Injector failure & A/F mixture???

If 1 or 2 of your injectors were to go out what would happen? Obviously the engine would run rough but it would run. I'm just thinking if the empty cyl were not burning anything it would more or less just pump air. So what would that do to the oxygen sensor and the A/F mixture in the other working cylinders?

Nice Question Jeff, That's actually one of the senarios on the CA. Smog Exam. On Pre-OBD II cars, this condition would cause the remaining cylinders to run rich. Depending on the engine displacement and how many cylinders, O2S, and banks the engine has, this could cause a minor to moderate rich condition. On OBD II cars, the PCM would be able to detect the misfire and isolate the cylinder. The PCM also has the ability to calculate the increase of Oxygen in the Exhaust Stream, and adjust accordingly.

but wouldnt it only occur when the o2 sensor is in closed loop operation?

but wouldnt it only occur when the o2 sensor is in closed loop operation? and also for people in Australia has any one had their EL onwards overheated? when the PCM detects it is overheating the computer starts shuting down injectors so the air that comes into the motor isnt burnt and cools the motor down, but the car wont go over 25kph

but wouldnt it only occur when the o2 sensor is in closed loop operation?

Yes, and for the most part, most cars can still stay in close loop, even when misfiring.

and also for people in Australia has any one had their EL onwards overheated?

What's an EL?

when the PCM detects it is overheating the computer starts shuting down injectors so the air that comes into the motor isnt burnt and cools the motor down, but the car wont go over 25kph

As far as I know, Only the GM NorthStar engine is capable of doing that. When coolant loss has occured and is detected, the NorthStar PCM will systematicly start cutting off fuel and spark to half of the cylinders in rotation to pump air and cool the engine down. For other engines, there are "limp" modes when an critical engine sensor has failed, such as Coolant Temp, Engine Load (MAP, MAF), or Throttle Position Sensor, PCM will go in to Open Loop and stay in a fixed Timing and Fuel Map to get car home. Usually limiting you to 25-30 mph.

i had an injector go out on my old altima before i started working on cars and my mechanic said it could possibly lean out a cylender and cause it to go boom

i had an injector go out on my old altima before i started working on cars and my mechanic said it could possibly lean out a cylender and cause it to go boom

Possibly, But most of the time when injectors go out, they're out for good. That would only happen if it began to become really lazy and started putting only half of what the required amount of fuel should be.

Rev, Sorry the EL is a Ford Falcon that is produced over here, you guys used to have them over there in the 70's i think but they stoped making them over there.....sounds similar to the north star thing.....most modern engines dont actually have a limp home mode.....the technical term for it now days (at least here) is limited strategy mode....they call it that cause most of the time when a major sensor fails the car can still perform nearly as good as before because they substitute learned values for the sensor....an every day driver could only tell because the check engine light is on.......and what i was saying about it only happening in closed loop was that the computer disregards what the O2 sensor is telling it (open loop) until it finds the right situation (eg certain ammount of throttle angle, certain engine speed, certain engine temp, no load...etc)...and then when it goes into closed loop the O2 sensor is taken into account alters pulse width accordingly, and then repeats over and over again....Do the OBD II cars run a O2 sensor per clyinder, I know alot of american cars are going that way?

most modern engines dont actually have a limp home mode.....the technical term for it now days (at least here) is limited strategy mode....

Sorry, Should have been more clear about that, I was referring to Pre-OBD II Cars. Over here, We call it Adaptive Strategy.

and what i was saying about it only happening in closed loop was that the computer disregards what the O2 sensor is telling it (open loop) until it finds the right situation (eg certain ammount of throttle angle, certain engine speed, certain engine temp, no load...etc)...and then when it goes into closed loop the O2 sensor is taken into account alters pulse width accordingly, and then repeats over and over again

Again, Sorry for not being clear. Yes, that's true. I guess my point there was that EVEN THO it's misfiring, The system can still go into closed loop. As I understand it, The only criteria for closed loop operation is Coolant Temp, and Actual Temp of the O2S. That's why they have heaters. But that's really all mute now, since they've been replaced w/ A/F Ratio Sensors. But just so we're clear this time, The O2S is only a correction sensor, it's fairly limited to the amount of influence it has over A/F mixture. The Coolant Temp Sensor, and the MAF/MAP have the greatest influence.

Do the OBD II cars run a O2 sensor per clyinder, I know alot of american cars are going that way?

Haven't seen too many yet. Seeing more and more O2S per car tho. The only car I've seen with O2S per cylinder was a late model Nissan Sentra.

so how exacly does the OBD II system determine which cylinder is misfiring?

Ahhh. Good question. The PCM is capable of determining this by the momentary drop in engine speed when a cylinder misfires. When the PCM detects this condition for X amount of times is a succession it sets a DTC and calculates which cylinder is misfiring by the position of the (CKP)Crank or (CMP)Cam Sensor when the misfire occurs. The code is usually P03xx, xx stating which cylinder. P0300 is the DTC for Multiple or Random Misfire.

so its basically an automatic sensing cylinder balance tester...

so its basically an automatic sensing cylinder balance tester...

Hmmm......Never really thought about that way. I suppose so. The PCM does monitor abrupt changes in Engine RPM. And it will allow for a certain amount of variance based on Vehicle Speed, ie. Pot Holes, Speed Bumps....ect. Even more so for 4X4s.
96-99 GM cars had a problem with false Misfire DTCs when the vehicle had a rough idle from dirty injectors or whatever, So GM had to de-sensitize it by giving the PCM a greater tolerance for Engine Speed Flucuations. So I guess it is a constant Cylinder Balance Tester.