Discussion in 'Engine Tuning' started by Escortlvr1, Oct 23, 2011.
Re: AFR numbers
my set up doing same thing leans out in 55-70mph
how about this, when i put on my 94 MAF on with my 92 ECU, the fuel lean was so bad it was bucking at 55+ MPH. after i put in the 95 ECU, the bucking stopped, but the idle was really low.
i'm sure it's running a little richer than usual with the 180* thermostat now but if i were to put back the original ECU for the idle, the bucking shouldn't be there, right?
At WOT and at higher RPM all engines are tuned to run rich and an AFR of 11:1 is hardly unusual. The cooling effect of extra fuel evaporating allows for less timing retard and this means more power. The loss of fuel economy is considered a non issue as it only runs rich on the rare occasions when you are demanding full power by stomping the throttle.
At cruising speed at relatively low RPM, best fuel economy (and lowest CO2 emissions) is achieved with lean fuel maps - usually AFR of 15-16+:1. However, stock ECU's almost never map lean (higher than AFR 14.7:1) because:
1) catalytic converters are most efficient at lamda=1
2) catalytic converters wear out faster when AFR is lean
3) NOx output increases dramatically when AFR is lean
U.S. law considers the above factors a higher priority than maximizing fuel economy or reducing CO2 output.
Here's the fuel map you posted:
You're running rich when the engine demands the most power, which is what is supposed to happen, and you're running at AFR = 14.7:1 (lamda = 1) at cruise - which is also what is supposed to happen.
The bottom line is: It 'aint broke - so don't try to fix it.
Re: AFR numbers
Strictly from a fuel economy standpoint you should be running as lean as possible, even above 16:1, although I would be leery about running at 17:1. Just how lean you can go is dependent on so many variables that predicting ahead of time is nearly impossible. If you have the ability to manually tweak the fuel map (as with the Megasquirt) then you can get to the optimum lean AFR by a combination of trial and error and comparing your results with those of other Megasquirt users with the same or similar engines (check out the MSEFI forums).
From a LEGAL standpoint, you should be running a catalytic converter and never running the engine lean. Keep it at 14.7:1 unless the throttle is more than about 40% open or the revs are above about 3,000 rpm, and then run rich as necessary.
Those curves you posted are all theoretical. When you start tuning let me know. These cars run well past the "optimal" air fuel ratio for "maximum power" . Again all that you said is theoretical, based on combustion theory. Based on my tuning what you say is completely incorrect for every car I've tuned. Furthermore, if everyone went by the "if it ain't broke, don't fix it" ideal, we would still be riding around in horse and buggy at best....
The cars run extremely rich based on my wideband readings with my Innovative meter. I provided a clear picture to show this. I have seen a VERY positive response in power by removing fuel at certain RPM's especially WOT where I've seen the A/F in the 10's . Even based on your little windows paint picture there, 12.6 is supposedly optimal, the car is running at 10 or lower, tell me where that's optimal? lol
@Hbar anything richer then 13:1 is for boosting, a N/A motor with a c/r > 10:1 does not need that much fuel for WOT. 11:1 A/F is rich for a boosted car.
I stand by what I posted for these reasons:
1) I did not anywhere in my posts dispute your statement that you are achieving power gains by lowering AFR in areas of the fuel map. If you say it's true for your vehicle(s) then I accept that at face value. If you are telling people it's a good idea to modify their fuel map to achieve HP gain, then I support what you're doing and it seems you've done a lot of work toward that end. I'm just pointing out what I see as a legitimate reason why someone reading your thread may not want to automatically assume their vehicle is running too rich and robbing them of HP because it's running an AFR of 11.0:1.
2) In the specific example you gave, you seem incredulous that Ford would run a fuel map as rich as what you are reading. This neglects to consider that it may be for good reasons other than optimizing power for your particular vehicle. Ford may want to provide a margin of error in rich AFR's to prevent pre-ignition in the many thousands of vehicles on the road as there are natural variations in individual engines from vehicle to vehicle. Also, many people modify their engines in simple ways and in more extensive ways that may make it desirable to run richer AFR's. And engines wear out or develop carbon deposits, sometimes making richer AFR's necessary.
3) Maximum usable power is more than theoretical (as you said). Even at its simplest, with a stock engine in perfect condition, it's a balancing act between spark timing and AFR varying with RPM and load, coupled with changes with ambient conditions and other considerations. Let's assume that by adjusting the AFR at WOT from 12.5:1 - 11.5:1 you lose 4% in HP. But suppose that by doing so this allows you to run a higher spark advance which gains 7% in HP. You gain 3%. Of course, the only way to know if these numbers work in the real world is by tuning and driving under various conditions.
4) The "little windows paint picture there" is straight from the Bosch Automotive Handbook - hardly something to sneer at. But it's inherently just a starting point for modification by experimentation.
Perhaps I was a bit glib in saying "If it aint broke don't fix it" and maybe you took that as an insult and a slam at the purpose of your thread. If so, that wasn't my intent and I apologize if it came across that way. I actually agree with most of what you're saying but I just wanted to provide an opinion that contradicts a specific statement of yours under certain conditions.
Everyone has a right to their opinions.
On your second point, while this may be true on the "play it safe" particular. Even the Mustang maps I've tuned don't roll that rich. The SPI fuel maps are MUCH better than the 1.9 Maps, I'm just appalled at how much fuel is wasted. Hence the post
On your fourth point. I find that funny that Bosch hired a 3rd grader to show the stoich fuel maps rofls.
Just curious, but how are you tuning the fuel maps in your vehicles? Aftermarket chips? Or are you programming with a stnadalone ECU? Or other ways?
Suppose I took your advice and wanted to optimize the fuel curve in my 2nd gen Escort, what would you recommend I do? Assume I already have an Innovate O2 sensor and can datalog).
I use Moates chips, standalones as well. It all depends on what the customer is looking for honestly. I'm not a professional business though, I do it here and there for a little cash 90% of the time. The here and there has been about 2 or 3 cars a week lately though lol. I prefer a standalone like Megasquirt, works real nice since they use a Ford EDIS for the ignition setup anyways. The latest versions auto calibrate to get you a base tune, then you tweak it from there.
If you are going to use moates you will have to get a calibration file from them. Which is not made as of yet for the 1.9 (2.0 has one though) .
The biggest part of the curve issue is not the ramp up, actually that ramp up is almost perfect (a little lean out of the gate). The part you need to control is the WOT fuel. If you are using moates you can trim it back with the WOT fuel multiplier or go to the base table and adjust the AFR based on RPM, Megasquirt you just adjust the AFR based on RPM as it really doesn't have a WOT fuel algorithm, just timing from what I've come across...
The other kicker on the stock Ford tune that really hasn't been resolved is the "Tip-in timing retard" , basically the factory computer pulls the crap out of timing when you shift to save on the transmission. It's much worse in an automatic than a manual. The best thing about Megasquirt is that algorithm is not there
Hey, thank's for that useful info.
I've run the Megasquirt on my '78 Mercedes using the EDIS-8 and I'm really considering setting it up on my 87 Escort. I'll probably start with the fuel map first to get it running and then switch spark control over to the EDIS.
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