97 Highway fuel mileage

Maybe. On my 91 w/ 105K I'll get 28-30 at 60 w/o air on. But bump it up to

The knock sensor sets a code, but does not light the light. You might try swinging by your local AutoZone and see if they will read out codes for you.

I hadn't done many strictly highway trips lately, so if I get the chance again I will compare numbers. On my daily commute (60% highway), I still can't get over 21mpg no matter how light footed my driving is. It also seems low for summer driving without AC.

You know, I've been meaning to do that, but you're right I need to really check. I had a knock sensor code this summer that I assumed was caused by the other codes, but if it has reappeared that would explain it all. (Funny, the plastic cover on the ECU has a new home under my drivers seat, and I think it will remain there permanently).

Dave

Do a code scan. Knock sensor doesn't trigger the CEL. Also, I'm told spurious knock sensor codes are common. Scan, if you have the code, clear, drive, then scan again.

That's probably a couple MPG low and at 124K the knock sensor is probably gone, but check the codes to be sure (and then reset and check again in a day or two). If it's no longer working it won't make any difference if you run 87 or 93 and will lack the punch it used to have.

I usually get 26mpg or better with no AC at 75-85 mph on my interstate commute. This on a 97 auto running 89 octane. I'm surprised by that because my luck with this car has not been great otherwise.

Before you assume the knock sensor, have you thoroughly eliminated all the basic stuff? Like:

air filter feul filter spark plugs tire pressure

Once those items are checked, then I'd go to the knock sensor. Also, when a car gets old, rust and corrosion on the ground contacts can have an effect on how well the ECU is reading everything from the O2 sensors to the MAF etc. I would also consider cleaning all the ground contact or invest in one of those kits that gives you more ground contacts on the car. But this would be a very last resort suggestion.

CD

These were done recently at the 120k tuneup. Good ideas.

Good idea - I will do this. The car has significant terminal corrosion (the green powder) on the negative terminal of the battery. Is this related?

Invest, no, waste. The way to do it is to buy 8ga amp wire from a stereo shop and make your own kit for $15. The folks who make those grounding kits have quite a racket going.

Dave

That (only 26) could be because you run it on 89. It wants 91. Your knock sensor is constantly in action.

Clean those, that won't hurt, and there are other ground connections on the car, like one on the cam cover.>

That's an even better idea:)

CD

I ran 93 for the first few months I had the car and noticed it got about the same mpg. The EPA highway rating on it for the auto trans was 27, right?

EPA was 21 city/28 highway for the automatic, 22 city/27 highway for the manual.

My '97 automatic always got 28-30 on the highway.

So I did a test (yesterday). Woodland Hills (LA area) to San Jose, CA. Freeways. 341 miles. 5 hours 15 minutes. Average speed 64.95. Fuel consumed 12.248 gallons.

Cruise control most of the way, set at ~75. Air conditioning on about 1/2 the time. Some stop and go at the start (Ventura Freeway) for about 5 miles. Some 45 mpg towards end (10 miles) behind two slow trucks on highway 152. There is a 4,000 rise for the Grapevine (and descent), and another ~1500 rise and descent after leaving interstate 5. 91 octane premium (Mobil).

Cheers,

The knock sensor does not affect gas mileage at all. Not in my case anyway.

I know for a fact that my sensor is bad. Instead of replacing it, I simply switched to regular gas and have been running with regular gas for more than a year now. NO engine knock at all.

Last week I make a round trip from Houston to Lake Charles and back. Total over 430 miles, mileage is 28.5mpg. Mine is a 95 SE with manual transmission, 198Kmiles on the odometer.

About the same as everyone else -