No, not directly, but a non OEM or bad gas cap can cause a P0440 or P0442 code. P0420 is "low efficiency catylist. Doesn't mean the converter is bad it could also mean that unburned vapors are not being recovered for re-burning. Also if you tend to "Top Off" the gas tank it can damage the vapor (EVAP) canister (Part of the EVAP system) that contains charcoal and spill into the vapor hoses, solenoids etc. Check out these threads:

https://montecarloforum.com/forum/mo...e-23231/page3/

https://montecarloforum.com/forum/mo...l-53759/page2/

I'm more suspicious than ever that you have a problem with the EVAP system, most likely the vent valve, vent solenoid, and or vapor canister.

 

So far it still hasn't died. A week and a day! I am also in touch wit the maniac about tuning the pcm. Keep your fingers crossed.

To recap, last thing we did was install an acdelco maf. Good since then.

 

I've began to encounter a similar issue with my '00 SS. I bought it bout 3 weeks ago, the first Monte ive owned! love the car, minus the fact it will completely randomly stall. She always starts right back up.

Changed plugs n wires, along with fuel/air filter, gave her a little seafoam, and other basic day-one love. Car hadn't stalled in a few days, then it died coasting @ 20mph (1450 RPM) today....But finally something showed up on scan tool! "02 bank 1 sensor 2". So naturally i glanced at the oxygen sensors, up-stream looked very new.. down-stream looked rusted and awful. New down-stream 02 sensor arrives in a week...

I'm hoping this will help,but not holding breath.. I'm used to world of carbureted 350's and distributors, i've never heard of a bad 02 sensor causing intermittent stalling.. I'll update with the results, I hope you have been stall-free since replacing MAF!

 

MN, The downstream O2 sensor probably won't make that kind of a difference. After the cat it's pretty much just checking emissions. Could be a tell tale sign of something else to do with emissions, like the EVAP system though.

 

Bob, Thank you for the advice! Sounds like me n Mandy might be having a similar problem, diagnosis of EVAP components is something i've never dealt with... I welcome any and all input

 

..That link on the "0440 EVAP code" was very informative, I dont suppose there is a way to test the vent valve sol.?

 

Don't know of any non-destructive test. You could also have a plugged cat, but here's a good video explaining the EVAP system.

 

Thanks for the link! very informative video.

She died again today This time, i popped the hood and checked for fuel in the rail by tapping a key on the nipple of check valve on the rail., gas shot out. I went back in the car , and she started right up.

With the car running i had the hood open, and since i was in a quiet neighborhood, i was able to hear a pretty significant vacuum leak @ the throttle where the fuel press. regulator and one other hose plug in. In the daylight tomorrow i will correct the vacuum leak, n well see!

 

A scanner that can read fuel trim values would help here. Values should be close to 0% short term/ 0% long term. It would have to be a huge leak to cause it to die. I'd be suspicious of the gasket between the throttle body and upper intake manifold. If that leaks it would be an indicator of a bad UIM which our cars are prone to due to hot EGR gases melting the plastic due to a bad design, allowing the gases to melt through the wall of a port causing further damage to the UIM. Dorman makes a replacement with a metal sleeve to reinforce the port.

Here's a thread I contributed to a while back that might help. Check out the videos about fuel trim and posts about the UIM starting on page 17.

https://montecarloforum.com/forum/mo...-52343/page18/

 

Well, that vacuum leak tuned out to be a big one in the daylight... The rubber junction that connects the fuel press. regulator along with the purge sol. to the throttle had split completely open. Im really quite surprised i was able to drive at all, theres no way any vacuum was being held there.

I "welded" the length-wise split in the inch-long boot back together with super glue, and slapped a piece of duct tape over it. Maybe ill get lucky and that was my problem; massive vac leak...