Fuel mileage dropping

[PursuitSpecial]

I've been keeping up with the fuel mileage on my Aspen since I started driving it and the last two times I've filled up the mileage has dropped off sharply. I checked the entire fuel system for leaks and there are none. The car went from getting about 16-18mpg in the city on regular gas now to 9mpg, and last time I filled it up I put premium in it and it only got worse. I checked the choke and it's opening, and the exhaust doesn't look black or smell rich. I only get on the throttle hard occasionally if I have to pass someone. I don't know if it's possible for a slant 6 to burn that much gas. I think someone might be stealing it, I live in a rough area and park near the road. I'm taking it on a 120 mile road trip tomorrow with a full tank so that'll either settle the question or leave me stranded from an unknown engine problem...

 

[Aspen500]

An S6 getting only 9 mpg in a car that got 18 would be about impossible without any other symptoms. My guess is also that some worthless loser is a stealing it. Suppose the test will be the 120 mile trip though.

My Aspen gets only 9-10 mpg also, but it's 500" lol.

 

[AMC Diplomat]

I tried to get an accurate mpg out of my Diplomat only one time. I came up with 7 mpg. I was pissed until I went to reset the trip odometer and instead of resetting it jumped ahead 40 miles and stayed there.

So, lesson is, don't trust a 40 year old mechanical trip odometer

But someone is probably stealing it. You can get a generic locking gas cap or go all fancy and get a Mopar branded one

 

[Camtron]

Well, if not a gas thief, when’s the last time your ignition system got a tune up? If the over all carb function seems right, and it’s not stalling, hesitating or shaking bad at idle, I’d start at ignition system, spark plugs/plug wires and check your compression while you check/change plugs.

 

[AMC Diplomat]

The other thought that occurred to me was you have a leak under pressure in the fuel system. So it's only leaking when it is running. So half the fuel gets pumped to the carb and the other half to the ground

 

[PursuitSpecial]

I checked my odometer against the GPS and it's accurate. I ride with the cowl vent open and I can smell anything under the hood so I think I would smell half the gas getting dumped out of the pump. The ignition timing and distributor haven't been touched since it left the factory as far as I know, it still has the original wires and cap and ignition box, but it idles smooth as glass and runs perfectly at 55. I made it the first 60 miles of my trip without incident, I'll be heading home soon and I'll fill back up to check it.

 

[PursuitSpecial]

I just got back and filled up, my mileage checked at 21 mpg highway on shell 93... Someone's definitely been stealing my gas. It ran perfectly there and back. I guess I need to start parking the car in my backyard and put up cameras or get a locking gas cap.

 

[AMC Diplomat]

Deleted, wrong cap per @Mikes5thAve

 

[Mikes5thAve]

That doesn't look like the right cap it needs the kind with screw threads.

 

[AMC Diplomat]

That doesn't look like the right cap it needs the kind with screw threads.

Another Ebay liar. I'm not surprised. I'll delete the link

 

[Mikes5thAve]

I tried searching the part number to find application but it came up with nothing.

 

[Camtron]

Lol, went to work this morning with half a tank in my car…went to leave work and barely had enough gas in the tank to get down the block to the gas station…gas theft is for sure on the rise. If that isn’t a sign of shit getting bad again, I don’t know what is…then I can’t help but wonder, is my stolen gas actually going in a car or does it get huffed on a damn rag.

If I come up on a locking gas cap #, I’ll share it here.

 

[AMC Diplomat]

Lol, went to work this morning with half a tank in my car…went to leave work and barely had enough gas in the tank to get down the block to the gas station…gas theft is for sure on the rise. If that isn’t a sign of shit getting bad again, I don’t know what is…then I can’t help but wonder, is my stolen gas actually going in a car or does it get huffed on a damn rag.

If I come up on a locking gas cap #, I’ll share it here.

If someone steals my gas I hope it throws off the timing in their delicate computer controlled 87 octane engine

 

[Mikes5thAve]

There are several locking caps listed on rock auto. If a local parts store has them in stock bring yours in to compare.

 

[PursuitSpecial]

It's getting absolutely terrible around here. Last night someone drove onto our property, loaded up 3 cars we had sitting in a field and stole them. I don't know if they had multiple flatbeds or made multiple trips, and the cars were immobile so they had to do some pushing and winching. The field they were in is pretty far off the road and they gained access through the power line easement, so we didn't hear them or get them on camera. They stole a 1973 340 4 speed dart and 2 Polaras, they were in pretty rough shape but we were using them as parts cars to fix some other mopars. They're probably gonna chop them up and sell the parts. We filed a report with the police but I doubt anything will come of it. A few weeks ago someone broke in my neighbor's shed and stole her lawnmower too. I have no idea if these incidents are connected or there are just that many thieves running around. You can't leave anything unattended around here anymore.

 

[Camtron]

It's getting absolutely terrible around here. Last night someone drove onto our property, loaded up 3 cars we had sitting in a field and stole them. I don't know if they had multiple flatbeds or made multiple trips, and the cars were immobile so they had to do some pushing and winching. The field they were in is pretty far off the road and they gained access through the power line easement, so we didn't hear them or get them on camera. They stole a 1973 340 4 speed dart and 2 Polaras, they were in pretty rough shape but we were using them as parts cars to fix some other mopars. They're probably gonna chop them up and sell the parts. We filed a report with the police but I doubt anything will come of it. A few weeks ago someone broke in my neighbor's shed and stole her lawnmower too. I have no idea if these incidents are connected or there are just that many thieves running around. You can't leave anything unattended around here anymore.

I thought my morning was rough throwing my alternator belt on my way to work.. sorry to hear. That sucks man.

 

[Justwondering]

Ouch ... thats a rough day.

 

[AMC Diplomat]

It's getting absolutely terrible around here. Last night someone drove onto our property, loaded up 3 cars we had sitting in a field and stole them. I don't know if they had multiple flatbeds or made multiple trips, and the cars were immobile so they had to do some pushing and winching. The field they were in is pretty far off the road and they gained access through the power line easement, so we didn't hear them or get them on camera. They stole a 1973 340 4 speed dart and 2 Polaras, they were in pretty rough shape but we were using them as parts cars to fix some other mopars. They're probably gonna chop them up and sell the parts. We filed a report with the police but I doubt anything will come of it. A few weeks ago someone broke in my neighbor's shed and stole her lawnmower too. I have no idea if these incidents are connected or there are just that many thieves running around. You can't leave anything unattended around here anymore.

Watch them be stupid enough to sell the parts on a car forum/marketplace/craigslist

I'd start hunting the other mopar forums/marketplace/craigslist and as soon as something pops call the detective assigned to your case. If you don't have his number, get it. Major felony theft like that is usually assigned to someone

 

[Camtron]

Yea, it’s so bad around, Chicago that you can find plenty of stolen Mopar shit on Fb Marketplace. They don’t even try to hide it in their post.

 

[Aspen500]

Man I feel lucky. The 'burb I live in, especially the part of it my house is in, don't have to worry about theft (or any crime)much, if at all. You could leave a car parked at the end of the driveway, keys, title and $100 bill on the dash, with the lawn mower and snowblower next to it, come back a week later and 99.9% probability it would all be as you left it, untouched. I mean, not going to do it but could with very little worry. It's the way it should be.