2003 Alero 2.2 hesitation and bad mileage

[Dobbie]

I have a 2003 2.2 auto (205,000 km = about 128,000 miles) that has a slight hesitation when going at a steady speed mainly noticeable around 40-70 km hour. You can feel it and when you do, the RPMs show it as well, nothing huge like 100-300 bumps.

Another thing to note is that the car has power when you want to push it. I do not have a check engine light on and yes is does come on when starting the car so it does work. The exhaust also smells like it's burning rich.

I have a funny feeling that it is also linked to the poor mileage I have been getting (I'm lucky to get 325 km a tank and used to get around 500). I keep an eye out for the tire pressure, injector cleaner, oil change every 5000 km, air filter just a few months ago, plugs a few months ago . . . the normal stuff.

I am thinking of replacing the o2 sensors but am not totally sure I should because how there isn't a check engine light. But I totally feel that this is a sensor issue in one way or another due to the mileage, the hesitation but the car still runs great when you put the petal to the metal, and the rich exhaust smell.

Any and all suggestion/info would help, thanks.

[danielsatur]

Replace the upstream H02 sensors only, they are used for feedback so the ECU can formulate the Air/fuel mix.

Keep the old one's for spare down stream sensors.

[Dobbie]

Originally Posted by danielsatur

Replace the upstream H02 sensors only, they are used for feedback so the ECU can formulate the Air/fuel mix.

Keep the old one's for spare down stream sensors.

Sounds like a plan. One thought though, isn't there different sensor for up versus down stream? Or are they interchangeable if they are original?

Thanks

[danielsatur]

The 4-wire H20 sensors are the same, it's usually the wire length, and connectors maybe different.

The down stream H02 sensor just tells the ECU, if the cat is good.
If the Heater go's bad , just recycle the old H20 sensor.

Did yor try cleaning the MAF, and IAT sensors with CRC MAF sensor cleaner?

[Dobbie]

Originally Posted by danielsatur

The 4-wire H20 sensors are the same, it's usually the wire length, and connectors maybe different.

The down stream H02 sensor just tells the ECU, if the cat is good.
If the Heater go's bad , just recycle the old H20 sensor.

Did yor try cleaning the MAF, and IAT sensors with CRC MAF sensor cleaner?

The 2.2 doesn't have a MAF but what is the IAT? Is that the little sensor on the intake tubing before the TB?

[tblake]

IAT stands for Intake Air Temp Sensor. It should be in the ductwork of your intake tube.

Although good suggestion to replace your upstream O2 sensor to help with milage, at only 128,000 miles, your O2 sensor shouldn't have any issues like getting "Lazy", and if it did have issues bad enough to cause such a large MPG drop, the PCM would trip the check engine light.

Also please note, the Upstream and Downstream O2 Sensors on this car are NOT interchangable as the plugs are different.

Upstream


Downstream


First off, before replacing any parts, pull the intake duct off, and check for moisture or fuel sitting in the bottom. The pull the vacuum line off your fuel pressure regulator, turn your key to ON but not start and look for fuel squirting out your FPR vacuum port. Any fuel coming out and your FPR needs to be replaced.

[Dobbie]

I haven't picked up anything yet (thanks for the PM). I can check the FPR but isn't that known to throw a random miss fire code or is it known to not throw it at times? I'm just trying to to learn more not trying to make you prove anything.

[tblake]

When the diaphram inside them ruptures and lets gas into the vacuum line, there is still adequate fuel pressure so there is no miss. However your car runs rich causing a stutter or chug sensation at varying throttle points, and of course, bad MPG. I would start there, as checking for a leaking FPR diaphram is free and easy check.

[Dobbie]

Checked the FPR and it's bone dry. One thing I forgot to note that when driving and it's wet out and hitting a puddle (one the right side not sure about the left, can't remember but know for sure about the right) I get a noise like the exhaust partly filled with water or a little like there is a slight hole in the exhaust manifold for around the next 5 mins or so and you can feel a slight power loss. It only makes the noise/feeling when giving it gas but doesn't do the same thing if you switch it to neutral when driving. I don't know if this might be a belt (I haven't really checked where they are on the Alero) but thought I would mention it.

I'm still thinking of doing the upstream O2 but still not sure because it's $101 locally.