Kinda need to know the engine size when talking about an engine problem. If yours has separate ignition coils, you can try switching two of them to see if the misfire goes to a different cylinder. You can do the same thing with injectors.

As far as compression tests, it's not whether or not a cylinder has compression. It's how much compression does it have and is it the same as all the other cylinders. From the way you described how it acts, it doesn't really sound like a compression / valve / piston ring problem. My first vote is for a coil.

The GXP has the 5.3, AKA 327 in it with the Active Fuel Management on it

Thank you for the info... It is running a lil rich, very smelly. and I will check the compression in comparison to the rest, thanks for the info =)

If its running rich, you may have a spark issue.
Read the guides below, they will help you figure it out

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/how-to-test-an-ignition-system

my service engine soon light came on in my 2008 Pontiac Grand Prix. Should I be worried about this and how soon do I need to get it scanned to check for problems?

The service engine soon light is on due to an emissions related issue. If there isn't a driveability issue, then you have may just left the gas cap loose or something that can wait until it is convienient for you to have the car scanned and the issue resolved.

My wife started her car in the garage backed it out of the garage and it died. the check engine light came on stayed on. all fuses look good, I cannot get my scanner to read her vehicle it keeps saying link problems. how can I get the codes without a scan tool what is the trick? Will not start.

it may be your scanner or there is a problem with wiring/connection. check crank sensor for ohms should be around 800-1000 then check fuel pressure with a gauge. See link. you might try another scanner if a friend has one.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Thank you, I believe it is the fuel pump. No humming when key turned on.

Hey Rusty,

Yep the fuel pump is a popular fail in that car. Here is a guide to what you are in for when replacing the pump.

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

Please let us know happens so it will help others.

Best, Ken

Well, two fuel pumps, MAP sensor, gas tank pressure sensor, oil pressure sensor, ignition relay, and it ran for a day,. Then would not start for a week, ran for a week and now will not start again for a week now.....no power to fuel pump?????????? No one can figure it out?????????

Started the car and it tried turning over but wouldnt, so I tried a few more times and nothing, then I tried once more and it worked, but the car was shaking badly and it was hard to accelerate without the car feeling bogged down and there was a bad smell coming from the car, the check engine light came on right away.

Have the codes read first to find out what put the check engine light on.

check the battery for condition sometimes this causes it otherwise the wiring will have to be checked to see if power is going through system also try putting dielectric grease on prongs of relay as it may be a fuse box problem with corrosion. Also oil pressure switch keeps power to pump when running so check that for connection

Pulled and checked every fuse, pulled and cleaned pcm connections, every connector I could reach or find.

452 ids fuel pressure sensor since the pump has been changed look for a cut wire or shorting out someplace along the harness or a bad connection it may be pinched due to the pump replacement. it may be the same thing for the 230 code and why no fuel pressure the harness may be pinched or cut as both show a short to ground/open circuit

my service engine soon light came on,,, car is running fine what would be a calculated guess as to what it might be? i also have a vibration on takeoff and have lowered my car about 2inches ,,, would this cause the vibration?

for the service engine soon light i would take it in to a auto zone and they will scan it for free, you can post the codes back here.

with the vibration, did it start right after you lowered it or did it take a few miles or days? did the light come on as soon as you lowered it?

well i just bought the car last week and it wasnt on i had talkrd to the guy i bought it from he said he had put new hub axles in when he lowered it but said it was normal for the vibration just wandering if there is any truth to that

there may be a little bit of vibration, how bad is it? when you lower a vehicle or raise it it changes the way the tires touch the road, you will need an alignment and the tires checked to make sure they are wearing properly and not vibrating.

get that code posted back.

i got the code checked it was the thermostat that i have in it is not letting the engine temp up to 195 like it is suppose to with the normal thermostat,,, so just get the front end checked to see if it is out of line,,, correct?

First I want to add it is supercharged.
We put a 3" downpipe on our Grand Prix now the check engine light is on and it is shifting really hard. It has a lot more power now and better gas mileage.
We also had to make the wires longer for the o2 sensor so that it would fit.
Can the upgraded exhaust be causing our problems? Is it the o2 sensor? Can we reset the computer or is there something we need to do to the computer?

yes, that is what i would do.

The first thing we need to do is see what codes you have in the computer otherwise were just guessing why the light is on.It could be the throttle position sensor circuit issue i have seen that cause a hard shifting.Also on the gm cars i have seen the ambient temperature sensor circuit cause a hard shift and a issue with the transmission pressure control solenoid cause a hard shift.Can you take it to a auto parts store for a free code scan?Then let me know the exact code numbers not code descriptions? That would be our starting point.

I tried to email this question earlier and it didn't work, however I did get confirmation that my dontation was accepted. So I'm sending this as a free questions. So I'm sending it again. The service engine soon light came on--what does that mean and what does it cost to fix? I mixed ethanol gas with regular unleaded--could that be a factor. I get excellent gas mileage and my cars runs great. I get my oil changed every 3,000 miles and the new oil change has only 1,000 miles on it. My mpg are 25 in town and 31 hwy.

Need to have the PCM scanned for trouble codes, that light is its way of telling you the monitored systems see a problem.Could be any one of a number of things, even well maintained cars get a check engine light occasionally

Hi, I was driving like normal today and all of the sudden, my service engine soon light comes on. I mean, it's not driving any differently, nor is it sounding any different. Any ideas?

Take the car to any autoparts store and get the codes read for free.

It could be as simple as a loose gas cap.

check engine light on, codes says 02 sensor bank 1 and 2. replaced sensors light still on, auto tech reset check engine light, now light out but computer and sensor not talking, reading not tested heater lead not on

Check the sensor to make sure the wiring to it isn't melted or damaged. Also, unplug it and check the connection.

Let me know what you find.