Fuel mapping strategy

[pwschuh]

In addition to the basic fuel map (with RPM on one axis and % throttle opening on the other?), does MS (or Motronic or whatever) also use a main 'fueling factor'? The one I am familiar with is a Mbit/sec factor on a main Start screen.

Obviously there are several degrees of freedom in general EMS tuning and changes in the basic map can compensate for an entry in the main factor that is not ideal. What I'm wondering is it best to shoot for a main fueling factor that is either low, medium, or high as a foundation from which to start refining the basic map?

In other words, if your main factor goes from 20 to 80, you could set it at 30 and then increase the values across the map to tune, or you could set it at 65 and decrease the map values throughout the range and generally end up with the same result. N'est pas?

Thanks.

[Alex Buchka]

I'm only familiar with a few different EMS systems. Megasquirt for example is a VE map based system so the fuel map has rpm vs manifold pressure (load), and VE expressed in percent on the z axis. This VE percentage is scaled with what is referred to as the required fuel number (fueling factor if you will). The Req Fuel is calculated based on displacement, number of injectors, an "ideal" lambda value, and some other factors.

I know John G (the apserator) has a Req Fuel value of around 4 when it should ideally be more like 8-10. John doesn't run astronomical amounts of boost so this gains him more headroom on the VE map. John can say more specifically but I'm fairly certain his VE values regularly exceed 200 on the map, because the Req Fuel is set so low.

[blkaplan]

with ms the req fuel number is supposed to affect the injector resolution, i can't remember off hand which way it goes. Its either a high req fuel gives better resolution or a lower give better.

[fryea]

low req fuel gives better resolution within the VE map

however

the difference between a VE of 171 and 172 cannot be quantified to the injectors if your running MS1, as the injectors can only be dialed down to .1 milliseconds. So the additional VE table resolution is not taken full advantage of unless you either upgrade to the Hi Res code or MSII.

[The Aspirator]

I'm running the high res code, so at the same time I changed my req fuel from the normal 8 down to 3.6. I also bumped up all my VE table values to basically double what they were before. The car drives the same as far as I can tell, but theoretically Paul you're right, the injectors will get a higher resolution signal. Before my fuel map used to spread from 40-160 ve with a req fuel of 7, now it spreads from 86-254 ve (ms maxes out the map at 255 ve, so if I need more fuel eventually I'll have to screw with my reqfuel even more).

What system are you running on your car? Is the tuning going well?

John

[pwschuh]

John,

I'm running an OMEX 710 EMS. Like everything else I do, tuning is proceeding at the speed of Dutch Elm disease. I have a good warm idle of about 800 RPM and 14.0 on the A/F gauge. I can rev in neutral and at steady RPM's up to about 4,500 I get good A/F ratios (11.9 - 13.5). However, I can't open the throttle at a normal rate yet. I can open very slowly and it's OK, or I can blip it very quickly and get the rev's up. But if I simply open it at a normal steady rate, it misfires and seems to go lean. I would assume this is a problem to be addressed by the transient accel enrichment table, but I haven't figured out how that works yet.

I am doing N/A tuning for the moment and 4 open TB's really scream nicely at 4500 RPM. :kitty:

[Karl Buchka]

John,

I'm running an OMEX 710 EMS. Like everything else I do, tuning is proceeding at the speed of Dutch Elm disease. I have a good warm idle of about 800 RPM and 14.0 on the A/F gauge. I can rev in neutral and at steady RPM's up to about 4,500 I get good A/F ratios (11.9 - 13.5). However, I can't open the throttle at a normal rate yet. I can open very slowly and it's OK, or I can blip it very quickly and get the rev's up. But if I simply open it at a normal steady rate, it misfires and seems to go lean. I would assume this is a problem to be addressed by the transient accel enrichment table, but I haven't figured out how that works yet.

I am doing N/A tuning for the moment and 4 open TB's really scream nicely at 4500 RPM. :kitty:

As soon as you crack open the throttle any faster than at a snail's pace, it's probably making your MAP values take a complete ****, putting you in an untuned part of the map.

[BabyBlue240]

John,

I'm running an OMEX 710 EMS. Like everything else I do, tuning is proceeding at the speed of Dutch Elm disease. I have a good warm idle of about 800 RPM and 14.0 on the A/F gauge. I can rev in neutral and at steady RPM's up to about 4,500 I get good A/F ratios (11.9 - 13.5). However, I can't open the throttle at a normal rate yet. I can open very slowly and it's OK, or I can blip it very quickly and get the rev's up. But if I simply open it at a normal steady rate, it misfires and seems to go lean. I would assume this is a problem to be addressed by the transient accel enrichment table, but I haven't figured out how that works yet.

I am doing N/A tuning for the moment and 4 open TB's really scream nicely at 4500 RPM. :kitty:

Richen up the area straight above your idle area. When you get on the gas as you start moving from a stop, your MAP goes almost straigt up a bit before the RPMs really start to increase. accel enrichments will help this too, but it should be somewhere close before you start messing with that.

[pwschuh]

Richen up the area straight above your idle area. When you get on the gas as you start moving from a stop, your MAP goes almost straigt up a bit before the RPMs really start to increase. accel enrichments will help this too, but it should be somewhere close before you start messing with that.

Hmm.. I will pay a little closer attention to how far up the axis the throttle opening goes before the RPM moves into the next cell.

I need to get the plenum back on anyway and start adjusting these values under conditions closer to operating conditions.

[The Aspirator]

Yup, just like the other guys said. And if accel enrichments are tuned poorly or non-existent, the car will go lean and fall flat on its face when you tap the gas too hard.

I've never heard of OMEX, but looking at their website it seems pretty cool.

John