Sudden (apparently) decline in gas mileage?

[nfpgasmask]

So, around the beginning of October, it seems my VX's gas mileage took a turn for the worse. Now, I could blame it all on winter blend fuel (ethanol) but it just seems to drastic, imo.

I always, always reset my tripometer when I fill up. And typically, I would get about 240 miles per tank. This was normal for me with the lift and roof rack, etc. But now my VX is right about 112,000 miles old, and I am getting about 190 miles or less per tank.

I'm still burning oil, no more or no less than "normal" and I am not feeling any performance loss or getting any CELs. The only thing different, is my VX doesn't like to start up like she used to. Normally, I would turn the key and vroom. Instantly my VX would fire up. Now, she labors a little on start up, a little skipping and then she runs smooth and normal. I recently got an alignment and my tire pressure is good. I will be needing new tires sometime soon but they are really ok for now.

So, what do you all think? I am thinking about changing the O2 sensors, possibly installing a new CAT, cleaning/changing my EGR and injectors. But with no CEL codes coming up, I feel like I could just be grasping at straws.

Or should I look at something else? Perhaps my brakes are dragging or something like that? I've checked my hub nuts and loosened them a little, as they were a little tight, but that has changed nothing.

Anyway, I just can't imagine ethanol is the reason, but maybe it is?

Bart

[MSHardeman]

Bart, I'm not really experiencing a drop in gas milage like you are, but Vicki is slow on starting up lately. Like you, I used to just turn the key and she would fire right up, but recently she turns over, sometimes for quite a while, until she catches and then runs like always. I did notice that if I turn the key on and wait for a while she will start right up as she used to. To me, and to some other that I asked for help here on the board, it sounds like a fuel issue; specifically a fuel pressure issue. When you turn the key on the fuel pump in the tank starts up and prime's the system and that is why I think she starts up after the key has been on for a few seconds.

Some of the suggestions where to replace the fuel filter and fuel pressure regulator (which I haven't done yet), and to check the valve on the fuel rail to see if it is pressurized after the car has been off for a while.
http://www.vehicross.info/forums/sho...t=cranks+start

Also, this weekend I got a CEL, and when I read the code it was a P1404 (I think), which translates to the EGR valve being stuck open. When that happened she REALLY didn't want to start, so I'll clean the EGR valve too to see if that helps any. I did knock on the EGR, lightly, and I think that jarred the valve loose because I haven't had the CEL show up again, and she has been starting easier.

That's my 10 cents. Hope some of it is helpful.

[BigSwede]

Bart, I'm not really experiencing a drop in gas milage like you are, but Vicki is slow on starting up lately. Like you, I used to just turn the key and she would fire right up, but recently she turns over, sometimes for quite a while, until she catches and then runs like always. I did notice that if I turn the key on and wait for a while she will start right up as she used to. To me, and to some other that I asked for help here on the board, it sounds like a fuel issue; specifically a fuel pressure issue. When you turn the key on the fuel pump in the tank starts up and prime's the system and that is why I think she starts up after the key has been on for a few seconds.

Some of the suggestions where to replace the fuel filter and fuel pressure regulator (which I haven't done yet), and to check the valve on the fuel rail to see if it is pressurized after the car has been off for a while.
http://www.vehicross.info/forums/sho...t=cranks+start
.

Sure sounds like a fuel pressure regulator to me...

[89Vette]

Sure sounds like a fuel pressure regulator to me...

[Ldub]

mine always goes from 230-240 mptank, down to 200 mptank every winter.

[nfpgasmask]

Well, my fuel pressure regulator was changed out probably 35,000 miles ago. Same with my EGR. I replaced it, not cleaned it.

Now Mark, I think you are on to something, because I notice the same thing. If I put the key in and turn it but not start up, I wait until the beep, beep, beep, beep is over and then usually it fires right up. Meaning the fuel pump has activated and got the right amount of fuel pumped up front. I sometimes wonder if it could be a tired fuel pump. The start up issues may or may not be related to my fuel consumption woes, but who knows?

I suppose I could pull my FPR and see if the screen has any holes in it, but again, I changed it a couple summers ago. I'll have to look back in my log book and find out exactly how long ago it was. Same goes for my EGR.

I was thinking though, when you burn a lot of oil, you are pumping a lot of soot through the exhaust system. So wouldn't my O2 sensors and my cat be pretty dirty? I mean, you would think I would throw a code if there was an issue, or at least experience some performance issues, which I am not, so I am kinda stumped.

Anyway, thanks for the thoughts.

Bart

[Ldub]

Well, my fuel pressure regulator was changed out probably 35,000 miles ago. Same with my EGR. I replaced it, not cleaned it.

Now Mark, I think you are on to something, because I notice the same thing. If I put the key in and turn it but not start up, I wait until the beep, beep, beep, beep is over and then usually it fires right up. Meaning the fuel pump has activated and got the right amount of fuel pumped up front. I sometimes wonder if it could be a tired fuel pump. The start up issues may or may not be related to my fuel consumption woes, but who knows?

I suppose I could pull my FPR and see if the screen has any holes in it, but again, I changed it a couple summers ago. I'll have to look back in my log book and find out exactly how long ago it was. Same goes for my EGR.


Bart

How long since you changed the fuel filter? That helped mine light up quicker, & is the cheapest / easiest / & maybe least fun solution to try first...

[Gussie2000]

Cold weather DOES play a role in this issue.

The colder weather is the demand for fuel is greater,especially when the VX has rest for several hours the fuel-air mixter during the engine pre-heat increases fuel use.

I noticed the increase in fuel use during these last 2-3 months,mostly when the temperture goes under 40~ i run the engine for no less then 10 minutes,during the first 5 minutes or so the high RPM can't accurately tell how much fuel were consumed during that short period of time until it goes down to normal but certainly is a good amount

[BigSwede]

So, around the beginning of October, it seems my VX's gas mileage took a turn for the worse. Now, I could blame it all on winter blend fuel (ethanol) but it just seems to drastic, imo.

I always, always reset my tripometer when I fill up. And typically, I would get about 240 miles per tank. This was normal for me with the lift and roof rack, etc. But now my VX is right about 112,000 miles old, and I am getting about 190 miles or less per tank.

I'm still burning oil, no more or no less than "normal" and I am not feeling any performance loss or getting any CELs. The only thing different, is my VX doesn't like to start up like she used to. Normally, I would turn the key and vroom. Instantly my VX would fire up. Now, she labors a little on start up, a little skipping and then she runs smooth and normal. I recently got an alignment and my tire pressure is good. I will be needing new tires sometime soon but they are really ok for now.

So, what do you all think? I am thinking about changing the O2 sensors, possibly installing a new CAT, cleaning/changing my EGR and injectors. But with no CEL codes coming up, I feel like I could just be grasping at straws.

My buddy's 2000 Trooper has recently dropped drastically in mpg also. I suggest pretty much the same things you have, but it is difficult to pin one thing down.

10% ethanol will drop gas mileage slightly, but not like you are reporting. An we have ethanol year round, here, so that doesn't explain my buddy's Trooper.

[blacksambo]

You're blaming the wrong culprit. It's the winter gas' high Butane level. I think it's more noticable this year due to new polution regs.

Have you tried Lucas fuel treatment? Cleans the injectors and plenum and boosts mileage, noticably. My wife (she drives one, too) and I are averaging 330 miles per tank now, almost 400 in the summer without the Lucas then, to counteract the Butane which leaves us in the spring. Hope this helps.

[nfpgasmask]

You're blaming the wrong culprit. It's the winter gas' high Butane level. I think it's more noticable this year due to new polution regs.

Have you tried Lucas fuel treatment? Cleans the injectors and plenum and boosts mileage, noticably. My wife (she drives one, too) and I are averaging 330 miles per tank now, almost 400 in the summer without the Lucas then, to counteract the Butane which leaves us in the spring. Hope this helps.

I'll try it! I just did a Seafoam treatment will little noticeable difference. We kinda got talking about two problems, one being the gas mileage, and the other being the slow start-ups. I bet changing my fuel filter will help with that a lot.

When I go buy a fuel filter, I will get some Lucas Fuel Treatment at the same time and see if things get better.

Thanks again,

Bart

[Mile High VX]

I use Lucas at almost every fillup...I'm getting about 15-16 MPG and typically have about 250-275 on the odo when I get gas. If I run it until the fuel light comes on it will always be over 300.

[89Vette]

You're blaming the wrong culprit. It's the winter gas' high Butane level. I think it's more noticable this year due to new polution regs.

Well this is the first winter with E10 (where we didn't have a lot of snow). With all the warm weather, people should be seeing higher avg MPG than E10 might dictate. (FWIW, if you didn't know: Alcohol returns less energy (BTUs) for a given combustion cycle. So, there's no way we'll get the same MPG as the 100% gasoline days.)

Have you tried Lucas fuel treatment? Cleans the injectors and plenum and boosts mileage, noticably. My wife (she drives one, too) and I are averaging 330 miles per tank now, almost 400 in the summer without the Lucas then, to counteract the Butane which leaves us in the spring. Hope this helps.

330? 400? It seems fairly hard to believe these vehicles are getting 20mpg on E10 (or gasoline for that matter)? The only way I could see that being close is if on long, continuous highway runs. That's because I've never gotten much over 250/tank. Jerry Lemond says it's really impossible to improve MPG over what I'm getting.

If this is really true, please say more about tires/wheels and percentage of hwy miles being run. Even the speed on the hwy would be relevant.

Any other mods (or significant service) too! Intake gasket? fuel injector swap? tuning?

[BigSwede]

Well this is the first winter with E10 (where we didn't have a lot of snow). With all the warm weather, people should be seeing higher avg MPG than E10 might dictate. (FWIW, if you didn't know: Alcohol returns less energy (BTUs) for a given combustion cycle. So, there's no way we'll get the same MPG as the 100% gasoline days.)

It's not as big a difference as you might think.

Ethanol contains roughly 80% of the btus of gasoline. So if the mix is 10% ethanol, you still have 98% of the btu as before. So you can expect 2% less btu and hence, mpg. So if you were getting 16 mpg before with straight gasoline, it will "plummet" to 15.68 mpg with 10% ethanol.

[89Vette]

It's not as big a difference as you might think.

Ethanol contains roughly 80% of the btus of gasoline. So if the mix is 10% ethanol, you still have 98% of the btu as before. So you can expect 2% less btu and hence, mpg. So if you were getting 16 mpg before with straight gasoline, it will "plummet" to 15.68 mpg with 10% ethanol.

I understand your point....I'll have to go back and refresh on that one. Thru the vette forum, I'm a long-distance friend to an injector rebuilder/seller. He figures a 5% change (drop in mpg) due to ethanol. He's got a micro-drilling rig and injector response machine. Both were purchased to design "in-between" injectors as replacements.

For example, a car the came with a 22lb/hr injectors will be fitted with a 23lb/hr injector as an ethanol replacement (to maintain stoich balance). The mapping machine helps him determine/compensate for non-WOT fuel delivery.