Need an Expert

[bestbiker]

Just purchased a 2004 6s Wagon with ~58,000 miles.
Ill start with some background info.

When i first bought it, it shuddered when you gave it throttle to the point of shifting, and the check engine light popped. The dealer replaced a coil and the spark plugs and the car hasnt done it since and the CE light has stayed off.

My problem is the gas mileage. I live in northern maine so it is winter, but i made a 1000+ mile trip down to mass and over 5 fill ups, every time i averaged 19-22.6mpg when the car should be getting close to 30. The prior owner who traded the car in about a year ago got close to 30 with it on the highway as well. In the city i get less then 10mpg and i notice it shifts into 4th gear around 20mph

The oil smelled a bit like gas, which they say is normal for cold winter starts. But i smell gas come through the heater vent after a few minutes when i start it after it has sat overnight.

Im wondering if they hooked a vaccum hose up wrong when they put things back together. The check engine light is NOT coming on, and they scanned it and no codes were regestering.


Im pretty frustrated because I had a v8 magnum durango that i could get 18 mpg on the highway. I figured out the simple secrets to get good gas mileage, but this car is just way off.

Any help would be great. The dealer has had it in twice and not found anything, and i havnt had the engine light come on since i bought it 3 weeks ago but the gas mileage is still horrible

 

[Blendercloud]

This is a tough one to diagnose without seeing the car. Something tells me you've got a broken piston ring. I would say the broken ring is probably on the cylinder of the coil and plug they replaced as well.

The oil coming up into the combustion chamber most likely fouled the plug for that cylinder. In turn, you also are getting gas from that cylinder into your oil. This is only speculation, as I would need to see the car for myself to say much more. If you just purchased this, are you covered by any sort of short-term (30-days) warranty? I would definitely be taking this car back.

 

[bestbiker]

This is a tough one to diagnose without seeing the car. Something tells me you've got a broken piston ring. I would say the broken ring is probably on the cylinder of the coil and plug they replaced as well.

The oil coming up into the combustion chamber most likely fouled the plug for that cylinder. In turn, you also are getting gas from that cylinder into your oil. This is only speculation, as I would need to see the car for myself to say much more. If you just purchased this, are you covered by any sort of short-term (30-days) warranty? I would definitely be taking this car back.

It was actually the coil, first the problem poped up in cyl 6 then they moved the plug to cyl 5 and the plug to cyl 4 and then the problem was cyl 5.

Ive taken it back twice since they did the work. They replaced ALL the plugs and as i said, it has been 3 weeks and 1200 miles since they did the work and the CE light has not come up and they plugged into the computer and there is nothing out of the ordinary.

 

[jaymangrum]

i wonder if the dealer did a comp. test? have you read the plugs since the trip or lately? i agree a tough one without being present w/the vehicle

 

[bestbiker]

I gotta say thank you to you guys for responding. I took some of your advice and i sat down with the garage that does the work on the dealer cars and pointed out (again) everything that i had come across with your sugestions.

They said all assumptions i had been making for the past few weeks have been acuratly based, But with no check engine codes coming up, and no problems with the engine, they are chasing ghosts. The engine runs and idles as it should, no noise, no hessitation, and its got 1300 miles and 2 weeks of driving since they replaced any parts so if something was wrong it should have shown up on radar

They said if it gives me peace of mind (so i dont call them every 2 days) they will do a compression check and check all the pulleys and tensioners to make sure things are as they should be. The dealer was willing to split the cost 50/50 with me. He offered to trade the car back for the durango that i traded in, and obviously i have good reason to avoid that offer. Dealer said he understood my frustration because they have had it for about a year just sitting and not moving or taking any interest because 1. its a wagon 2. the nearest mazda dealer is about 200+ miles away.

I figure if the compression test comes back with normative results and the check engine light isnt springing, Ill just deal with it for now. All the work and check-ups are on record so if something happens just outside the extended warrenty that relates to the symptoms im experiancing now, it should be covered.

Now I just gotta wait for income tax $$ to start making it unique. My #1 dislike about the car is the in-dash cd player setup. Its stupid expensive to put an aftermarket system in it cause you have to rebuild the entire dash.. O well

Thanks again everyone

 

[Blendercloud]

I also had an idea. I've actually been thinking about this for a little while now and what you just posted makes me really wonder...

When was the last time the fuel filter(s) were replaced? I'm not sure if the Mazda 6 wagons have one or two fuel filters. Some cars have one in-line and another in the tank. That could very well be your problem when you consider the car sat for a year most-likely with the same gas in it.

At 58,000 miles you're probably due to replace them anyway.

 

[bestbiker]

I also had an idea. I've actually been thinking about this for a little while now and what you just posted makes me really wonder...

When was the last time the fuel filter(s) were replaced? I'm not sure if the Mazda 6 wagons have one or two fuel filters. Some cars have one in-line and another in the tank. That could very well be your problem when you consider the car sat for a year most-likely with the same gas in it.

At 58,000 miles you're probably due to replace them anyway.

Wow cant believe that hadnt crossed my mind yet. Definetly going to check into that! Thanks again!

 

[jaymangrum]

i agree, reading that changes things in my mind to, especially with the status of fuels of the past couple years. I was having to change fuel filters (or backflush) on my truck/car/bikes all the time due to crap fuel at most the stations in my area. IF this were my car, i would grab a factory service manual (rosenthal mazda online), do a full fluid and filter change on everything and a full service on everything else (visual inspect--to replacement). If for nothing else, the peace of mind. good luck to you.

 

[2003protege]

Could the PCV valve affect gas mileage that much? Just a thought if nothing else is coming up.

 

[Blendercloud]

Could the PCV valve affect gas mileage that much? Just a thought if nothing else is coming up.

It probably wouldn't affect it that much without throwing a code.

 

[FORZDA 1]

Sounds like the air filter is clogged or the little high rpm flapper door isn't working. The car is running terrible rich, so you should see the problem with an OBD2 data reader. The engine vacuum, fuel trims, and AFR(O2 response) at idle, just above idle, cruising, and at WOT tells the whole story. You need to do proper diagnostics rather than throw parts at the car. If your dealer was worth a s***, they could find your issue in an hour or two with their Mazda Diagnostics tool. Hell, if you lived close enough, I could hook up my laptop and tell you...

 

[2003protege]

It probably wouldn't affect it that much without throwing a code.

wasn't sure how quickly a bad PCV could throw a code.

and I have to agree with the comment about your shop / dealer above. troubleshooting 10 mpg city is not chasing ghosts.

 

[bestbiker]

Sounds like the air filter is clogged or the little high rpm flapper door isn't working. The car is running terrible rich, so you should see the problem with an OBD2 data reader. The engine vacuum, fuel trims, and AFR(O2 response) at idle, just above idle, cruising, and at WOT tells the whole story. You need to do proper diagnostics rather than throw parts at the car. If your dealer was worth a s***, they could find your issue in an hour or two with their Mazda Diagnostics tool. Hell, if you lived close enough, I could hook up my laptop and tell you...

so will a compression test determine any of these? or what should i ask them to check? the engine is the same as the taurus had so they definetly have the correct equipment to check it.

As mentioned, nothing is off enough to trip any sensors to make the check engine light come on

also would like to add it isnt at high rpm very often, its in 4th gear going around town at 25mph (5 speed auto/slapshift)

 

[bestbiker]

The car is running terrible rich, so you should see the problem with an OBD2 data reader. The engine vacuum, fuel trims, and AFR(O2 response) at idle, just above idle, cruising, and at WOT tells the whole story. You need to do proper diagnostics rather than throw parts at the car. If your dealer was worth a s***, they could find your issue in an hour or two with their Mazda Diagnostics tool. Hell, if you lived close enough, I could hook up my laptop and tell you...

Talked to the dealer again, they have a pretty high tech snap on tool that they had hooked up to a laptop as they drove around and they wernt able to find anything out of the ordinary.

I really am at a loss as to why they cant determine whats going on. Maybe the computer on the car itself is screwed up and not regestering codes??

 

[LBV]

Things to check that come to mind:

- air filter like was mentioned (a clogged fuel filter would cause other issues like sputtering or lack of power, not bad mileage)
- spark plugs were incorrect ones??
- egr & pvc system
- dirty throttle body not properly opening
- dirty MAF sensor reading air flow incorrectly

Gas mileage does get worse during the winter though too. That's all I can think of for now.

 

[redspeed6]

It takes an act of God to get a code/light to set on these Ford computers. I would recommend checking your PVC system. They are real finnicky on the V6s and cause alot of driveability issues without any codes popping up. This could cause your issue with gas smell in the oil.

Also look at your LongTerm Fuel trims - Lfuel LF and Lfuel RH (if i remember right) if the levels are high like above 12 or so, that tells me that the computer is dumping fuel to compensate for either an air leak or bad reading from an O2 sensor.

There are so many things that contribute to your problem and as stated earlier, a few hours and decent tech should be able to hunt it down and figure it out.

Just my .02 Let me know if this helps.

 

[LBV]

That's one I missed.. a bad O2 sensor reading AFR incorrectly.

 

[bestbiker]

Finally! With just under 70,000 miles I drove 3 hours and had a dealer hook up to it at the risk of the scan being very expensive.

Bad Catalytic converter. It wasnt plugged, just bad. Federal warranty covers those for 7 years and 70,000 miles so I got very lucky. No check engine codes got thrown because the way the cat went bad, was causing the engine to alter the fuel ratio to try to counter it based on the O2 readings

Fan relay module was bad as well, it was causing it to kick on and off every few seconds.

The combination of those 2 being swapped brought my gas mileage to 18 in town, and 26 on the highway. Far better then what I had been running at.