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HELP! HELP! Injectors not firing. Track day tomorrow!

 
Old 12-07-2001, 11:16 PM
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sprbxr
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Post HELP! HELP! Injectors not firing. Track day tomorrow!

Just finished getting the 951 ready for the VIR track day. Drove it home and then on my way back to my friend's shop it cuts off and will not restart. I wait about 5 minutes and try to start it and it starts and runs for about a minute then cuts off and will not restart at all now. I have fuel pressure and spark but no signal to the injectors. Anyone have any ideas? I guess I will miss Saturday at VIR but Sunday is still salvageable if I can get it running. By the way the car has run perfectly for weeks since I figured out the overboost problem (bad boost sensor in KLR). The only thing that was done to it today was put some new pads, rotors and SS Lines on it. Help me salvage my track day.
Thanks.
Justin
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Old 12-08-2001, 01:01 AM
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Luke
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Its the factory alarm. (engine refference sensor??)
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Old 12-08-2001, 01:40 AM
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What do I do to fix this? Where is it located? Is there a way to bypass this?

Justin
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Old 12-08-2001, 02:16 AM
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Luke
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Pull out the carpeting under the pass. foot well and look for loose wires around the DME. Sounds like its deffinately DME related.
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Old 12-08-2001, 03:46 AM
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I don't want to lead you in the wrong direction, but could this be the DME relay? I see a lot of people post this as a no-start solution.
DanD
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Old 12-08-2001, 08:33 AM
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David Salama
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I had a similar problem which was fixed simply with a new DME relay. In the meantime, try tapping on the relay to see if it will work again.
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Old 12-08-2001, 04:19 PM
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DME relay seems to be functioning. Both contacts are activated when the key is turned on. I am thinking the DME itself is the culprit. Unfortunatly I do not have a spare with which to swap. BTW, I have used my code tester and I am getting no fault codes. I guess my weekend at the track is a bust.

Justin
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Old 12-08-2001, 04:27 PM
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Justin,
Did you get the documents I sent you? I can send them again. Also, here is great fuel systems page that might help. It's written by Rob Langely, and mostly covers 951 mods, but also is a good source of info for troubleshooting.

Great Fuel Systems Web page
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Old 12-08-2001, 06:29 PM
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keith
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Have you tried pulling one injector connector and trying to crank? If it starts up, your FPR is bad (too much fuel pressure).

That is a common problem. Good Luck.
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Old 12-08-2001, 08:17 PM
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Yep. Tried it. I am getting no signal to the injectors.

Justin
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Old 12-08-2001, 08:37 PM
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Justin,
I resent the docs. Here is a section of one of them describing a troubleshooting process.

------Info I found in the archives -------------

With all the talk about DME lately...Here is some very basic info.

Generally for a no start situation, I first crank the engine and listen for compression. If it sounds normal...then I start searching. I next listen for injector fire..if you can hear the injectors "tick" on cranking (actually, I use a "noid"..LED) then the DME is sending the signal to them to pulse open and closed. If you hear this "tick", then as a rule, you can assume the DME relay is functioning ok. I then check for spark (there are a number of ways to do so, here is a simple way) by pulling a plug connector off of a spark plug, stick a thin screwdriver into the plug connector and hold the metal shank of the screwdriver about 1/4" away from the engine (usually the top cam housing) and watch for spark as someone cranks the engine--or if you do it correctly, you can crank the engine yourself and watch for the spark to jump the gap from the shank to the engine housing. As the engine cranks over, the spark should pulse.

If I do not get any ignition spark, and I am sure that everything is hooked up...I pull the coil wire to the igntion cap and do the same thing...if I have spark there, then the rotor is usually bad (or not turning). If I get no spark from the coil...my search is usually over.

As a rule, I go straight to the DME control unit, pull it out and open it up. My experience tells me no spark situations are usually just cracks at the solder joints in the DME, usually on the side where the pin connectors are soldered into the board. I have found as many as 15 bad solder joints...usually along the pin connectors and also three places around the large silver thingeydo (sorry for the ignorance. I am assuming it is some form of transistor) found on the right side of the board close to the pin connector joints. I resolder every bad joint I see and put it back together...doesn't take very long.

I have not had to replace a DME for a 944 in the last three years...I have always been able to repair them. Usually the symptoms are backfiring and intermittent dying or intermittent no start...just like the key is being turned off and on (which is in essence the spark coming and going intermittently). Sometimes I have to look real close...but yes, there it is...a crack. On some cars, I can even "whack" the DME when cranking and get them to start.

For no injector pulse problems, I usually find that the DME relay is at fault or the fuel pressure relay is bad. I disconnect an injector and crank the engine...if I then have injector pulse (ticking) out of the three remaining injectors, then the fuel pressure regulator is defective. If I still get no injector pulse, I check the relay. Again, I have found cracks in the solder joints of the relays and sticking contacts, but I usually just replace the relay since they are not very expensive.

I know that there are a world of other possibilities, but these are some of the simple fixes. In the real world of repairing Porsches everyday, some of the troubleshooting is not that hard (but I must remember that I have been doing this a long time).

Don I.
------- and some more --------------

First: If your car all of a sudden dies/won't start, it is suggested that
you check the DME relay. Carry a spare to the track or on long trips. More
subtle is the check of the fuel pump fuse. If it is blown, the pump won't
run. I have seen at least two 951 cars with this fuse blown. Cause was a
shorted oxygen sensor connection, which is on the same fuse as the fuel pump.
In both cases, oxygen sensors were recently replaced, and the wire harness
was routed too near the hot exhaust side of the turbo. Powering the
ignition would immediately blow the fuse. Check these things before buying
a new DME.

Mike M.
-------------------------------
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Old 12-09-2001, 11:04 AM
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I pulled my DME today. Upon opening the DME I discovered that at some time prior to my ownership the DME got wet. There was corrosion on the circuit board. On some spots it had corroded enough to bubble up the clear coat on the boards. Could the corrosion cause arcing of circuits within the board?
I would like to swap the DME with a known working example. I would be willing to buy one if anybody knows of one for sale.
Thanks.
Justin
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Old 12-17-2001, 08:00 PM
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Problem Solved!!! Turns out the injector plug to the #1 injector was shorting out causing all of the injectors to not work.

Justin
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Old 12-17-2001, 08:27 PM
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Bill
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Sprbxr,

Thank you for posting a fix!

Many people ask for solutitions but far too few, post the fix. We all learn, and can see trends, when a fix is posted.

In my mind, this forum becomes invaluable when one such as yourself brings the post full circle. Kudo's
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