gasahol afr, startup afr, decel afr

[flatbill]

After getting going and some successes at tuning, I recalled a chart in the literature, somewhere, that stated that 14.7 was the right afr for gasoline and 4.2 was a correct afr for 10% gasahol. The 10% is all you can get around here so I plan to redo the required fuel with this 14.2 afr. Is there anything I should know before doing this?

When I start up the afr is very rich. Was around 9! I have backed off on the SUE and it is getting better, but I think I need to go more. On start up it runs rough till the afr goes leaner.

On decel with fairly low rpm ( 750-850 ) and low map the afr goes rich (10.5-11.5 ). I have tried to lean out the VE table in these lower map bins with some success. Is this the way to go on this? I redid the map bins so I had bins in the very low map areas so I could tune there. On decell my map can drop into the 18 area.

Thanks, Bill

MSII, V3, 2.891, 335 inch Desoto motor, 350 Chevy TBI, 55 pound injectors, Innovate WBO2

[flatbill]

More info. I did the VE tune at idle ( to minimize map ) and any leaner than about 13.5 and it doesn't like it. Starts to miss and run rough. My pwm is around 1.4 at idle. I think I have the injectors set to 2 squirts simultaneous. I was wondering if I should drop down to a lower pound/hr injector set to get the pwm up a little at idle. Thanks, Bill

[flatbill]

I meant 4 squirts. Bill

[flatbill]

I find that no matter what I do to the VE table My AFR goes really rich to around 11 to 12 when I am decellerating. Once the deceleration is over, the AFR leans out to a more reasonable number. This includes backing off to come to stop and while letting off the gas going down a hill. While running around today in Automatic Mix Control, I saw that the injector pulse width was running around 1.1 to 1.2 on decel when the mix was rich. This seems really short and still gives a rich mix. I have a 350 Chevy throttle body injector with 2 injectors that are supposed to be 55 pound injectors. I am running 4 squirts simultaneous. The throttle body regulator keeps the fuel pressure at 12 pound, which is right where it should be. The required fuel is 8.4 I think. All this makes me think I need smaller injectors. I could easily install 4.3 injectors that have a 45 pound rating, I think. I assume that I would then have to do the required fuel again and retune.

Would it help with the current injectors to go to fewer or more squirts and/or alternating squirts, and do the required fuel again?

This is a 330 inch Desoto motor with 9.0 to 1 compressiion a very mild cam and tri-Y headers and a manual transmission. I use a locked down Mopar electronic fuel injection distributor and an MSD 6A box. I am controlling fuel and spark with Megasquirt-II V-3, 2.891.

[drmiller100]

You can turn the fuel off on decel if RPM is above a certain level.

If Matt says otherwise, Matt is correct and I am wrong.

[flatbill]

I could be wrong on this, but I have an idea that I'm getting oil down the intake valve guides at high vacuum. This may be causing the O2 sensor to see what it thinks is a rich condition. I find that if I open the throttle even a very small amount it goes not-so-rich. I am in the process of pulling the heads to redo the intake guides and add good seals. Does anyone have an opinion on the added oil showing up as a rich afr? Thanks, Bill

[R100RT-2]

Thought I'd offer an opinion, and hopefully your situation isn't this.
On my motorbike install, wall wetting/ puddling seemed to be a major factor in creating similar symptoms to yours, excessive rich decel readings followed by lean readings as throttle position is brought back on - both somewhat short term but of varrying times depending on speeds and loads.
When X tau corrections started to make sense and I tried them, that brought the corrective behaviour I was looking for, but perhaps due to my particular arrangement (injectors far upstream to inlet ports etc.) the corrrections began to take on a level of complexity that rivaled everything else. I have since created a "close to inlet valve" bung and 2nd set of injectors which takes care of all AFR unstability issues 100% (with the exception of not being as eager to cold start).
Perhaps if that is a contributing factor it might save you some time through X tau corrections.

[drmiller100]

r100 sure seems to make sense.
what kind of manifold are you using bill?

does it have cross over heat?

[flatbill]

My setup is decidedly old tech. I have an original '56 Desoto cast iron 4 bbl intake. It does have exhaust heat, although there is no heat riser valve to force the exhaust through the intake. I have a somewhat bulky aluminum adapter to go from the 2 bbl throttle body to the 4 bbl inlet.

Right now I have the heads at the machine shop getting new intake valve guides and the best stem seals we can find. This is a low rpm motor and runs on the highway at about 1900 rpm in overdrive. I think the decel fuel cutback is only good above 1500 or 1200 rpm.

I should have the heads back early next week and hopefully will see an improvement. The intake ports were pretty wet with oil and the intake valves had heavy, for the amount of miles run, oil deposits on the back side.

Thanks for all the input. Billk

[drmiller100]

cast iron does not transfer heat like a more modern aluminum one.

and with the low RPM, your air velocity is going to be pretty slow.

Where does the engine get its air for the engine? If you are not worried about power, you could try using some warm air off the back of the radiator or off the tops of the exhaust manifolds to get warmer air going down the TB.

The idea would be warmer air would have less pooling of fuel in the intake manifold.

Also true is alcohol requires 3 times the amount of heat to vaporize as does traditional gasoline. so the gasohol is going to be "worse" then straight gasoline.

[flatbill]

I'm going back together with it now. I will check to see what my intake air temp is and try to get some readings of what the intake manifold temp is. I hope that I've got the oiling problem solved and can go on to better tuning. Thanks, Billk