Double-check my ignition curve? (CDI+)

[Jonny042]

Originally Posted by TeeJayHoward

Oh! I thought you could ONLY adjust settings inside the red area, not that you COULDN'T adjust anything in the red area. Crap.

Unfortunately, this is it. The dizzy is maxed out. I pulled it out, set the rotor back a single "tooth", and then put it back in, and I couldn't get the car to start regardless of where it was adjusted to. Thinking I screwed it up, I pulled it back out, rotated it the other way two teeth, and put it back in. The car wouldn't start then either. The dizzy will only function if it's maxed out in this one location. I have no idea why.


I was assuming that PMO's documentation on the stock 3.0L Distributor curve was correct. Is there a different document I should be going by? (Remembering that the vacuum advance is completely disconnected) (EDIT: GOT A DIAGRAM FROM THE PORSCHE MANUAL)


edit: And now that I'm reading it more closely, there's a difference between a 3.0L Carerra dizzy and a 3.0L SC one, isn't there. Dad gummit. It's pretty close, though.

This is the advance curve of the distributor, at the distributor shaft, so you need to double the number for crankshaft degrees.

Not confusing, at all!!!! LOL

You need to measure and map out YOUR distributor or you'll never know exactly what you have.

[snbush67]

Ok you’re using distributor degrees for that chart, that’s different than crank degrees.

But you’ll never want 35 degrees of distributor advance because that would be 70 degrees at the crank. That’s why the confusion. So your target is 35 degrees at the crank but your chart doesn’t differentiate.


Good! Now that’s cleared up.

[Jonny042]

Yeah but you need to double the values in that chart but also need to add the base timing of XX degrees at idle.

And don't forget the chart RPM is distributor RPM not crankshaft RPM.

This gets back to my original point of making sure you understand what you're doing here.

You need to be able to double check what you're doing with what YOU know and verify the timing on your motor, with your timing light.

If you mess up and use a dial timing light against the wrong timing mark on the pulley you could end up measuring the timing wrong.

You need to verify with the light that you aren't getting more than the desired timing (lets say 32 degrees for a stock SC with low compression and stock cams).

[TeeJayHoward]

Okay, operating under the assumption that you're supposed to double both axis and add 3-5*, I created a quick ignition map.



So, in theory I could just flat-map the CDI, hold the engine at 1000, 2000, etc RPM, adjust the dial on the back of the gun until TDC lines up, and note the number I set it to. That's how I'd get my distributor's numbers... Right?

[Jonny042]

PS - if you're taking the distributor out and moving it a tooth, just make a sharpie mark (or two) that point you to the rotor tip.

After to yank it and adjust it one tooth, when you put it back in, move the body of the dist. the same direction until the mark lines up. Timing should be the same but with the distributor in a slightly different location.

[Jonny042]

Originally Posted by TeeJayHoward

Okay, operating under the assumption that you're supposed to double both axis and add 3-5*, I created a quick ignition map.



So, in theory I could just flat-map the CDI, hold the engine at 1000, 2000, etc RPM, adjust the dial on the back of the gun until TDC lines up, and note the number I set it to. That's how I'd get my distributor's numbers... Right?

Not sure about the map, but without checking it, it looks closer. But yes to the flat map. You should probably get that working first, and map out what you have. You can even mess with the trigger angle a bit and get a feel for how that affect things.

You'll get there!!

[TeeJayHoward]

What the hell is going on?

I set the map I had in my last picture. I idled the car. (1000RPM) It worked. I stopped and started the car. Now it won't idle. I unlock and rotate the dizzy all the way one direction. Nothing. All the way the other direction. It runs! Kinda. I pull out my timing light and rotate the knob until I see TDC. It takes a LOT of rotation. The knob is at 50*. What the...

I turn the car off, select the flat map and check "fixed timing." I believe this is exactly how the CDI+ ships. It still tries to die. The timing light shows 40*.

I pull the CDI+ and put the old Bosch unit back in. It starts and idles, but spits and sputters. I'm off by 4* with the dizzy at the extreme edge of adjustment. So that's... 9* BTDC @ 1000RPM? I can't get it to go any lower.

I'm ripping this distributor out and taking it apart. What the HELL is going on here?

[donbecker1234]

I'm in a little different place as my CDI+ won't be here 'till Monday, and I have a 930 but:

- I'm not sure what you're trying to achieve with the CDI+...do you need it to handle advance?
- If you are uncertain of your distributor setup, have you tried setting the CDI+ to not deal with advance and let the distributor handle it?
- Have you cleaned out the mechanical advance on the distributor to make sure it's not gummed up?

I see a benefit with the CDI+ even if it doesn't handle advance. That's going to be my first step. HTH.

[donbecker1234]

Another thing to add...these cars ran for a loooong time with stock parts. But if you dont' have history running the parts you have reliably, anybody's guess as to what you have. I'm not sure about the non-turbo cars, but there are differences in distributors that I know about on the turbo cars. So have you looked up the part number on your distributor? Is is the right one for your car and engine?

If you have the wrong/different distributor setup, it might be harder to try to "fix" it with the CDI+.

[TeeJayHoward]

Originally Posted by donbecker1234

- I'm not sure what you're trying to achieve with the CDI+...do you need it to handle advance?
- If you are uncertain of your distributor setup, have you tried setting the CDI+ to not deal with advance and let the distributor handle it?
- Have you cleaned out the mechanical advance on the distributor to make sure it's not gummed up?

-I need it to handle advance. I've got carbs now, and need a distributor recurve. I am trying to use my CDI+ instead of recurving my dizzy.
-I have not. It's got this stamped on the side: 0 237 304 016 (PGFU 6 ->) I'll look it up in the PET in a second. (edit: PET says Porsche part number is 930 602 021 06. From this picture from our host, I can verify that the markings are identical to the official part number. I think it's the correct distributor.)
-I can't get to the mechanical advance. I have to pull off the stator, and all three socket head cap screws are basically welded to the dizzy.

After I took the dizzy apart as much as I could and realized I couldn't go any further, I put it back together and re-installed it. I pointed the cap at spark plug wire #1, and... It slid in to place? I'm no longer offset by half a tooth? What the deuce?

Oh, and with the Bosch CDI, it idles at 1000 RPM at... 5* BTDC. Exactly where it's supposed to.

edit: swapped back in the CDI+. It now works just like the Bosch CDI, using these settings:



It's 8:30PM here. I can't rev my engine to try and find out what the timing is with just the distributor weights, so I'm going to have to call it here for a night.

[Jonny042]

Watch you don't get tripped up by thinking you've made a change to the CDI+ map but forgetting to load it to the unit. Is there a chance you had it running live on changes on the software but then shut the car off and on again and lost the changes?

I do know that you need to be very deliberate and sure of what you're doing with the software. It's been close to a year since I last played with it so it's not on top of my mind, just trying to think what could be happening.

[Jonny042]

I'm assuming if you select "fixed timing" it also overwrites the trigger point setting to zero. So fixed timing is different than programming a flat curve and assigning a trigger angle.

Since you can't run the car, spend your evening reading the manual again...... it will probably make more sense now on re-read.

[snbush67]

Originally Posted by TeeJayHoward

-I need it to handle advance. I've got carbs now, and need a distributor recurve. I am trying to use my CDI+ instead of recurving my dizzy.

Maybe, but probably not. Do you know what your current distributor capabilities are. Why do you think you need a recurve?

As these distributors age, the springs should get weaker and then they would advance quicker, also you can bend the limited tabs at the bottom of the housing and that would allow more advance. All you need to do is pull it apart, clean it, and lube it.

[TeeJayHoward]

Originally Posted by snbush67

Maybe, but probably not. Do you know what your current distributor capabilities are. Why do you think you need a recurve?

Because the guy who designed my carb kit told me I do. From PMO: "All 911 SC distributors need recurving."

edit: Wow, that was a lot ruder than I intended. Sorry if offense was taken. As a part of swapping from CIS to carbs, I disabled my vacuum advance on the distributor. Between that and the official install instructions telling me to recurve my distributor, I felt as though it was probably a good idea to purchase a CDI+ and start tinkering with it. I was given a table with target advance values at given RPMs, and it is indeed higher than the mechanical advance reaches.


I'm not positive that the red line is correct, but it seems to line up pretty well with the workshop manual's chart, adjusted for base timing. I intend tomorrow to write down what the actual advance values are. Just can't be holding my engine at 6000RPM at 9:30PM.

[TeeJayHoward]

Originally Posted by Jonny042

I'm assuming if you select "fixed timing" it also overwrites the trigger point setting to zero. So fixed timing is different than programming a flat curve and assigning a trigger angle.

Since you can't run the car, spend your evening reading the manual again...... it will probably make more sense now on re-read.

If you select "Fixed Timing", then write to the CDI+, the next time you open the window, it may or may not be selected. There seems to be a bug in the software.

And you're absolutely correct about the re-reading. It definitely makes a lot more sense this time around!

[snbush67]

No, not rude at all, but, what the guy at PMO should have told you is that check your distributor for total advance and consider a recurve if it isn’t meeting the specified curve. No need to recurve a distributor if you don’t know that it isn’t already doing what you need it to do.

That’s all water under the bridge now, you now have what you need to get whatever curve you want. You’ll get there. It’s a lot to wrap your head around.

[TeeJayHoward]

Originally Posted by snbush67

It’s a lot to wrap your head around.

You ain’t kidding. I seriously doubt I could have done it without the patience and knowledge on this forum. You guys rock!

[Jonny042]

I'm pretty sure you know this, but it might help others in the future to understand what you can do here. If you don't want to mess with locking out the distributor you can program the CDI+ to add (or subtract) advance to the distributors advance curve to get the desired result.

In the below graph:

RED = current advance curve

GREEN = CDI+ curve

BLUE = RED + GREEN = desired result (suitable for carbs)



Note that if you were to set the CDI+ to "flat" and change base timing on the factory curve to, say, 10 degrees BTDC, you'll be most of the way there, and your car will run a lot better, with 32 degrees total timing above 2500 RPM. It would also change the position (but not the shape) of the green curve.

If you want to try this make sure you double check and triple check the total advance with the timing light dial against TDC with the motor spun up to 4000RPM (you should have all your advance in by then). Check and triple check that the mark you are using is TDC not the factory timing mark.

[Jonny042]

Originally Posted by snbush67

No, not rude at all, but, what the guy at PMO should have told you is that check your distributor for total advance and consider a recurve if it isn’t meeting the specified curve. No need to recurve a distributor if you don’t know that it isn’t already doing what you need it to do.

That’s all water under the bridge now, you now have what you need to get whatever curve you want. You’ll get there. It’s a lot to wrap your head around.

The PMO instructions are very poorly written (at best).

[mysocal911]

Originally Posted by TeeJayHoward

You ain’t kidding. I seriously doubt I could have done it without the patience and knowledge on this forum. You guys rock!

Please explain how your '81 911 SC ignition system has benefited from your efforts in converting it from the Bosch CDi ignition with the original centrifugal advance,
resulting in basically still having the same advance curve. Not only have you incurred the cost of buying another ignition system, but also your time to learn (38 posts)
the new system and then setup it up so the engine starts and runs properly.