Need help, mechanics and dealership dont know what it is!

1999 Lumina 3.1 liter V6 - 150,000 miles
Hey, i have a problem with the car but only when it heats up. It runs fine while its cool, but after it warms up, the car stutters and stalls, its hard to make it up a hill. Brought it into a shop and had several readings but it couldnt find anything. The CEL isnt on either.
The dealership doesnt know, a mechanic doesnt know. We changed the MAF sensor but that wasnt the problem. the spark plugs are about 6 mos. old.
The problem occurs ONLY when its heated up. also, i dont know if this is wrong or not, but on the temp gauge, it doesnt go half way... i dont know if thats normal or not. it stops at a little over a quarter. maybe about 130 degrees? half looks like 180.
When i come to a complete stop, sometimes it will just stall.
When i go up a hill it shakes and sputters and that also happens when i push on the gas a little more.
If anyone can help you'd be smarter then a dealership. if you need to know more specifics ill tell you.
thank you.
:uhoh:

Wild guess here but it sounds lke it's running lean after it warms up and starving for fuel/air. I guess I'd start by looking at emissions controls and things that change the fuel/air mixture as the car warms up, like the coolant temperature sensor and the O2 sensor.

any other problems like loss of coolant, smoke or steam from exhaust, you say no CEL, but did they scan it anyway for pending codes? I agree it sounds like an emissions issue, possibly EGR related or an intake/vacuum leak.

im going to check it out, if anyone else has had this problem or think other wise, im open to anything

thanks so far, its a big help

Did any body check fuel pressure when this happens?

1999 Lumina 3.1 liter V6 - 150,000 miles
Hey, i have a problem with the car but only when it heats up. It runs fine while its cool, but after it warms up, the car stutters and stalls, its hard to make it up a hill. Brought it into a shop and had several readings but it couldnt find anything. The CEL isnt on either.
The dealership doesnt know, a mechanic doesnt know. We changed the MAF sensor but that wasnt the problem. the spark plugs are about 6 mos. old.
The problem occurs ONLY when its heated up. also, i dont know if this is wrong or not, but on the temp gauge, it doesnt go half way... i dont know if thats normal or not. it stops at a little over a quarter. maybe about 130 degrees? half looks like 180.
When i come to a complete stop, sometimes it will just stall.
When i go up a hill it shakes and sputters and that also happens when i push on the gas a little more.
If anyone can help you'd be smarter then a dealership. if you need to know more specifics ill tell you.
thank you.
:uhoh:

THis happened with my Lumina too! Check the O2Sensor. My Lumina was sucking in too much air. then when I put heater on, or when engine warmed up, fan wouldn't "kick in", it spluttered and stalled on hills. Get someone to check using the diagnostic under the dash.
For Gawds sake DON'T add more gas, by pushing gas pedal, it makes it worse!!

1999 Lumina 3.1 liter V6 - 150,000 miles
Hey, i have a problem with the car but only when it heats up. It runs fine while its cool, but after it warms up, the car stutters and stalls, its hard to make it up a hill. Brought it into a shop and had several readings but it couldnt find anything. The CEL isnt on either.
The dealership doesnt know, a mechanic doesnt know. We changed the MAF sensor but that wasnt the problem. the spark plugs are about 6 mos. old.
The problem occurs ONLY when its heated up. also, i dont know if this is wrong or not, but on the temp gauge, it doesnt go half way... i dont know if thats normal or not. it stops at a little over a quarter. maybe about 130 degrees? half looks like 180.
When i come to a complete stop, sometimes it will just stall.
When i go up a hill it shakes and sputters and that also happens when i push on the gas a little more.
If anyone can help you'd be smarter then a dealership. if you need to know more specifics ill tell you.
thank you.
:uhoh:

I've had this happen to me on a '92 cutty... you need your fuel injectors cleaned/replaced :)

Thats gotta be embarrassing for a dealership to not finding what's wrong with your car~! Don't worry, you're not the only one who has problems with garages. They are great if the problem is clear/obvious, however, a car such as this one, they'd rather not mess with it because they might spend half a day just diagnosing the problems while they could have a dozen other small jobs taken car of during that same time. Don't forget, garages are out there for the money too.

One time back in the day i had an eclispe that was acting similar and it ended up being a plugged up cat. converter.

In your year Lumina the Coolant Temp Sensor also controls the temperature gauge. It won't necessarily trigger the Check Engine Light if it is just a little out of range. Just Replace the Temp Sensor and your problem should go away.

In your year Lumina the Coolant Temp Sensor also controls the temperature gauge. It won't necessarily trigger the Check Engine Light if it is just a little out of range. Just Replace the Temp Sensor and your problem should go away.

SO not true...

There are two, there is a sending unit for your computer/gauges (on the rear side of the block), and there is a switch for your fans (directly underneath the thermostat housing)

Both of my Z34s have 2 temp sensors, but one is in the tranny end of the front head, and the other is under the throttle body. One is for the gauge, the other is for the ECM, and the ECM controls the fans.

Notice the poster said 1999 3.1. That makes this a 3100 gen 3, which has one ECT sensor. Not two, not one just for the fans, not one in the trunk.

Don't rule out TCC operation. It can mimic fuel starvation sometimes. I agree in that it does sound fuel-air related, but don't skip over your transaxle.

GYL and Cad are correct, the 99 only has one CTS, it sends a signal to the computer which in turn controls the fans and the guage as well.

Overly lean will usually produce intake backfire when the throttle is stomped.

Maybe (?) try unplugging the O2 sensors and running it (to keep it in open-loop operation, no ECM comtrol over mixture) and see if it still does it.

If so, a mechanical cause is suspect, if not, a sensor or ECM is at fault.

In your year Lumina the Coolant Temp Sensor also controls the temperature gauge. It won't necessarily trigger the Check Engine Light if it is just a little out of range. Just Replace the Temp Sensor and your problem should go away.

Is this sensor on the block or on the overflow jug?

Location Please..........Im tired of looking for it......:wink:

Is this sensor on the block or on the overflow jug?

Location Please..........Im tired of looking for it......:wink:

autozone.com has a free component locator and service information....about all they're good for:shakehead

autozone.com has a free component locator and service information....about all they're good for:shakehead


Thanks again Jeff.

You guys are lifesavers.
Perhaps i can help someone here someday.

It's located in the intake manifold, drivers side of the engine, near the t-stat housing.