MAP sensor and O2 sensor question

[whateg01]

I have a question about how my car uses the MAP sensor and O2 sensor. I have a '92 Civic LX. It has the D15B7 and an auto.

On my F150, the ECU uses the O2 sensor under certain conditions, but on the highway, it switches solely to the MAP sensor and a look-up table.

I have been reading about the Hydroxy systems lately, and looking for a bit more gas mileage, it seems to be an inexpensive experiment at worst. At best, it will save me some dough on gas. (The car is itself already saving me a bunch since I am able to park my F150 most of the time.) Anyway, from what I have read, people have mixed opinions about these systems, and that's fine with me. Flame away if you want, but I'm going to test it out and decide from the results I get. One of the things that has to be overcome is the computer's desire to keep the a/f mixture right. Adding extra 'un-accounted-for' fuel in the form of the extra gas tends to make the engine run rich because of the elevated levels of oxygen in the exhaust, or the fixed level of fuel being dumped in due to the MAP. So, the engine must be told that it's rich, so that it will lean out the mixture a bit. The two ways of doing this are to reduce the MAP signal and to bias the O2 sensor voltage. That all makes sense to me.

But I'm not sure if the Civic uses one sensor all the time, and the other part of the time, or if it uses both sensors all the time, or if it uses one now and the other later, or what. Can anybody tell me how Honda chose to use these sensors?

Dave

 

[lkailburn]

dave if you want to just make the car run leaner then chip the ecu and retune the map. just manually tune it leaner yourself. you'll pass inspections fine since your car is obd1. crome free is free, free log is free, a used wideband can be had for 150 bucks, you can make a datalogging cable or buy a used one for around 20, find a friend with a chip burner. and bum a laptop if you dont' have one.

the primary o2 sensor is used to correct the fuel maps at all rpm ranges and all map ranges but under 80% TPS (throttle position sensor). above 80% tps the ecu switches into what's called open loop and does not correct fuel values based on o2. the secondary o2 sensor (which your car should not have because you are obd1 not obd2 is used to verify the correct function of the cat).

btw when you chip the ecu and retune the maps you can disable the o2 sensor and run permanently in open loop. this way the ecu wont try to recorrect your leaner map.

-Luke

 

[whateg01]

Thanks, Luke! The info on the programming is good to know. I may just take that route.

Do I understand rightly that...

at <80%TPS, the system is closed loop and >80% it is in open loop? That sounds much like the truck. In open loop, then it is relying on the MAP, right? Is the MAP disregarded below 80%TPS?

Thanks again for the explanation.

Dave

 

[Takiyon]

anyone have any advice for a 1999 civic. I just bought a OBD scanner hopefully to monitor everything you just described for your 91. I.E. Map throttle O2 sensor.

 

[lkailburn]

Thanks, Luke! The info on the programming is good to know. I may just take that route.

Do I understand rightly that...

at <80%TPS, the system is closed loop and >80% it is in open loop? That sounds much like the truck. In open loop, then it is relying on the MAP, right? Is the MAP disregarded below 80%TPS?

Thanks again for the explanation.

Dave

no the map is always referenced. it is the x axis of the fuel and timing maps.

the o2 sensor is disregarded above 80% tps

-Luke