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Top 2GNT Technical Turbo/Nitrous Tech topic #91644
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Subject: "RE: Fuel Delivery Problems/Turbo" Previous topic | Next topic
TeamAvengerNov-30-05 01:09 PM
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#91693, "RE: Fuel Delivery Problems/Turbo"
In response to In response to 20




          

Originally posted by evotunedscc
Dude look, I've brought the car to a certified mechanic who graduated from NADC when they were an awesome school, he can't even figure out what's going on. If ya'll wanna sit here and hound on me about not knowing my stuff then just dont talk because it's not helping get the problem fixed. I'm not a total dumbass, I've listed the symptoms. According to the autometer air/fuel gauge and a narrowband O2 sensor the car just leans out when I give it fuel. This is the worst in 5th gear. It's not fuel cut because the engine continues to run. Say for example I'm in 5th gear at 60mph. I increase throttle to 40% to pick up speed or climb a hill. As the needle crosses into boost it fuel cuts. However, if im at the same speed and in 5th gear and give the car full throttle, it will NOT fuel cut, but it will lean out really badly. The solution to this problem used to be to drop to 3rd gear where it already has power at that speed and give it full throttle.... it would lean out for 2-4 seconds and then go stoich like it should. As an indication the problem is worsening, the last time I did this... I dropped to 3rd, the car leaned out and then fuel cut. From there on home I drove the car as easily as possible. But normally it didn't fuel cut, it would just lean out for a little bit, then go stoich/rich. I know you guys are telling me to check fuel pressure at idle and wot... but im at school and wont see the car till this weekend so I wont be able to check it until then. I also have a large EVAP leak I cant get rid of if that helps any.


Blair, quit hounding. You're not helping plus you're not giving him anything insightful to try past the "you need a missing link".

1. Fuel cut. When you experience fuel cut your engine will not stop. That's not what fuel cut is. You're right in your assumption that the ECU will not fire injectors during it but it doesn't continuously maintain the state. It goes off and on around where the MAP is seeing positive pressure. The car will feel like it's bucking more or less.

2. I understand that you're using your narrowband to check your A/F ratio. It's been discussed that it's woefully inaccurate on here countless times. It's why no one really trusts it. Also, one of the problems with using it is that as the o2 sensor fails it'll give you false readings which in turn causes the car to supply the incorrect amount of fuel which in turn again causes you to see all sorts of wierd shit on your A/F gauge. Endless cycle.

Another point on your narrowband A/F gauge. Your example of 40% throttle is a bad one. Why, because if you're only giving it 40% throttle you may or may not be going into open loop. This is determines how your ECU is supplying fuel. If you're still in closed loop your car will be trying to keep the A/F around 14.7:1 (using the o2 voltage). This translates out to seeing your blinky A/F gauge bounce back and forth between rich and lean. You should also see this condition under cruise.

In open loop, the ECU uses a predetermined fuel map and doesn't use A/F correction (o2 voltage) to determine the amount of fuel to deliver. This scenario tranlates to your blinky A/F guage pegging out over in the green side. If it still cycles you aren't in open loop.

3. A point about the AFC. Everyone one here NOW says "it's horrible, don't use it, it'll blow shit up" blah blah blah. But they forget that's what we all used initially. Anyway, it's got it's pros and cons. I'm also telling you this from a I used it and I know what the heck I'm talking about standpoint not a I read this on here and I'm just telling you what I read standpoint.

I'm sure that you already know that the AFC is a voltage modifier. On our cars the voltage it modifies is the MAP sensor voltage since our MAP sensor is the main value used to calculate the amount of fuel to deliver. As we've already also mentioned our cars have a fuel cut threshold that is directly related to MAP sensor values (voltage). It's just a hair before atmospheric pressure (roughly around 4.7V). Because of this condition, the AFC is limited to only REMOVING fuel! This means if your maps on your AFC have positive correction, you're only making your fuel cut issues WORSE!

For arguments sake though lets say your car is like a 95 that doesn't have fuel cut. Positive correction is still useless. Here's why. When you are in boost, your MAP sensor will be maxed out at roughly 4.7Vish (probably a little higher). As that value runs through the AFC, it will add X% of that value on top of that based on what you've programmed into the AFC. So say +10%, the output value will be 5.17V (4.7 + .47). This value then goes to the ECU. The ECU will see this and pretty much not have a clue what the hell that means because it expects MAP voltage to be between 0V-5V (its' a 5V sensor). So the ECU will just dump the largest value that it has for it ... which conincidentally will be the same at anything past 0psi. Pretty useless.

What some of us have done in the past, is to use it as a fine tuning tool and to increase ingnition timing. Using FP to supply a rich condition and then using the AFC to trim out little bits of fuel to run optimum power. People have varying results (some unpredictable) but most people tend to stay away from it now because there are products out there that are better and more predictable (which is what you want in tuning).

4. You mentioned something about stoich at full throttle. That's a BAD THING! You should never EVER be stoich at full throttle! It should read rich on your blinky gauge. That's exactly where it should be. WOT with boost you are really looking for somewhere along the lines of 11.5:1-12:1 A/F ratio.

Lastly, we're not trying to blast you or anything. You've mentioned your symptoms but this situation is not a clear cut ... it does this so it must be that. We are trying to help you but we just still do not have enough information to give you a definitive answer. So this weekend find out what you can and post back and let us know. That'll give us greater insight. It'll help us rule more things out and hopefully find your problem.

-"Easy Mac"
05 Mazda RX-8 (RR8 #88)
99 Eclipse RS 398whp & 372lb-ft

  

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Fuel Delivery Problems/Turbo [View all] , evotunedscc, Nov-28-05 06:20 PM
  RE: Fuel Delivery Problems/Turbo, selmerguy2003, Nov-28-05 06:39 PM, #1
RE: Fuel Delivery Problems/Turbo, BumpinTalon, Nov-28-05 06:40 PM, #2
RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-28-05 06:46 PM, #3
      RE: Fuel Delivery Problems/Turbo, Blizare, Nov-28-05 06:59 PM, #4
           RE: Fuel Delivery Problems/Turbo, BumpinTalon, Nov-28-05 07:20 PM, #5
           RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-28-05 07:22 PM, #6
                RE: Fuel Delivery Problems/Turbo, BumpinTalon, Nov-28-05 07:40 PM, #7
                     RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-28-05 07:51 PM, #8
                          RE: Fuel Delivery Problems/Turbo, Darrell, Nov-29-05 05:10 AM, #9
                               RE: Fuel Delivery Problems/Turbo, DSMchevy, Nov-29-05 05:24 AM, #10
                                    RE: Fuel Delivery Problems/Turbo, BumpinTalon, Nov-29-05 05:37 AM, #11
                                         RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-29-05 10:31 AM, #12
                                              RE: Fuel Delivery Problems/Turbo, rs_smoked_you, Nov-29-05 10:40 AM, #13
                                                   RE: Fuel Delivery Problems/Turbo, TeamAvenger, Nov-29-05 12:07 PM, #14
                                                        RE: Fuel Delivery Problems/Turbo, BumpinTalon, Nov-29-05 01:22 PM, #15
                                                             RE: Fuel Delivery Problems/Turbo, Blizare, Nov-30-05 08:17 AM, #16
                                                                  RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-30-05 10:10 AM, #17
                                                                       RE: Fuel Delivery Problems/Turbo, Blizare, Nov-30-05 10:24 AM, #18
                                                                            RE: Fuel Delivery Problems/Turbo, Blizare, Nov-30-05 10:26 AM, #19
                                                                                 RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-30-05 10:43 AM, #20
                                                                                      RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-30-05 12:38 PM, #21
                                                                                      RE: Fuel Delivery Problems/Turbo, TeamAvenger, Nov-30-05 01:09 PM #22
                                                                                      RE: Fuel Delivery Problems/Turbo, willmayo, Nov-30-05 01:33 PM, #23
                                                                                           RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-30-05 02:43 PM, #24
                                                                                                RE: Fuel Delivery Problems/Turbo, evotunedscc, Nov-30-05 02:53 PM, #25
                                                                                                     RE: Fuel Delivery Problems/Turbo, Blizare, Dec-01-05 07:36 AM, #26
                                                                                                          RE: Fuel Delivery Problems/Turbo, rs_smoked_you, Dec-01-05 10:20 AM, #27
                                                                                                               RE: Fuel Delivery Problems/Turbo, Blizare, Dec-01-05 11:57 AM, #28
                                                                                                                    RE: Fuel Delivery Problems/Turbo, evotunedscc, Dec-07-05 06:07 PM, #29
                                                                                                                         RE: Fuel Delivery Problems/Turbo, Blizare, Dec-08-05 07:17 AM, #30
                                                                                                                              RE: Fuel Delivery Problems/Turbo, TeamAvenger, Dec-08-05 07:26 AM, #31
                                                                                                                                   RE: Fuel Delivery Problems/Turbo, Blizare, Dec-08-05 07:27 AM, #32
                                                                                                                                        RE: Fuel Delivery Problems/Turbo, evotunedscc, Dec-08-05 12:38 PM, #33
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, evotunedscc, Dec-09-05 07:40 PM, #34
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, DarkEclips96, Dec-10-05 02:53 AM, #35
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, Blizare, Dec-10-05 06:02 AM, #36
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, evotunedscc, Dec-10-05 07:10 AM, #37
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, evotunedscc, Dec-10-05 11:55 AM, #38
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, evotunedscc, Dec-10-05 12:16 PM, #39
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, DarkEclips96, Dec-10-05 05:19 PM, #40
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, Blizare, Dec-11-05 07:00 AM, #41
                                                                                                                                             RE: Fuel Delivery Problems/Turbo, evotunedscc, Dec-11-05 10:18 PM, #42

Top 2GNT Technical Turbo/Nitrous Tech topic #91644 Previous topic | Next topic
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