computer brains. I was doing some additional testing and this is what i've found so far. With an amp meter in line I can see about a 1.45 Amp current draw with nothing turned on. This seemed really excessive so I started looking at the fuse box. I found that by just unplugging the DME relay the current dropped to about 60 mA... which is alot better and much more in line with what I would expect. So I plugged it back in and it shot back up to 1.45 Amps. I then uplugged the 7.5 amp fuse for the DME and the current draw dropped to 1 amp, so that fuse alone took it down by 450 mA's... Nothing else I unplugged made a significant difference.

Ok.. now for the rest of the story... I unplugged the DME computer completely and as suspected the current draw goes down to about 60 mA's. So the current draw is definitley coming from the DME computer.

Now as far as the engine performance goes... The car starts and runs fine at an idle and anything under 3000 rpm's. Once you take it above 4000 rpm's you get motor ping and you can see the air box sucking in on itself. The engine wont sustain 5000 rpm's.. it gets there but then acts as though it running out of fuel or air. So I tried removing the air filter and sure enough the engine runs better and can sustain 5000 rpm's.

But i think all of these things are just symptoms of the bigger problem. I think I have a computer problem that isn't triggering the Variocam system and therefore the timing advance isn't working. It makes total sense that the engine would run well below 3000 rpm but fall on its face above 4000 rpm's.

Again, mechanically i've inspected all of the parts and they all look great with little to no wear. So i'm sure its electrical but I didn't want to spend the $450 on a new brain if that wasn't the problem. I thought maybe someone out there might have a spare brain they'd be willing to part with for just a bit so I could run a basic test. If it is the problem then i'm sure its well worth the money spent to get my car back in tip top shape.

I appreciate all of your help so far and keep the suggestions coming... I may have over simplified this but I took the car to a Porsche dealership hoping the masters could tell me what was wrong and the scary thing was it turned out I knew more about my car than they did and I ended up showing them a few things.

As far as the fuel system goes. I started troubleshooting there first as I thought it was a fuel delivery issue. I even changed fuel pumps and the whole nine yards.. All test show that I have plenty of pressure and plenty of flow so.... that wasn't it either. I feel that i'm close to the solution but was just looking for some moral support I think...

Thanks again.. this is a great site and glad to see it running again.

Mike

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[flash]

just because you see the current draw change with the dme relay and dme connect/disconnect does not mean that either one of those are the culprit - the dme tells other stuff to turn on and off, as well as is the conduit for circuits to those components - that's a lot like saying that unplugging your telephone got rid of the telemarketer that was calling

after checking, cleaning and tightening your grounds........

first run a blink test - see if a fault code pops up
then, pull each fuse and watch the ammeter

if none of that turns up any indication, then yes, try a different DME in there - it is incredibly rare to have one go bad and still allow the car to run

remember occam's razor

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[nevilmi]

<!--quoteo(post=70528:date=Apr 18 2009, 01:00 AM:name=flash)-->QUOTE (flash @ Apr 18 2009, 01:00 AM) <{POST_SNAPBACK}><!--quotec-->just because you see the current draw change with the dme relay and dme connect/disconnect does not mean that either one of those are the culprit - the dme tells other stuff to turn on and off, as well as is the conduit for circuits to those components - that's a lot like saying that unplugging your telephone got rid of the telemarketer that was calling

after checking, cleaning and tightening your grounds........

first run a blink test - see if a fault code pops up
then, pull each fuse and watch the ammeter

if none of that turns up any indication, then yes, try a different DME in there - it is incredibly rare to have one go bad and still allow the car to run

remember occam's razor<!--QuoteEnd--><!--QuoteEEnd-->

Thanks Flash.... I did actually pull each fuse and there wasn't any that had any significant change on the current draw. The only one that changed by 500 mA's was the dme 7.5 amp fuse. I guess that was a piece of info I left out of my briefing. I wasn't sure how often these things fail. When a computer fails, a lot of times they have a "run safe" mode or "limp mode". Do you know if these dme's had something like built in. Where it allows the engine to run but not any kind of performance.

I think I will go ahead and try another DME.. I was hoping someone out there with a parts car might have one I could try to see if that makes a difference. Ok, again, thanks for the feedback.

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[flash]

i think there is a "limp" mode - this is the first i have heard of such a set of circumstances though, and would still suspect bad continuity over bad circuitry

also, if it does turn out to e the DME, there is likely a problem that caused it to fail, such as a bad ground, and the new DME would likely suffer the same fate - i would definitely go through the grounds and main power cables before swapping out

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