"Sawtooth" rev pattern when I gun it.

[jbradley]

All,

I have a 97 Lumina Sedan (3.1).

It idles a little rough, but not so much that it would cause too much concern. The weird problem happens when you rev the engine in park. It revs then stops then revs then stops (kind of like a sawtooth pattern). It does this as long as you keep your foot on the gas. Also the "Service Engine Soon" light is ON. I replaced the plug wires, it went out for a day, but now it's back on.

Does anyone have any idea what could be causing this? Vacuum leak? EGR?

PS: Is there a way for a mortal to reset the SES light?

Thanks for any help.

Jeff Bradley

[cadgear]

The rev limiter is to prevent the engine from freewheeling. It does this by cutting off fuel until revs drop below 4500.

As for the SES light, taking off battery voltage will do it. Though places like Autozone will pull (and clear) codes for free.

[jeffcoslacker]

I don't know why you guys are revving your motor that high without a load on. You're scaring me. You want all your whirly bits to fly free?

[decollect]

Originally Posted by jeffcoslacker

I don't know why you guys are revving your motor that high without a load on. You're scaring me. You want all your whirly bits to fly free?

Couldn't agree more, Jeff. I'm an old "shade tree" mechanic that is being forced, due to finances, to learn all this "new fangled" stuff that they're sticking on engines these days.

However, ONE basic rule never changes. NEVER NEVER NEVER over-rev a motor without a load.

But... "whirly bits to fly free"? Tell me you and I didn't go to the same high school! I'm all FOR keeping ones whirly bits right where they're supposed to whirl! nice to meet your sense of humor.

[jeffcoslacker]

Originally Posted by decollect

Couldn't agree more, Jeff. I'm an old "shade tree" mechanic that is being forced, due to finances, to learn all this "new fangled" stuff that they're sticking on engines these days.

However, ONE basic rule never changes. NEVER NEVER NEVER over-rev a motor without a load.

But... "whirly bits to fly free"? Tell me you and I didn't go to the same high school! I'm all FOR keeping ones whirly bits right where they're supposed to whirl! nice to meet your sense of humor.

I can't remember exactly where I saw that, but it was one of the Commandments of motorcycling:

"Keep thy tach in the black, lest thy whirly bits should seek communion with the sun" or something like that

I always liked that

[decollect]

[quote=jbradley]All,

I have a 97 Lumina Sedan (3.1).

Also the "Service Engine Soon" light is ON. I replaced the plug wires, it went out for a day, but now it's back on.

Does anyone have any idea what could be causing this? Vacuum leak? EGR?

PS: Is there a way for a mortal to reset the SES light?


Mine was doing the same thing, I replaced the plugs which changed the OBDII code from 305 to 300 (Cyl#5 misfire to Random Cyl Misfires) and thought "Well gee, we went from bad to worse".
However the light usually only stays on for a day or so. I have an OBDII reader that clears the codes, but when I got tired of turning the light out everyday, I just left it go. It seems to be resolving itself as it doesn't turn on as much as it used to. Found out one day while flogging the car a bit (it's a former police car so I HAAAAD to find out what she'd do) I was hearing a radical spark knock starting at about 3800 RPM and continuing up to shift point. I threw a few tanks of High-Test in it and the problem is resolving. I'm guessing that the computer on my engine is set to need the higher octane. Given that it is a former fleet vehicle and the fleet was police duty, it makes sense that they'd want to run a higher octane. However I wonder if it actually was "set" to need it or if it is just the nature of the beast.

Anyway, the code will clear itself after a while as long as the problem causing the code is not still occurring from what I hear.

[tblake]

um, yeah, I believe the light will turn off usually after 2 "trips" without a malfunction. A "trip" is defined by, when the car is brought up to highway speeds, 55 to 60 mph, and ran for about 15 minutes. The code should clear on its own if you take it out for a 15 minute drive, stop shut it off, start it up, and do the same thing again. Then shut it off, and start it up, it should clear on its own. Otherwise, just remove the negative battery cable for a few seconds. That usually does it.