EVAP leak and misfires??

Post by **polskamafia mjl** » 02 Jun 2010, 18:34

Does anybody know of any connection between a leak in the EVAP system and a misfiring/stumbling engine? I believe that either my EVAP cannister and/or the hoses that connect to it may be damaged and, in the past 2 days while it is about 66 degrees outside, the car has a tendency to stumble every once in a while. When it stumbles, she slows dramatically for a second and then resumes normal driving. In addition, the CEL comes on for that second while the engine is stumbling but then goes out immediatly afterwards.

I would say it is just a misfire but I thought the CEL stays on after a misfire is detected...

Any thoughts?

- Marcin

Edit: The other day I had my codes read and cleared. The only one that came up was a leak in the EVAP system...I'll try to "Keep It Simple Stupid" and make sure my gas cap is tight, but I doubt this is the problem.

Post by **jblackburn** » 02 Jun 2010, 18:58

I don't know why, but lately the solution is purge valves. I suppose that would depend on what EVAP code you got, though...you could have a broken hose at the charcoal canister which would be unrelated to the stumbling.

That said, a purge valve will cause exactly those symptoms (a random misfire), and hard starting. It lets the fumes from the canister into the intake manifold at idle/starting, when it is supposed to wait til a higher RPM and then burn those fumes off.

There is a hose with a one-way valve in it that runs from the purge valve on the radiator fan through a white one-way valve and then into the intake. Unplug that line at the white valve, and see if your situation improves. Don't run for a long time with it disconnected, though. Hot engine + gas fumes = not good.

The CEL will flash for a misfire, and it will store a code but it will not stay on right away. Read your codes and see which cylinder(s) is misfiring.

Post by **phils94850** » 02 Jun 2010, 19:04

I had a evap code kept coming up on my car, i noticed when i took my old gas cap off i couldnt hear any press. escapeing so i went to a-zone and bought a new cap, no more evap code

Post by **polskamafia mjl** » 02 Jun 2010, 19:18

Idle and starting are perfect, lol. Does that still fit the bill for the purge valve being my issue? It has so far only happened while driving. And phils, as far as the gas cap being the problem; my car was involved in an unforunate series of events recently and I found my cannister hanging by the hoses. So it hooked back up and kept on motoring. I think somehting got jarred in that system, that's why I'm not holding my breath for the gas cap. I will check though.

Post by **phils94850** » 02 Jun 2010, 19:22

lol.. oic, well, in that case, if the prob. started after the incident i would start there..

Post by **polskamafia mjl** » 02 Jun 2010, 19:26

haha I took pictures and made a post about what happened.

I want to start there but I first want to figure out if a leaky EVAP system can cause stumbling/misfiring while driving...

FCPEURO · Post by **FCPEURO** » 02 Jun 2010, 19:27

phils94850 wrote:I had a evap code kept coming up on my car, i noticed when i took my old gas cap off i couldnt hear any press. escapeing so i went to a-zone and bought a new cap, no more evap code

This seems like it would be way to simple but 9 times out of 10, with these cars, it is the simple thing that fixes the issue. I would try this first just to see if it helps. If it does not fix the issue, then it is probably the purge valve. Let us know how you make out.

Post by **polskamafia mjl** » 02 Jun 2010, 19:37

I'll start there, but can anybody definitively answer weather a leaky purge valve is capable of causing stumbling while driving at highway speeds on a cool morning but not do it while driving at highway speeds when it is hot outside? lol I'm trying to take this one step at a time

Post by **jblackburn** » 02 Jun 2010, 19:41

Probably not. It usually bogs down when taking off and can cause hard starting on hot days. That's usually when you see that manifest itself.

Does it hiccup on the highway at cruising engine speed or when you're on the gas merging onto the freeway?

Post by **polskamafia mjl** » 02 Jun 2010, 19:45

So far it has only happened while driving with a constant speed between 50 and 70 mph; never on any ramps or anything. I actually had the cruise control on once when it happened. I'm really bamboozled as to why hot weather and engine work better than hot engine and cooler weather.