77 2.7 no spark "help"

[IMR-Merlin]

Oh boy, I have done it again. I have a buddy of mine who's had his 77 Targa in a non-running condition since 2004 and I agreed to take a look at it for him (possible purchase).....

He had the engine rebuilt and it was running. But after a few months of sitting, it never ran again. Car was never driven.

I opened it up and noticed a few things that were concerning.

1) no oil at all!!

2) battery was connect backwards...

3) told me coil was not factory and his "mechanic" added a VW style coil to bypass some of the "useless ignition stuff"

4) cut and missing wires all over the place. Looks like the WUR is hot wired also....

So I will will take some pics this weekend and start digging into the horror show.

Anyone have a good flow chart for me to start chasing this issue.

I have a wiring diagram from my 79 SC so I am hoping their similar....

[Jonny H]

Battery reversal will definitely put the Bosch CDI into the 'useless ignition stuff' category!

Good luck!

[IMR-Merlin]

Oh I am fully prepared for this big can of worms... poor car, it has sport seats too... I am thinking of making an offer on it and swapping the running gear into another shell I have. Carb'd 2.7 light weight to go along side my 930.

[timmy2]

Search fo "Kettering ignition" as that may be the way the ignition system was bypassed.
'77 is similar, but different than '78 up.
Here is a link to the '77 schematic:
https://www.dropbox.com/sh/jxno8o6qae3roun/AADW1qBcRc53LoEG0TPbRwFva?dl=0

[T77911S]

when I built my 914-6 with a 2.2e motor, I had it setup so that if the CD went bad I could easily swap to just points and coil.

it really is a shame to see what some people will do to these cars. I smile every time I work on my 930 because things like that are unmolested. no its not stock but things like the wiring are so nice and clean.

[IMR-Merlin]

Originally Posted by T77911S

when I built my 914-6 with a 2.2e motor, I had it setup so that if the CD went bad I could easily swap to just points and coil.

it really is a shame to see what some people will do to these cars. I smile every time I work on my 930 because things like that are unmolested. no its not stock but things like the wiring are so nice and clean.

I hand built my harness on my 930 and have a wiring harness copy in my build book if I ever sell the car. It's nice having a simplified system that uses modern technology... an EFI...

[IMR-Merlin]

awesome, thanks for the files and link.

I am in the shop this weekend and will post up some pics.

Originally Posted by timmy2

Search fo "Kettering ignition" as that may be the way the ignition system was bypassed.
'77 is similar, but different than '78 up.
Here is a link to the '77 schematic:
https://www.dropbox.com/sh/jxno8o6qae3roun/AADW1qBcRc53LoEG0TPbRwFva?dl=0

[IMR-Merlin]

Here's what I have so far. I have a bunch of unplugged items and some jumped crap...

All not my doing.

I have a no spark issue with the CDI box unplugged. Can anyone walk me through the wires in going to the CDI plug. I have no power or ground when probing.

Thanks

[Walter_Middie]

On my 1975 (which should be very similar to yours) there are only 3 wires going to the original CDI unit, two white wires and a red one.

A way to remember the CDI wiring is "B" for Battery, "C" for contact (the points) and "A" for achtung, don't electrocute yourself! The other coil primary terminal goes to ground of course.

1. One white wire goes to the + coil (or transformer) terminal
2. The other white wire goes to the distributor points and the tach
3. The red wire is +12 volts switched through the ignition switch on the dashboard.

Each of the white wires is wrapped with a grounded shield that is connected to the CDI unit case at one end, and the other end is connected to:
• The + coil white wire ground shield connects to the – coil terminal and to one of the posts that the coil mounts on.
• The other white wire ground shield connects to the engine near the distributor.
• The red power wire to the CDI box goes through a two prong white plastic connector that includes +12 volts switched through the ignition and the tach signal wire (black with purple stripe) – just follow the red wire from the CDI unit to the white plastic connector.

The red wire from the CDI unit also goes to a small canister about an inch in diameter and two inches long. I believe my manual refers to this as an RPM sensor for the tach. The CDI power wire does not go through the fuse box on my car (1975). The power comes straight from the ignition switch to the white plastic two prong connector in the engine compartment.

A 3-pin box can be tested fairly simply; remove the 3-pin connector and run individual wires to it. Pin B (center) is +12 volts, Run a wire from pin A to the coil (the other side of the coil is GND) and then hook a wire to pin C. Connect a spark plug to the output wire of the coil via a high voltage cable and ground the spark plug.

Once you provide +12 volts to pin B of the box you should hear the 3kHz whining noise. Once you touch the wire from pin C to GND you should see a spark being generated.

[Jonny H]

What's your goal here? Just get it running or put it back to how Porsche intended?

I see a whole bunch of non standard wiring, conduit and other parts that should not be there (e.g. condenser on the dizzy).

Tbh, it will be difficult to give you advice unless you want it back to a standard setup as we have no idea about how the PO's mechanic wired your ignition.

[IMR-Merlin]

I want to get it running first to check the engine. It's a buddys car and I am just helping him out. I am assuming that he wants to get it back to running and reliable. I was able to get it to fire briefly on ether today after I got constant power to the coil. Bad news is, only the left bank had temp....
I will dig in more tomorrow.

I have the factory wiring diagram and can do pretty much anything when it comes to wiring. I hand built my harness for my 930, but want to keep this original for him, so if needed he can have it serviced later down the road and people arent in this mess..

[IMR-Merlin]

Originally Posted by Jonny H

What's your goal here? Just get it running or put it back to how Porsche intended?

I see a whole bunch of non standard wiring, conduit and other parts that should not be there (e.g. condenser on the dizzy).

Tbh, it will be difficult to give you advice unless you want it back to a standard setup as we have no idea about how the PO's mechanic wired your ignition.

get it back to stock

[Jonny H]

Ok, if you want it stock then start by removing all the non stock wiring.

As Walter says, 12V on the centre pin of the CDI and OV to the case should make the CDI box emit a high pitched whine. If it doesn't, it is dead. Do that simple two wire test first before you get to hooking up a spark plug.

Beyond that, the CDI harness is simple. Again, Walter's advice is spot on. Remove that condenser on the distributor though or the timing will be off.

[IMR-Merlin]

thanks guys, I am an old VW Rabbit but but haven't been in the CIS game for decades.

my 930 is twin plugged EFI with stand alone engine management.....

I'll get there.

[mysocal911]

Originally Posted by Jonny H

Remove that condenser on the distributor though or the timing will be off.

The condenser (.22uf - .47uf) will have basically no effect on the timing since the internal points
load resistor is either 30 or 100 ohms in the Bosch CDI. The time constant for the rise time is about
47 microseconds worst case (negligible).

[Jonny H]

Originally Posted by mysocal911

The condenser (.22uf - .47uf) will have basically no effect on the timing since the internal points
load resistor is either 30 or 100 ohms in the Bosch CDI. The time constant for the rise time is about
47 microseconds worst case (negligible).

That's still a couple of degrees lost at high RPM.

Lose the condenser, it isn't meant to be there.

[IMR-Merlin]

Thanks for the help gentlemen, after further talk with the owner, it became painfully obvious that the person rebuilding the engine had zero clue what they were doing and a complete tear down will be needed.

I appreciate all the help.

[mysocal911]

Originally Posted by Jonny H

That's still a couple of degrees lost at high RPM.

Lose the condenser, it isn't meant to be there.

Remember, the timing is set and checked at higher RPM so the potential 1/2 degrees is compensated for. Plus it helps reduce contact bounce and noise at the trigger input.

[obscene]

sometimes with basket cases like this you're better off starting from scratch. my '77 was hacked up pretty harsh but runs happily now with an MSD and carbs...

[Bob Ashlock]

Don't get discouraged ... the fun has just begun! Several contributors have given good advice above. Do the test explained by Walter to determine if the CDI is good (or not). If good, leave that temporary test setup in place and now just connect the wire from Pin-C (that you touched to ground during the test) to the distributor points. If you had spark during the momentary release from ground during the test, then each time the points open during rotor rotation, you should also see a spark from the coil. If this goes OK, then you are in business. You can then go back and troubleshoot all the crazy wiring stuff knowing the basic components (CDI, Coil, Points) are working. I see the coil in the picture is not correct for the CDI setup ... it appears to be a generic Kettering coil. That's fine for initial testing, but if you run the original CDI setup then you need to score a proper Bosch 'Transformer' to enjoy maximum spark energy. These are pricey and original black ones are hard to find, but you can also buy a good one from Kurt at Parts Klassik that works good. Do not buy the Bosch replacement that comes in a silver can (made in Brazil?) as they are notorious for failing spontaneously.