Fuel mileage question

Can't quite get a handle on what's going on with my daily driver. Just bought a '93 Olds Cutlass with the 3.1 V6. Coming home from the dealer, I filled it up. In bad need of a tune up, it ran like a 3-legged dog especially when in a pull, missing and such. I bought new plugs and wires when I got home. The old ones were fried, with at least a .200 gap. Looked even wider, but conservatively at least .200. Anyhow, in go the new ACs gapped @ .045, like the decal says. I got almost 28 mpg with the old plugs. Gas mileage dropped to 25 mpg with new plugs/wires, and today, I filled up again and am getting only 23. Wondering if re-gapping the plugs to about .100 would help. If the coil will fire the plugs that came out, .100 should be nothing. Any thoughts?:confused: Wondering if this Ethanol might have something to do with it?

 

If the ethanol causes you to "feel" like the car is a bit sluggish then you may compensate by pressing on the gas just a bit more.

 

I didn't even know a car would run with a .200 gap or how one may be obtained without breaking the center ground tang. I guess the electrode could be severely deteriorated, opening the gap. CRAZY! I wonder if they were intentionally gapped that way to mask another issue.

Anyway, I would leave the plugs gapped at .045, disconnect the battery for 10 minutes. The re-connect and start the car and let it run at idle for about 10 minutes with no accessories. Then go fill it up, write down your mileage and check the next tank. The reason I say disconnect the battery is to let all of those little chinamen that are running around in the "brain" of the car have a rest and realize that there is something different. Then the 10 minute idle will re-calibrate sensor input. Whether or not this will help on a 1993 I do not know, but have learned that with computer controlled cars they have a calibration routine since the timing is not manually adjustable.

Also I often forget that I deviated my driving route or pattern on a given tank. Its not uncommon for me to see a 30% variance from tank to tank when town/country routine differs (or steppin' on it!).

Rodney

 

The plugs were burned up. I have a plug gap gauge that goes up to .080, and I think I could have gotten 2 in there with room left. I don't see how it ran at all, but it ran great except when stepping down on the gas. Then it would miss. The check engine light is coming on. I will see what kind of code it is showing before I do the battery trick. I have cleared the codes before on my wife's Blazer. Check engine light stayed off for almost 6 months. An old mechanic told me one time that he used to open plug gaps to increase fire and mileage. Think I will try some ethanol-free gas next just to see what it will do.

 

Gap open that far and ran fine is an odd problem, may be running a bit on the lean side now with the proper gap.

I agree with others, yank the cables and wait 5 mins. May also need an oxygen sensor or two at this point, check the tire pressure too, one could be going low dragging you down lol.

Throw in a new fuel filter and a bottle of seafoam. Ethanol fuel sucks!!! Try different stations around town till you find one that produces the best mileage and stick with it.

 

I believe you, but you have to admit that is an awful big gap. On an older car, one would just about have to change the timing to get it to run; bigger gap fires later.

Keep us posted. I like gathering information on all types of cars and issues.

Are you calculating your mpg or relying on an "instant economy" readout on the car (if it has that option)?

Thanks
Rodney

 

Only readout I have is my calculator. I fill up, drive, refill and calculate. I had one code. It is for the intake air temp sensor. Got a new one ordered from Rock Auto. Probably be here Monday or Tuesday. Cheap enough to see if that is the culprit. I even fill up at the same station at the same pump, so the position of the car is the same. The engine light was not on when I drove it home from the dealer. We'll see.....

 

I already changed the fuel filter. I don't like the ethanol stuff. Some of the stations here are also offering non-ethanol fuel. Plan to try that. The best mileage I ever got was on Texaco gas. This was 3 years ago, or so. No Texaco stations here anymore. Mostly Exxon, BP and independants. I think all the gas is about the same. I see the same tanker at many different stations.

 

Update...... Last fillup, I got a little over 29 MPG on the Olds. Best yet. Mostly all highway driving, quite conservatively, except blowing the doors off some dork in a VW who thought he was Mr. Badass (just one time). Did absolutely nothing but add a small bottle of Lucas fuel injector cleaner. Can't believe the cleaner made that much difference. We'll see what this tankful does.

 

I buy the gas Lucas additive by the gallon.
It's great stuff.

 

I buy it by the quart. Started useing it in our taxicab fleet some years back.

 

Can't believe it would run with that kind of gap. My Cavalier couldn't get up to 55 when I got it, the plugs were about .080. Just a regap made it run well but I put in new ones anyway.

Sounds like you're getting about the mileage you should be getting with that Olds with normal driving.

 

i bet the intake air temp sensor had more to do with it than the injector cleaner since the engine now knows how to mix the fuel properly but the injector cleaner was a good choice as well, glad you figured it out :2_thumbs_up_-_anima

 

I used the cleaner before I replaced the sensor, so, don't really know what helped. Got 27.5 last fillup. :banana:

 

Thats great! wish i could muster better than 20 mpg with my wagon!