SiberianDVM

Today I had my 1984 911 at Carolinas Motorsports Park for a DE, and it ran great for 2 sessions. Tried to start it for session 3 and it cranked well but would not start. Swapped out DME relay with a new one with no improvment. Pulled a spark plug wire, used a spark plug, then a screwdriver, no visible spark.

Checked voltage at coil: 12.5 volts
Checked coil fuse: good

Car just had new plugs, plug wires, coil, rotor, distributor cap installed 2 months ago.

So I winched her onto the trailer and came home. Tomorrow I'm planning on swapping in the old coil and old coil to distributor wire.

After that? Reference and speed sensors? I'll have to order those. Any other things I can check?

Thanks

theiceman

what was the new coil ? if it was the bosch brazilian silver coil that is the problem.

SiberianDVM

Yep, that's the one. You mean I got a bad Brazilian?

What are my other choices?

ron mcatee

Some have stated problems with crank sensor & CHT (head temperature sensor. There possibly a few more. Have it checked by a competent Wrench.

SiberianDVM

Swapped out new silver Brazilian coil for old black German coil: still no spark. Checked continuity of coil to distributor wire: WNL. Checked fairly new rotor and distributor cap. Still no spark.

Competent old Porsche mechanics are scarce around here. I'll consult with the guy who does my tech inspections.

SiberianDVM

Just did a ohmage check on the reference and speed sensors. Reference (BG) measures 1.064k Ohms across 1-2, and INFINITE across 2-3 and 1-3. Speed (DG) measures INFINITE across all combinations.

How the heck can both go bad at the same time? I didn't run over anything.

Amber Gramps

Buy the 944 sensors.

SiberianDVM

Just removed both sensors and swapped them. Still no start.

Why the 944 sensors? Don't confuse me, now. I'm tired, pissed off, and covered in grease.

Ed Hughes

I'd go through the Bentley trouble-shoot sequence.

Ed Hughes

You could have a DME issue too-perhaps a cracked solder joint. Check all connections, grounds, main harness on the firewall, etc.

ron mcatee

The 944 sensors are much cheaper.

SiberianDVM

Have worked my way through this several times. I keep coming up with no spark.

Coil is good.
12.5V at #15 on coil.
Coil to distributor wire is good.
Spark plugs and wires are new.
Reference and speed sensors did NOT check with normal Ohmage. Have ordered new ones and will replace them along with CHT sensor as soon as they get here.

The DME is worrisome. If all sensors don't fix it, I will have to mail the DME to either Steve Wong or Pelican for evaluation.

theiceman

those sensors definitely sound suspect. i am shocked it wasnt the coil as those things are a pos.

i got.a high vibration msd blaster coil but i think your ignition is a different system.

i think the Bently tells how to test those. i think you put your meter on ac and wave a magnet by them or something.

SiberianDVM

New reference sensors are on order. Need to figure out a way to visually check to make sure the pin on the flywheel is still there: I don't have anyone handy to either turn the crankshaft or look in the hole.

During the 2nd (and my last) run session I did go a bit wide on a turn and we went through some rough gators. The tach bounced like mad, but the car kept running so I thought nothing of it. I bet I jarred something loose.

AFAIK, this car still has the factory alarm system. Would it cause a crank but no start? I thought it worked by killing the starter.

theiceman

ok now we have the rest of the story

I dont like parts swapping but i think the parts you have ordered are good PM parts anyway. With a rough off now we know there has been excessive vibration. After putting the sensors in I would seriously consider looking at the DME to make sure you dont have a cracked Solder joint. Anyone near you with a Carrera ?