No vroom vroom

[AJH]

I took the 71T for a run yesterday and was just thinking how reliable it's been. However as I was pulling into my garage it died. At least it chose the best moment and I could push it in. I suspected ignition as it cut cleanly and did not even give a splutter when I tried to crank it.

The transparent fuel filter was full and I could hear the pump running. I can also hear the high pitched zing from the CDI box. I checked for spark with a timing light and got none. Fuses are ok. The car doesn't have an immobiliser. With the cap off the rotor is turning. Given the high voltage I don't quite know how to test things.

The coil is new and has a warning sticker about putting a tester on it.

Can I assume that the CDI box is working because it's making its usual noise?

I do have a Pertronix electronic ignition module in the Bosch distributor which is also quite new. Could this be tested by putting a light in series with the return wire that goes to the CDI box? Would I expect to get the light on and then flashing off for each ignition signal as I crank it? If that's my correct understanding of how the old points would have signalled the CDI box.

Also when cranking the engine with the ignition on but distributor cap off should I be making a temporary path for the coil discharge to ground to prevent damage to the coil or CDI?

I have the old Marelli distributor which I could put in but I would ideally like to narrow it down a bit before doing that.

[Merv]

Sounds electrical Andrew. Are the fuses all inserted correctly? Remove and refit as a start. My experience with Pertronix is mixed. On one car it was great but on another it suddenly died and was replaced under warranty. Took me two days to find out.

Spare CDI box?

If all else fails, call the mobile autoelec and for about $100 he will do a safe diagnosis for you if you are worried about the voltages.

[72_sporto]

Hi Andrew,

Is your shed dark? You can usually see most ignition leaks in the dark.

One reasonably simple test is to pull the No 1 lead out and use a dry, insulated pair of pliers to hold the end near a grounded part of the motor and have a friend crank the motor. The exposed end will need to be reasonably close- probably 5mm- but not touching. You should see a well defined spark. This should tell you if the Pertronix or coil are faulty. You can use the pliers to rest against the motor but make sure the pliers are not grounding the end of the lead inadvertently.

If you do manage to "get booted" it will certainly liven you up but won't be the end of the world- unless you have a pace-maker. (Wear rubber gloves if you have one of these...)

I also have a Pertronix fitted to my 72E. No problems for years.

Forgot to add- make sure you don't have any fuel leaks- before you start.

[AJH]

Thanks Bill and Merv

The fuses are in and ok (the CDI box is powered and Pertronix gets power from same wire)

If I remove the centre wire to the cap I don't think I will get a spark. But that still won't tell me why.

Either the Pertronix is not giving a signal (what I suspect)
The CDI is getting a signal but not triggering the coil
The coil is being triggered but not firing.

Perhaps I should just go ahead and fit the Marelli and that will eliminate one item.

[72_sporto]

I had a problem a few years ago where one of the supply wires into the engine fusebox was corroded just enough to cause the motor to die when hot. My motor fired up again on cooling, though...

Do you have/ are you handy with a multimeter? (My guess is not, as you would have posted some readings....)

The light you mentioned might tell you if the Pertronix is triggering. But it may not tell you if you have a low voltage situation.

You mentioned the coil was new. Did your old one fail?

I think I might have a spare CDI I can loan you if you need. How far from the inner North are you? (PM me if you like.)

[HughH]

Is the coil comparable with a CDI ?? Even though it is a new coil you need a special type of coil for the factory Porsche cdi's. A normal coil can burn out in a very short time if it is not compatible. Even the newly made "silver" replacement coils have a reputation for failing.

[72_sporto]

I forgot to say last night, if you use a light to test the Pertronix, it should be a LED due to the low current load it places on it.

Hugh is right- as usual. The CDIs boosted 400V output may fry a normal 12V coil.

If it is not a blown coil then, my best guess is that, it is most likely a blown SCR or thyristor in your CDI. That's why you can still hear it. If a cap blows they normally go quiet.

There is some info and a cct diagram for the 3 pin CDI here-

http://forums.pelicanparts.com/porsche-911-technical-forum/374009-3-pin-cdi-repair-question.html

and

http://forums.pelicanparts.com/porsche-911-technical-forum/226517-history-bosch-cdi-toubleshooting-info-parts-list-changes-schematics.html

[AJH]

Thanks for all your input.

I have vroom vroom again! Just before refitting the Marelli I decided to replace the new coil with the old one that I had kept just in case. Presto - she fired right up! I even put the new one back in again to check that it hadn't been a loose connection that I had unknowingly fixed- but it was dead again.

The irony is that I only replaced the coil as the exisiting one looked quite old and I figured it was good preventative maintenance even though at $170 it's not exactly cheap. It's the correct Bosch one from Pelican for the CDI and has the same part number. Very annoying that it should fail with only about 1000km on it.

I'm reluctant to buy the same poor quality one again but I don't have much choice. Having a spare is essential because you can't buy a standard coil if you get stuck somewhere.

[HughH]

andrew find an old black coil with the correct part number and have that as a spare
they come up regularly on early S for sale
i have one in my car at all times.

[AJH]

Thanks Hugh, I'll give that a try. I would have thought they would be unobtainium but perhaps they come up from people upgrading to MSD etc.

[reedminor]

I was about to say coil - I had a silver one fail on me in less than 12 months.

I had a few black spare coils but sold them all when I bought one of the new cdi boxes and coils that Kurt sells on early s from Parts Klassik. The old back coils got me out of trouble more than once, and sold remarkably quickly.

Justin

[AJH]

Just looking on the Partsklassik website I see that they also offer a black CDI coil. You would never know if it's made in the same factory in Brasil as the silver one but they do offer a 12 month warranty on it and it's slightly cheaper at $149USD.

Searching on Early S it seems that OE black coils get snapped up very quickly when they come up.

[Fishcop]

How much do the early coils go for? I may have my old one here for you Andrew (I run the Crane CDI and Blaster Coil).

[green gauge]

I think I read on pelican at some point that a lot of those Brazilian coils are garbage.

[AJH]

How much do the early coils go for? I may have my old one here for you Andrew (I run the Crane CDI and Blaster Coil).

Hi John

A quick search on Early S showed one for $155 and one for $165 both used. I think Tony may have bought one of them. NOS ones would be more of course.