travisgreen

I was getting no tach bounce at crank but noticed I was for a split second after crank so I replaced the ignition switch since jumping the starter starts the car up.

didn't help though so im trying to go through wiring to figure this out
my question for anyone that can help is what wire would power the DME when cranking that wouldn't when in the on position?

I have 12 volts at the battery, I tested pin 4 at DME harness while cranking and im only getting a little over 10 volts

seems fairly simple as theres only so many wires that run to the ignition, anyone with any insite?

travisgreen

.....

alex_cristocea

I think the first thing you should check if the tach doesn't bounce when you crank it's the DME relay, speed and reference sensors.

travisgreen

Sensors are both new. I do have tach bounce and the car runs, I just don't have tach bounce while cranking. If I jump the starter or pop start the car it's fine. That's why I replaced the ignition switch but oddly enough that wasn't the problem

travisgreen

Also tried 3 different dme relays and I know they aren't all bad

homerj

would an electrical diagram for the 944 turbo help. i have the porsche book just terrible at reading them

travisgreen

Yeah it would. I had one of the ignition switch wires from the web but can't find it now

miragezero

For certain it doesn't have an alarm/starter kill?

travisgreen

Nope

Ronin-951

Engine vibration from cranking/running may have helped complete the circuit. I suspect the Reference Plug on the 'car side' [since you have new sensors] may be the issue, wire's on BOTH side's age and crack. The 10 volt issue, I'd start with a Ground path check, only takes a second, and it IS a known issue.

travisgreen

I originally thought it was the reference sensor. When I took it out I noticed exposed wire coming out of the plug so I thought for sure I found the problem, I replaced both wile I was down there and surprisingly it didn't fix it. I checked resistance at the DME plug just incase it was a harness issue, both tested good



That's when I noticed I was getting spark and tach bounce after I stopped cranking, I jumped the starter anD it fired right up, thought for sure I found the problem so I replaced the ignition switch, so a few new parts later I'm where I started

I noticed the PO taped into a few wires and I'm trying to figure out where they go, I suspect the radio but non of those points seem to be bad or loose. I'm going to retrace some grounds. I'm trying to figure out where each wire goes out of the switch harness, I have another ignition switch harness but would hate to get in there upside down and inside out soldering if that isn't the issue

travisgreen

Also I'd rule out vibration only bc it's VERY constant spark ans bounce every time after cranking, I can usually even get it started by cranking and letting go quick until it catches itself and fires