Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 924/944/968 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: Nov 2003
Location: Littleton, CO
Posts: 78
DME eating 944S.......Why??

Car in question is an 87 944s. Problem is that in the last 2 months it has eaten 2 computers. The symptom has been the same in both cases. The car was running flawlessly, when i went out to start it at lunch it wouldn't start....appeared to be totally flooded. replaced the DME with a known good used, car started and ran fine. put old DME back in.....no start. AHA, problem solved! 2 months later drove car on Friday...ran flawlessly. Saturday morning...no start. Same symptoms......totally flooded. This time a rebuilt DME and started and ran fine. Put most recently failed unit back in....no start. The question is, is there something in the Motronic system, or the electrical system in general which could be eating the DME?? At $300 or so per unit I don't want to be replacing this every 2 months just to keep the car running. Guidance would be greatly apreciated.

Thanks,

Pat

Old 11-18-2003, 08:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
SoCal Driver's Avatar
 
Join Date: Feb 2002
Location: Costa Mesa
Posts: 8,587
Garage
Most common DME failures is the high voltage from cracked spark plug cables, water in the DME from holes under the battery, loose solder joints. Or all of the above.

As you report the problem to be the same with three DME's I suspect the high voltage from the spark plug wires coming back through the injector harness.
__________________
Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 11-18-2003, 09:55 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
Join Date: Dec 2002
Location: Monett, MO
Posts: 1,085
check your grounds! especially the one at the back of the motor/bellhousing area, if it's had a clutch job, they're probably loose
Old 11-18-2003, 10:18 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Moderator
 
AFJuvat's Avatar
 
Join Date: Feb 2001
Location: Viera FL
Posts: 5,643
Also, Water intrusion will fry a DME in short order. Is your battery box leaking?

AFJuvat
__________________
Es geht nicht darum wie schnell man faehrt, sondern wie gut man schnell fahren kann.

Ihr Brunnen der nutzlosen Porsche Information
Old 11-18-2003, 06:38 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
Join Date: Nov 2003
Location: Littleton, CO
Posts: 78
Thanks for the replies! There is absolutely no sign of water intrusion in the computer area, nor any on the computers themselves. I checked all the plug wires for cracking or other signs of breakdown and found no breaches of integrity on them, however the coil wire appeared to have been pinched to the point there was a small hole in it in the pinch area. No sign anywhere of arcing, but i replaced it anyway. I inspected both fried computer plug areas for signs of melting or other high voltage problems and both appeared clean as new. Right now the car is running fine, but I'm still a bit gunshy, wondering how long it will remain so. If anyone has any more ideas they would be greatly apreciated.
__________________
87 944S Black/Black Club Racer
87 944 Kalahari Beige/Brown Daily Driver
82 911SC Platinum Metallic/ Brown Garage Queen
Old 11-19-2003, 07:56 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: Nov 2003
Location: Littleton, CO
Posts: 78
Oh, I almost forgot....I also checked all the grounds and the sensor connection, as I put a clutch in the car about 6 months ago and everything was clean and tight. I suppose this could all be coincidence, but as the failure mode of both computers was the same, I am skeptical.
__________________
87 944S Black/Black Club Racer
87 944 Kalahari Beige/Brown Daily Driver
82 911SC Platinum Metallic/ Brown Garage Queen
Old 11-19-2003, 08:01 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
SoCal Driver's Avatar
 
Join Date: Feb 2002
Location: Costa Mesa
Posts: 8,587
Garage
Send a bad one to Wilk. He will be able to tell you what failed.

As to the high voltage. It doesn't take much. Doubt it would leave any visable damage.

Next time you check your wires do it with one hand on the engine and one hand going along the length of the wires -- with the engine running.

Use stock wires by the way.
__________________
Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 11-19-2003, 08:54 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
ae1969's Avatar
 
Join Date: Jul 2001
Location: Edmonton, Alberta, Canada
Posts: 4,530
Send a message via ICQ to ae1969
The grounds on these cars are just garbage. I took an old ground wire I had replaced with Icesharks kit last year and I sliced it open. The cable looked good on the outside, and I had cleaned corrosion of the ends, but the inside was totally corroded..... The cable on the outside looked just fine other wise.
__________________
Alex - PCA Polar Region - Boxster Muncher
86' 944 Turbo - Megasquirt - 326 rwhp/340lbft @ 18 psi SOLD
www.edmontonhomelife.com
www.edmontonrealestate.ws
Old 11-19-2003, 10:02 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
bennydean's Avatar
 
Join Date: Sep 2002
Location: Melbourne, Australia
Posts: 28
My 1988 944S has only just had its electrics sorted out. It would mostly run like a piece of crap despite the thousands of dollars spent on a (very) major service.

The DME had blown two pins in the connection to the wiring loom, a result of failing grounds. Prior to this I had to have blown tracks repaired in the DME as a result of the same poor grounding.

I had an auto-electrician completely redo all of the cars earth points and now everything is purring along. Some of the major earth leads exhibited signs that they had been exposed to extremely high temps (they'd failed).
__________________
1988 - 944S Alpine White
Old 11-19-2003, 05:03 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
SoCal Driver's Avatar
 
Join Date: Feb 2002
Location: Costa Mesa
Posts: 8,587
Garage
Wilks, How would you fix this to keep it from happening?
__________________
Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 11-19-2003, 08:41 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
BlueQuestTSi's Avatar
 
Join Date: Jun 2003
Posts: 396
Quote:
Originally posted by FR Wilk

The early 944 suffers from being designed by a totally competent person. It is grounded beautifully. A single ground wire to the frame behind the fuse/relay box. Only one ground.
Makes you wonder what they were thinking? Best possible ground is short and sweet, and all ground points should be attached to the same place. What ever made the later engineers think, "We can put a ground here, and then another one here, and one here, and that should work." is beyond me.....


Does the case ground tie in with the other 2 grounds through the circuit board? I'd almost think you can eliminate the runs by tagging the 2 wire runs to the case, then beefing up the case ground. I can kinda understand why they'd run grounds to the engine(same ground potential as the sensors), but at the same time it could promote failure of the DME when engine ground suffers, or ignition wiring fails.
__________________
Jack
86 Red 951 - Turbo Twists, otherwise stock for now
83 Black 944 w/86 951 front end - still down and out, but coming back slowly.
02 Altima SE 3.5 - grocery go-getter
00 Yellow Ducati Monster 900i.e. 88 Chrysler Conquest TSi
Old 11-20-2003, 06:08 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered User
 
Join Date: Nov 2003
Location: Littleton, CO
Posts: 78
Thank you for the latest replies. Taking Mr. Wilks suggestion, we (I have now enlisted the help of a friend who is much less electronically challenged than me) opened both failed DMEs and found the LANS on both were fried on the bottom of the PCB in the same place. (lower right hand corner with the connector facing me) My next question would be, do you know which 2 pins on the connector are the grounds? I'm sure we can trace back through the harness and find them but it would sure save us some time if you knew. We plan on trying the jumper cure you recommended, but certainly don't want to jump the wrong wires. Thank you again for all your help and we will press on. As an incidental bit of information my friend repaired the LAN on one of the boards and we reinstalled the DME. It still doesn't work but there may be more damage than we know in the DME.

Pat
__________________
87 944S Black/Black Club Racer
87 944 Kalahari Beige/Brown Daily Driver
82 911SC Platinum Metallic/ Brown Garage Queen
Old 11-20-2003, 09:47 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
 
Registered User
 
Join Date: Nov 2003
Location: Littleton, CO
Posts: 78
A thought. Mr. Wilk, if you would like I can send you one of the failed DMEs (which I have absolutely no use for) to play with. I don't know if this is something that would interest you, but if it is and you would send me shipping info I would be happy to send it off.

Pat
__________________
87 944S Black/Black Club Racer
87 944 Kalahari Beige/Brown Daily Driver
82 911SC Platinum Metallic/ Brown Garage Queen
Old 11-20-2003, 10:22 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Registered User
 
ChrisBennet's Avatar
 
Join Date: Aug 2001
Location: Nashua, NH USA
Posts: 8,092
Quote:
Originally posted by SoCal Driver
Next time you check your wires do it with one hand on the engine and one hand going along the length of the wires -- with the engine running.
You're kidding right? Never put both hands in high voltage circuit (and believe me, Motronic spark plug wires qualify).
When you make a circuit with both hands the current goes though your heart.
Your method will give you one hell of a zap - if you are lucky. If you are unlucky, that zap will stop your heart.
-Chris

P.S. Anyone remember the voltage in a motronic system?
__________________
'80 911 Nogaro blue Phoenix!
'07 BMW 328i Coupe
http://members.rennlist.org/messinwith911s/
Old 11-20-2003, 01:12 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Registered User
 
SoCal Driver's Avatar
 
Join Date: Feb 2002
Location: Costa Mesa
Posts: 8,587
Garage
Quote:
Originally posted by ChrisBennet
You're kidding right? Never put both hands in high voltage circuit (and believe me, Motronic spark plug wires qualify).
When you make a circuit with both hands the current goes though your heart.
Your method will give you one hell of a zap - if you are lucky. If you are unlucky, that zap will stop your heart.
-Chris

P.S. Anyone remember the voltage in a motronic system?
No I'm not kidding. His reported inspection of the wires was way to simplistic to catch any real breaks in the insulation.

Best way is to run the car in a very dark location with the hood up looking closely at all of the points the HV wires come close to the engine and DME wire harness.

Since Wilk's has identifed the actual failure I still would not ignore the possibility of bad HV wires.
__________________
Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 11-20-2003, 01:48 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)
Registered User
 
Join Date: Nov 2003
Location: Littleton, CO
Posts: 78
Actually, although iI understand the significance of this contribution to a failure, as far as I can tell, none of the plug wires are anywhere near the DME harness. Remember, this is a 4 valve car and the routing of the plug wires is such that they are not near much of anything else electrical that i can see.
__________________
87 944S Black/Black Club Racer
87 944 Kalahari Beige/Brown Daily Driver
82 911SC Platinum Metallic/ Brown Garage Queen
Old 11-20-2003, 01:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #16 (permalink)
Registered User
 
SoCal Driver's Avatar
 
Join Date: Feb 2002
Location: Costa Mesa
Posts: 8,587
Garage
Gesh! You're no fun.

Yes the plug wires do run opposite the injector harness but they still can arc to the engine block and back through the seperated grounds to the DME.
__________________
Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 11-20-2003, 03:11 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #17 (permalink)
Registered User
 
Join Date: Dec 2002
Location: Monett, MO
Posts: 1,085
"Excellent question Hugh! It was a RennLister (mail not forum) who sent me the DME in the first place. Had a charger on the battery, hit start, boom!"

hey FR that was me! well actually not me but I'm the one that sent it to you. He toasted it badly as you could tell, it was due to bad grounds. Haven't had any problems since. Interestingly, it was on it's way out before he hooked up the charger. He was going down the road when it started surging. He killed the battery trying to figure out what was wrong, then he hooked up the "jumpstarting" battery charger and really fried it!
Old 11-20-2003, 10:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #18 (permalink)
Registered User
 
Join Date: Dec 2002
Location: Monett, MO
Posts: 1,085
he just did his clutch!
Old 11-21-2003, 12:35 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #19 (permalink)
Registered User
 
Join Date: Nov 2003
Location: Littleton, CO
Posts: 78
True, I did the clutch several months ago. When this thread first started I went back and checked the ground wire bolt tightness and it was tight, but I am now going to remove and clean them in addition to the wiring harness mod suggested by Mr. Wilk. BTW, speaking of Mr. Wilk.....do you ever sleep? I noticed the last post was send at 1:29AM.

__________________
87 944S Black/Black Club Racer
87 944 Kalahari Beige/Brown Daily Driver
82 911SC Platinum Metallic/ Brown Garage Queen
Old 11-21-2003, 08:07 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #20 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 08:41 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.