rpm's drop real low when cold start up
11-27-2004, 02:44 AM
#11
5th Gear Member
Join Date: Mar 2004
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Posts: 4,813
RE: rpm's drop real low when cold start up
The ECU can only control the fuel supply and engine timing, it can't adjust the air flow, you do that with the big right foot on the gas pedal. The ECU responds to air flow changes by seeing the MAF signal, the TPS signal, the MAP signal, heck all the damn sensors and it then adjust the pulse width of the fuel injectors and the timing to get the proper combustion for both power and emissions. I know when the engne is cold, it sprays more fuel since SEFI sytems don't have a "choke" like the old carbs do to make it run richer at a cold start. as it warms up , it reduces the fuel flow and then adds/subtracts fuel as the other engine sensors tell the ECU what the driver is trying to do with the gas pedal. under less than WOT conditions, the ECU functions in a closed loop system using the O2 sensors to adjust the fuel/air mixture according to how the sensors read the rich/lean condtitons in the exhaust gases for best emissions control. under WOT, the system goes into open loop controls and ignores the O2 sensor input and just gets the fuel and timing settings from maps built into the chip for various sensor inputs with the throttle wide open for maximum power output. most chip tuning is done by changing these maps to more agressive settings for fuel flow and timing at WOT, but they can also change other maps used by the ECU when the gas pedal ain't on the metal too.
it's good that you're trying to learn even though you're only 15, wish more kids would show some interest in cars instead of computer games and rap music!!! we need more skilled mechanics and less rappers for sure IMO. ha. ha. ha
it's good that you're trying to learn even though you're only 15, wish more kids would show some interest in cars instead of computer games and rap music!!! we need more skilled mechanics and less rappers for sure IMO. ha. ha. ha
11-27-2004, 02:50 AM
#12
5th Gear Member
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Join Date: Oct 2003
Location: Mishawaka,Indiana
Posts: 3,742
RE: rpm's drop real low when cold start up
aint that the truth!!!!!!! thanks a lot man! know i know what closed and open loop means! i always wondered that too. you always got the answer!
11-27-2004, 03:25 AM
#13
5th Gear Member
Join Date: Mar 2004
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Posts: 4,813
RE: rpm's drop real low when cold start up
Well, not always but more often than some out here!
If I don't have the answer, I usually don't attempt to answer the question unless it makes me really curious and then I try to look it up somewhere if I feel like being a nice guy!
If I don't have the answer, I usually don't attempt to answer the question unless it makes me really curious and then I try to look it up somewhere if I feel like being a nice guy!
11-27-2004, 04:40 PM
#17
2nd Gear Member
Join Date: Jun 2004
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Posts: 330
RE: rpm's drop real low when cold start up
hey roundman
how does the ECU operate when the O2 sensors are unplugged or fouled?
I remember a post a while ago about a member having bad fuel economy and them
unplugging his O2 sensors and improving it......
how does the ECU operate when the O2 sensors are unplugged or fouled?
I remember a post a while ago about a member having bad fuel economy and them
unplugging his O2 sensors and improving it......
11-28-2004, 12:03 AM
#18
5th Gear Member
Join Date: Mar 2004
Location:
Posts: 4,813
RE: rpm's drop real low when cold start up
not sure, ain't read that far yet in the EEC IV manual I bought several years ago. LOL
most ECU's have what's called a "limp home" mode in the event a sensor(s) go bad so you don't get stranded on the road, maybe that's what it's doing but I really don't know for sure how it works with the O2's unplugged. my guess is it goes open loop and just uses the built in maps for fuel and timing and ignores the missing O2 readings.
most ECU's have what's called a "limp home" mode in the event a sensor(s) go bad so you don't get stranded on the road, maybe that's what it's doing but I really don't know for sure how it works with the O2's unplugged. my guess is it goes open loop and just uses the built in maps for fuel and timing and ignores the missing O2 readings.
