Does load affect your final A/F?

Which would mean in 1st you would have a different A/F then you would have in 3rd.

Does temperature affect A/F?

During the summer you would be a lot richer than in the winter.


Ever since I got this Wideband Commander the results have been driving me crazy. My tunes seem to have gotten richer the hotter it gets. And I have had this problem with leaning out in the upper RPM that I can't solve. It is real bad in 1st gear, I have hit 15:1 before in 1st and as high as 13:1 in 3rd. The truck feels slower, I guess mainly from the heat and rich A/F. I'm afraid to lean it out cause the upper RPM's will just lean out worse. Its not the gauge because the same thing happend on a wideband dyno run.

What are some of the things I could of overlooked that sould cause my truck to lean out.

Thanks,
Mike

 

Mike the easy and obvious first place would be Fuel Filter and Injectors. If the filter is more than a few K old I would change it. You may want to try some good Injector Cleaner too.

Of course there's always the dreaded fuel line fell off one of the fuel pumps in the gas tank nightmare.

I saw those charts of yours and I would be concerned too ???
but since we never get to see those numbers (A/F in 1st, and 2nd gear) I personally don't know if it's normal to be that lean ???
But def something I'd want to check out.

Please do let us know how it goes......

 

This morning, I ordered one the same Wideband Commanders you're using. That probably means my life is going to become as miserable as yours while we figure out what's going on. Without talking to someone who really knows the ECU programming, we may figure it out or we may just get more frustrated.

I remember when I thought computerized fuel injection was going to fix the problems we had with carburetors.......But, from my limited knowledge of engine management, I'll give you my guesses on your questions.

Does load affect your A/F ratio? That's one to think about. Under heavy load, you'd have a greater throttle opening with the same RPM than no load. As such, the ECU should retard the timing a bit, but the Mass Airflow Sensor should also be telling the ECU exactly how much air is going into the engine. The pulse width on the injectors should then match for the correct ratio. Heavy load should increase the cylinder filling because the throttle is open and the RPMs are down because of the load. But, at the same time, the heat generated on each stroke is much greater than under low load. So if the chamber, piston, valves and cylinder walls are hotter, they are going to change the atomization of the fuel and more importantly, there will be greater reversion of hot exhaust gases because of the greater pressure in the exhaust system coupled with the effective overlap period of the camshaft being longer, again because of the lower rpm. I'm guessing that exhaust reversion is the primary culprit, because while the MAF measures what's coming in the intake, there's nothing to measure what's coming back from the exhaust. The first set of O-2 sensors should read lean and alert the computer, but the OEM O-2 sensors are probably too slow to respond. Very fast Bosch sensor are available, but they are priced to match at well over a grand each.

Your second question was about temperature and A/F ration. As you know, air density changes rapidly as the temp goes up. Again, the MAF is supposed to sense it and have the ECU compensate accordingly. The real question is, does the ECU use the input from the temp sensor below the blower to modify the progam based on the actual air density being seen at the cylinders? I doubt it. I'd suspect that all that lower sensor does is pull timing as the temp goes up.

The factory ECU is a pretty sophisticated device for the price, but it is nowhere near something like a Motec sytem. I'm curious enough to call the local Motec rep and see if they can provide an interface-able unit for the Lightning. All their systems I've seen use several additional sensors and usually replace the entire system from sensors to harness to ECU. That does a real good job of eating about 10 grand for a basic sytem. Probably not what we're looking for. Is there anyone in the group who knows the Ford ECU progamming in detail?

 

I bet Sal @ PSP is one of the best on this board. I hope he chimes in on some of the questions.


I used my race tune last night, a tune that I got from Sal back in February. On the dyno, the tune was pretty much flat 11.5:1 across the board in 3 rd gear. Well last night in 88 degrees with 100% humidity it was max rich (<10:1) all the way through 2nd and 3rd gear. So I'm guessing the heat had to be what caused the tune to get so rich, nothing else has been changed. Is that what people mean with summer and winter tunes meaning the A/F is corrected for the temperature?

 

This is basically what Rob alluded to in his post,


What variables affect A/F?

From my understanding, and I am NO expert, I would say the main thing that affects the A/F ratio is the fuel delivery system. To maintain an ideal A/F ratio the volume of fuel must increase in direct proportion to the volume of air.

Therefore if you accept that you’re MAF, Mass Air Flow sensor is working correctly and measuring the air molecules flowing past it then the fuel delivery system must work correctly or you could have a lean condition.

A few things to consider with the fuel delivery system are first the obvious which is the fuel filter. Then of course is the fuel pressure up to par and is it constant or spiking (possible bad fuel pump) an important note is a fuel pump can test fine on a bench test but not perform under real world conditions and loads, are the fuel injectors firing properly as in the correct pulse duration (how long the fuel injector stays open delivering fuel), are the fuel injectors correctly sized so your not operating at 100% duty cycle (the time required for one injector pulse divided by the time available) if you have the wrong injector size for a specific application you could run into that problem. Usually if you run into a problem with being at 100% duty cycle or fuel pressure is a problem it should show on a graph as a flat line that does not move up as engine RPM’S increase or in other words you are delivering the max amount of fuel possible and regardless what any sensors tell the computer you are not going to get more fuel. In that case if you continue to pump more air into the motor it will continue to get lean since the ratio of air is going up and the ratio of fuel is at a constant, or stand still.

You get to a point because of the size of an injector that you can only deliver so much fuel per engine revolution or fuel injector pulse duration.

Since the computer is calibrated to the injector size it knows how long to keep it open (pulsed) for a given amount of fuel to be delivered (determined by tables in the computer program). Therefore if you have dirty or clogged injectors the computer will not know that and deliver less fuel then it thinks it did and that can affect A/F.

So my opinion is if there was a concern about A/F and you feel the program is fine then insure the fuel filter is good and that the injectors are clean. That is the two easiest things that could be done.

There are of course many other things that can affect A/F with other sensors but the most important, in my un-expert opinion, is knowing that the fuel delivery system is in good working order and working properly before looking into other possibilities.

 

01 XLT Sport is correct. I got into looking at potential problems in the design of the fuel system - which would mean any of us who made the same mods would have the same problems.

If the problem is specific to Sharpshooter's truck, the first place to look is at the fuel supply system. I'd think that injector sizing would only come into play at higher RPM, but if they are marginally small, they may not provide enough at high load, low RPM wide open throttle.