No spark and no tacho bounce

[dean1057]

A head scratcher that I’ve been trying to sort since Sunday.
Had a full engine rebuild by MB and drive back about 100 miles with no problems since.
Put the car away last week in the garage after refuelling.
Car definitely getting fuel through, checked that.
Car turns over, checked for spark and nothing in dark garage, tacho does not bounce when cranking.
Replaced coil with another good classic black one that gives good readings.
Checked dizzy cap good, replaced rotor arm as I thought it could be that.
Green dizzy wire was replaced on rebuild.
Any fuse I should be looking at, or under dash Ignition wires etc.
First time it’s let me down
Car is a78 911SC targa.

[inaglasshouse]

Do SCs have points? If so: points clamp screw not tight post rebuild adjustment, so points gap never opens, so no spark trigger?

[DustyM]

Can you hear a high pitched whine from the CDI box with ignition on? If not then it has no power or has failed.


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[PeterK]

No points in an original SC

As above, check for whining first. If no noise, then CDI power comes from the rear fuse panel. It should not be fused, but is wired into the hot side of Fuse 22 (on 3 fuse panel in engine compartment, lowest amperage fuse with 2 red wires on hot side). The second red wire on the hot side of Fuse22 runs to the hot side of Fuse11 (on 21 way fuse panel) in the froot. CDI was not originally fused but wiring may have been ‘adjusted’ since it was built.

Check CDI plug has power & that plug is fully plugged in.


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[dean1057]

CDI has power as it’s making the typical noise.

[Jonny Hart]

See my post on how to check wiring etc here:

https://classic-retrofit.com/forum/inde ... omment-170

[dean1057]

All sorted. Ended up being failure of new green dizzy ignition lead.
Replacement arrived today. Pulled dizzy checked lead again and no ohms, replaced lead checked again and 590ohms. Put back together and fired up first time.
Just shows just because a part is new don’t rule it out when fault finding.
Thank you Jonny Hart and Mike Bainbridge for help along the way.

[Jonny Hart]

^ Do you still have the faulty one? Would quite like to see that.

[dean1057]

Hi Jonny,
Heritage parts want it back as it was still in guarantee by a day. Lol
It’s in a Jiffy bag ready to post back.
Regards
Dean