Mysterious Purge Solenoid Problems in Hot Weather

[mrbalihai]

Hi All,

 

My 2003 Baja is having some bizarre purge issues when the temps outside go above 90 degrees. The Subaru mechanics at my dealership have identified the problem, but haven't been able to fix it, so I'd like to get some ideas as to what my next steps should be

 

About a year ago, my Baja started "bucking" in hot weather. This happened most frequently when I would get off the freeway after about 15-20 minutes of driving, or for a mile or two after filling the gas tank. I got the mechanic to take a drive with his laptop diagnostics hooked up, and he found that the A/F sensor was swinging between a rich and lean mix when the bucking was occurring, so I had them replace it. Things seemed to improve after that, but the weather had cooled down, and car was still bucking after filling the gas tank.

 

This summer, it started doing it again, so I went for another drive with the mechanic, and this time he noticed that the purge solenoid was opening up all the way when the car was bucking. The A/F sensor was acting up again too. He thought the purge behavior was not normal, so he bypassed the solenoid by plugging the manifold inlets and unscrewing the gas cap, and had me drive it over the weekend. It drove beautifully...no chugging at all...but I noticed is that I never got a warning due to the loose gas cap, which seemed odd.

 

I brought it back to the shop on Monday, but when I picked it up again in the afternoon, the mechanic told me he had changed the A/F sensor again, but had done nothing to the purge system. I was not too happy about this, but he said he'd test driven the car with the solenoid bypassed and could still see the A/F sensor hunting between rich and lean. He also said he talked to Subaru tech support, and they were unable to tell him what inputs controlled the purge solenoid. I found that a bit hard to believe, as I could find that information easily enough off the web. When I questioned the shop manager, he said that they had some other ideas, but they were "expensive", so they decided to replace the sensor again because it was still under warranty.

 

Anyway, things again seemed better after the sensor replacement, and the bucking seemed to be much reduced after filling the tank. However, the weather had cooled down, so I really couldn't tell if it was a true fix. Now that the weather has gotten warmer, I definitely notice the car bucking again when coming off the freeway, so I will have to take it in for further work.

 

If anyone has an idea of what's going on here, I'd greatly appreciate some suggestions. I love my Baja, but I've had so many expensive engine problems in this vehicle over the past 5 years, I'm at the point where I'm about ready to cut my losses and sell it if I can't get this fixed.

 

Based on my research, I think the following components could be involved, but I don't know how to rate them in order of how likely they are to be causing it:

 

ECU

Purge solenoid

Leaky vacuum hoses

Charcoal canister

Wiring harness

 

All suggestions welcome and greatly appreciated!

 

Mr. Bali Hai

 

[mrbalihai]

Should also mention that I've had no CEL codes related to purge/evap system since this started.

[uniberp]

Run a tank of premium through it. Alcohol may evaporate off in the fuel lines or something.

[1 Lucky Texan]

good idea running some premium fuel with Techron or SeaFoam added thru a tank or 2. Throttle body cleaning too.

 

I admit, I don't see how it could be related, but a longshot would be to check the fuel pump for the cap/o-ring problem.

[mrbalihai]

Thanks for the suggestions, but I've tried premium and Sea Foam already...no help. Throttle body was replaced last year because the Baja was going into idle failsafe. Since this is only happening when it's hot out, I'd been wondering about fuel pump problems like vapor lock.

[Fairtax4me]

The O2 sensor reads exhaust oxygen content, it can't tell you exactly what's going into the engine, only what is coming out. The sensor swinging back and forth is the reaction to a changing A/F ratio, not the cause.

 

The purge solenoid is easy to check, and I've seen them get clogged with carbon from the charcoal canister.

It should be under the rear intake runner on the passenger side of the engine. Remove the hoses going to it and attach a hose that's long enough that you can easily breath into the hose.

Find the green connectors under the drivers dash, plug them together, and turn the key to ON. The ECU will go into test mode, all of the solenoids and relays under the hood will start to click, and the fans will cycle in about 1 second intervals.

Check that the purge solenoid emits an audible click, put your finger on the housing to feel for the click as the solenoid opens and closes. Use the vacuum hose you attached to blow through the solenoid as it is clicking. Air should flow then stop in conjunction with the clicking of the solenoid. If no air flows at all the solenoid is clogged. If air flows all the time carbon has jammed it open.

A clogged solenoid may not be allowing vapors to be sucked into the engine until vapor pressure is high and engine vacuum is very high (off throttle coasting down an off-ramp). The fuel mixture goes rich and the ECU adjusts the injector pulse width to lean, when you hit the throttle next time the mixture leans out and causes the misfire.

 

A stuck open purge solenoid could be allowing the engine to pull vacuum all the way back to the gas tank and draw liquid fuel into the carbon canister. Which would mean liquid fuel could be spraying into the engine through the purge valve. If the carbon canister gets liquid fuel in it its best to replace it, but you could try removing it for a few days and allowing it to vent and see if it helps.

 

The solenoid can be partially disassembled with some small pliers to bend the fork tabs that hold the steel outer casing on. If you find the cause to be little bits of carbon stuck in the solenoid, replace the charcoal canister. Clean reassemble and test the solenoid, that should be reusable once its clean.

 

There are some other solenoids and valves near the tank (should be in the passenger rear quarter panel below the bumper) which you can check for operation by feeling or listening to them click while it is in test mode.

Edited August 17, 2013 by Fairtax4me

[mrbalihai]

Thanks! I will definitely give this a try. I had also considered the possibility of liquid fuel being pulled into the canister, but thought it might have been caused by me overfilling the tank at some point, not vacuum due to the open solenoid.

[mrbalihai]

I used your procedure to test the purge solenoid this morning, and it appears to be operating correctly, but since the engine was cold, and high temps bring out this problem, I should probably try it again when the engine gets hot. We're supposed to be back into the 90s next week, so I'll retest then.

[mrbalihai]

Thought I'd come back and update this thread. I've been driving the Baja for several weeks with outside temps in the 90s, and the problem seems to have gone away entirely. All that I can think of is that putting the ECU into test mode a couple of times may have unstuck a sticky valve or solenoid in the purge system.

 

Now the Baja's got another weird problem going on, but that's a topic for a different thread....;-)