Hello All, I have been reading on this subject and trying to solve for days now and would some guidance if you have a moment. I bought my daughter a 2003 MDX as her first car. I would have preferred a smaller 4cyl but her mom wins the safety argument with the MDX.

The car has been having terrible fuel economy. My daughter feels like she adds fuel every other day and of course my natural reaction was to say "Keep your foot off the gas". I took the car down with her and completely filled up even to the point of "Top it Off' where I couldn't fit another drop in the car. I reset the tripometer (manual one behind the steering wheel) and also reset the trip on the navigation screen. She drove it and when the low fuel light came on I told her to call me and tell me how many miles where left on the computer and how many she had traveled via the tripometer and she said 162 miles. To me that seems extremely poor so I began to investigate. The check engine light was on so I took down to the local shop and they ran the codes indicating that Cat1 in bank1 was bad. replaced it ($635). I had them test the O2 sensors and they said were good on whatever machine they use to test. I had them pull some of the spark plugs and they looked good as well. Check engine light is off, no codes are present. I checked tire pressure and set them all to 34 PSI. I drove and noticed alignment is off and car pulling to the right. I also heard the CV axles making noise so I will replace them and have an alignment performed.

Short of that I am at a loss. After the cat work was done i took car to gas station today and filled to the brim. I reset the tripometer, notated the exact mileage on car (195461 BTW), and reset the navigation trip mileage. The navigation trip mileage says 227 miles until empty. Doesn't that seem low or off? Can you guys offer anymore direction as to anything else I can check or advice?

Thanks in advance!

Hi and Welcome!

Did you investigate the MDX prior to purchase? MPGs was not the best feature of the MDX specially the 1st gen.
I would continue to diagnose by doing a full compression test on the engine, as low compression can lead to higher fuel consumption.
According to fuelly the average for that year is 19mpgs with owners reporting as low as 10mpgs.

Goodness, I'd LOVE to see 19 one day!

Best I've seen on my 06 is 18.8 during my trip to / from Miami (from Orlando).

My average is 13.3, I do have a heavy foot though...

Thanks for your reply! I really just looked up the standard Google search 17/23mpg when I bought it. I didnt really do alot of forum searching.

I read yesterday that with this motor, and other honda's as well, the the EGR valve gets clogged up from the intake manifold and that causes poor fuel economy as well. Anyone have experience with that issue or am I fishing the wrong direction?

Catalytic converters don't just go bad.
The engine is doing something and if the computer thinks that the air/fuel mix is not right, it will try to compensate for the rich or the lean ratio.
When you have a rich (too much oil) burn, the computer adds more fuel (bad for your MPG) to correct the richness. At the same time the rich burn leaves more of an oily deposit in the catalytic converter. Little by little the deposit builds up and clogs the cat and it will need replaced.
A compression test (see youtube) will help to point you where you need to go.