Part throttle A/F question for you tuners out there.

[ALA G8R]

I am currently running a 2.76 pulley with the other mods in my sig.

I recently installed a WBC and have been using its software to datalog A/F. I am noticing that at partial throttle (even with considerable boost) the PCM strives to keep the A/F at stoich. Only when the throttle position approaches WOT does the A/F drop to 11.5:1ish. I have experienced the same behavior with a custom Predator tune and a custom SCT tune.

It seems to me that there should be better control over the part throttle A/F ratios of these engines, especially when pullied. If the engine is seeing 5lbs of boost, the A/F should be starting to drop to say 12.5:1. When the engine is seeing 10+ psi, the A/F should be below 12:1. This should happen regardles of throttle position. Seems to me that A/F should be more a function of MAF, RPM, and MAP, ie load.

Can one of you experienced tuners come in here and explain what parameters go into commanding a certain A/F for varying part throttle load conditions?

Your expertise is greatly appreciated.

 

[MikeW]

Bump

I have a DJWBC and would like to know too.

I have added 11% fuel to my amazon tune down low an still see mid-high 12's, nice 11.7's up top. I'd like a litte more "tip-in" fuel down low just to be safe.

ALAG8R can I PM you a log to look at so we can compare DJWBC logs?

 

[ALA G8R]

No problemo. I sent you a PM. In addition to A/F, I also hooked up TPS and MAF inputs to the WBC.

 

[MikeW]

Humm I have TPS AF and RPM.. How did ya hook into MAF? I like the sound of that..

 

[ALA G8R]

Analog channel 2 input on the WBC. I'll provide more detail when I get home 2nite.

 

[LargeOrangeFont]

The reason the car is still trying to run stoich is because the car is still in closed loop fueling at lower load sites during partial throttle. This is a problem in almost all forced induction cars.

Below a certain RPM, below a certain % TPS, or below a certain load site the car will stay in closed loop fueling, and therefore the car will always try to run 14.7:1 AFR or so. This is not a good thing under boost. The temporary solution is to either let out of it to fall off of boost, or give it more gas to get it into open loop mode.

I plan on getting some logging software soon to find out the exact point at which the ECU switches from open loop to closed loop fueling. I have extensive experience w\ this problem in turbocharged subaru applications, And know how to fix it, but it is a question if there is a tool out there that allows this issue to be resolved.

The problem is when you up the boost and get a "tune", you are only tuning open loop values (higher load sites, higher TPS values) with the majority of the popular tuners on the market.. I can't tell you exactly what you can do from a tuning perspective at this time to solve this problem. I can't even tell you what software will solve the problem yet, as I haven't finished my research of all the available options for mustangs.

I think this is a key issue because This can be a problem that lends to engine failure, as these cars dont have any sort of knock sensor. I am fearing that part throttle high boost conditions such as these may not be being corrected by the ECU, because it dose not see knock.
I plan on doing some datalogs very soon to get some more information for you guys.


Ashley

 

[MikeW]

Nice! thanks LargeOrange

I have noticed that my a/f really starts to drop at 75% TPS. Adding fuel via predator makes minimal difference. 11% in the predator resulted in about a 5% change (down low)

 

[LargeOrangeFont]

Most cars I have tuned work like this (I'm assuming the mustang works in a similar fashion as it is OBDII).

The ECU in closed loop will adjust the fueling into a preset window, say from 14:1 to 15:1 for instance.

The ECU also has a fuel trim window, Lets say that is +\- 25%.

Lets create a random example to illustrate how this works.

So you are crusing up a hill, 35% throttle, closed loop fueling, 2500 RPM and you AFR is 14.5:1 , you are making 5 lbs of boost. You want to richen the car up a bit. Plug in the predator (or whatever else you may use) add 5% fuel and try driving up the same hill again. Your AFR drops to 14.2:1 ?? You are confused as to why the car didn't richen up more. You add another 5% and you drop to 14.0:1. You have now added 10% fuel and have dropped half a point. You add another 5% fuel and the AFR stays at 14.0:1. You get upset and frustrated. Why?

Heres why. In closed loop the car has a target AFR range (Some cares even pinpoint this to a target AFR w\ little to no range). Remember our hypothetical range is 14:1-15:1. You added in total 15% fuel at this particular load site. The cars fuel trim (+\- 25%) is active in closed loop only, and cut out almost all of that extra fuel. If you were to add more fuel, you would eventually max out the fuel trim, and you would get a check engine light.

In open loop fueling, the car does not have a target AFR. The car relies on the maps programmed into the computer to run, and is only really governed timing system (off of IAT I believe, please correct me if I am incorrect) which will retard timing if it sees a problem, and possibly richen the car up as well.

This is why cars come rich from the factory. The factory needs to account for the worst possible scenario, and as a safeguard makes the cars a bit rich to cope w\ different adverse conditions the car may be exposed to. Of course, the car also learns you driving habits and will "tailor" its program more agressive or conservative according to you driving style.

You get more visible and dramatic results form adding 5% of fuel when doing all out power tuning. Because you are in open loop fueling, you do have total control of that portion of the map. Your car may be great on the dyno, but suck on the street. It may seem fine on the street, but detonating itself to death, or running lean under part throttle. I believe that these other driveability issues need to be looked at as well when tuning. A good road tune and\or datalog on a LOADING dyno (not a dynojet) is also necessary when tuning for a proper tune unless you drive WOT everywhere you go.

This may be a reason so many people have blown up there cars. Some fail to understand the improtance of tuning. By tuning I mean actual tuning, not trading maps over the internet, or downloading maps from some tuner.

A possible solution here is a tuning program that would allow you to CHANGE the crossover point from closed to open loop fueling. This would give you full control over the cars entire powerband (or however much you wanted to control), and you would be able to add necessary fuel to richen up those part throttle positive boost conditions.

:beer:

Ashley

 

[ralphy1798]

I noticed on my L that as soon as i got into boost, part throttle or anything, i noticed the A/F drop to 11.7:1 or so. My Cobra does not do the same thing, it does what it described in this thread.

I cant imagine Ford sending all of these cars out with the A/F at 14:1 at partial boost...

how is it possible on the L and not the cobra to drop the A/F?

Another thing... i dont ever hear pinging at partial throttle, 14.7:1, and any amount of boost.

Jeff

 

[mlambert]

Maybe one of those little black boxes for imports made to adjust TPS crossover percentage from CL to OL? If someone knows what the crossover is triggered by, besides TPS, that might be an adjustable value as well.

Would be best to have a nice high resolution load map that you could tune that was independant of throttle position. I have absolutely no idea what these cars have in their ecu though.

 

[mlambert]

I noticed on my L that as soon as i got into boost, part throttle or anything, i noticed the A/F drop to 11.7:1 or so. My Cobra does not do the same thing, it does what it described in this thread.

I cant imagine Ford sending all of these cars out with the A/F at 14:1 at partial boost...

how is it possible on the L and not the cobra to drop the A/F?

Another thing... i dont ever hear pinging at partial throttle, 14.7:1, and any amount of boost.

Jeff

If the L ecu does that then thats a really good thing. I have no means of datalogging yet so I'll just have to take your word for it.

The reason it would do it though is open loop fueling tables based on something like MAP. If it does a MAP value of > X it jumps to into open loop and fuel/timing is set by a static value for that amount of load. This is how it should be, but isn't for most forced induction cars.

 

[LargeOrangeFont]

I noticed on my L that as soon as i got into boost, part throttle or anything, i noticed the A/F drop to 11.7:1 or so. My Cobra does not do the same thing, it does what it described in this thread.

I cant imagine Ford sending all of these cars out with the A/F at 14:1 at partial boost...


Another thing... i dont ever hear pinging at partial throttle, 14.7:1, and any amount of boost.

Jeff

Well this wouldn't be as big of a problem @ stock boost levels, but you would be suprised and how bad some forced induction cars knock form the factory....



This may not even be an issue, mabye the car isnt knocking in part throttle high boost conditions?? This is just food for thought, and stuff to be aware of. I don't know enough yet to make a judgement call that something wrong, but at this time it dosen't seem correct.

Ashley

 

[ALA G8R]

I got a pretty darn good reason for the part throttle A/F response from Jerry@SCT over at ModularFords.com.

This is interpretation of what he said.

At partial throttle the PCM strives to keep A/F at stoich thus optimizing fuel economy. At the same time the PCM pulls timing, based on RPM and load, to keep the engine from knocking.

When you want more power, go past the WOT throttle position and the PCM commands the open loop A/F to maximize power. At the same time timing is advanced to maximize power, but not enough to cause knock.

Makes pretty good sense to me. I never have experienced audible knock at part throttle, under load.

 

[LargeOrangeFont]

I got a pretty darn good reason for the part throttle A/F response from Jerry@SCT over at ModularFords.com.

This is interpretation of what he said.

At partial throttle the PCM strives to keep A/F at stoich thus optimizing fuel economy. At the same time the PCM pulls timing, based on RPM and load, to keep the engine from knocking.

When you want more power, go past the WOT throttle position and the PCM commands the open loop A/F to maximize power. At the same time timing is advanced to maximize power, but not enough to cause knock.

Makes pretty good sense to me. I never have experienced audible knock at part throttle, under load.

If that is true that would be awesome. Anyone have logs proving this?
These cars make so much noise it may be difficult if impossible to hear knock.

My car is stock, but I will do some pulls using the knock sensor on my WB02. It has a headphone jack so it is very easy to hear if indeed there is any knock.

Has anyone done logs to see what the timing actually is during these conditions??

Ashley

 

[JB]

If that is true that would be awesome. Anyone have logs proving this?

if J says its true, then it is....

 

[LargeOrangeFont]

if J says its true, then it is....

Can we get him on here to talk about it?

 

[ralphy1798]

AHHH, this is true, i forgot...

I remember using my predator to look at timing and as soon as any boost is heard, timing is pulled. :beer:

 

[badboy]

Great thread. I think we really need to understand what is going on with our cars so we can safely make the changes we want to make. I'd like to hear more.

 

[Black2003Cobra]

I agree. ALA G8R and LargeOrange - great and informative thread. This should go in the tech section, IMO.

 

[jimh]

You can tune the EECs to switch to open loop at whatever TPS or load you want. With a pulley I'd have it go open loop between 1/2 and 3/4 throttle.

Also remember, at part throttle the load is not that heavy on the motor. Yes, you are under boost but the load is not as high as at full throttle with the same boost. If you stay at part throttle boost usually drops very quickly. Plus the pcm can pull timing.

.02
jim