Sudden (apparently) decline in gas mileage?

[circmand]

when was the last time you had the engine tuned? How often should it be tuned?

[nfpgasmask]

So last night I changed out the fuel filter. I also added some Lucas additive.

Now, to answer some questions, my spark plugs were changed just this past summer. Off the top of my head, I can't remember what brand. However, after I changed my plugs, I did not notice a marked decrease (or increase for that matter) in my gas mileage, so I doubt my plugs would be to blame.

Now, the O2 sensors and CAT I have been thinking about. With all that oil burning, they could potentially be full of soot. But, if an O2 sensors was flaking, wouldn't I throw a CEL code? I mean, I know our CPUs are intelligent and they "learn" to compensate for certain conditions, so maybe not?

My next plan of attack will be O2 sensors and FPR. I think we have two O2 sensors, right? One upstream and one downstream?

I will keep you all posted.

Bart

[89Vette]

With a CEL for two specific cylinders, shouldn't you concentrate on them?

I'm not familiar with the code/meaning that you're describing (or even if you've posted the exact msg). But, I would suspect the plugs or coil packs -- having gotten that code.

And, TBH, I haven't (yet) figured out how spark is distributed on a coil-pack ignition system. IOW, without a distributor, if there's any other component that could fail and cause this condition. (Obviously, the older systems would require you take a look at the distributor -- for cylinder misfires.)

[BigSwede]

You should have 4 O2 sensors, one before and one after each cat. My understanding is the ones after the cats are not particularly important, it's the two before the cats that are key.

[89Vette]

Have you ever deviated from the stock engine and components? I mean it! Air filter, plugs etc.??? If you have, you will get less mileage. How I get 20 mpg in summer is simple. No engine change items. (Tried a K&N air filter once and watched mileage plummet...really!) In winter, I run higher tire pressure due to lower ambient temperture not causing over inflation. Take the roof rack off, not only quieter but better mileage. The old addage more HP=less mileage is true. Stick to 215hp. Also, synthetics in drive line and engine cut resistance and boost mileage. That's all for now, I'll think of more later.

Are you the person posting improvement with Royal Purple? What speed to you drive in the hwy?

One of these days I'll try that sea foam stuff. I assume it cleans the valve for better atomization? (I've heard water vapor works for that too.)

I tried injector cleaning but that only got me .5 mpg. (Hard to imagine fuel cleaner would help.) Pumping up the tires helped a bit tho, Mine are (street-tread) 31's. I wonder if that oversize helps, hurts, or is a wash?

Many moons ago, I tried 14" wheels and larger tires on an early generation Honda CVCC. (lightest and smallest car I ever owned.) The mileage went down with the larger tires. Quite a bit IIRC.

I've never driven on the hwy long enough to figure out the max mileage. My trips are usually 5-10 miles. Can't help that its running in open loop such a high percentage of the time.

[MSHardeman]

Bart, wanted to give you a heads up. Don't know if this will help your gas mileage issue, but I was changing my FPR out today due to the VX taking a few more cranks than usual to get started, and I noticed that the rubber tube connected to the FPR was cracked and wasn't getting a good seal. I haven't started the VX after it has sat for a while to see if my slow start issue has been taken care of, but I'm wondering if my FPR was just fine and I just needed to trim the tube down so it could get a better seal.

[nfpgasmask]

Mark!! Thanks very much, I will have a look at this. I still need to replace mine again. I have a few things that need attention, my brakes as well, up front, which could be dragging a little. Anyway, I will definitely check this out.

Thankfully, I have been roaming around Reno in my new to me Trooper RS. I'm enjoying the little 4 banger and getting about 300 miles per tank! This little goat hauls!! Its got some issues that will need attention, but so far I love it.

Thanks - Bart