Poor Mileage+Thick Carbon

[mgm13]

Recently purchased a 2003 Dodge Ram 1500 truck, 3.7L auto with 54,000 miles. Changed air cleaner cause it was filthy, installed new plugs and changed oil and filter.Put 12oz AR-X in engine and 6ozin trans.Have run 1,000 miles since and truck runs good but is a major gas hog steady 70mph on a 220 highway run and under 18 mpg, also I can scrape carbon out the tailpipe with a spoon because there is so much of it.Oh I also ran 32oz of Techron concentrate tank before last. Any suggestions please I could sure use some help?

 

[adam123]

Oxygen sensor maybe. 18MPG in a truck is not bad, Have heard many times the v6's in newer trucks gets less mpg than their v8 brothers.

 

[ALS]

Ditto what Adam123 said about the gas mileage and the O2 sensor. I have read many posts over the last year on this board and others about the dismal gas mileage the Dodge trucks are getting.
From your post this truck sounds like it was neglected when it came to maintenance.

 

[Drew99GT]

Keep at it with the additives. Run another round of Auto-RX at least, and a few more runs of Techron or Redline SI-1. Doing that has really cleaned out the carbon in my Toyota and the tailpipe is visibly cleaner now.

 

[Matt_S]

That truck is rated 16/21 city/highway, so there seems to be room for improvement. I'd look into the O2 sensor and possibly cleaning out the intake. Spark plugs might also be an issue.

 

[mgm13]

Is there a way to tell which oxygen sensor may be bad? It looks like there are 4 of them, 2 up front and 2 in back I hate to think about changing all of them because $ are pretty tight.

 

[Craig in Canada]

If the truck is like other vehicles I'm familiar with, only the "front" O2 sensors are actually responsible for mixture control. The "rears" just check that your cats are working.

Lots of carbon usually means running rich. Either the PO floored it alot, or you might have an O2 problem. A clogged air filter won't help - it may have been running rich a lot for the PO.

You might want to make sure that you reset your DME/ECU. This might be done by disconnecting your battery for a while (30 minutes? Every car is a little different). This would get rid of any fuel trim or other settings that may have been caused by a clogged air filter.

What kind of gas do you run? Maybe try stepping up one octane rating and see if you notice any kind of improvement. Again, resetting the ECU after changing octane is the best/fastest way of making sure your engine is adapting to the new conditions.

Tailpipe carbon alone in no way suggests that you need autorx but it can't hurt (I liked it). Redline SI-1 and other cleaners may help clean up the combustion chambers etc... A "steam cleaning" with water through a vacuum line might work better and faster. Inspect the chambers through the plug hole to determine if you're just wasting money on more cleaners.

 

[Tempest]

The 3.7 in my Liberty gets lousy milage. No carbon in the tail pipe though.

 

[Rickey]

In addition to the others comments:
Be sure that the tires are inflated properly.
Check thermostat, does it have a temp gauge...if it never warms up to full temp mileage will suffer.

And it may be that what you are getting is as good as it will do... there may be nothing wrong with it.

Good luck sir.

Rickey

 

[Merkava_4]

Quote:

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Is there a way to tell which oxygen sensor may be bad? It looks like there are 4 of them, 2 up front and 2 in back I hate to think about changing all of them because $ are pretty tight.

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You should have a "Service Engine Soon" light on the dash right now with a code stored if one of the oxygen sensors is out of range. You can throw parts at it, but getting the truck scanned by a Tech II scanner would probably save you some unnecessary parts purchases. You can always pay to have someone run a scan - and then change the parts yourself; that's what I do until I can afford my own scanner.