Double-check my ignition curve? (CDI+)
 

https://i.imgur.com/8g60uSkl.jpg

1981 3.0 SC w/ PMO carb conversion

• Standard CIS distributor, NOT recurved
• Vacuum lines disconnected
• Mechanical advance not locked, disabled, or altered in any way

Does this look right? I'm trying to follow the curve recommended in the paperwork that came with the carb kit, which is listed below:

• 1000 RPM: 7*
• 1500 RPM: 14*
• 2000 RPM: 23*
• 2500 RPM: 30*
• 3000 RPM: 35*
• 7000 RPM: 35*

But I'm not sure if I have to disable my mechanical advance, or if these numbers take that into account.

OK - first off a little tough love here. It maybe sounds overly harsh. Maybe it's warranted, maybe it's not, but it's for your own good. A single miss-step here can permanently harm your motor and I don't want to see that happen.

By the questions you are asking it seems possible that you don't fully understand what you are doing here. Make sure you have the knowledge and tools you need or you can severely damage your engine. That includes knowing how to operate a dial type timing light if you have one and how to read the marks on the crank pulley. And which marks to use depending on which type of timing light you have and how it's set.

The installation manual for the CDI+ is available on the website. It's excellent and contains everything you need to know. By the looks of your programmed curve it looks like you need to go back and do a little more homework.

You are going to need to choose between controlling advance with the distributor or the CDI+, or combining the two curves in which case the values are added together (this is referred to as "overlay" in the manual.

If you install the CDI+ as you have it programmed without locking out the centrifugal advance you'll get 70 degrees of advance and BOOM!!!!

To take full advantage of the programmability of the CDI+ you need to lock out the distributor. centrifugal advance. There are many detailed posts about this in my build thread. Here is one that shows the timing curve I'm running at present:

Tee Jay,

Listen to Jonny, He has the CDI + and is very familiar with it.

You are going to need to choose between controlling advance with the distributor or the CDI+, or combining the two curves in which case the values are added together (this is referred to as "overlay" in the manual.

If you install the CDI+ as you have it programmed without locking out the centrifugal advance you'll get 70 degrees of advance and BOOM!!!!

To take full advantage of the programmability of the CDI+ you need to lock out the distributor. centrifugal advance. There are many detailed posts about this in my build thread. Here is one that shows the timing curve I'm running at present:

This info from Jonny, is of the utmost importance !!!!!!!

Ian
I run 30 degrees total 3.0 cis
@ crank, 900 rpm 8* , 1200 rpm 12*, 1800 rpm 18*, 2200 rpm 22*, 2900 rpm 30*. all in

Nothin' but love, bruh.

I got a single sheet of paper with my CDI+ that I thought was the "instruction manual". I'mma head off to their web site now and see if I can't find something more. Thanks for letting me know!

Yes, the distributor's mechanical advance needs to be prevented, but the engine won't run at 70 degrees advance anyway.
The engine will start to misfire at about 2000-2500 RPM, if the centrifugal advance is not disabled.

The full install manual on the website is pretty good. It'll steer you in the right direction.

If you look on page 51 and 52 of my build thread you'll see a bunch of stuff I did to my distributor - locking out the centrifugal advance and removing the weights, locking out and removing the vacuum advance, changing the trigger angle, and altering the rotor phasing.

None of that is really necessary but in my case one thing led to another - removing the vac advance changed things enough that I felt I should check and correct the phasing, etc.

Don't get too confused by all that. That's just me sharpening things to the finest possible point I can.... but you might find it interesting.

One other useful bit of info is the rotor from a 3.2 Carrera fits the SC distributor, and doesn't have the goofy spring loaded rev limiter so you'll be free to set up yours in the software instead. It also has a slightly wider tip so the rotor phasing matters a bit less.

Read the manual. Re-read a couple of sections to make sure that I understood it. Looked at the sheet I was given with the carb setup. Re-read that too.

As I understand it...

Measured at the crank wheel, timing should be 7* BTDC @ 1000 RPM. This is handled entirely by the mechanical advance on the distributor. With the OEM CDI installed, you rotate your dizzy until you get this configuration.

That literally bottoms out my distributor's adjustment. I cannot rotate it any further. But hey, that's exactly where I need it, right? So onwards.

Now, I install the CDI+. Timing is locked. Flat profile is selected. Car shows... 7* BTDC @ 1000RPM. Perfect.

Now, I need to adjust the timing curve because there's a heck of a difference between the 10.5* of timing the dizzy will give me at 3000RPM and the 35* I need at the same RPM. So, I switch from the Flat profile to the Overlay profile. I change NOTHING else. It's set to 0* at 1000RPM. The idle drops dramatically. I hit the crank wheel with my timing light, and see that I'm now at about 21* ATDC. (Reiterating here, that's AFTER top dead center.) In order to get the same 7* BTDC on the crank pulley that I'd expect, I need to set my curve to adjust by +28*...

So, let's assume that somehow, my dizzy is off by 21*. That's an easy enough adjustment to make - assuming that it's linear. So the table would be...

https://i.imgur.com/vbGQ47o.png

The graph on the CDI+ software only goes up to 40*!

This does explain how I was able to drive around with the profile I had in the original post without dying. It may also explain my drivability issues. I was running at a ridiculous retardation rate.

So, uhh... How do I fix this? Do I need to pull my dizzy and rotate it by a tooth? Should I just create a new profile (or change Full Control) and set it to the final values in the above table? Or am I still not fully understanding how everything works?

you must first lock your distributor , then you can work on your curve .
It sounds like you are also 1 tooth off on the dizzy gear. This can be fixed when you remove your dizzy to lock the advance plate, this is a video link. go to 6;10 minutes and the lock procedure is shown
Max advance 30 degrees total , not 35

it is important to note in the video that he has set a 5* static or starting point ,
so that needs to be added to the curve total of 20* to total all in curve of 25*

https://www.youtube.com/watch?v=GK-gD9_gziU
Ian

I would start by programming a flat line into the CDI+ at 0 degrees so you know it's not altering the timing. You might need to play with the trigger angle so it will idle at 7 degrees without changing anything.

You don't NEED to lock out the distributor but it does allow you to take full control of the timing. Also keep in mind your trigger angle needs to be greater than the max advance you'll ever want. I have mine set to 40. You could probably use 30. Check the manual for suggestions.

Checking off the "show adjust room" might help visualize that, too.

Genius! This was it! Changed the trigger angle to 0 and now it idles at 1000RPM at about 7*.

Now I can just do an "Overlay" style graph with a simple "TARGET minus MECHANICAL" formula... Right?

https://i.imgur.com/mWDMekW.png

My mistake , no need to lock the dist advance , but I do because I want full control.
Sorry for miss leading you .
Ian

The "adjust room" when you set the trigger angle to zero is preventing you from having the unit add any more advance.

It will be necessary to change the trigger angle. Start with 20, then rotate the distributor 10 degrees (which is 20 crankshaft degrees) to compensate. Hopefully you have room for the dizzy to rotate, or you might have to take it out and move it a tooth. Be very aware of what you are doing and make some sharpie marks before you do anything so you can get back to where you were.

I'm sorry I don't have more time right now!!!

Oh and BTW your mechanical advance isn't working, if those are measurements you made with your timing light?

If it all of a sudden shakes loose and gives you a bunch more timing it will be trouble!!!!!

The stock SC curve should have much more advance than that. Much more.

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)
https://i.imgur.com/BJB3XDkl.jpg

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.
https://i.imgur.com/HlaF50bl.png

If you can’t get the car to start after rotating the dizzy one tooth then setting the timing then something else is going on. Check the rotor and make sure that it is seated completely in its groove and doesn’t have play. Check the green wire and make sure you have good continuity, is it wedged against something, are the wires frayed?

Still can’t get it going? Then start over, zero out the CDI curve and use the dizzy mechanical curve or lock the dizzy and use the CDI curve. Sounds like their battling each other right now so you have to lock one of them out.

I think what Jonny was referring to with the curve, is that your chart shows that you have 10 degrees mechanical at 3500 rpm’s with a target of 35 degrees. He is telling you that dizzy mechanical advance is normally more like 35 degrees. So if yours is stuck at 10 degrees and it unsticks you’re up around the 70 degree range if you also add in CDI advance.

Reference below screenshot from your posted chart. This is a mess, it can’t happen, and if it is then your advance is stuck with some type of intergalactic goo. And it isn’t locked out if that is happening.

http://forums.pelicanparts.com/uploa...1651358545.jpg

Now get back out there and figure out WTF is happening, we are all rooting for your Jedi build!SmileWavy

What makes you think it can't happen? I've heard multiple people say this, but the numbers listed are in both the PMO literature AND the official Porsche documentation. I'm not saying you're wrong, I'm just wanting to learn how to do it right!

Oh, and I got the car running one tooth off! I must have gone too far last time.
https://i.imgur.com/i1jW2jz.png

35* of trigger gives me enough headroom, too.

edit: OK, What the hell. This is from the Porsche workshop manual:
https://i.imgur.com/IGXqmRhl.png https://i.imgur.com/5EyAQWUl.png

"You need to be at 30* BTDC @ 4K RPM" but vacuum and centrifugal advance combined would only be 15*. Am I supposed to be doubling the Y axis on these charts?

edit2: Apparently that's exactly what I'm supposed to do.
But this contradicts the manual, which asks for 3-5* @ 900RPM (The exact numbers on the chart)

Gah!

edit3: If I add the 5* the manual wants, and double BOTH axis, I get something that kinda looks right?
https://i.imgur.com/UEGeYZF.png

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.

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.

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).

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

https://i.imgur.com/QC3zbT9.png

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?

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.

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!!

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?

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.

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+.

-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:
https://i.imgur.com/cj6rWT3.png
https://i.imgur.com/bl4OUuT.png

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.

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.

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.

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.

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.
https://i.imgur.com/fHVgVTm.png

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.

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!

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.

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

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)

http://forums.pelicanparts.com/uploa...1651406949.jpg

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.

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

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.