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commdiver's Avatar
Join Date: Oct 2007
Location: Northern, CA
Posts: 1,992
Intermittent rough running no start and rich 951

So I have had very good luck with a turbo S engine I completely went through 5 years ago new everything, harness was great too. Runs excellent for almost 6 years well I did some minor things like take out airbox and swap out a hose and put new plugs and oil in her and whammo next day when I start it up fine and it runs for 20 min then when hot it starts stumbling and bouncing way up to 2500 and back down. Wide band is going crazy itís so rich black smoke out the back. I canít drive it barely get Home shut it off and no start after for minutes. 45 min later it fires right up and runs normal for 10 min then itís back wow this is nuts.

So I systematically start going through entire fuel and ignition system. All the usual checks and nothing is helping 3 days later and maybe 8 hrs in I find that the 2 pin blue plastic plug on engine wire harness in front of valley plugged into the blue cylinder head coolant temp sensor that goes to dme for map processing is shorting out. Bye mere accident too as I just hit it a few times while it was running working on setting the tps back to its normal spot to screw down tight. So I peel back the boot behind the plug and the wires are typical frayed and exposed right where they bend and shorting our intermittently and most likely I hit them when doing work in there a week before and when it got hit they were running together giving dme a full short and wigging the fuel maps all over the place. So I fixed it right bye redoing that plug and wow the car never idled so good and ran stable!!!

I have redone the fuel injector plugs and the reference sensors as well but the tps and afm and this temp sensor are a must as well for 30+ year old harnesses everybody a warning when you have a weird running issue that the simple things donít fix assume your harness and plugs are prob not giving the dme what they need too! Good luck and merry Christmas
Old 12-22-2017, 09:59 PM
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In the Fires of Hell.....
kdjones2000's Avatar
Join Date: Oct 2007
Location: Phoenix, AZ
Posts: 2,892
Check your speed/reference sensor gaps. That caused me some similar type issues recently.

Good luck with it...
NASA/PCA Instructor
'88 951S - with LBE, Guru chips, 3Bar FPR, 1.3mm shimmed WG, 3120 lbs, 256 RWHP, 15 psig boost
1987 924S 944 SPEC racecar - '88 pistons/DME, short 5th
1987 944S - Restored salvage title, ready to live again
Old 12-23-2017, 06:30 AM
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