Jake28

Howdy all,

New guy here, new to Porsches, with a new (old) Porsche 911 in the garage.

The Issue:

I can’t get the 911 to start reliably. The ask: assistance and advice.

Primary resources:

• this forum
• https://www.holley.com/support/troub...ng_techniques/

The specs:

1975 911s. 70K miles, only driven 159 miles in last 6 years by PO. Largely sat.

Motor: 1984 3.2, built. ~260HP at the crank per dyno sheet

Intake: Weber 46 IDA carbs

Fuel: MSD hi flow pump

Ignition: MSD everything: Timing Computer, Timing Control, Digital Ignition Control, blaster 2 Coil, Helicore wires

The issue/ symptoms

• Just before I bought: owner said that she was having issues with the car stalling out sometimes, but “it would always start back up”
• Transporter:” the car died and then I couldn’t restart it”
• Me on day 1: car started fine cold (first crank) but wouldn’t restart when hot. Had to let it sit for ten minutes in order to restart it. Then ran great.
• Me in day 2: car wouldn’t start at all.

The changing nature of the symptoms gives me pause.

Diagnosis:

Electrical: in day 2, When it wouldn’t start in my garage, I did the following:

1. Checked for fuel pressure at the carbs. Confirmed with fuel pressure gauge on the regulator.
2. Pulled a distributor plug wire and put in a new plug: no spark
3. Checked ground from MSD to motor, it is tight.
4. Put a plug on the coil wire: no spark
5. Replaced the coil wire which was cracked: no change.
6. Cleaned the distributor cap contacts: no change / no spark
7. Confirmed the distributor top rotates when cranking
8. Measured resistance across coil and confirmed primary and secondary resistance are in spec.
9. Measured for 12V at wires coming OUT of MSD computer and in to coil with ignition on, and found 0V. As I understand it, because The MSD unit is a CDI, that is normal. https://www.holley.com/support/troub...ng_techniques/
10. Confirmed there is power going to the MSD unit and measured 12V at fuse bay in motor compartment.
11. Pulled red and green trigger wires and shorted them with plug in the coil wire, per Holley instructions. Confirmed no spark

Hypothesis: MSD computer is bad and needs to be replaced.

Does anyone have sage advice they can offer and other things to check?

I spent plenty of time readily on these forums and rules out the likely suspects like the DMF relay, since, AFAIK, this car doesn’t have one after the carb and MSD conversion.

I’m more than happy to get a new MSD unit, and would be delighted if that’s as the issue, I just want to see if I’m missing anything else obvious first.