Constant CEL Code 35

[mjc1310]

Hello!

For starters, I would just like to thank the kind people who freely give there time and expertise to a website like this. I seriously tour around it for hours learning about my sub, planning future projects or figuring out the current ones. So from a forum newb to the pros, you are appreciated.

Okay, now to the problem. Bought a 1990 Legacy (auto, LS) about 6 months ago with 114,000 miles on it. She's been great, and after tweaking minor things that were on the to do list, this is the big stumper. The CEL has been on since I bought the car. I quickly figured out it was giving me code 35 for a purge valve solenoid. I replaced it with a new one (Partsgeek was the cheapest if you are looking) and cleared the codes, but the light came back on. I then replaced the gas cap, and oddly the light went off for about two days then came back on. The light will stay on consistently, unless it is raining or of high humidity outside (weirdest symptom). I am getting about 5mpg less then what I should be, so would really like to get to the bottom of this. I have also tried replacing the fuel vapor canister but was no help. I don't believe it is due to a vapor leak bc if I undo my gas cap there is still pressure there giving me that hiss sound when I go to refill.

I need to replace one of my sending units which will be done this week, but other than that I don't know where to look next. I was going to try replacing the fuel vapor separator? Could this problem potentially be related to the sending unit? Anyone ever heard of the ECU not putting out correct voltage to this sensor?
Any help would be greatly appreciated!

[Someperson]

how are your vac lines?

[mjc1310]

They look really good, no dry rot or cracking that I could find anywhere in the bay.

[Someperson]

Hmm... Plugged hard lines from the separator maybe? Or it could be wiring gremlins such as a bad ground?

[Legacy777]

Typically code 35 will only come on if the ECU detects an electrical fault. I would suggest checking the wiring and the new solenoid you bought. You can download the 92 manual from me which has the troubleshooting section in 2-7 and tells you what the resistance of the solenoid should be.

http://www.main.experiencetherave.com/s ... and_Elect/

Alternatively, you can plug the green connectors in only and leave the ignition in the ON position. That will cycle all the relays on and off. You can feel the purge solenoid to see if it's clicking or not.

[mjc1310]

Alright, so I ran the system with the green plug connected and had all of the relays cycling. The purge solenoid was clicking, and I even did blew on one end to see if it would with hold the air pressure, then release it which it did. Should I begin checking other electrical problems, or look for a potential clog/ leak in the system..

Question: when the purge valve opens, does the ECU count on the added fumes by adding less fuel into the mix and this is what makes it run like crap? I ask because if so, I could potentially have no vapors stored in the canister so when the light goes off and the solenoid opens, there is nothing to draw making the ECU think the solenoid is faulty.

[Legacy777]

Ok, so it sounds like the wiring and the solenoid are working.....you've proven it's opening and closing.

I do not know if the ECU counts on added fuel vapors.....I really would think it doesn't, because there's no way to determine if or how much fuel vapor will be in the canister. This is why the purge solenoid only opens during certain times where ingesting some additional vapor should not affect the engine.

You may want to do the active diagnostic mode with just the green connectors to see if it brings up code 35. If it doesn't, you clear the codes, and the problem comes back, I'd say you've got an intermittant issue, which could be the wiring, or could be the sensor. You can use a multimeter to check the wiring from the solenoid to the ECU. Usually I'll try wiggling the wiring around to make sure the readings are steady.

[mjc1310]

Update: I went poking around with my meter and the sensor is reading correct ohms and the ecu is sending signal to the solenoid. I had seen on here that these models run a little better on 89 octane rating gas and went out on a hunch with a few gallons of non-ethanol 89 octane. Call me crazy, but THE LIGHT TURNED OFF IMMEDIATELY! I've been playing with several types of fuel but this seems to calm the problem the best, as the light will come on maybe twice for about 15 seconds each with a half tank of gas. Not sure about other states, but in NC we have up to 10% ethanol at each pump. Anyone heard of something like this? I am going to dig into some tuning/ cleaning of the fuel system to see if that helps. Still don't understand why that would trip a PVC solenoid...

[Legacy777]

That is a little weird. I know that when I first got the CPC check engine light back in 97 it would intermittantly go on and off. So the solenoid may be on the edge of being bad. If it comes back on again, you may want to just replace it.

[mjc1310]

Just wanted to update this for anyone who may come across the same problem. After replacing the solenoid, I still am having the code come up intermittently, but much less than the previous several months. I ran some Seafoam, have been running more quality gas (89 non eth makes for the best results, but is the cost worth it?), and have upped mpg from 23 to 26 city. The light still will come on for short periods but it's becoming less frequent as if the higher quality gas is slowly cleaning up something. Hope this helps someone!

[Legacy777]

If you're still having issues and have replaced the canister purge solenoid, I would suspect there is a wiring issue some where.