eb110americana

iTrader: (4)

My car isn't as bad as yours, but I've been tracing bad MPG for a week or so now. I just moved and am now driving all city, no highway, and getting just over 15MPG = 220mi/14.5Gal. My car is a '98, auto with 181,000mi, mostly stock with just a Flowmaster muffler BTW.

I did the fuel filter (long overdue), cleaned the MAF, new PCV valve, new air filter last weekend. My intake is all oiled up, so I'm going to try to clean it with the Mopar stuff soon, plus I have 3 new O2 sensors sitting next to me waiting to go in (replaced 1 about 1-2 years ago, cleared a code for another a couple months ago).

The car always runs smoothly, but I do smell a rich condition from the exhaust. I have relatively new plugs, but I should check those due to the oil. I also had 2 new cats put in a few years ago, so those are working well. I'll keep you posted if anything improves the situation. When you cleaned the MAF, did you look inside the intake manifold through the throttle butterfly? Those PCV valves are really cheap, so I'm going to be regularly replacing mine from now on to avoid another oily mess.

Midnight02

iTrader: (8)

Call me crazy, but that doesn't seem that far outside of the norm if it's primarily stop and go driving.

I have a 3 mile commute to work each day. When I drive my car back and forth to work and don't mix in any highway time I would expect between 160 - 180 miles on a tank of gas. Granted, my car has plenty of mods that contribute to reduced fuel economy, however it doesn't seem that much different than when the car was stock.

The guys who speak of "averaging" 300+ miles to a tank of gas in these cars amaze me. I could pull it off if I drove all 300+ miles on the highway with the cruise set at 65, however I wouldn't expect anything over 250 miles on a tank when I mix in some city driving. Heck, my 6-cylinder Grand Am is lucky to get over 250 miles on a tank of gas when some city driving is mixed in.

As a general rule, I'm thrilled to get over 200 miles to a tank with my standard mix of driving.

oberth1

iTrader: (6)

Thats still pretty damn bad. i dont think i have ever been lower than 230mi a tank on my hawk or any f-body i have owned. 28.8mpg highway (@80mph for 460mi) and about 20 local, but i drive right lane most of the time at the speed limit.

If you need a stock maf to test out anything i have the stock one from my 2000 i would be more than happy to mail out to you... 13k miles on it works perfect. Your paying shipping of course :-)

desalator089

iTrader: (5)

its weird cause i was getting about 190 to a tank for awhile 75% city driving then i dumped a whole can of seafoam into my gas tank and it went to about 226 for the next few tanks doing the same exact driving but i was driving probaly 6-8 times a day at most a mile at a time between destinations.

LS6427

iTrader: (2)

If you lightly to moderate modded guys aren't getting 200+ to a tank in city driving....you have problems. I get 230-ish miles with my built, old ***, 427ci. And I drive aggressively every day to some level. Whether its a bunch of hard accelerations in the city or a 160mph run on an open highway.....its not all casual driving ever. I could get 250 miles if I drive casually through a whole tank in the city. 14-15 mpg isn't allot to ask out of these cars.
Now I also do a ton of my driving in the city in OD, cruising steady on decent stretches at 45-50mph. Staying in "D" is not how to do it, and I know allot of guys do. Manual guys, high gear is the way.
Sounds obvious, but I don't see why so many lightly modded cars are getting such terrible mileage.

Considering your tunes are OK......most are probably dirty *** injectors, leaky injector(s), or failing 02 sensors making you run rich.

.

The_One

iTrader: (6)

Is your tire pressure correct?

Brakes dragging?

Alignment OK? Excessive toe can lower fuel economy.

These are little things, but should not be hard to check.

Onyx_Black_Z28

iTrader: (2)

Oberth1, that would be fantastic on the MAF - I appreciate the offer. I may seriously be taking you up on that. I'm trying to make some sense out of my recent experiment. I just took a road trip over the weekend - about 220 miles to my destination. Way there, I ran with MAF disconnected and SES light on. I had about 35 miles of city driving in the tank before we left, and about 30 more when we got there. Went to 300 miles before the gas light came on. On the way back, I plugged the MAF back in and reset the PCM (PCM IGN and BAT fuses method) to make sure the codes were cleared and the MAF was being used again. Filled up just before we left and made it to 220 miles with nearly a half tank of gas left? So I'm really confused. Both ways, driving was between 80-90 mph the entire way with a few hard pulls to get around people. So my highway mileage is fantastic, but city mileage is abysmal? Anyone care to chime in on this?

Agreed! A close friend of mine with an 02 T/A M6 actually took the same road trip (see reply to above quote) as I did this weekend. His mileage on the highway was extremely similar to mine, yet he is able to get 220-230 miles a tank in the city no problem. He also has more extensive bolts on than I do. I'm going to try running a can of seafoam through my gas tank today to see if maybe cleaning out the injectors will help.


Haven't checked the tire pressure, I'll check that today. I've heard/seen dragging brakes, and see nothing to think that is the case here. Alignment is a tad off - car tends to pull slightly to the right when left to it's own devices - but nothing terrible. Think this could be causing that big a difference?

Thanks everyone for the help! It is greatly appreciated.

Onyx_Black_Z28

iTrader: (2)

Missed this post the first time around. This is interesting - maybe this is the culprit for me also? I've done the seafoam in the brake booster (which I'm now reading was possibly dangerous and at best a waste of time) but haven't done the gas tank method.

DREAMZ28

iTrader: (1)

This must be a common problem. I got my 98 T/A this saturday. Although mine has 103k miles on it, it has been maintained pretty well.

On sunday I drove it around a little with my mom, I'd estimate maybe 40 miles at the most, and it went through a 1/4 tank of midgrade. With the windows down you can smell the car is obviously rich, I don't know if you're smelling gas or not but otherwise it seems like the same problem. I'm going to subscribe to this thread and update along with you, hopefully having two situations with the same problems will help in finding the cause.


I haven't tackled the problem yet but tomorrow I"m going to do the normal plugs wires and the air filter. I'll keep you posted.

Onyx_Black_Z28

iTrader: (2)

DREAMZ28, sorry to hear you are having the same problems. I actually realized my tires were underinflated - showing 28 PSI when warm (calls for 30 PSI plus an additional 4 PSI when hot). This can supposedly cause a decrease of .3% for every tire for every PSI it is underinflated (from fueleconomy.gov). So after I drove it around for a while (in the 80's here today), I filled em all up to 34 PSI. Also put the Seafoam in the gas tank, so we'll see how those two things work.

DREAMZ28

iTrader: (1)

Hmm, I'll check the tire pressure on the way to Pepboys, I'm going to see if they can scan the o2's when I get my plugs. I have a bottle of GUMOUT for the injectors, I'll try that next fill up.

01 ss vert

iTrader: (1)

How do you check for a leaky fuel injector?

strokerrace

iTrader: (8)

Pop the rail out with injectors still on, prime pump and look for leaks. Or if your fuel pump etc are good then a pressure test should show it but not which ones or one.

bluestreak98

iTrader: (21)

My automatic 2002 WS6 has a lid and catback and it gets 17MPG mixed driving. I go about 210 Miles on a tank of gas.

DREAMZ28

iTrader: (1)

Well, I popped the plug wire off of cylinder #1 only to realize I don't have a 15mm Socket. But the next time I drove it, no more fuel smell..... Hmm, well I'll still be swapping the plugs wires and air filter but apparently my problem is fixed?

johnny89345

iTrader: (1)

my car is also absolutely terriblle on gas 130-140 miles per tank on a good day doing mostly highway in 6th. since i bought it last year i have done slp intake/ ram air. new gm mass air, msd wires, ngk plugs, new fuel filter, ls6 pcv swap, fast 92/92, full exhaust and a kaltech tune. o and just recently 4;10s...i fogged out the motor to fix every last vacume leak. the only problem i had was when i got my tune before the new maf i was told my cars running a little lean. what else should i try, i also cant take driving....forgot to add if it makes a difference i had the egr/air/rear o2s tuned out with no change.

Onyx_Black_Z28

iTrader: (2)

Here is an official update for those of you following the thread. So far, there doesn't appear to have been one specific culprit causing the problem. With that being said, I did a number of things that helped a little bit.

I replaced my O2 sensors, plugs, plug wires and fuel filter. I used two cans of seafoam - one via the brake booster line (yes, I know now I shouldn't have done that now) and another in the gas tank. I also added air to my tires - all four were about 4 PSI low. I also ruled out the MAF by confirming that running speed density for a tank of gas made no change. I noticed a small improvement each time I did one of the things on the list above. The end result? About a 20-25% increase in fuel economy. It's still not quite as high as what a lot of you are getting, but it's much better.

As a point of reference, the first post showed 167 miles to an empty tank. I was getting about 11 MPG.

Here's a picture from today:


Using the miles driven/gallons consumed method, I am now getting about 15.25 MPG. This is on 90% City/10% Highway driving. I have yet to check the injectors to make sure there are no leaks - I will be sure and post the results when I do. It will likely be a while.

I've noticed there seem to be a lot of people having similar issues on the forums. Especially for those of you like myself that bought an LS1 that has been sitting for a few years, these cars are just gonna need a little love to get back into the shape they were in 98-02. Thanks again for all the help, everyone.

chrysler kid

iTrader: (14)

15mpg highway????? Wow.

Symptoms of a bad injector is that the car has hard starts where it takes a while to crank

If your mileage is that bad I'm gonna say you have a serious problem, bad wheel bearing, sticky caliper or something

Take your car and have it dyno tuned. And efficient vehicle making 300hp has no reason to make less than 24 highway

Onyx_Black_Z28

iTrader: (2)

15 MPG Highway? Are you talking about my posts (the original poster) or one of the other people who have chimed in? My 15 MPG is on 90% City driving (as referenced above). I recently went on a road trip and at almost entirely 80-90 MPH, my MPG was 22-23 mpg.

Daniel Richards

iTrader: (1)

15 is down right criminal, my brother has a 79 T/A Auto with the 403 olds. engine and when it was in running order it got like 16 highway and 13-14 around town depending on how many burnouts I did that week.

I've got the v6 in my 99 and i'm averaging a little under 21 in my daily driving which gets stuck in stop n go in front of the local middle and high schools but the rest is mountain cruising between 30-55 mph and I feel like mines lower then it should be so I dumped a bottle of the every oil change Lucas stuff in last fill up and will be changing my fuel filter next weekend. and If I don't get what I want from that then I'll look into plugs and wires possibly some MSD coil packs down the road. The guy I bought mine from had replaced the original engine when he bought it so I have the coil pack base, upper intake plenum/throttle body, all 6 injectors and the fuel rail there attached too for spare parts.