Running Rich While Purging

peoplethatcant

peoplethatcant

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Joined
Feb 2, 2024
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31
Location
Victoria, BC Canada
I've been tracking through a bunch of issues with the Jeep, but as it stands my fuel trims for both banks immediately go to -10% to -15% as soon as I apply any throttle.

I noticed the purge solenoid goes from it's normal slow clicking to pretty fast clicking the second the throttle is opened slightly (which I assume is normal). This made me try disconnecting the purge valve, and I can raise the throttle and the fuel trims stay in normal range with it unplugged.

I've tested the purge valve, it holds vacuum and doesn't leak down over time. I've also put a vacuum gauge on it while running, and it shows a vacuum reading between the intake vacuum and ambient, so it is opening and closing.

I'm wondering if there's anything in the system that would cause too much fuel vapour to be pulled through? The evap system diagram shows the canister vented to air, would this being clogged mean too much vapour flow? Or if the canister was saturated with fuel? Or do I just need to replace the purge valve even though it seems to test good?
 
Or the canister's charcoal is spent...

I get an occasional 0441 on my 97. I need to start troubleshooting too.

IMG_20240520_201406.jpg


-Mac
 
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Well, the canister sounds like dry sand not sloshing fuel, and it only stinks like vapour when you blow air through the one direction. Also I didn't see any charcoal chunks in any of the lines. So I think the canister is still good.

According to the FSM the flow management valve seems to just be a correctly sized hole to control flow (similar to the CCV) so I can't imagine that could fail to allow extra vapour through.

I did clean the canister filter, it was dusty, but not so caked as to completely block flow. Also after looking at the diagram closely, the only way I think that filter would create a situation where way to much vapour was going into the intake was if it was completely blocked and the tank was pressurizing. But in that case, the purge valve would suck it back to neutral fairly quickly I imagine and then the flow of vapour would be restricted not amplified. Plus I'd have filling issues.

The leak detection pump could fail allowing unmetered vapour into the intake, but it has a separate line and so unplugging the purge solenoid wouldn't have fixed the issue, plus I'm sure I'd be getting codes if it was the pump. Also that line does hold vacuum with the vehicle off.

Also this:

Screen Shot 2024-05-21 at 1.34.36 PM.png


So I think I'm left with replacing the Purge Valve that tested good with crossed fingers that it's just closing slowly or something that screws up the duty cycle open times.

Canister.jpeg


EVAP.jpeg
 
I got the jeep up to temp, then watched the trims go to -12% on both banks when I held it at 1500 RPM. Then I swapped in the new purge solenoid, and repeated the RPM hold. Trims stayed right near zero combined.

So I can confirm a purge valve can test good in every way, and still be off metering vapours.
 
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Well your woes were enough to motivate me... replaced my charcoal cannister with a VC-120 and a Standard Motor Products purge valve solenoid. Original valve was chock full of charcoal.

Cleared my codes and we'll see if they return.

Thanks for the motivation!

-Mac
 
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