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1986 Porsche 944 turbo, intermittent start issue

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Old 08-12-2018, 11:01 PM
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Aktive1
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Default 1986 Porsche 944 turbo, intermittent start issue

Hello ,I'm new to the forum and would like some help. I have changed the dme relay, fuel pressure regulator, filter, fuel pump, both reference sensors and I'm still having issues with it starting. The last items that I changed were the reference sensors .after changing the car started instantly .took it for a ride then ,parked it in the garage .came out the next morning and back to the no start issue. Installed a new dme relay, still no start but did start after I smacked the area where the key goes. It ran for a minute then shut down I'm thinking because I left the ball bearing out of the fuel rail. I reinstalled the ball bearing and cap ,tried to start and nothing . Is my next option a new dme? Thanks for the site and any help is much appreciated .
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Old 08-13-2018, 01:40 AM
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KVDR
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Same issue I've been having. Probably the DME. Check for tach bounce when attempting to start.

After intermittent problems over the past year, mine wouldn't start at all the past month...but suddenly started up no problem Friday night. I left it running and wiggled every wire in the engine bay, then pulled out the DME and KLR and jigged the wiring harnesses. Nothing seemed to make the car stall or stumble.

So I just left it running for about a half hour, and then I heard it almost die before catching itself. Then a few seconds later it did die. Tried starting - no tach bounce. So I tapped on the DME with a screwdriver handle and tried again. Fired right up. Then I tapped on the DME and it would stumble again.

I've opened up the DME and I don't see any obviously bad solder joints. I've previously touched a few up, but I think I'm done with trying to keep the 32 year old DME going. Time for a standalone system.

You might want to try looking for cold solder joints on yours first though - might be an easy fix.
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Old 08-13-2018, 02:11 AM
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Do you have sparks at each plug? How old are the plugs?
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Old 08-13-2018, 01:53 PM
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KVDR, I think I'm going to purchase the dme just so I know its done, the car sat in storage since 2009 and only has 68000 on the clock, I'm a believer in preventive maintenance. I'm going to remove the dme this evening when I get home and tap on it a few times to see if anything happens. if I have extra time im going to open it up and take a quick look. I plan on using specialized ecu repair for the repairs. one thing that I did find odd yesterday is that after cranking it over it seemed like it would try to start during the release of the key, I thought it was coincidental so I cranked it over a few more times and it did the same thing, almost like something is wrong with the key switch but it may just be my imagination..lol. I did not have tach bounce at the time of cranking. ill keep the board updated on my progress,

DJANTLIVE, I'm going to bring my spark tester home this evening and try it, ill keep you updated on my progress.
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Old 08-13-2018, 02:08 PM
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Dan Martinic
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Since it started immediately after changing the speed & ref sensors, my first suspicion would be the connection of those sensors. I know a few here found the original brown-wire side connections to be all green corroded inside the plugs. There is a replacement harness widely available.

I only suggest looking into the connections first as I was once convinced of a DME failure but it turned out to be something totally different.

Out of curiosity, what brand of sensors did you install?
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Old 08-13-2018, 03:27 PM
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Dan Martinic,,, if I'm not mistaken they were the Facet brand, changing the sensors was a project. the first sensor came out with some effort , the rear sensor I got to twist back and forth but would not move upwards and ended up breaking off. I ended up having to take the sensor bracket off and reset the gap. after I installed both sensors it started instantly.. I actually thought I finally had it fixed because a few days before it wouldn't start. It did the same thing after changing the fpr. it seems to start every time I add new parts but only once after the new parts are in, then intermittently when it wants to.. the fpr I needed to replace because I could distinctly hear the fuel pump struggling to feed the correct pressure to the injectors, the fuel pump would make a loud whining noise then the car would stall. I purchased all of the common problem area parts so I could change at my convenience when I had time to mess with the car.

Last edited by Aktive1; 08-13-2018 at 03:29 PM. Reason: spelling
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Old 08-13-2018, 11:46 PM
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Dan Martinic
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These stories of intermittent “works! doesn’t work!” are fascinating, along with all the tapping and screwdriver play. I am dreading the day.......

Anyway, sounds like the sensors are fine
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Old 08-14-2018, 12:40 AM
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Here's my update for today's testing, I tried starting it again with no luck. I decided to install the old dme relay just to check if the new relay is defective , again no start. I took the advice of KVDR and removed the computer from the mount but didn't unplug it yet. The car fired right up. Then I tapped on the side top of the computer and the motor stumbled but didn't shut off. I tapped again and the engine stumbled. The next tap was a little harder and the car shut down .this time when trying to restart the car I had to tap on the dme and it started again and allowed me to wiggle the harness and the other computer (klr I think ) and harness and it stayed running until I decided to shut it off .each repeated attempt it started easily .I tapped on it again while it was running and it still ran perfect .If I have time tomorrow evening I plan on taking a look inside and also checking out where the harness attaches to the dme.hoping to find something that doesn't look right. I'll keep everyone posted if I can get to it tomorrow. Thanks again to all that responded.
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Old 08-14-2018, 08:52 AM
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MAGK944
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Search is your friend Faulty DME Solder Joints causing intermittent no start.
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Old 08-17-2018, 06:26 PM
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I has intermittent starting problems with an "S" I have been working on. After two weeks of testing, the wires for the flywheel sensor on the harness end under the rubber BOOT were broken.
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