FAQ: Improving Bad Gas Mileage

brutusk1 wrote:

Reporting back as ordered, Sirs:

I changed out the AC Delco front O2 sensor to a Denso and achieved this mileage:

365/15.7 = 23.25 mpg August 13th - Normal workweek commute 30 miles highway one way.

Then I changed out the Castrol GTX 10W-30 to Mobile 1 synthetic 10W-30

433.8/18.3 = 23.77 mpg September 29th - Normal workweek commute 30 miles highway one way.

So no appreciable difference was obtained. Has anyone who cleaned / changed out injectors noticed a mileage improvement ? I would think dirtly injectors that don't atomize well would cause a mileage drop in the same way that a dirty fuel filter would.


Thoughts / comments ?

The difference *is* appreciable -- you picked up roughly 1/2 MPG which in an 18 gallon tank gives you an extra 10 miles or so which is 1/3 of your daily grind per tank.

Albertj

I have a 95 S/C bone stock Series I..
I get calculated 12-15 mpg in the city/highway. I live 2 miles off of the interstate but mostly drive through city here in St. Petersburg, FL. It just doesn't seem right!!!

I'm able to keep a steady mpg staying under 3000 RPM, staying off the SC as much as I can. Practically drive like an old woman would.
I've come to notice a decrease in oil.
Went to change the oil and noticed the entire pan was covered in oil and it was everywhere.
Going to need to replace pan, but as of right now it doesn't leak oil onto my driveway or smell of burning oil.
Tranny is smooth. Engine rattles and almost wants to die out most times when I start up. Sounds like it needs a choke. SMH

I've cleaned the injectors,
Monitored TP (33 psi with same size stock tires)
Coils/plugs/hoses all replaced a year ago.

Any ideas or precautions I should take?

The good news is, the engine doesn't seem to be burning much oil, since you can see where it's coming from. Leaking oil doesn't impact your MPG, so it must be something else.

Have you changed the fuel filter? That's probably not it, but worth doing if you've bothered to clean the injectors. It's about $25. Btw, did the bad mileage exist before you cleaned the injectors?

Next I would find a can of CRC electronic parts cleaner (or similar spray made for cleaning circuits). Carefully remove the MAF sensor and spray it off really good. Replace and see if your starting improves.

Wouldn't hurt to pull those plugs and inspect the electrodes. I lot can happen in a year if the engine is not running 100%.

Check your brakes. If you can, lift the car off the ground and spin the wheels by hand. If one or more is very hard to turn, investigate why that brake is sticking.

Ask around for a tech who can scan OBD1 or OBD1.5 diagnostic systems. This requires a specialized scanner. Some shops or local parts stores will do it for free, or a small fee. Any DTC codes they find will make trouble shooting a lot easier!

How many miles are on the car? If higher miles, you may be ready for a new O2 sensor, or the catalytic converter may be failing. These are harder to diagnose, and more costly to replace. Recommend you have the car scanned for DTCs, or have a tech test your car for these items before replacing. $40-50 is a lot cheaper than $100-400 for parts that may or may not need replaced.

Finally, one last thing. Did you read the Welcome page? At the bottom is a link for new members regarding some rules on posting. Check it out when you have a minute!

Your engine should be turning about 1600 RPM at 60 MPH on the highway. If it isn't, you may have lost 4th gear overdrive, and possibly the lock up in the torque converter. That will seriously decrease your MPG.

Hey guys im new here! A bone stock 97 Riviera is my daily driver and my plans are to keep it a daily driver, but i want to make it fast... I know, thats what everyone wants, right? I've been weighing my options as far as mods and i figure i should get some opinions from more seasoned Riv owners before i do something stupid. Which of these would kill my mileage? keep it the same? help it?

-cold air intake
-headers
-intercooler
-higher ratio rockers and/or cam
-smaller pulley
-180* thermostat
-ported heads
-ported supercharger
-ported throttle body

I am planning on getting a proper tune after i do any of this... I just dont want to get done and be running 13s but getting three miles to the gallon haha any tips or feedback is appreciated very much!

Typically pretty much any "performance" mod or anything that makes power takes from economy. You may get away okay with the porting, the T-stat as well it just allows the engine to run cooler..

I know first hand that OEM fuel economy (16/25) can be retained with the following mods:

- cold air intake
- headers
- higher ratio rockers
- smaller pulley
- 180* thermostat
- PCM tuning
- cooler spark plugs

Of course, the potential exists to use more fuel, but only if you press the gas pedal more. Actually, with the above mods, you'll find that pressing the gas the same amount results in more power, so to get stock performance, you press it less. Economy is unaffected if this rule is followed regularly.

In theory, the following mods shouldn't impact economy, but I've not tried them to be certain:

- intercooler
- ported heads
- ported supercharger
- ported throttle body

The one mod that imo WILL DECREASE fuel efficiency is an aftermarket cam. The reason is that while added valve lift (rockers) doesn't seem to impact MPG at low RPM, a cam affects the valve duration at all RPM, which means lower MPG all around.

Performance transmission mods usually will have a negative impact on MPG as well. Stall converters, non-lock-up toque converters, and shorter gears all take their toll on efficiency. Some mods, intended for better durability and quicker shifts, shouldn't have an impact on MPG.

Hi all, I am looking for a list of items to check on my 95 NA to improve MPG. I am not trying to hypermile but I would like to achieve 30 mpg on the highway. Past experience with a 97 lesabre tells me this should be achievable. The only differance I see is the body and OBD 1.5 vs OBD II. This goal is a prerequisite for me to keep my car. I am currently driving about 90/10% (HWY/CTY) and get about 24 mpg at all speeds. I guess most people would be satisfied with that but i think with the current prices of gas and a relatively fixed income I need to do better. I am not looking for trouble shooting aid just a list of things to check/change that might help achieve my goal. Thanks in advance.

Priority # 1,is to find a used set of injectors from a junkyard and send them out to be cleaned. check the fuel pressure.check spark plugs and wires.keep the throttle body clean.clean the maf sensor every now and again.
same maintenace schedule for any other car applies to the Riv.
first and formost,no fat people in the car.remove the passenger seat if you must and discourage lard asses sitting in the back.

Plugs, air filter, basic maintenance will get you a small amount. Inflating your tires on the high side (35-40 PSI) can buy a few fractions of an MPG. Like robo said, loosing weight helps, too.

Make sure your transmission's torque converter is locking up correctly. To test, while driving in 4th gear (OD), and cruise control off, keep your right foot on the gas, then tap the brake with your left. Just enough to activate the brake lamps. This should correspond to an increase in RPM. That means your TCC is working correctly. TCC lock-up is important for good MPG.

My experience indicates the biggest factor to improve MPG is your route and driving style. I was surprised by this, because I always thought maintenance played a bigger role. First rule: use the cruise control as much as you can. This helps in a couple ways: keeps RPM low, and it discourages you from hitting the brake pedal. The brake can be more of an MPG killer than the accelerator. The more you drive pretending like you have no have no brakes at all, the better your economy will be.

Since your engine is NA, hitting the gas from a stop or slow roll isn't going to hurt you much. It's what you do with the established inertia that makes the difference. If you maintain the car's motion over a long distance, 30 or even 35 MPG isn't out of reach. If you don't let the car roll as far as it can, you're back down to 20 MPG instantly. Our Rivs are excellent free-wheelers. Take advantage if it!

Sometimes the chosen route can make efficient driving difficult. Change the route and see what happens over a tank of gas. I like state routes with as few stops as possible. Sometimes it hard to cruise at efficient speeds on the interstate. 48-60 MPH is the sweet spot for 30+ MPG.

Last thing: sitting idle gives the worst MPG possible: zero. Most people know this, but they don't realize just how much it hurts. Minimize the time your engine is burning fuel when not moving, and you'll see big improvements. It no longer true that restarting your engine takes more fuel than if you left it running for a minute. I usually shut'er down if I know I'll be stopped for more than 20 secs. Everyone's different with this one. I know this much - the Riv's starter motor is near indestructible, and our engine doesn't mind being restarted frequently.

Best of luck, and let us know your results.

That brings up a question.
Is there an after market product that imitates the shutdown-startup routine (as in waiting for a traffic signal) that some newer cars use?

I thought Hybrids were the only ones that did that?

Hmmm, I could be wrong, but I seem to recall reactions to the original "gas crisis" of the '70s resulted in a few stop-start engines. Maybe they were diesels?

Don't think so, diesels are even more economical while idling than gasoline engines.

Okay. I couldn't find data on that, but still recall an efffort after the 70's trouble.
However, in 2010, Ford announced it would move stop-start technology into it's mainstream engines beyond hybrids. I think Mazda has a system that can restart in.35 seconds.
It's estimated to be a 5-10% fuel savings. (?)
Doesn't sound like a retor-fit thang, but maybe,

My old commute involved a lot of traffic lights. I did the shut-off thing for a couple of months and had no recordable change in my economy. I decided it wasn't worth the effort.

Well, I suspect that an automated stop-start might be different than a manual routine. Probably would have to be so in order to make the difference it does.
I could live with it, unless I was trying to jump the guy next to me as we approached a merge
Maybe a retro-fit would allow a pass when desired

I don't think you want to start the car in gear. Not sure why, but my gut says don't do that. So that means at least shifting to Neutral before shutoff, and waiting for the revs to come back down after restart before you drop it into gear. I got pretty good at timing it, so I would coast the last few feet with the engine off in N, and start it right when the light changed (as long as I wasn't the front of the line) so I could drop it back into gear when it was my turn to go.

I agree with Derek on the start/stop effort not providing a huge benefit while rolling from light to light. It's a lot of effort for almost no gain. I also agree with his technique of only starting stopping in N, not while in gear.

Where this really benefits MPG is in cases where you're sure to be stopped for long periods, as I said more than 30 secs without rolling. Like drive through lines, and "warm-up" periods in the winter, where the car can be just sitting, drinking gas. I think it really does impact combined MPG. I try to avoid these situations entirely, and have been getting ~21 MPG average, and that's running 8.5" wide summer performance tires. I also tend to drive in the 70-80 mph range a lot of the time, which isn't the most fuel efficient.

Btw, remote starts are a hugely inefficient idea. You're directly swapping convenience for MPG.

For winter months, I have stopped the old "get the car warm and comfy" routine. Instead, I scrape the windows first, then start the engine, activate the seat warmers, then start the car moving right away, letting it warm up in the drive. I don't rev the car much above 2kRPM until the t-stat opens. Even then, I take it easy until about 10 mins into the drive (oil takes a little longer to heat up).

AA wrote:

I agree with Derek on the start/stop effort not providing a huge benefit while rolling from light to light. It's a lot of effort for almost no gain. I also agree with his technique of only starting stopping in N, not while in gear.

Where this really benefits MPG is in cases where you're sure to be stopped for long periods, as I said more than 30 secs without rolling. Like drive through lines, and "warm-up" periods in the winter, where the car can be just sitting, drinking gas. I think it really does impact combined MPG. I try to avoid these situations entirely, and have been getting ~21 MPG average, and that's running 8.5" wide summer performance tires. I also tend to drive in the 70-80 mph range a lot of the time, which isn't the most fuel efficient.

Keep in mind that my old commute where I was driving the Riv and used this method was 12 miles, and usually took close to 1 hour. 25-30 minutes for the first 11 miles, and 25-30 minutes for the last mile. (I could walk there faster if there was parking where it all stopped) This meant sitting light cycle through light cycle, sometimes starting the car to pull 2 lengths forward, then sitting for 2 minutes, then pulling forward again, etc etc. This is why I started trying the stop-start method, and believe me I was shocked that it made no difference. Good news is that the 3800 is a very efficient idler.

I got 256 miles on my last fill... dammit.

15 gallon tank, right?

18.5 gal. I'm seeing 300-400 mile per tank, depending on the type of driving.

holy shit. I didn't even know 400 was possible. ~320 was my all time best.

I was like 2mm left of E with E light on and I fill up 14.5 gallons. That's why I assumed a 15 gallon tank.

I can typically get about 400 miles out of a tank as well, with my regular driving routes. I never let the tank get that low though. Premium fuel (93) here is about $3.79, depending on which station.

wow. Why is my mileage so off, I wonder.. I drive like a semi-normal person..