911SC no start

[dntlft]

First off, thanks to OSI930 for sending me his Bosch CDI unit for me to try in my
'83 911SC. Guys like him, and timmy 2, have been instrumental in helping me wade through the complexities of diagnosing a no start/no spark issue...

That's where the good news ends. For those new to the previous thread for this ongoing issue (It's been 2 months since I've driven my beloved 911), I've done the following while trying to diagnose this:
-No spark at any of the plug wires
-Plug wires are in spec for resis
-coil wire is in spec, as is the ignition coil
-Green wire coming off of distributor has good continuity to/from terminals 7 and 31d, reconnected this and the 2 vacuum lines to dizzy when reinstalling.
-Spark plugs all replaced and gapped to 0.7mm
-All fuses checked in front trunk, none burned, rotated all of 'em for good contact
-new ignition rotor and distrib. cap within spec for resistance
-triple checked correct ignition wire locations on cap and plugs, checked all for good contact.
-spark plug wires are new Magnacore
-Finally, got a working CDI from OSI930 today, plugged it in, engine cranked but again, no start.

I know this is not a no fuel issue, because I could smell raw gas from tailpipe easily after attempting to start 3 or 4 times.

Anybody got a silver bullet for this increasingly frustrating problem?

[timmy2]

Are you seeing sparks with the new CDI unit?
( pulled and grounded)

[Bob Kontak]

Ohm out the coil pack in the distributor. Look for 600-ish ohms.

Pull your coil wire at the dist, ground it on the engine or such when cranking.

If no spark, borrow a coil or buy a cheap one for testing. Try again

Your problem is before the secondary ignition system.

[dntlft]

Bob Kontak,
When I pulled the distributor, I tested the ohms by connecting the neg lead of the multimeter to the 2 male connectors where the "green wire" connects, and the + lead to the reluctor. when I was careful to avoid contact with the body of the dizzy, I was getting infinite resistance reading, when the lead touched the body or housing of the dizzy, I got resistance values all over the place. When turning the rotor/reluctor, no slop or play was noted in the dizzy...

[dntlft]

Dennis,
Pulled coil wire from dist. cap and plug wire #1, nothing.
I can also hear the high pitch squeal from the CDI unit that OSI930 sent to me...

[timmy2]

There is a coil inside the distributor that Bob is referring to. When we talked it sounded like it was working, but you need to check it's value. If it is connected the way I believe it is, you could pull the six pin CDI connector and check the coil value by measuring the resistance from the green wire to the shield with the other end connected to the distributor. Post the result.
( green wire in plug to the one in the row above it, usually black meter on ohms)

[dntlft]

Dennis, I tested terminal 7 and 31d which correspond to the green wire, black wire you're referring to... 604 ohms

[pete3799]

Have you tried a different coil?
No idea where you are located. Maybe someone would loan you one to try.
What color is the coil your using? They have had troubles with the blue ones.

[boyt911sc]

Use an inductive timing light to see if you are getting ignition spark signal. If you are not getting any flashes, the engine won't start. If the signal is good and consistent proceed to check fuel pressures and vacuum leak.

Tony

[dntlft]

Hi Pete,

I have not tried a different coil. I went to some local auto parts stores around here (I live in central MO, btw, aka BFE) and their off brand coils started at 150 bucks and went up from there. None of the parts stores had one in stock that I could take home and test.

The coil in my 911sc IS the blue coil and was replaced along with the CDI box by the PO 3 years ago. I imagine this is one of those parts now made in Brazil, or maybe China knowing our (enthusiasts) luck.

I did test the resistance of my coil with 6 pin connector to CDI disconnected, it appeared that the resistance values were in spec. Can a coil still be bad and still show correct resis values?

[Bob Kontak]

Crap - your pick up coil in the distributor is ok.

Double crap on the ignition coil availability.

Get one from *********.com for a 67 Chevy Bel air for $13.

67 1967 Chevrolet Bel Air Ignition Coil - Engine Electrical - Accel, MSD, Standard Motor Products - *********

Can't imagine a parts place would not have an old cheap chevy coil. Surely you have a bone yard or two around there. Buy two to be safe from the bone yards. :-)

If found to be the problem, then get a proper coil.

[Bob Kontak]

Originally Posted by dntlft

I did test the resistance of my coil with 6 pin connector to CDI disconnected, it appeared that the resistance values were in spec. Can a coil still be bad and still show correct resis values?

Good question. I do not know the answer to this.

[fred cook]

Since you seem to have covered the ignition and fuel basics, here is another area to check. Open the air box and remove the air filter. See if there is a pop off valve. If the valve is not seating or has come unglued, the engine won't start. Has the engine experienced a significant backfire? A cracked air box will also prevent the engine from starting. I hope this will help get your car back on the road!

[dntlft]

Bob,
An ignition coil from a 1967 Chevy will work on a 911SC? What brand coil is that?
Is this something that should be used for testing purposes only?? Are we all fools for paying 260 bucks for blue coils made in Brazil???

Thanks for the tips, I will probably order this $13 part and try it. Have you used this tactic when you've had a bad coil?

[dntlft]

Fred,
Good tip, but I have looked in the airbox, no popoff valve, and it has not ever had an explosive backfire since I've owned this SC. Would a cracked airbox cause the no spark situation of the secondary ignition system like I'm experiencing?

[Bob Kontak]

Air box is separate from no spark. Put that one on the back burner.

Testing purposes only for the el-cheep-o coil.

Borrow one from a neighbor with a tractor. Just get /borrow/steal one to eliminate the variable.

[Bob Kontak]

Originally Posted by dntlft

Have you used this tactic when you've had a bad coil?

Yes I have.

Over a longer duration these coils are not what you want to use.

I can't say specifically why, other than I believe they will fail in the medium term.

For the short term you need a cheap-ass sacrificial test drone that will take a signal from the CD box and amplify it to a spark that can jump a spark plug gap.

For a few dollars, it's worth the comfort regardless of the outcome.

[MongooseGA]

I didn't notice it mentioned, and it may not even be worth looking into, but I'm going through similar problems (no-start) in my 3.0 911 and someone suggested checking out the AME (or DME?) relay under the driver's seat.

If anyone with knowledge that I don't havecould shed some more light on this, it may be somewhat beneficial.

Good luck!

[theiceman]

Its the coil
Get and msd blaster anti vibration coil... Done ... !!

[timmy2]

Yep, I have the MSD blaster II high vibration coil in my car, been good for almost 2 years.
eBay, our host, most flaps have it.