PCM Equivalent of Carb Accelerator Pump ?

[final5-0]

I found some old stuff digging around in my tuning notes that I threw up on my site and I thought I'd just paste it here too ... BECAUSE ......

:SNSign: peeps are more than Worthy

Here it is

LEAN SPIKE at throttle transition from Cruise to WOT

A problem I had for quite some time was I had a nasty lean spike that at times, would go as high as 18.0 to 1.0 when I would mat the skinny pedal from a cruise driving condition.

Back in the old school days when we had carbs, you had an adjustment you could make to the accelerator pumb to give a larger squirt of fuel to take care of any lean problems like we speak about here.

Over time, I found the same thing in the pcm values as the old carb accelerator pump.

It is a Scalar called manifold_volume. This Scalar is used to describe the size or volume of the upper intake plenum. The stock value is 5.5 liters.

For my combo, the fix was to change that value to 3.0

I have a screen shot of data that shows two datalogs in comparison mode. The 2646 log is the baseline data and the 4448 log is the result of the Scalar change.

The driving conditions of both logs were 3rd gear cruise at about 1500 rpm when I would go to WOT to about 4K rpm.

Not much need to explain anything as you can clearly see the lean spike is gone in the newer log.

Notice the drop in ratio around the start of data events 17 and above. That is the break point in the maf transfer of Close Loop and Open Loop conditions.

Grady

 

[bimmertech]

good stuff as always Grady.

i guess my tech input here would be what is the ecu using to determine the transfer? is it basing it soley off of tps, or a combo. i bet this is of extreme importance on a kenne bell car.

 

[final5-0]

good stuff as always Grady.

i guess my tech input here would be what is the ecu using to determine the transfer? is it basing it soley off of tps, or a combo. i bet this is of extreme importance on a kenne bell car.

When you use the word "transfer", I'm guessing your talking about the moment you go from an almost closed throttle to wot.

Is that correct?

Grady

 

[CManT1914]

Great info Grady! Now if only I had a wideband to see what my A/F ratio really is. I think I'm running lean up top since I never installed a bigger fuel pump.

 

[bimmertech]

When you use the word "transfer", I'm guessing your talking about the moment you go from an almost closed throttle to wot.

Is that correct?

Grady

yeah

 

[Starman]

I always had the problem of it going super rich for a split second when mashing the gas.

Although I use a SpeeBrain, there is a table called "Transitional Fuel Inrichment (Accelerator Pump)" and the table has "Throttle Rate (deg/sec)" and goes from 0-5000 and has "Fuel Multiplier" that goes from 1.00-2.00.

Does the EEC have any similar tables??

 

[final5-0]

bimmertech

A couple of things that come to mind right off the bat that tells the pcm you went wot is

1) tps sensor for sure
2) load factor

At some point in time while the above two things are happening, you go from Closed Loop to Open Loop.

The O2's exit stage right to allow the Fuel/Spark tables to be the main act of the WOT show.

I bring up all that stuff to let you know this bit of info.

I played with that dadgum fuel table until I was blue in the face but that nasty lean spike continued to give me the finger

I'm not gonna admit to how long it took me to figure out the fix

but

I did have the last laugh

Grady

 

[final5-0]

I always had the problem of it going super rich for a split second when mashing the gas.

Although I use a SpeeBrain, there is a table called "Transitional Fuel Inrichment (Accelerator Pump)" and the table has "Throttle Rate (deg/sec)" and goes from 0-5000 and has "Fuel Multiplier" that goes from 1.00-2.00.

Does the EEC have any similar tables??

My knowledge of this stuff is limited to a perspective of how the EEC Tuner and Tweecer present everything. Very narrow for sure, lol.

I suspect Tweecer, EEC Tuner, SpeedBrain and others have their own names for the values in the pcm. Don't you think so?

After all, they all use the same programming Ford put in the pcm.

I don't recall anything that looks like what you describe in the things I've seen with the Tweecer. Then again, there is so much in there that I don't know about, so I don't hose around with it, lol.

Grady

 

[Don 95Vert]

The TPS is the sole sensor that tells the EEC you are at WOT - on a stock T4M0 it's at 642 AD counts or the equivalent of 3.133 volts. On a Kenne Bell car this really should be modified.

Newer processors and some of the older Fox bodies have a accel pump function, but not SN95's -Grady has discovered a little trick that us tuners use to fix the lean spike on rare occasions - but you have to be very careful using it - sometimes bad things might happen. Usually if the MAF transfer function is dead nuts on, you won't get it at all. Pro-Ms especially give this lean spike if they are even a little off.

Don

 

[xkuntrycowboyx]

reveiw of what was said?

soo again for me.... if you have no tweecer or the sort, how might you cure this prob?? Im deff having it.
my temp solve was unpluggin the AIT which overfuels the car (appearently- deff runs rich at idle, and starvation when smashin it is noticably less)

would like to solve this prob correctly.

my sig has most of my mods. need any info plz holler at me. really need help here plz!

 

[final5-0]

soo again for me.... if you have no tweecer or the sort, how might you cure this prob?? Im deff having it.
my temp solve was unpluggin the AIT which overfuels the car (appearently- deff runs rich at idle, and starvation when smashin it is noticably less)

would like to solve this prob correctly.

my sig has most of my mods. need any info plz holler at me. really need help here plz!

Is this lag in power something that has just started to happen?

With no tuner or chip, you are left with mechanical adjustments only for tuning options. Twist the dizzy for spark & play with fuel pressure for fuel.

Do you think the fuel filter may be clogged?

What about the condition of the cats?

Maybe your hb has slipped a bit and your spark value is less that you think.

You basically have the same combo as a Cobra with the addition of a larger tb and pulleys but running smaller inj's.

I see you got a larger in tank pump which is good.

I see the K&N and that will lean things out a bit.

Do you have an afpr and if so ... have you tried upping the pressure?

Then again ... What makes you think you are too lean?

Grady

 

[xkuntrycowboyx]

Bought the car with this prob. (been about 1.5-2 yrs)
had 93K now has 102k

Cats Cond. .. dunno, or how to check
No AFPR ... how much would that run me?

trying to solve, i started with
Set timing base 10* ..moved to 11*
Runnin Premium (also had a bit of a ping, less after timing change, and less after premium)
Change Fuel Filter
Change Fuel Pump (thought old may be failing)
Run Fuel cleaner with gas
Changed Cap n' Rotor
new Wires n' Plugs
Cleaned filter
Cleaned Maf (helpd some)
Replaced AIT

Concluded it was lean after none of these worked and when upluggin AIT and runnin it runs allot! better, but still not properly, cuz obviously AIT should remain plugged in. and it only runs better that way for about 5 min, then returns to how it was.

Also... thoughts were to solve problem before adding chip or tuner, (can't afford right now) and would rather have it running properly before adding those, if that makes sense.

 

[OrangeMustangGt]

possibly when you unplug the IAT, your throwing the computer into "limp" mode...which richens it up?

That, or take the rag out of your intake