I have a 98 Ram 1500 Quad cab, 2WD with a 5.9 V8 and automatic. It has 102K on it, I bought it with 19K on it. Until about 6 months ago I got around 13 mpg city/suburb and 16 - 17 highway. Basically what most all of these get.

Over these past 6 months I get 8.5 to 10 city/suburb and 14 - 14.5 highway. Power might be down a tad also, but that's a tough call. I read somewhere that if the timing chain has excess stretch mileage will fall off bigtime. I replaced the water pump about 10 months ago and don't want to tear the thing apart only to find no major issue. Most of my miles are highway, like 80 - 20. This is my first Dodge so I don't know if these things can go from O.K. to needs replaced this quickly.

Lots of good stuff in here, so I hope one of you folks can advise.

 

Welcome to DF!

Have you checked your plenum? Have a look down the throttle body, use a flashlight, and maybe even a mirror. (use of a mirror requires removing the throttle body...) See any oil? Might be a blown plenum gasket.

 

I did the plenum fix, polished the internal manifold flashing, TBI polish deal a couple years ago. It uses minimal oil.

 

I also replaced the cat and both O2 sensors this past February. Spark plugs (stock heat platinum) have around 20K on them

 

i had a lot of slack in my timing chain when i changed it at 120K, also pinging and a little low on power.... but my mpg was not affected. its been stable at 13-14 city and 14-16 highway before and after.

does any one of you spark plugs look black and rich? like maybe an injector leak.
did the poor mpg begin with any of those service events? maybe a bad O2?
there have been reports of bad IAT sensor telling the pcm its -200 degrees, causing a very rich mix.

 

Usually, timing chains will need to be changed at 100k intervals. Alot of slack in the chain will cause power loss.

 

what did you replace the plenum with? if you only replaced the gasket, its probably blown again...you'll need a Hughes kit, or APS Kit....

 

Where are you getting your MPG from? Are you calculating it out our using the overhead console?

 

Thanks to all of you for the feedback. As a retired "gearhead" engineer, I figure mileage the old fashioned way - miles driven by the gallons used. I keep a log on all my vehicles from the day I get them. Everything goes in, including every gas fill up.

I have to check my log, but the IAT deal will be checked. I had relocated it near the passenger headlight in my air inlet tube. I wanted the "cooler" air temp read as I was towing an 18.5 foot car hauler from central Illinois to NC during our move in 2004. It gave me more grunt over the mountains. When I replaced my water pump last year I put it back into the manifold. A few months after that is about when my mileage dropped. When we moved to FL in January this year, towing the same hauler, the truck did not perform near as well. I will pull the plugs also.

Thanks again folks. I'll keep you posted.

 

Got the truck done yesterday. I pulled the plugs and they looked goo, just the gaps all had grown .010 -.020! The cap and rotor chewed on also. MSD is obviously working. Plenum still dry, and I rolled the engine four times, marked the rotor, reversed the rachet, and the rotor moved the opposite direction within 5 degrees (timing mark on housing). I put Autolight double platinum 5224's in. Gapped them at .045, and indexed them. IAT good. Fired it up and WOW! New truck! All the house buying/selling and moving............ Feel like a rookie. Thanks every one for the good input. This is a great site.