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Morning all, i am currently studing imi motor vehicles and i am stuck on working out the correct air feul ratio for overrun cut off (no feul injection)
anyone able to enlighten me on this subject?
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Current Fleet:
2004 Audi A4 1.9tdi Sport Avant
2014 Ford Fiesta 1.25 (wifes car, curse word box)
1987 Volkswagen Polo CL
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20% Oxygen, 79% nitrogen, 1% whatever else the engine sucks in. isn't the clue in the question  |
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they ask for the ratio, i had writtnen down as 1:0 and got marked wrong, somebody did suggest it being 20:1 but i throught this was to high to be the correct ratio for overrun cut off
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Current Fleet:
2004 Audi A4 1.9tdi Sport Avant
2014 Ford Fiesta 1.25 (wifes car, curse word box)
1987 Volkswagen Polo CL
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whats the exact question?
i.e. there is no fuel so how can there be a ratio?
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the question is, give examples of thwe correct air feul ratio for overrun cut off (no feul injection)?
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Current Fleet:
2004 Audi A4 1.9tdi Sport Avant
2014 Ford Fiesta 1.25 (wifes car, curse word box)
1987 Volkswagen Polo CL
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odd
there is no fuel so no ratio
does it mean what the Lambda sensor measures? I thought they went open loop on overrun but then I have't done vehicle electrics for many years. |
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Last Edit: Jun 7, 2013 9:08:12 GMT by Bozwell
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i think with it being a no feul injection engine, i presume is for a carbed engine. so therefore the ratio would be 0:0. throught i throught they would have to inject some feul to keep the enigne running at low revs
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Current Fleet:
2004 Audi A4 1.9tdi Sport Avant
2014 Ford Fiesta 1.25 (wifes car, curse word box)
1987 Volkswagen Polo CL
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the tutor has spoke to me and he has said the correct ratio is 24:1 on overrun for both si and ci engines???
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Current Fleet:
2004 Audi A4 1.9tdi Sport Avant
2014 Ford Fiesta 1.25 (wifes car, curse word box)
1987 Volkswagen Polo CL
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ask him to prove it. also why would you be learning about carbed engines anyway? also on some carbs they used to have a cut off valve on overrun which switched back off at about 1100rpm to allow the engine to idle. (about the same with a fuel injection engine)
question is a little vauge and the answer doesn't seen right to me. that answer must be what a lambda sensor reads which is probably its limit as it cant read infinity which would be a closer answer to the actual ratio. |
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there is another 3 ratios i had to provide, from experiance at idle i had 14.7:1 so basically it is stating that it is 14.7 parts of air to 1 part fuel. according the tutor it is 24 parts of air to 1 part of feul on overrun, am not happy with the info and cant find anything on google that backs this up. am waiting on the tutor being free so i can speak to him about it. The amount of bull i have come across on this course makes me wonder how anyone can be a mechanic. I would of rather stuck to experiance.
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Current Fleet:
2004 Audi A4 1.9tdi Sport Avant
2014 Ford Fiesta 1.25 (wifes car, curse word box)
1987 Volkswagen Polo CL
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if the question asked what the lambda reading was on overrun then it's probably correct but for actual ratio it is wrong.
when cats first came out the fuel economy got really bad for a while as the perfect fuel ratio for a cat to work fully is 14.7 to 1. carbs prior to that ran leaner at light loads for economy. they are a lot better now though.
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ask him if he wanted the answer as volume, or mass
If it's by volume, then stoichiometric is 14.7:1, but if it's by mass, then 24:1 sounds about right (a litre of air weighs far less than a litre of fuel)
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You're like a crazy backyard genius! |
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I thought the 14.7:1 was by mass? Otherwise a two litre engine would use about half a litre of fuel / second at idle!
As to the OP, I have no idea how 24:1 can be the answer.
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I've got Rovers.
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Yes it is by mass but i agree with everyone in the answer of 24:1 being wrong i cant see how they got such a higher figure for no feul lol
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Current Fleet:
2004 Audi A4 1.9tdi Sport Avant
2014 Ford Fiesta 1.25 (wifes car, curse word box)
1987 Volkswagen Polo CL
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24:1 sounds reasonable for a closed throttle coast, but it would vary from car to car. I'm interested to find out the explanation.
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I've got Rovers.
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gruss
Part of things
Posts: 242
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I get 22:1 on my wideband on overrun if that helps.
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Daihatsu Mira TR-XX
Suzuki Alto Works
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22:1 is just the max a wideband can read.
You answer is 1:0, no fuel, in cut off there is NO fuel entering the intake system.
I think your tutor has given you the maximum reading an oxygen sensor will put out in that situation, the same as gruss gets, 22 or 24:1.
J
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