Basic newb question about stock fuel map
 

I know the injector duty cycle is governed by rpms...the higher the rpms, the higher the duty cycle. But my question is...I guess the simplest way to say it is, does the ECU know the difference between when I am and am not making boost?

Example: I take the car to 7K rpm @ WOT, making full boost, vs. I take the car to 7K rpm w/ light throttle so I stay in vaccum/at 0psi the whole time (yes, it can be done). Does the ECU see these two things as different, and thus assign diff amounts of fuel for the two scenarios? Or is the fuel purely based on rpms, and is tuned accordingly for max boost only, so in the latter example, the ECU would pump out enough fuel in the engine to handle say, the stock 10 psi, even though I'm not making any boost? (ie run hella rich)?

While I know in the latter example, I said increasing the throttle lightly, again, to my understanding injector duty cycle is rpm-specific, so I'm not quite sure how much of a role the actual throttle makes in such a case (since easing onto the throttle keeps you out of boost, vs getting on it makes boost).

Thanks
~Ramy

PS: My disclaimer's in the title lol. It's a newb question, I know ;)

If Im not mistaken the ecu does know the levels of boost the car is seeing. Hence the MAP sensor. But I am not positive on this.

Ha, I also think its funny that you are asking a "newb" question with your post count so high. I have also read much material you have posted which has helped my knowldge of this car. I guess it just shows that there is always more to know.

yes, the ecu uses map vs. rpm vs. tps for it's fuelling scheme, but i also believe it is in open loop past 3400rpm (correct me if i'm wrong)

timing should be the same as well (timing advance should drop and ramp back up slowly WOT but remain pretty high under light load for emissions/fuel economy)

a lot of people bitch about the hesitation near 3000rpm when you're near the vac to boost crossover, my honest opinion is it's a matter of a sloppy programmed ecu map that coulda been fixed with a factory reflash

From the FSM page F-94:

"The total fuel injection amount is determined by engine speed, intake manifold pressure, intake air temperature and atmospheric pressure".

also,
"When the engine speed is above 2750rpm and the total fuel injection amount is above the present amount (pre-programmed in the ECU), the secondary fuel injector operates".

I couldn't find a good diagram of the fuel map though.

Dave

yea forgot about IAT, it should be richening up slightly and pulling a degree or two of timing WOT if the IAT is above a set point

i would like to know at WHAT point it goes into open loop and brings the secondaries online under load, i thought i had read 3400 (this is useful for cruising on the highway BELOW this point to sustain mileage, I sure hope it's higher than 3k, i shift @ 3k on the street and try to keep the revs from 1800-2500rpm at cruise)

Post count doesn't mean much lol. Lots of ppl on here w/ the smallest post count have an enormous wealth of info stored upstairs. I just happen to know about commonly asked simple stuff, like audio, exterior, and the basic newb things you can find in the FAQ :rofl: But yea...the more you learn, the more you realize you know so little. I'm gettin there...;) Glad I could help tho!

That pretty much answers it. RPM plays a factor, ALONG w/ intake manifold pressure. So it is boost sensitive as well.

Intake air temp?? :scratch: The ECU changes fuel injection based on the air temp? Wow...I had no idea. Is that a compensation for colder air = more dense = more combustion, and visa versa? Kind of like a defacto protection against spike? Or am I way off?

EDIT: Just read what BoostFrenzy wrote. So it is based on combustion changes at varying temps, huh? Impressive lol. Didn't know it was that detailed!

You can see the ECU switch into open loop very easily. Use an air/fuel gauge. In closed-loop, the O2 voltage will oscillate between .1 and 1 volt as the ECU tries to maintain a 14.7:1 ratio for optimum fuel economy and emissions.

When it goes into open loop, the O2 voltage heads over to .9 to 1 volt area.

Sonny

Ramy, you should see how many correction factors there are to the fuel and timing maps on the PFC if you think that's bad.....:)

Bah...that PFC overwhelms me. All I see are lines and dots...I feel like a dumbass looking at it lol. I guess that just goes to show how oversimplified I made it out to be, since I have no real background in it. But I think that holds true to pretty much everything. At passing glance, it looks simple...the whole "hey, even I can do that!" typa thinking. It's not until you really study and learn about something that you see how in-depth it is, and how there are 1001 variables that interplay w/ one another.

I figured hey...air, fuel, spark, and you're good to go. Ok, MAF can play w/ air density changes more (and Jim taught me about the speed density sensor on the FD), you can change timing, and fuel is rpm based Poof...you're good to go haha. Back to howstuffworks.com I guess ;)

The PFC is actually a very "simple" standalone. You wanna see complicated? Download the AEM demo software. The PFC is a great ECU and I would be very comfortable having one in my car, but it just runs so damn well with the M2 ECU...I can't justify "fixing" it because it isn't broken enough (yet). ;)

The FD and Honda MAP-based ECUs are very very similar. The Honda stuff is pretty much all mapped out and totally configurable using free software. You can't run your FD with a Honda ECU, but if you can learn a lot about MAP based systems by looking at the Honda editors. The only real difference is the staged secondary injectors on the FD. I love MAP-based systems...they are so simple and powerful enough to get the job done. After getting my FD, I was very happy to be playing with another MAP system.

Sonny

here is a basic map showing Some of the stuff the ecu looks at.

Heard of this class? www.efi101.com

That's where I got my start. I figure we spend so much on our engines that 500 bucks for education isn't bad...or do rebuilds cost less now?

I'd recommend it and I've only ever heard good things. Tell me what you think. :bigthumb:

Wow...I never heard of that. It looks pretty good. But someone like me prob needs to go to Lincoln Technical Institute first :p: I have a sketchy foundation at best. I KNEW I shoulda taken the Automotive Mechanics 2 hrs a day class in high school...it offered a certification at the end too! We had all sorts of certification classes at my high school.. heating & A/C, etc... Instead, I ended up takin MIS. Got my MCP in Windows 95 and NT 4.0. The day after my Exam, Windows 98 came out lol. I was like screw this crap! lol