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#58069
I have tried the MS table generator and it generates max advance of far more than the factory distributor my engine came with. I have had the bast performance and mileage with what is in the current tune I shared.

I also can not get the engine to idle low enough with the high advance numbers down at idle range in the MS generated table.

The bentley manual states that the timing should be set for 3º ATDC with the stock distributor at 800-1000rpm ( the stock distributor had a double action vacuum advance on it with ported vacuum retard at idle and vacuum advance off idle.)
I really wish I had a distributor dyno so I could really see what the advance curve looks like.

I used these values from the bentley to come up with my table:
049 905 206B (distributor p/n)
1050-1400------advance begins
2200-------------15-20º
4000-------------22-26º
5000-------------16-30º

I also had taken a previously generated spark table from the generator, scaled it down and mashed it up with averaged numbers from above in my generation of the current table.

all that being said I don't mind a little experimentation. I mean this whole thing is a big experiment isn't it?
User avatar
By PSIG
#58071
The factory had different goals than you do, including various regulations, NVH, etc. Consider for example, that most cars up through the '90s used 5 to 10° idle timing, which was partly emissions, but also to reduce the acrid smell of the exhaust for customers. I assume you don't care as much about the exhaust smell as the engine operation?

The engine can only run as fast at idle as the fuel and air supply allow, no matter the ignition timing. I would get that sorted first, then begin applying most-effective timing for best performance in every area of operation. For example, I see at low-cruise that your timing is only 10°, which is making the exhaust very hot on exit, and you can see your engine temperatures are affected by it. Worse, your valves are likely overheated and reducing their life. While the factory mechanical curve may indicate that timing was stock, I'll bet there is another component for advancing timing under low loads that you did not figure-in, like vacuum advance? ;)

While I suggest tuning to best timing as the most direct route, and that will coordinate with your fueling for best efficiency and performance; if wanting to begin with a factory-equivalent timing table from factory spec's, perhaps try this method: Creating a stock-equivalent Spark Table from factory service manual specifications
#58087
Thanks for the replies guys! I have done all sorts of testing and experimenting since my last post.
Heres what I have been doing:

1) gave a try to a freshly generated timing table from the MS table generator. It worked well at idle and somewhat at cruise but the engine would die on decel.

2) made a "wedge" table and gave it a try. engine ran much smoother and very little judder at cruise.

3) Had a look at the post that PSIG shared then gave it a shot making a blended ignition table based on published OEM data. This worked out the best.

4) Re-checked the timing, both initial valve timing ( I had in earlier escapades in CIS tuning advanced the camshaft one tooth) and Ignition timing. I reset the valve timing to factory, checked the ignition timing with a timing light at idle and it was way off. Reset the trigger offset and got the idle timing in tuner studio and on the truck to read correctly (at the flywheel). In combination with the blended "Stock " ignition table and correct valve timing, it idles and revs nice. Exhaust fumes have gotten better too.

5) noticed that the timing wanders a bit and if i stab the throttle and rev and let the engine return to idle the timing advances up to 50º BTDC and does not return to idle value. was reading through the WIKI and noticed this in the description for "Missing Tooth (cam speed)":

"Missing tooth cam or distributor wheels can be used with cam or distributor wheel modification or fabrication as no OEM systems use it originally. The wheel must have at least as many teeth as cylinders, not including the missing tooth. This generally requires double the number of teeth as cylinders or more. As many teeth, slots, or other readable features (sensor targets) as possible in the limited space is recommended in order to satisfy this requirement, and to maximize resolution. The sensor must be capable of reliably reading smaller or closely-spaced teeth.:

Having read and re-read this paragraph I think that I may need to make a new trigger wheel. The sentence of note is the one stating that the tooth count should be as many teeth as cylinders NOT including the missing tooth. Does this mean that I need to make the wheel with 16 readable teeth and 1 missing? essentially making the wheel 17-1 physically?

Also I read a nice quote by cx500t here https://speeduino.com/forum/viewtopic.p ... 3&start=10
explaining that it is not favorable to have the missing tooth correlate to TDC on any cylinder. Since I have my wheel setup with the missing tooth corresponding to cylinder 1 TDC I am going to change that first thing this evening and test to see if It fixes my wandering timing problem. It is also completely possible that the resolution of the trigger wheel is too fine for the Hall sensor to reliably trigger off of. The only conundrum is that I have had no sync losses while driving or running. I only get sync loss as i key off the engine and none during cranking.

Cheers again guys you have all been helpful. :beers:
User avatar
By PSIG
#58090
zwelsh91 wrote:
Fri Aug 12, 2022 3:55 pm
Speeduino WIKI wrote:Missing tooth cam or distributor wheels can be used with cam or distributor wheel modification or fabrication as no OEM systems use it originally. The wheel must have at least as many teeth as cylinders, not including the missing tooth. This generally requires double the number of teeth as cylinders or more. As many teeth, slots, or other readable features (sensor targets) as possible in the limited space is recommended in order to satisfy this requirement, and to maximize resolution. The sensor must be capable of reliably reading smaller or closely-spaced teeth.:
Having read and re-read this paragraph I think that I may need to make a new trigger wheel. The sentence of note is the one stating that the tooth count should be as many teeth as cylinders NOT including the missing tooth. Does this mean that I need to make the wheel with 16 readable teeth and 1 missing? essentially making the wheel 17-1 physically?
OK, so you can only say so much without writing a book. :lol: In-effect, you could have 5-1 on a 4-cyl distributor wheel, but that is horrible resolution, so the easy answer is to double the teeth (#Cylinders*2=tooth count) or more and remove one for the missing tooth. That's minimal for concept.

However, you can do alternative counts, so long as the non-missing teeth are #Cylinders or more, and evenly divisible into 360° so 8-1, 18-1, 36-1, whatever. Considering the distributor tooth count is for two crank revolutions, the resolution is half that of a crank wheel. ;)
#58093
Ok, I am not going insane, just reading incorrectly :roll: :P

Sorry for the last couple posts being so long. They have been more of a brain dump than anything.

At present my trigger wheel is 16-1. Physically installed I aligned the first tooth after the missing tooth to just trigger at TDC on No. 1 cylinder. Surprisingly enough when I initially set up the trigger offset I had to put in -182º (this was close to my estimate that the offset would be in some increment of 45º based on the wheel tooth count). Last night when I changed the valve timing I had to adjust the trigger offset to -205º (which an adjustment was expected due to timing belt tension) to get the idle timing to match what was showing in TS at a steady number. I have also found that whatever error i see with a light at the crankshaft for example TS says 10º BTDC and the light shows 20º BTDC needs to be put in as 1/2 of the interpreted value. So if the error is +10º advanced the Trigger offset would need to be advanced by +5º to bring the timing in line at the crankshaft.
#58099
Are you locking the timing (in TS) when applying the timing light? Perhaps turn off the idle advance, as that is easy to get backwards.
Myself, I preferred an advance trough in the ignition table. :)
#58100
@LPG2CV Since your last response I have turned off the Idle advance settings per your suggestion. It has in many ways, simplified things. The most of which the hysteresis I was getting as the engine dropped down to idle is no longer there. Along with stabilizing the idle timing. Thanks!

I am planning on doing some tests with the timing locked at a set value to figure out why the timing is wandering. most likely it's me and something generally simple that I am not seeing yet.
#58104
I figured out the root of my timing problem. Long story short the shaft in my modified distributor is two pieces and the upper half with the trigger wheel on it was slipping. So I cross drilled it and installed a spring pin, Re-installed everything. Reset the trigger offset and viola! We are back in business.

I fired it up, let it get up to operating temperature and using the fixed timing feature in TS checked for timing variations. At idle I get some jumping around, I suspect that is due to backlash between the distributor drive gears or lack of resolution on the wheel or a combination of both. With timing fixed at 15º I did a couple revs to about 5000 and back to idle. Under acceleration and decceleration the timing was dead steady at 15º and at sustained rpm the timing stays steady as well.
#58167
So far so good. Tuning has been a treat with stable timing..... Who would have guessed? :lol:
I went through my manual and have modeled the factory distributors and exported their corresponding tables. in an effort to see the differences between them all, I'm doing a day or two of driving on each table to decide what is closest to where I want to get to for economy and drive-ability. Just fixing the Trigger setup, so it is not wandering around has helped to increase fuel economy.
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