I have an 03 Monte SS with a 3.8L. Yesterday I drove it about 20miles to a friends and parked it for 10hours. the low fuel light came on - on the way there, but i normally have 60miles until i need guess. The car ran great all the way there and has been. I got back and went to start it and it ran like crap...just kept going up and down in RPM and then died. It runs like 2 spark plug wires are pulled off, just up and down. I thought..i might be out of gas so I added a few gallons from my buddy. It still missed. Then i drove it a few feet and then it ran great. I could rap it up and it felt good. A few minutes later it was missing so bad it wouldn't run.

I went back today and changed the fuel filter hoping it was low on fuel and just kicked up some debris. No luck. Here is the weird thing. I drove it in to town (10miles) and it ran perfect. I stopped to put new gas and some seafoam in it, then it took about 10 minutes to get it started.

I made it to Autozone and here are the codes they gave me.

C1245 (low tire) - I wish it was that easy
C1276 (ABS deliver torque Sensor) Not sure what this is
PO128 (coolant temp) - basically I think I need to add coolant or I have a bad sensor
PO141 (Bad 02 Sensor)

I have had the bad O2 sensor for awhile, but surely it would make the car run this bad? Both exhaust pipes seem even pressure so i do not think it is a plugged CAT.

Anyone have any ideas why it runs great for a short time, then like crap for awhile, then like crap again?


Thanks,

 

It could be that the of has finally failed and affected the car I'd deff go replace that first if you getting a code for it. Must I add I recommend getting nothing but an ac Delco replacement

 

Well I got it to run great for about 20 minutes and made it home. It ran for about 10 minutes idling in the drive way then died. Then it ran horrible for about 10 minutes and wouldn't stay running.

I did some research on line and some say it may be the Mass Air Flow sensor. I unplugged it and it ran fine 20 minutes straight. I will try again tomorrow. Anyone know if GM has a code for a bad mass air flow sensor? I just don't get why it runs great for a short time, the bad for awhile, then it runs great again.

Thanks,
Cody

 

Here is a link to a page on the forum that has a listing of all the codes and what they mean

https://montecarloforum.com/forum/fw...de-list-17144/

I know when my MAF was bad it threw a code.

One way to check your catalytic converter, which does cause similar problems to what you are saying is happening is to look under the car when it is running, if it is glowing red, odds are it is clogged.
The 02 sensor you should probably replace if it is throwing a code.
Wouldn't hurt to check your coolant level just in case it is low.

You can always pick up a can of MAF cleaner and give it a good spray while it is out of the car and let it dry, only takes a short while, just be careful as it is basically a very thin fillament, almost the same width as a hair, so it is easy to get ruined by accident

 

So I replaced both the O2 sensor and MAF (mass air flow sensor). All the check engine lights went off and the car runs much better (kinda). It will idle fine and appears to run fine. The problem is when I turn it off and then start it up within 10 minutes (like running into a store to pick up a few items) it will start and then die and the idle goes up and down for a few seconds. It will normally come out of it after the second start then idle fine at 1000rpm. If the car sits for a few hours or over night it starts fine.

I also am getting good worse mpg. I use to get 25-26 mpg, but after I changed the o2 and maf it is getting 21mpg. It will be at 2000rpm going 60 mph down the highway.


Anyone have any idea? I am about ready to just unplug the maf sensor to get better mpg.

 

When you put in the new MAF.... Did you buy an AC Delco? or something else? If you bought like a (Bosch) for instance...there junk and have a very high failure rate.... Always use genuine AC Delco parts/MAF.

Have you checked the fuel pressure at the fuel rail?
If the fuel pressure is low... (since you been running it on empty) I wouldnt be surprised if its a bad fuel pump (worn out) as your driving... it gets hot and has a hard time building enough fuel pressure...you stop at the store now it has no flow to cool it down... thus the hard starts/stall condition..

after siting overnite..it cools down while sitting and will act normal until it heats up again. and goes into fail mode with out an evap code...
It could also be even though you changed the fuel filter.... It could be clogged... again from running on empty... Never let your fuel gauge run below 1/4tank...as it causes the fuel pump to work even harder... and thus will continue to pick up residual crud that sits in the bottom of the tank...
Hope this helps..
Keep us posted on your progress..

 

x2 on the MAF - I bought one from Autozone and it was crap, a buddy of mine bought one online and still had issues. Got a genuine ACDelco and all was well, in both cases.

 

I had a mechanic check the fuel pressure at the fuel rail and it was 55 psi running and it would go down to 45 psi when shut off. He didn't have the specs of what it should be but thought the numbers where fine. We checked after a few mile drive then a longer one with similar results. Anyone know normal ranges?

Thanks

 

that sounds pretty much normal to me, what brand maf sensor did u get? if you got anything but an ac delco you might still have problems these engines are a bit stubborn, the same goes for the o2 sensors as well. another thing. i dont know if u did this but check the fuel pressure dont start it at all just turn the car to the on position and watch the gauge closely if it delcines at all you have a bad fuel pressure regulator, that would be cheaper than a pump and more likely

 

spec fuel psi is 52-59psi when running. Yes it will bleed off when engine shuts down. Fuel pressure you mentioned is right in spec