How does MS II work without an O2 sensor?

[cody2dog]

I'm just starting my project to megasquirt a Pontiac 400. I plan to use V3 with MS II, only for the robust design of the V3 PCB and because my TB has an IAC (it's from a Chevy truck, with two 85 lb injectors). Since headers tend to develop small leaks, I think I'd like to NOT use an O2 sensor. I assume I could do a 'set-of-the-pants' tune and read my plugs, and make the MS run as well as a carb even without the sensor - is this pretty much the case? Also, even though I've read the manual a few times, I'm not sure I have a good picture of the right way to configure the MS to use an HEI with 4 pin module. I think I need to invert the signal in the MS - is this correct? I plan to start with no spark control in the MS, but that could change. Are there clear advantages to letting the MS control the spark? I use MSD 6AL on this car.
Thanks

[pluisje]

you can try if you have 10 cars to run on 10 maps,
1 with a low fuel map on idle up to 10 with rich fuel map on idle,
and try with fits best.
then you try 10 different cars for 10 different fuel map on high load,
and 10 different cars with fuel maps for poor load
and 10 different cars with fuel maps for middle load

you can have a team of 100 people preparing the cars, jumping
from car to car, burning 200 dollars on gas in 1 weekend and find
the right map all together.

you could do that.

or just invest on a wide band sensor and make your map in 4 hours time on 1 car,
you’ll find the right idle VE in 10 minutes, in stead of 1 hour and 4 gallons
later,
you’ll run your car down the street on middle load in 30 minutes,
in stead of 2 days
and you will 80% progress in 1 weekend, driving to work on a normal
map on Monday, or spend half a year trying, before you even dare
to get some cigarettes at the corner store with your car,
hoping not have it pushed back.

Try to find on the forum about people that have a small band
tuned cars;
they found more improvement in 1 hour with a wide band,
as they did end up after half a year testing on a small band,
they wished they went for a wide band from the start.

[devastator]

I'll agree with pluisje in that tuning with a WBO2 is much easier and faster. But, to answer your question:

I assume I could do a 'set-of-the-pants' tune and read my plugs, and make the MS run as well as a carb even without the sensor - is this pretty much the case?

Yes, you can do that. It'll take longer than with an O2 sensor, but it's do-able. Having a good "butt-dyno" can help you when the O2 sensor gives false readings, (like during a backfire). Don't let leaky headers stop you from using an O2 sensor though. Even with the sensor, you may opt to run a little leaner or richer in different places on the AFR table. Just because the O2 sensor shows stoich, certainly doesn't mean your engine should run there.
You might have to post your HEI question in the ignition forum to get an accurate answer
.

Are there clear advantages to letting the MS control the spark? I use MSD 6AL on this car.

I found it very useful since I can't take enough timing out of my dizzy under boost without idling at, almost, TDC. With MS, I can set whatever advance I want at whatever boost level I have. I would recommend, however, that you get your engine running with just fuel first, as it's just 1 less thing to tune. Many Ms'ers use the MSD 6AL without any problems.

[73Eldo]

MS can be set up to not use an O2. I had problems with mine so I just went into megatune and turned it off. Drove the car for 2 weeks with no issues but I already had my tables pretty well set up. If you are really good at tuning or know someone that is you may be able to do it without one. You will for sure need a driver so you can tweak or teach someone how to make the adjustments while you drive. You will also have to have the car somewhere where you can easily and safely get to an area without traffic so you can get the initial drivability dialed in. Then you will need a quiet area you can work on some higher speed stuff without getting in trouble or anyone elses way. With the wideband you can do quick runs with the log on then pull over and make a few tweaks and then go again. It can be hard to tell if you are rich or lean because often the will respond the same. Good thing if you have a co-pilot and a safe area you can just go rich lean by trial and error till you figure out which way you need to go.

Keeping the vac/mechanical HEI is a good thing for starters, just one less thing to worry about. To start with the easy way is just to set up the MS to use the basic 'tach' signal from the - of the coil which is the 'tach' terminal on the HEI cap. There is no polarity or adjustments needed. My car had some noise issues and I did not have any of the electronic parts that were in the manual to try but I did have an extra 4 pin module. You can parallel a second module with the existing one and with a loading resistor use that to drive the MS. Eventually the electronic timing is the way to go. If you can find a dizzy out of an 81 with the 265 it should drop in to your motor. This will have the locked rotor and 7 pin module to make for a neat clean install with MS. You can also lock and index the dizzy yourself and fit a 7 pin.

[devastator]

Hey 73, would it be easier for him to pick up a tach signal from the MSD 6AL?

[73Eldo]

I missed the 6al thing in his post. I assume the A is just the current version of the '6' and the L means it has the limiter? I have 6's but not on my MS project so I have never read much on it. To start with I would think he could use the tach output from the 6 box and setup the MS to work on points. I have not done this or read that it can be done but it does seem like it has come up so a search here or in the manual should tell for sure since the 6's are so popular.

I would think the best way to get timing control would be to set the MS to do direct coil control and set/ wire the 6al to think its connecting to points. The direct coil control of MS should look just like points to the 6 and it can then do its thing. Other than locking the rotor and getting it indexed you wont even need to switch the dizzys since the MS will be the 'module'. Since MS wont be carrying the full load of the coil I would not expect any of the minor issues I have read about using that feature. I have not read that this can be done but from what I have read it should work.

[cody2dog]

Thanks for all the great feedback, all. Of course I was talking about 'seat-of-the-pants' - not sure how a 'set of pants' would apply to tuning
I have a narrow band sensor in each collector, but they always read 'full-lean' after warmup. I don't know if this is caused by aging of the sensors or a leak in the header gasket.

From running scans on OBD-II cars, I've learned that O2 sensors experience a slow toggle between rich and lean when they get old, which is a problem for the OEM ECU. Is this also a problem for MS?

The car is a '67 Firebird. It has a 455 with a Comp Cams XE268, a Q-jet carb, HEI, and Mallory coil. I'm running an 86 Corvette transmission, known as the 4+3. First gear is 2.88, and the tallest overdrive is .6:1. With 3.31 gears it runs at about 2K RPM on the highway, so it's economical there, but lousy in town. That's why I'm building a 400 with a much smaller cam and a little more compression. I plan to do initial tuning of the MS on the 455.

[73Eldo]

Good plan getting it to work on the 455. The built 400 should not be that much different so it should be easy to dial it in. Ya hate to hurt a new motor learning how to tune the system.

[olavxxx]

I would say that tuning without o2, would be more like using a carburettor.
The only reason one would then run MS instead of carbs, would be ignition and control of other units.

However, I would invest in:
LC1 or JAW
Bosch LSU wbo2

Total cost is not that high.
Also I would buy knocksenseMS tuned to your cylinder bore.