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Need help with cold start tuning.
https://www.slantsix.org/forum/viewtopic.php?t=46892		 Page 1 of 2
Author:  Sam Powell [ Sun Nov 06, 2011 1:23 pm ]
Post subject:  Need help with cold start tuning.
ON Wednesday I reset the base timing at 10 from 12.5 in an attempt to get the idle a little lower without closing down the throttle further. When I went outside to start it today, it did not want to start with the temperature at a mere 50 degrees. It finally did start after maybe 30 plus seconds of cranking, and now starts fine, but is not dead cold any longer. This is the first time it has behaved this way since I put the MSII in, and it has started at 30 degrees this fall. At 30 degrees it took a little longer than in warm weather or warm start, but nowhere near as long as today.

If I had not played with the timing, I would suspect fuel issues. It got cool fast this Fall, and went from 70 to 30 in just a few days. So maybe I have not seen 50 before.

Four questions:

1. What determines the cranking timing in MSII? Is it the timing table, or the base timing? I cranked it with the timing table open, but no cells lit up as they do once it starts.

2. Since you only get one try with dead cold, I am at a loss as to determining if there is too much or too little fuel on a cold start crank. Once it starts, regardless of the changes you make, it will then start up faster, and give you false impressions. What might actually be worse will appear to be better right then and there. You might have made a change that will make the next cold start harder, not better. And even if you crank on it a bit, and it does not start, and you then change something, and it subsequently does start, how do you know it was not the previous cranking that got it ready to fire?

3. What is the difference between the effects of the priming pulse, and the cranking pulse?

The manual gives you a technical difference but not a behavioral one.

4. Do you think I should retime the base timing to 12 BTDC? Or, is there a cranking timing you can set? I could not find a window for that.

In general I am looking of a strategy for determining if cold crank issues are those of too little or too much fuel.
Thanks as always.

Sam
Author:  SlantSixDan [ Sun Nov 06, 2011 3:10 pm ]
Post subject: 
How about an oldey-timey trick to see whether you're too rich or too lean at dead-cold: Open the throttle plate, push the plastic straw of a spray can of B12 Chemtool or another good brand of carburetor cleaner past it, give a 3-second spray, close the throttle plate, hook back up the air intake hose, and then attempt a start from dead cold. If it takes less cranking, your tuning is too lean. More cranking, your tuning is too rich.
Author:  Sam Powell [ Sun Nov 06, 2011 6:24 pm ]
Post subject: 
Thanks for the ideas Dan. That is probably worth a try. Then there is the question of whether I need to increase cranking fuel, or priming fuel if it is too lean. One clue here, (MAYBE) is that it started after I stopped cranking and then cranked again. Each time the fuel pump starts, I think it injects a bit of a prime squirt. I "think". This would lead one to think maybe increasing the prime fuel would help. This is determined by a table that is temperature tunable.

The thing that puzzles me is that it was only 50 degrees out, and it acted like it was 15, except it cranked pretty fast.

Still would like to hear from someone who knows if crank timing is base timing or set by a field somewhere.

Sam
Author:  SlantSixDan [ Sun Nov 06, 2011 6:35 pm ]
Post subject: 
Quote:
Still would like to hear from someone who knows if crank timing is base timing or set by a field somewhere.
I think you may be on a productive track seeking this information; recall our previous discussion on that topic from a long time ago.
Author:  Sam Powell [ Mon Nov 07, 2011 5:26 am ]
Post subject: 
Thanks for that link Dan. I read it all with the realization that at that time I did not know my fuel pressure gauge was wrong, and giving me faulty feed back. That does not make the logic wrong, just made it hard to interpret results correctly.

In thinking further about this it seems almost certain that this start up issue is fuel related and not timing. I only changed it 2.5 degrees. ONe issue I considered was if I was changing the distributor phasing enough to make the spark unreliable enough to give cold start problems. I concluded after some really headache inducing thinking that the phasing of the distributor was not changed at all in base timing. Both the reluctor and cap were changed the same amount as I turned the entire distributor 1.25 degrees clockwise.

I will look at the fueling numbers in the start up quadrant of the ve map. Reading that thread was a good reminder. Thanks.

Sam
Author:  Sam Powell [ Mon Nov 07, 2011 5:52 am ]
Post subject: 
I just had another thought. With MSII the slant seems to idle fine with much lower injector open times. It idles at about 1.9 MS when warm. Both Accel and MSI required closer to 3 ms of open time. Maybe this is because of the faster processor and quicker adjustment times.


This would not necessarily translate into similar shorter times for starting, which would mean I would likely need to have a higher percent of of warm ve injector timing for start up. I feel encouraged to go play with this. Thanks again.

Sam
Author:  Matt Cramer [ Mon Nov 07, 2011 8:40 am ]
Post subject: 
Quote:
I just had another thought. With MSII the slant seems to idle fine with much lower injector open times. It idles at about 1.9 MS when warm. Both Accel and MSI required closer to 3 ms of open time. Maybe this is because of the faster processor and quicker adjustment times.


This would not necessarily translate into similar shorter times for starting, which would mean I would likely need to have a higher percent of of warm ve injector timing for start up. I feel encouraged to go play with this. Thanks again.

Sam
That's a crude tool for adding pulse width across the board. Set the injector opening time to the actual injector dead time (it's actually opening time minus closing time) and add fuel by adjusting the VE table - that's the right way.
Quote:
1. What determines the cranking timing in MSII? Is it the timing table, or the base timing? I cranked it with the timing table open, but no cells lit up as they do once it starts.
On MS2/Extra with an HEI setup, I believe it's JUST the distributor base timing. Other ignition setups have an adjustment for it under Basic Setup -> More Ignition Settings where you can specify cranking advance directly.
Quote:
2. Since you only get one try with dead cold, I am at a loss as to determining if there is too much or too little fuel on a cold start crank. Once it starts, regardless of the changes you make, it will then start up faster, and give you false impressions. What might actually be worse will appear to be better right then and there. You might have made a change that will make the next cold start harder, not better. And even if you crank on it a bit, and it does not start, and you then change something, and it subsequently does start, how do you know it was not the previous cranking that got it ready to fire?
In addition to Dan's method, another tip - if you have it start faster by giving it a bit of throttle, you've got too much fuel.
Quote:
3. What is the difference between the effects of the priming pulse, and the cranking pulse?

The manual gives you a technical difference but not a behavioral one.
You get ONE priming pulse when you turn the key on, then when the engine starts turning, a continuous stream of cranking pulses.
Author:  Sam Powell [ Mon Nov 07, 2011 7:15 pm ]
Post subject: 
Matt, Thanks for the input. It helped much. I think I gave you the wrong impression with my choice of words. I was not considering changing the fuel map anyway other than one cell at a time in normal tuning mode, or with autotune activated. I was just saying that since the MSII ran nicely with less fuel across the map than the old MSI, the cold start would need to be a higher added percentage than the old MSI had, since its base fuel map was richer.

I increased the prime pulse this morning for the ECT temp at that time and it started faster. So, it seems the start up fueling has been lean all along.

I increased it a bit more before coming home, and it got better yet.

Wizard's comments in the old thread were actually quite a help too. Thanks to him and to Dan for linking me back to it. I think I am on the right track now.

Sam
Author:  Sam Powell [ Tue Nov 08, 2011 6:58 am ]
Post subject: 
Matt, Does the priming pulse come when the fuel pump starts up, or when the ECU first sees RPM? If I turn the switch on to check tuning tables, and thus wait a bit before cranking, has time passed then since the priming pulse?

Sam
Author:  Matt Cramer [ Tue Nov 08, 2011 9:16 am ]
Post subject: 
Priming pulse is fired when the ECU is powered up.
Author:  Sam Powell [ Sat Nov 19, 2011 7:29 pm ]
Post subject: 
Things were not getting better quickly with my step at a time approach to tuning the cold start. After reflecting on how I had to pump the crap out of the throttle on my carbureted slants to get them to start when cold, I figured I needed to up the priming pulse. So, I tripled it. And, it fired up pretty fast. Apparently slants are hard to get to fire the first time when really cold. Matt's last post was the key. It is the EFI equivalent of pumping the throttle to inject fuel. I'll keep you posted on how this progresses.

Another clue was that it would eventually start, but take a long time. If there was too much fuel, then it stood to reason that more cranking would make things worse, as it would get wetter and wetter in there. And, opening the throttle during cranking did not help. Thanks all for the advice.

I don't think I ever flooded a carbureted slant when it was cold. Now when it was hot, that was another thing. Even my wife learned to carry a pencil to prop the choke open when the choke would close while the engine was still relatively warm. Lesson there, don't turn up the prime pulse for the high ECT values.

For those who don't know, MS has a flood clear setting which you can tune. So too much fuel is actually a little easier to overcome than too little.

Sam
Author:  SlantSixDan [ Sat Nov 19, 2011 9:01 pm ]
Post subject: 
Hoorah for progress!
Author:  Dart270 [ Sun Nov 20, 2011 5:34 am ]
Post subject: 
I tried to be a skinflint with fuel on warmup and startup for a while, but eventually gave in and realized how much fuel it needs when cold.

Lou
Author:  Sam Powell [ Sun Nov 20, 2011 10:43 am ]
Post subject: 
Lou, I find that the slant idles with less fuel when cold with MSII than with MSI. I don't know why. Maybe the quicker reaction time of the processor. This is based on the AF ratio displayed. But it still needs lots of fuel to get started. I guess at that cranking stage the processor is not really doing much yet.

Even with the leaner mix, the economy when driving just 4 miles to work and back is pretty bad. It yields a poor 16 MPG. That is higher than it ever did with the MSI. In mixed driving it is now 18 MPG which is not too bad as that includes some of that short trip stuff. On the road I have gotten as high as 23 with MSII.

Any ideas why the slant takes so much fuel to get fired up?

Sam
Author:  Dart270 [ Sun Nov 20, 2011 10:52 am ]
Post subject: 
I think ALL engines need a lot to get started. It's just that we don't know how much with a carb or without numerical data. The numbers are scary high at cold temps on a cold motor (50-70 % higher than hot running numbers). My cousin's Prius surprised him in that the cold running and warmup economy was about 2X worse than when fully warm. I told him that I think all cars are like that, it's just we never see it on a gauge.

Personally, I think EVERY new car should be required to have a fuel mileage readout with different averaging times/distances available. If people knew more about their economy, they might make different choices. Most people driving big SUVs have no idea how bad it is, or how bad it is at high speeds. That's because gas is still so dirt cheap compared to other new car costs that they just don't bother to think about it.

If you are getting 16 MPG just on short hops to work only, I'd say you are doing very well.

Lou
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