Coincidence?

[Gardd]

1999 Taurus SE Wagon, Duratec

Yesterday the traffic was lousy so to avoid having to make an hair-raising left turn across oncoming lanes to get to my usual Shell station, I went to an Esso station instead. Filled the tank with 91 octane (no reason, just on a whim I guess), whereas at all other times I've put 89 octane in.

After filling up, a few seconds after starting the car the Service Engine Soon light came on. Stopped the car to check if the gas cap was seated properly -- which it was. And the Service light came back on when I restarted.

Naturally, the silly question that came to my mind was, is this just one of those coincidences? Or could there be a connection between the Service light coming on right after my a) switching brands and/or b) putting higher octane gas in the car?

The car ran smoothly all day yesterday -- no hiccups, no stumbling or whatever. But I'll be keeping my eyes and ears open...

[Huney1]

Here's what I was told. Taurus engines are designed to run on 87 Octane so no need to use higher octane. No idea as to why the service engine light came on unless the octane or knock sensor got confused.

From USA Today article: "Today's engines use highly evolved versions of a device called a knock sensor to adjust settings automatically for low-octane gas. And more engine control computers have adequate memory to allow separate sets of instructions for various octanes. The engine control computers keep pushing to maximize performance on whatever grade of fuel is used. Engines designed for regular fuel don't improve on premium and sometimes run worse. And today's engines designed for premium run fine on regular, too, their makers say, though power declines slightly. (Background: About Octane ratings) "

I guess running a tank of 91 octane through it helps, but I use el-cheapo gas from the cheapest station and every 5K miles I dump a can of injector cleaner in my 03 Vulcan and let 'er dig. 40K mi on it and far as I know it's never drank anything but 87 proof.

[shorod]

Swing by a chain parts store or other place that will pull the diagnostic codes for free. Get the code numbers and post them here. Depending on the codes, they could or could not be related to the switch in fuel. However, without having an idea why the Service Engine Soon (SES) light is on, it's impractical to speculate as to if it's coincidence or not.

-Rod

[brokenantimatter]

Originally Posted by Huney1

Here's what I was told. Taurus engines are designed to run on 87 Octane so no need to use higher octane. No idea as to why the service engine light came on unless the octane or knock sensor got confused.

The number one thing for determing octane rating is the compression ratio. A 10:1 or higher is almost a must (that includes the 24v Duratec & V8 SHO imo) for running higher than 87.

[drdisque]

Duratec taurus owner's manual recommends 87.

[Millermagic]

I run 89 in my 2001 Taurus with the Vulcan (pushrod) engine and it doesn't set the CEL.

[brokenantimatter]

Originally Posted by drdisque

Duratec taurus owner's manual recommends 87.

Ford has to recommend that on their most commonly used engines in order to avoid fines from the epa.

[drdisque]

so, as long as they recommend it they tune the engine to run on it. In fact I've run 86 in my duratec with no problems.

There is NO point in running any more than 87 because the ECU won't advance the timing enough to take advantage of it.

[Gardd]

Thanks for the replies & advice, folks!

Unfortunately nobody in my neck of the woods (not far from Montreal) will read codes for free, so this week I'll put regular gas in, and if the light remains on I'll make an appointment at the dealership for a look-see. Will post the results (if any) here FYI.

For now, I'm not worried as the car is running just fine -- smooth and powerful as always.

[brokenantimatter]

Originally Posted by drdisque

so, as long as they recommend it they tune the engine to run on it. In fact I've run 86 in my duratec with no problems.

Ford recommends 5w20 now for the Duratec Taurii want to run that in your engine?

[bruker]

Originally Posted by brokenantimatter

Ford recommends 5w20 now for the Duratec Taurii want to run that in your engine?

FWIW, I used 5w-20 in my `01 Windstar and it had 204,000 miles on it when I traded it in. No oil related engine problems ever.

[Huney1]

"Unfortunately nobody in my neck of the woods (not far from Montreal) will read codes for free," That's really wierd because here the paerts stores do it free hoping you'll remember them when you buy the parts to fix whatever's wrong. Friday afternoon around quitting time get a cold six pack of Beer and stop at an independent shop, walk in with the six pack and tell 'em you'll be glad to swap a six pack if they'll pull your codes. Doesn't take two minutes and they should be glad to get six cold ones for two minutes work.

What's wrong with 5W-20? Millions of vehicles cruising fine with 5W-20 in them and many of them go 200K miles and better on 5W-20.

[drdisque]

you can't compare oil and gas. Various oils don't really make a performance difference and thus the ECU doesn't have to correct for them. To take advantage of fuel with octane greater than 87, the ECU would have to advance the timing, which it won't do.

[Gardd]

Now the light's out?!

Still cycles on & off normally when the car is started so I know it's not burned out.

I don't get it.

[Huney1]

"Now the light's out?! I don't get it."
If the 'puter doesn't see any errors then it shuts the CEL off. I *think* it has to go through seven NORMAL cycles, or something like that, before it will turn off. So whatever the problem was it has evidently corrected itself because the computer is once again happy, happy, happy.

Tarus to Gardd, "turn me loose 'cause I is ready to rock!"
Sometimes I crack myself up.