I lost my spark, please help, we miss each other

[Gilbert '71 T]

Hi guys,

Hope you can help me with a little ’no spark’ problem, please bear with me I‘m a novice with electrics….

Background:
Car is a 71T and I’ve put in a ’77 Carrera 3.0 engine (Just been rebuilt)
All electrical terminals cleaned prior to install
Has a Bosch 3-pin spark box
CIS all tested with k-jet specialist prior to install and fitted all new injectors

Got the 3.0 in the car, and gave it a good running in drive of over 500 miles over the festive period, apart from an odd cold starting stutter (Could this have been the tell tale sign of the impending problem?) the car ran great though, pulled strong and all gauges appeared normal.

Went to start car yesterday, it just cranked.

Check for fuel - OK

Get assistant to crank the engine (wife to be), pull the king lead from dizzy cap and check for spark, no spark

Ignition switch on check for whining from CDI, quiet as a mouse

Check for +12 at middle red wire for CDI with voltmeter, get nothing when applying ground to the ground wire connector which goes onto front of CDI, but get +12 when applying ground to grounding point behind accumulator etc.

I jumped a new ground to this point from CDI, switch on ignition, CDI now emits high pitched whine, crank engine & check for spark, no spark.

From the diagrams below it appears that I should be running the ground from the CDI box to Terminal 1 on the coil? Is this significant to the system (I did say I was a novice) Should I jump a fresh ground wire to from CDI to Terminal 1 at the coil as I guess my ground wire could be perished inside the harness?






If no change is this a logical next step? check the points with test lamp? With +12 and turn engine by hand from crankcase pulley with negative wire connected to the points to see if they are opening? I heard something about a break in of points and that they can close up after around 500 miles, any truth?

Any pointers much appreciated

[ael911]

Did you check the coil? the ohms should read 0.4 to 0.6 between the two outside terminals. From the center to terminal 4 should be around 1.2 or so I think. My Bosch coil blew a few weeks ago and I found it leaking a brownish oil.

[ischmitz]

Well, I would make sure to understand WHY the ground wire perished first. Maybe it burned due to overload. The CDI box should draw about 1.1 Amps with the engine not running and no more than 3 Amps at 6000 RPM.

I would first put an Amperemeter in series with the new ground wire. If the box CDI box draws exessive current it needs service. Next you can trigger sparks by shorting the points in the dizzy.

Hope that helps,
Ingo

[pa911]

I'm not sure you can run a 3pin Bosch on a 3.0 I think you need a 6pin?

[Gilbert '71 T]

Originally posted by pa911
I'm not sure you can run a 3pin Bosch on a 3.0 I think you need a 6pin?

thanks but it's a ROW '77 3.0 Carrera, which definately used the 3-Pin CDI

Think I've found the faulty now though, better light today has enabled me to turn the engine by hand to check if the points were openeing correctly, it appears that the rubbing/fibre block on the points set has totally worn away, meaning I'm getting no gap. I understand there should be some special grease that I also need to apply to the dizzy cam, as It's now New Years Eve it doesnt look like I'll be able to find any points/grease until Tuesday.

Thanks for the pointers & Happy new year everyone

[Gilbert '71 T]

err nope scrap that last post , i wasnt wearing my specs

I decided to check that the points were opening with a test light, they were, then connected the test light to Terminal C on the CDI plug, again, when points open, points close, light goes off/on.

Can anyone explain in detail the Telegraph Key Test, as this will be my next port of call

[ischmitz]

I have not heard of a telegraph test but I assume that's triggering the CDI box without the dizzy. A 3-pin CDI box gets triggered when you ground pin C. That is usually done by the points in the dizzy closing. You can take the single wire with the spade connector that goes to the distributor and short it against the engine block. With the box whining this should release a spark with the spark plug connected directly to the coil output (4) and to ground. If not I it can only be the trigger wire being bad in the harness or the CDI box itself.

Keep in mind that whining alone does not necessarily mean the box is functional

Good luck,
Ingo

[Gilbert '71 T]

Thanks Ingo, that makes sense, I’m beginning to understand the system a bit better now, I’ll give that a try later today or tomorrow, once I recover from last night’s festivities that is. If there is anyway I can test for a break in Terminal A wire I’ll try that too, if that checks out ok, and I try the grounded sparg plug test and still have no spark then I suppose I can put it down to the CDI. Next step would be to try and get it to a know running car and see if it works on that or not, if not, then CDI rebuild I guess.

Btw I just noticed your signature, 3.6, oh yes, that must be something in a narrow body Targa, great looking car too in a cool period colour. I bet it’s awesome on a sunny CA day with the Targa top off, I’ve yet to sample mine with it’s 3.0 motor and top off yet, I’m looking forward to the summer.

I’ll report back with what I find.

Happy new year

[grandadg90]

Hiya mate.

i am having the same problem with my 1979 3.0 Sc but mine has the 6 pin. I am not getting a spark and my auto electrician diagnosed it to be the silver box ignition unit CDI. If i unplug the unit and plug it in again and just mess with the plug it starts.

I am thinking of operating on it. Any ideas. A second hand one is £495 from my scrap yard.

Cheers
Ray

[KillerDynoSoar]

Good Luck with getting it sorted buddy.

Happy New Year to you aswell!

[Gilbert '71 T]

Originally posted by grandadg90
Hiya mate.

If i unplug the unit and plug it in again and just mess with the plug it starts.

Hi Ray,

Yours sounds like it could just be a dirty connnection or bad earth, I'm far from expert on this stuff, but if you're wiggling the connector and it starts i wouldnt write off the box just yet buddy. £495 can be a handy thing to keep.

Only advice I can offer would be to take the box out and clean all the connections and those inside the plug too, i also believe yours might have a green trigger wire from the dizzy or something, clean the connections there as well.

Plug it all back in and bob should be your mum's brother , it's well worth doing as it doesnt cost anything, just a bit of time.

Good luck

Hey Alam, how ya doing down under, Happy new year to you too my man. Looks like it's a bad cdi box in my case, i tried it out on a running car today and it wouldnt start with my box. I've spoken to Tim he says he'll check it out for me

[grandadg90]

Cheers gilbert.

The problem is that it doesnt start and so if i take the box off and then reconnect the plug and with a wiggle after about 20mins of wiggling it starts. i will try the earth connections and clean it up and will let you know. £495 is something that i hope i can keep and use elsewhere on the car.

have you had any joy with yours yet. i have now found a place which do a replacement unit by permatune. It is 340+VAT new. if you want some info let me know.

Cheers
Ray

[Gilbert '71 T]

Hi Ray,
that sound like a connection issue to me, rather than a problem with the box itself, from reading up on these things I think they either work or they don't, is there any chance you can get your box to a known running car and try it in there. Thats what I ended up having to do and it turns out the my box has stopped working, thankfully i have someone in the UK who can fix it for me (I hope), if you have no luck with the wiring or connections let me know and I'll ask if he knows anything about repairing the 6-pin boxes.
All the best
Darren

[304065]

Darren, sparkless Anglophone brother from Across-The-Pond:

I'd work from the distributor out. Make absolutely certain that the distributor is properly lubricated, as sticking advance weights can make trouble for you later on. Search here under early_s_man and distributor lube for a good thread on how to clean and lube the distributor.

Next, make certain you have a good set of points. The gap isn't critical with the CDI as it is with Kettering-ignition, just make sure you have a gap, and that the points aren't accidentally grounding out. With the points closed you should measure continuity from the 1/4" faston terminal on the outside of the distributor to ground. With the points open, you should get infinite ohms, i.e. no continuity.

Next up, you should be absolutely sure that you have a proper ground between the CDI box and the chassis of the car. I would recommend rigging up some metal braid temporarily between the CDI box and the chassis of the car and the engine block. You might attach this temporary ground strap to one of the port-side chain cover bolts.

Now, your coil's ground connection is pin #1, not pin #15. I doubt it makes a difference but let's leave nothing to chance. Yes, you should check for a break in the blue wire with yellow stripe that runs from Terminal A of the CDI to terminal 15 of the coil. Verify also that you have a good solid 12 volts from terminal B (ignition) to ground. Terminal C can be verified between the connector itself and ground when the points are closed.

That's about the size of it, the beauty of the Bosch CDI is that it's so simple. Perma-tune, in my opinion, is a retrograde step. The only other replacement I can recommend is the MSD 6AL, but the Bosch should be fine, they used it in the 935.

Good luck!

JFC (old Oxonian)

[Gilbert '71 T]

Originally posted by john_cramer
Darren, sparkless Anglophone brother from Across-The-Pond:
JFC (old Oxonian)

Thanks John,

these are a good set of notes, but then I'd expect nothing less from an old Oxonian I've made all the checks you listed and eventually tried my CDI on another car, it wouldnt start using my box so I have sent it to a guy i know who has repaired some bosch CDI's in the past. I'd prefer a repaired bosch unit rather than going down the MSD route, because as you say if it was good enough for the 935

Also that's a very good point you made re the distributor, I think I'll embark on a side project and pull the distributor, strip it down to check for wear, replace parts and re-lube whilst my bosch unit is being repaired, it would be nothing but a good thing in the long run right. Also a saving grace (if you can call it that) is that it's 3c outside and snowing, so it's not like I'll be doing much driving of the 911 on our salted roads

Thanks for your input on the thread.
Best
Darren

[grandadg90]

Cheers Darren, thanks for the advice, your a star. I am going to try it today. I have already added another earth lead so will today clean all the connections and re-fit the CDI. I will let you know how it goes.

Have you had any joy with your yet. I have sourced another unit which is a different one but comes with a harness and a coil for £250, a lad in Birmingham has it installed on his 930 and it works fine.

[grandadg90]

I have just tried my CDI box back on and no joy. Dosnt start, even after messing with the wires. Im going to have try the box on somebody elses car, but problem is I dont know anyone with a 3.0SC.

Can anyone help.

[Early_S_Man]

grandad,

I would hope that 'messing with the wires' included cleaning and retensioning all of the Faston connectors that connect to the CDI, and cleaning all six terminal tabs on the CDI unit itself ... rather than just wiggling here and there!!!

Have you tested at terminals #7 & #31d for 600 Ohm reading [+/- 10 %] of the magnetic pickup coil? How about an AC Voltage during cranking at the same two terminals of the wiring harness???

What condition is the green coax cable at the distributor in? Cracked or old & distressed brown cables need to be replaced!

6-pin SC/Turbo CDI unit repair documentation

[grandadg90]

Will have to try the above, cheers

Cheers Early_S_ Man