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Registered User
Join Date: Jul 2013
Posts: 40
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Really stuck! 951 Won't start, I need ideas
Here goes a long story. I pulled this 951 into my shop running very poorly. I replaced the radiator (Hole), replaced the thermostat, Removed Intake manifold, replaced intake manifold gaskets, rebuilt injectors, replaced the J-boot, rebuilt and replaced several vacuum lines and fittings under the manifold. When everything was buttoned back up 5 Gallons of brand new fuel was put in.
Initially the car didn't want to start, but then it fired up and was running beautifully. I let the car just sit and idle for about 15 minutes while I measured and observed the cooling while also bleeding the system. Here is where it goes wrong... The car just died. I started it up and began to back it up, but it just died again. Now it will not start or run. Fuel system checks out. Pressure at the rail. No-spark to the distributor checked at the coil wire. (spark plug in coil wire grounded to head) The coil is good, measured resistance and grounded the (-) lead seeing a spark at the output. When cranking the tach needle does twitch, but when I hooked a test light up to the negative lead (green) to the coil I'm not seeing any signal blink. I tried bypassing the alarm box as described in Clark's 944 page Although I unplugged the connecter and jumped the leads from the connection side leaving the box out entirely... Nothing. I tried bypassing the KLR by disconnecting it and jumping pin 9 to 16... Still nothing. I'm stumped now. Any help would be greatly appreciated! |
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Registered User
Join Date: Jul 2013
Posts: 40
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Come on you resourceful Pelicans, someone has to have some ideas for me here.
In addition to the tests/ work described above I have removed, tested, and replaced the ignition switch, -replaced the DME relay with a brand-new one -attempted to bypass the KLR - torn out my hair |
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In the Fires of Hell.....
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Do you have the DME Test Plan document? It goes through how to bypass the KLR and all that. It also has all of the signals to check out with the DME.
I am assuming that you have looked to see if you are getting fuel and a injector pulse at the injectors? Noid light checks it out? What about the Speed/Reference sensors? They are connected at the back of the intake manifold, and you may have compromised already brittle/cracked connectors. That could be the cause of your problems. Have you replaced/jumped out the DME relay? Check out the No-Start checklist at Clarks Garage too. It's most for NA's, but a lot of it crosses over just fine. Last resort is to send the DME unit out for testing. 944 Online and some others will test it for free.
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PCA Instructor: '88 951S - with LBE, Guru chips, 3Bar FPR, 1.3mm shimmed WG, 3120 lbs, 256 RWHP, 15 psig boost |
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Registered
Join Date: Feb 2003
Location: SF East Bay
Posts: 1,856
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If you are getting power to coil & injectors, the DME-relay and DME is most likely fine.
Check the speed/ref sensor connectors at the back of the intake-manifold. I've had a car where it would stop running just like yours, but the tach would twitch when key ON. Squeezing the speed/ref sensor connectors together and wiggling the wire coming out of the rubber-boot fixed the problem for a while. Eventually, I trimmed off both female connectors from the harness and replaced them with new sockets. |
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Registered User
Join Date: Jul 2013
Posts: 40
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Fuel is definitely not the problem.
I have Pressure and injector pulse, but just to be sure I did "jumper" the DME relay to no avail. I also installed a new DME relay for safe measure. At this point I have to chase the speed and reference sensors. |
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Registered User
Join Date: Jul 2013
Posts: 40
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I re-tested both the speed sensor and the reference sensor,
Both have crumbling plastic plugs on the sensor side, but nothing that effects the connection. Both sensors tested out correctly with resistance and with voltage during cranking. I don't have an oscilloscope, so I was just looking for voltage while cranking. I then tested both harnesses for continuity to the appropriate pins on the DME plug and all tested correctly with continuity. Should I proceed with sending the DME out for testing/ repair? Who should I send it to if that is the next step? |
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In the Fires of Hell.....
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__________________
PCA Instructor: '88 951S - with LBE, Guru chips, 3Bar FPR, 1.3mm shimmed WG, 3120 lbs, 256 RWHP, 15 psig boost |
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Registered
Join Date: Feb 2003
Location: SF East Bay
Posts: 1,856
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You can go through the DME_KLR_Test_Plan.pdf troubleshooting guide from Porsche.
Quote:
The DME#1 fat-green wire going to the coil is grounded by the DME to dump the coil. And it's not firing the coil. Did you do anything with the harness grounds in the engine compartment? If those have bad connections or is not connected, all the power goes through the DME ground and fries it. Open up the box and look for the fat-trace along the sides of the circuit board. Is it crispy and burnt? |
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Registered
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If you haven't already, check your compression numbers.
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1988 944 turbo |
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Registered User
Join Date: Jul 2013
Posts: 40
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Thank you to everybody chipping in ideas.
I did follow the Porsche diagnostic guide except for using an oscilloscope for testing sensor output because I don't have one. As I stated in the beginning of the thread the car was running at idle when it died. There was no catastrophic failure, just a quick stumble-and die. I haven't checked the compression figures on the car because I can't see a reason to at this point. I ended up sending the DME computer out to Specialized ECU for diagnostic and repair. I'll let you know what they find and the results of the repair. I suspect that some damage may have been done to the DME. The car also came in with a non charging alternator so the battery was dead. Several jumps, and time on the charger could have damaged the DME. By the way the alternator issue was simply an inexperienced mechanic installing a new starter and putting the alternator cable on a different solenoid post than the battery cable. (always look out for the inexperienced) |
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Registered User
Join Date: Jul 2013
Posts: 40
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Short follow up-- I realized there was no conclusion to this thread.
The problem turned out to be grounds. Some of the grounds were in bad shape, but the main body ground was missing entirely. With the grounds restored the car came right to life and many of the other electrical gremlins have been eliminated at the same time. Cheers |
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Registered User
Join Date: Apr 2011
Posts: 161
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Thank you for following up with a positive result.
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Registered
Join Date: Jul 2004
Location: Upstate New York
Posts: 3,267
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Easter egging a problem rarely fixes it, and is no substitute for proper diagnosis.
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Good luck, George Beuselinck |
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Registered
Join Date: Mar 2009
Location: Northern Virginia
Posts: 269
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Criticaldrew,
What do you mean by "main body ground"? where is it located? I am chasing a similar problem. Thank you raulg |
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Porsche 944S Club Sport
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Guys and Gals:
A Floating Ground is a really bad problem to have. Tip.Run a Ground strap from your exhaust to the body or battery (-) terminal (best)... Electrical charges build up there and will throw everything(DME, Instruments, sensors readings) off and increases your ambient noise references.... You can see this with a oscilloscope.. PM me if you need to,Later...
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Guru944 ![]() 2006 955 Cayenne S Titanium Series - Marine Blue, 1987 Porsche 944S Club Sport. 1987 Buick Turbo-T Lightweight "Great White", +500HP, TA49 Turbo. http://www.blackbirdmotorsports.com, 944/951/968, 911 and 955/957 Performance Solutions. Thank you Lord, for your Loving Kindness, Tender Mercy, and Grace. Only You are Faithful. |
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