Does raising the fuel pressure actually richen up the WOT mixture? Seems simple right? Unless, you are me and you over-think it.....

My logic is: If the BLMs are lean (>128) and then say the car achieves WOT thus locking the BLMs at 128 this will provide a richening effect. going from 140 to 128 means richer? And vice versa.

So, now we raise the FP, what does this accomplish at part throttle? Lowering the BLMs. So when I go into WOT, I start at 110 and go to 128. This would lean the mixture, right?

Please read this carefully as I am not looking for yes/no answers, Thanks

 

With the BLM's locked at 128 that means the computer stops learning or using the sensors to do the fuel calculations, meaning, when in WOT, it uses the base fuel maps and the WOT tables to know how much fuel to put in, it does adjust or care what gets dumped, it just dumps it. I don't know if that makes any sense or not, but basically, when they are locked and your in WOT then the BLM value is worthless.

 

So at WOT, an MAF car becomes like a SD car that is not using any sensors, in the sense that whatever values are in the tables, that is what it uses?

 

Are you speaking MAF or MAP?(If you were speaking MAP disregard the next questions) What about maxing the MAF? Why would I care about maxing the maf if the ecm is just "ignoring" it anyway?

 

You guys didn't read what he said correctly. In WOT there is no BLM learn, not that the ECM doesn't use sensors at WOT. At WOT the ecm resets the BLM to 128 which means there is no adjustment being made to the VE or MAF/LV8 tables. Remember, the BLM is being used with the o2 to try and get 14.7. At WOT, you don't want that. Now to add a twist, I've read that if the BLM is lean (higher than 128), some ECM's will use that value to avoid running lean at WOT. As far as MAF goes, once you max it, the ecm can't calculate from it anymore so it just takes the 255 value and gives it that much fuel plus whatever amount it adds on the RPM @ WOT fuel adder.

 

So a MAF car would still use the sensor to calculate fuel? OK, back to the original question on fuel presure!

 

Going from 140 to 128 BLM means going leaner. Remember, higher than 128 means it's adding fuel and less subtracting fuel. So, raising pressure should drop the BLM down from 140 and also add more fuel at WOT. And yes, the MAF is used at WOT.

 

No, richer. As the BLM drops, the mixture is richer and the ECM pulls fuel away.

 

Glenn, I need your help on this one.

Hector, way to shoot yourself in the foot. j/k

 

For 7730

The ECM uses cylvol, inverse mat, (map-egr partial pressure), and VE to calculate air in grams per cyl.

It also looks up the desired A/F ratio for the given circumstance.

It takes the air in grams per cyl and divides by A/F Ratio to get GRAMS of fuel per cyl then it multiplies this by the injector constant in seconds per gram to get sec per cyl of injector time.

What this means is that the ECM calculates time on. Since there is no correction at WOT then the ECM simply turns on the injector for the calculated time. If the injector flows more fuel per time(because pressure is higher) then the A/F ratio will be richer.

For closed loop operation the ECM scales the time by BLM/128 to get the right pulse width.

HTH

John

 

Glenn, I'm a little confused. If you are at 140 BLM it is because you are lean in that area and the ecm is corecting. Now, you go to open loop and there is no ecm correction, so you are running at 128. Wouldn't this mean you are lean, running at 128 since the desired fuel would be at 140 BLM? Now of course if you are at WOT you are adding fuel through the PE adder which is not shooting for 14.7 but something much lower which of course would mean rich for 14.7, but not actually rich since you are in PE. So if the BLM in the area were higher than 128 and you go WOT and it returns to 128 the PE adder wouldn't be starting from 14.7 and lowering it from there, it would start at a higher AFR and lower the % called for. Which if you are off enough (140/128=~10% lean) you wouldn't get the target AFR you are shooting for at WOT. Is this thinking wrong? I think you thought I meant that going from 140 to 128 BLM during closed loop, not going from 140 to 128 because of WOT kicking in.

 

My comments earlier are universal, for SD and MAF. I've ran both(my car is an 87), when in WOT the car stops adjusting for fuel like it does with the BLM's when out of WOT. It uses the MAF for incoming air up to 255g/sec of course and on a MAP system it uses the KPA to know what to do(get base fuel from). Since it knows your in WOT it takes the base fuel + the WOT fuel or percentage change.

 

Gofaster, just wonderng if you got an answer you can use or if you're still wondering?

 

I guess I have just accepted that WOT and non-WOT are 2 separate entities. Unless you can help..

 

Originally posted by GofasterFirebird:
Yup, that's pretty much it.
Like when at part throttle the required air/fuel ratio is somewhere in the neiborhood of 14.7:1 or so (sometimes leaner), and at high load (ie WOT) the commanded A/F ratio is likely to be 12.x:1 or maybe richer.
WOT Power enrichment is an issue not dealt with when at part throttle.
The O2 sensor is only accurate at 14.7:1 A/F so it can be used to make corrections in the injector pulse width commanded by the PROMs calibration via BLM and Intigrator to fine tune (correct) the A/F to 14.7:1 (or there abouts). When going WOT many conditions such as the amount of air being ingested into the combustion chamber (of course) and the required richer A/F ratio as well as the tables in the PROM that into play at WOT, such as "power enrichment", "pumpshot" and such make part throttle and WOT entirely different worlds.

Since there is no correction for A/F at WOT (BLM and INT) the pulsewidth will remain as commanded by the calibration in the PROM. Increase fuel pressure via an AFPR and the A/F will be richer at WOT. No matter what the BLM and INT values where under previous part throttle conditions, and whether it was correcting for a rich or a lean condition the pulse width is as commanded by the calibration and gets no BLM/INT correction when at WOT.

Also with higher fuel pressure the A/F will be richer at startup before going closed loop. With higher fuel pressure, the A/F will also be richer during throttle transittions at part throttle (such as tip in) even when in closed loop do to the lag time of the O2 sensor and the following BLM and INT corrections.