76 911 - Repeated ignition failure - why?!

cstreit · cstreit's Garage

Hey gang,

I've got a mystery on my hands.

I'm dealing with a 76 911 2.7L that seems to have a repeated ignition failure. When I first got it, it would not start. Went through the electrical system from the alternator, battery, ignition switch, Permatune, Dizzy, and coil. Turns out the coil was weak and the ignition wires were pretty high on resistance. Replaced these items and car ran fine for a few months.

Recently got the car back and diagnosed a failed permatune. (A-D termnial resistance at Infinite which Permatune says could be related to a weak coil) so coil checked out fine, replaced permatune, checked wiring and system voltages and everything worked good for another 4-5 weeks of nearly daily driving.

Well the owner called me and the car was running fine (although they mentioned it was a bit hard starting the last few days), they shut it off and tried to re-start within a few minutes, and it won't catch! Not even attempting to fire...

Any ideas what sort of thing might cause this? The system voltage seems clean while running at about 13.7-13.8 volts.

THANKS!

MotoSook · 03-23-2005, 05:42 AM

Are you sure it's the ignition this time? Or the CIS?

widebody911 · widebody911's Garage

First off, it was hilarious that a post about repeated failures got duplicated 3x

Second, get rid of the permatune

Third, check the condition of the wires to the distributor and CD box. I had a very similar problem with my car back in my CIS days, and the root cause turned out to be hardended, corroded wires which would open the circuit at random. I spliced in a new section of harness from a junked car and the problem was solved.

cstreit · cstreit's Garage

Pretty sure it's ignition... However I haven't seen the car yet. Weak cold start, no hot start might make sense, but given the cars history..

Thom, interesting point... I did notice some of the coil power feed wires did look a little ratty... I suppose if heat/water/open contact caused weird coil voltages it could fry the permatune...

cstreit · cstreit's Garage

Any other ideas folks?

dhoward · dhoward's Garage

Agree with wiring. Marginal power and grounds can play hell with electronics.

dpriebe · 03-23-2005, 01:28 PM

Although you said that the current coil is still good, I have just gone through 2 Brazilian made Bosch coils in the last 2 months on my '77 2.7. Finally replaced it with a Permatune brand coil. And so far so good.

Early_S_Man · 03-23-2005, 02:35 PM

Chris,

The A-to-D test is just testing a bleeder resistor for the main 1.0 mFd 400 Volt charge staorage capacitor ... not really conclusive, unless zero or lower than normal. The connection or resistor has gone open.

You may want to check and see if the 'A' terminal is at +350 - 400 Volts with ignotion switch on and engine not turning over.

Sounds like the Permatune has started on a downward spiral ...

Joe Bob · Joe Bob's Garage

CIS and Hot Start is more likey a bleed off issue of fuel pressure. Check valve in the banjo fitting on top of the fuel pump.

RoninLB · 03-23-2005, 03:11 PM

I had an inconsistant ignition crash when driving. It all started in Area 51, no kidding. I looked around and didn't see anything, thankfully. Usually 10-20min cool down and it'd run for 25-200mi till another ignition crash. All testing said ok, and new power wire didn't help while I was waiting to replace the Permatune and coil. Got the new Permatune and coil and prob fixed. Sent the prob Permatune to an EE acquaintance for his entertainment. Eventually got home and I went to another ign mfg w/ same mfg backup. I don't really trust the good Permatune replacement. Actually I don't trust any CDI.