[Nounours]

Hello everyone,

Since a few months, my 2002 2.0 NB is doing only 400 km per tank instead of the usual 550 km, which is quite a decrease. Tire pressure OK, and it's not because of winter since this started some months ago. Timing belt was replaced in 2009, spark plugs two years ago along with the coil pack (but not the wires). Fuel filter replaced about 4 years ago, air filter brand new, wheels and brakes OK (not stuck), and no check engine on. Car feels jerky on accelerations, as if in need of air or fuel - unfortunately hard to say for me as I'm not a mechanic. Also, injectors were cleaned for the first time just a month ago - not much difference though.

So what could it be ? Is there any possibility that Check Engine would not lit and I'm running on three cylinders ? I would think it's impossible, but I'm not sure... Any other ideas or clues ? Crankshaft or camshaft position sensor wrong ?

Thanks a lot in advance for any help.

 

[Smileybug]

I would try scanning for codes. Not everything triggers a CEL.

 

[jfoj]

Plenty of things can cause the engine to run poorly and impact fuel economy without ever triggering a CEL.

So the first thing you need is an OBDII scan tool that can read Live/Real Time data and Freeze Frame info.

Long Term Fuel Trims and finger printing O2 sensors can be helpful. See graph of a lazy Bank 1, Sensor 1 on a car that had no CEL but the Emission Readiness Monitors would not clear for the O2 sensors.

$35 or under, see the first link below in my signature.

The single biggest item overlooked when it comes to fuel economy is the engine temperature. Soft thermostats are overlooked all the time. You need an OBDII scan tool to monitor the engine temperature. Engine should reach about 205F at idle after about 10 minutes of driving from cold. See the 2nd link below in my signature for Thermostat and Temp info.

Also you are located in Canada. Do you warm your car up for an extended time before driving the car in the morning? How far is your typical one way commute or trip each morning?

 

[D2Beetle]

Off the top of my head; you might want to check your cylinder compression; a low compression in one or more cylinders can result in poor gas mileage.

 

[Nounours]

Thanks everyone for your replies.

Engine temp is normal - blue light turns off after the usual time, so it's not the thermostat, and I don't warm the car up either.

I'll try to get codes/data ASAP. At least, it's reassuring that it's unlikely I'm running on three cylinders (as this would damage other things).

O2 sensor is in my mind since a while - resonator is leaking more and more (will be replaced at some point), so maybe this lowers the pressure in the exhaust system, creating a erroneous reaction from the O2 (constant rich mixture).

I hope it's not low compression, as this probably implies very expensive fix.

 

[jfoj]

Engine temp is normal - blue light turns off after the usual time, so it's not the thermostat, and I don't warm the car up either.

You cannot confirm the engine temperature by determining if the blue light turns off after the usual time. Did you read my thermostat and temp info?

O2 sensor is in my mind since a while - resonator is leaking more and more (will be replaced at some point), so maybe this lowers the pressure in the exhaust system, creating a erroneous reaction from the O2 (constant rich mixture).

Post Cat exhaust leak should not factor into the fuel mixture much.

You need to get an OBDII scan tool and provide Long Term Fuel Trim info.