Double-check my ignition curve? (CDI+)

[TeeJayHoward]

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.

[Jonny042]

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:

Originally Posted by Jonny042

I've been trying to figure out a lean misfire - it's pretty obvious when driving there is a low throttle, low rpm, surging/misfire occurring, and this is confirmed by the datalogging.

From what I can tell the misfire is AFR dependent. The log below shows a period of smooth steady state running around 12.9 AFR and then a period of lean misfire at 13.9 to 14.0. You can see the baseline AFR with spikes into the 15's - this is 100% not a fuel delivery issue but a failure to ignite the air/fuel mixture.



I'm not at my wits end just yet, but I think what I discovered last time out was interesting - as an experiment, I added a few degrees of timing (up to 34 degrees total advance from 2600-3400, dropping back to 30 total) and it actually lowered the AFR threshold at which this occurs, rather than raise it!!!

So in other words I'm not as smart as I thought!! But it also means adding a vacuum advance isn't going to help matters, which is great. I really hate adding variables.

Next up - set the timing to a simpler curve, 29 degrees from 2650rpm and up, and try that. At least it will tell me if I'm simply getting a misfire from too much advance in that area:



I'd like to be able to tune the part throttle cruise to the mid 14's and be tolerant of some slightly leaner mixtures at low load (which will make tuning a little easier).

[icarp]

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

[TeeJayHoward]

Originally Posted by Jonny042

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.

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!

[mysocal911]

Originally Posted by Jonny042

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:

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.

[Jonny042]

Originally Posted by TeeJayHoward

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!

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.

[TeeJayHoward]

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...



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?

[icarp]

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

[Jonny042]

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.

[Jonny042]

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.

[Jonny042]

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

[TeeJayHoward]

You might need to play with the trigger angle so it will idle at 7 degrees without changing anything.

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?

[icarp]

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

[Jonny042]

Originally Posted by TeeJayHoward

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?

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!!!

[Jonny042]

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!!!!!

[Jonny042]

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

[TeeJayHoward]

Originally Posted by Jonny042

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

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

Originally Posted by Jonny042

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.

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.

Originally Posted by Jonny042

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

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

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.

[snbush67]

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.

[snbush67]

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.



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

[TeeJayHoward]

Originally Posted by snbush67

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.



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

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.


35* of trigger gives me enough headroom, too.

edit: OK, What the hell. This is from the Porsche workshop manual:


"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.

Originally Posted by psalt

Hello Otto,

You do realize that these charts are based on a distributor test machine. To get crankshaft degrees and rpm you must double the fiqures as the distributor turns at half crank speed. Are they ROW or US charts ? For ROW cars, the MFG fuel spec was changed, so your compression comparisons are not apples to apples. Porsche was conservative with advance, with temperature being the key factor. The 911 is a knock sensitive design, so the cooler the engine and air intake temperature, the more timing you can run for a given octane.

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?