[CPH]

Originally Posted by aargee

Couldn't understand this; are you saying the ratio of 8 to be the quantity of air or fuel? If you say 8 is air, then 8:1 is lean mixture, but if you say 8 is fuel, then the vehicle WILL never start. Pls help understand.


Well, its the other way, plug fouls when there's too much of rich mixture. Well, I'm talking about motorcycles as I've learned the hard way through experimenting.

The AFR ratio usually refers to air in weight to fuel in weight. If the first value is lower than then refer to richer and if it s getting higher it refers to leaner. The more fuel is in the air the richer the mixture.

8:1 is an extremely rich mixture, which in constant use would foul the plugs.

A high Lambda value above Lambda 1 refers to a leaner mixture (Lambda 1 = 14.7:1) and belowc to a richer mixture than the stochiometric ratio.

[geeta]

Also, one of the most likely causes can be the burnt exhaust valve or a blown head gasket. If the engine is overheated or loosing coolant, the problem is with the head gasket.

[aargee]

Originally Posted by CPH

If the first value is lower than then refer to richer and if it s getting higher it refers to leaner. The more fuel is in the air the richer the mixture.

First value lower? I'm under the impression that the ideal ratio of AFR is 5:1. Is this incorrect?

Originally Posted by CPH

8:1 is an extremely rich mixture, which in constant use would foul the plugs.

101% agreed; that's how I fouled 2 of my plugs. That too when the vehicle was in idle

Originally Posted by CPH

A high Lambda...the stochiometric ratio.

Sry, couldn't get on this one.

About a year ago, I knew nothing about carbs & my regular mech did some nonsense to the carb due to which my motorcycle was jerking heavily & I felt very embarassed to ride in slow speed. Finally one day, I picked up courage, learned few stuffs from net, consulted few friends & then opened up the carb & only to find the needle above the float was set in the bottom most position. Then when I put it back to top but one, the jerks have stopped, but its fluttering like mad now when the throttle is opened up (ie when the main jet is working). I need to now experiment with lower jet (165) from the existing 180. BTW, the carb in this question is TM28 on a 135 cc 2S motorcycle.

Since I'm learning on this, appreciate if you can point out some guides where I can get things straight?

[im_srini]

Originally Posted by aargee

First value lower? I'm under the impression that the ideal ratio of AFR is 5:1. Is this incorrect?

The correct ratio is 14.7:1 by weight, i.e. you need 14.7 gms of air to fully burn 1 gm of fuel. Hence, values lower than 14.7 denote a rich mixture (more fuel than air required to burn all of it).

Originally Posted by aargee

Sry, couldn't get on this one.

Lambda is the ratio of the actual (measured) air-fuel-ratio to the stoichiometric air-fuel-ratio (14.7), hence if you're engine's running rich (< 14.7), the Lambda value is < 1 & if it's running lean (> 14.7), the Lambda's > 1...

[nitindangoria]

My brand new petrol i20 elite sometimes misfires/backfires, especially when I rev it from 2nd or 3rd gear. The noise is so loud that other car owners stop to look what that noise was all about.

Hyundai mechanics are at a loss to tell us the actual problem. The car has already gone twice to the workshop. They are coming up with the theory of ignition coil failure, lead wires faulty etc.

This problem, however , is quite infrequent but does occur sometimes in quick succession.

Could our experienced members help me give their suggestions about how to solve this issue. Thanks in advance.

[1self]

We will need more details, like, when does the misfire happen, engine hot or cold, A/C running or not, mileage of the car, any fault codes, at what rpm does the misfire occur etc.

[sandeepmohan]

Originally Posted by nitindangoria

They are coming up with the theory of ignition coil failure, lead wires faulty etc.

This can be correct as symptoms like this can relate to a faulty ignition coil and possible damage to the high tension wires running from the ignition coil to the spark plugs.

The technicians seem to be on the right path. You do not have anything to be worried about. It is a new car (A Hyundai too) with full warranty to back you up.

[pixantz]

Hi friends. This is a problem which is bugging my car since a while now. The problem has had different shades and hues as I went on adding fresh components on the way in hope of fixing the issue. Car in question is a Santro Xing erlx 2006. About 86,000 Km's on the odo. I had slight hiccuping since a long time now on and off which has grown ugly of late. Have changed fuel pump motor, fuel filter, spark plug leads, air filter, etc, had my mpfi and erg serviced by a good FNG, also valve clearance setting done. There was also a little tapper noise before but that vanished. But the hiccuping doesn't seem to budge. It happens on and off and not regularly. When taking off slowly from second or third gear mostly. Shakes up the engine quite a bit.

Things suggested by some guys are cleaning/replacing of the crank shaft sensor and also changing the flywheel and maybe clutch and pressure plate along with it if needed. The fight goes on.... Anything familiar encountered by anyone? Help would be appreciated. Thanx in advance.

[SS-Traveller]

^^ What's the FE currently?

Are these hiccups happening while you drive with the air-conditioner on, or off? Or doesn't switching the AC on/off cause any difference?

Please check again and report.

[pixantz]

Originally Posted by SS-Traveller

^^ What's the FE currently?

Are these hiccups happening while you drive with the air-conditioner on, or off? Or doesn't switching the AC on/off cause any difference?

Please check again and report.

FE is normal. About 12 in the city and 15-18 on the highway.

The Ac multiplies the problem about three fold but it's very prominent without Ac too.

[SS-Traveller]

Thanks for the reply. More questions first:

Do the hiccups occur when the engine is cold, or hot, or does it not make any difference?

Have you you used any fuel additive like System-G in the recent past? Did that make any difference?

When was the clutch replaced, if at all? Do you feel any shudder when the clutch is being engaged while moving off?

[ssjr0498]

Check the compression (cold) and check for blow by!

Get the injector's cleaned by some Bosch/knowledgeable guy and if possible get the injector flow tested!

The ignition system could also be the culprit!

Help us more so that we could help you.. Start off by putting some pictures of your spark plugs after the car has been substantially driven around!

Think you could rule out the clutch, pressure plate and flywheel! They won't cause irregular hiccups! They will give you a feeling of "the car revving" but not going anywhere feeling, all through!

[saket77]

1. Hope the petrol tank is clean and the fuel is unadulterated and water has not found its way into the petrol tank.

2. Check the electrical system. More importantly the ignition coil, spark plugs and the distributor, the condenser inside the distributor and the wires of distributor.

3. If all above are okay, see if the injectors/ fuel lines are clogged.

4. Check air intake.

5. Lastly check the compression/ blow-by.

Hope that will help.

Regards,
Saket.

[pixantz]

um, thanks for the pointers guys. I've got new ngk original plugs about a year ago. Tank also was cleaned about the same time. Didn't check plug condition yet, but since FE is ok, dunno, but will get it done. After a long drive of about 1500 kms, the fuel filter was quite clogged maybe due to crappy fuel bunks on the way. This was in gujarat, by the way. Anyway, changed the filter but not sure if some gunk may have got past and then playing funny with the injectors maybe.

This seems like an ignition/electrical related problem to me. Just run out of places to check. Will jot down the other points by all the kind fellow bhpians and go about my checking spree. Will start by checking out the crank sensor and ignition coil first as these have not been checked yet. Thanks again fellas. Will keep you posted

@ ss-traveller: engine cold/hot is no different. I never use any kinds of additives. CLutch not replaced yet but there is judder slightly while clutch is being released.

[SS-Traveller]

Originally Posted by pixantz

CLutch not replaced yet but there is judder slightly while clutch is being released.

The hiccups you describe does not appear to be engine or misfire related. Suspect it to be related to an unbalanced pressure plate / uneven wearing of friction plate.

Get the clutch pressure plate and friction plate changed, and have the flywheel turned and balanced, or replaced.