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1997 Jeep Wrangler Sahara 4.0 error code 31

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citadeltango26

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Discussion starter · #1 ·
I've been doing research on this for about 3 weeks and I can't figure it out. I was getting error codes 43 and 31 but since I replaced my spark plugs and wires code 43 is now gone but code 31 is still up. I have already replaced the purge solenoid and the check engine light did not come back on until I drove about 120 miles. I bought the jeep used in December with 116000 and had no problems with it. I drove a little over 400 miles from College Station, TX to Mcallen, TX back home with no issues. I did change oil before making the trip back and it was really dark. Any suggestions on this fix would be greatly appreciated. Thanks.

Repairs done:
-replaced thermostat- heater now works
-replaced O2 sensor- cleared bank 2 O2 sensor code (used bosch sensor, I wish I would have read the forum on O2 sensors before buying it but I have not had problems so far)
-replaced idler pulley- ceased up and fell off
-replaced plugs and wires- I am sure they were the orginal spark plugs (the gap opened up to about .85)
-replaced belt (burned off with idler pulley)
 
#3 ·
After verifying you have a good gas cap seal, check your connections between the solenoid and the canister (rotted hoses). If all that is well, consider the canister itself may have gone bad. Mine did about 3 years ago.

You have two O2 sensors, I would have replaced them both.
 
Discussion starter · #4 ·
Boogieman, thanks for the links. I actually looked into both those links and that's why I changed the purge solenoid and checked my vac lines. Jeff, I'll look into buying a new gas cap. I did not want to replace it since my wife uses the jeep sometimes with our dogs and I am sure she will leave the gas cap on roof after she fills up the gas tank (it is rare but it happens sometimes). I was thinking it was probably going to be the evap cannister. I'll keep you all updated.
 
#5 ·
citadeltango26 said:
Boogieman, thanks for the links. I actually looked into both those links and that's why I changed the purge solenoid and checked my vac lines. Jeff, I'll look into buying a new gas cap. I did not want to replace it since my wife uses the jeep sometimes with our dogs and I am sure she will leave the gas cap on roof after she fills up the gas tank (it is rare but it happens sometimes). I was thinking it was probably going to be the evap cannister. I'll keep you all updated.
Click to expand...
The good thing is that the evap canister is under the hood (driver's side)on your Jeep and not above the rear wheel well like on newer models.It's easy to inspect the hoses.
 
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Discussion starter · #6 ·
I replaced the gas cap yesterday after work and disconnected the battery to reset the check engine light. I'll let you know if the CEL comes back. Yeah, the cannister seems pretty easy to replace. I hope it's not expensive especially since I spent way too much on a gas cap from a new 4 Wheel Parts store that just opened up yesterday.
 
Discussion starter · #7 ·
After 55 miles of traveling the check engine light came back on again. It's not the gas cap (replaced this week) and not the purge solenoid (replaced). I did notice a small crack on the vacuum line but I don't think it's leaking from there since it is above the steel line. Going to replace the rubber vacuum line. I take it if that doesn't work I will likely replace the canister.
 
Discussion starter · #9 · (Edited)
Just to close the thread, I replaced the two vacuum lines that dry and cracked going from the canister to a steel line that eventually leads to the gas tank. The vacuum line was bought from O'Reilly's and it cost me 99 cents a foot. I bought 4 feet (in case I needed more). I have driven a little over 300 miles now and the CEL has not come back on (I reset my Jeep's error code with an OBD II scanner). Hopefully, this is the end of the Jeep's suspected emission leak/incorrect purge flow.

Parts Replaced
-Purge Solenoid
-Gas Cap
-Certain portion of vacuum lines
 
Discussion starter · #12 ·
Yeah I wish I had researched the O2 sensor issue before I bought a 60 dollar direct fit Bosch sensor. RockAuto has them for 37 bucks and NGK which is what my jeep came with. I just bought a Vapor Canister yesterday and it should be in this afternoon. I re-checked all the lines except for the ones connected to the gas tank and the ones I checked were good. Driving the jeep to beach tomorrow so I hope the code will reset itself during that 260 mile round trip.
 
Discussion starter · #13 · (Edited)
I installed the new evap canister last week. Purchased it off the dealer for $45. Reset the check engine light and about 30 miles later it came back. Checked all the vacuum lines and could not find a leak. This morning I remembered when I changed out the purge solenoid that charcoal leaked out of the solenoid. I checked the new solenoid and it had charcoal! I think the old canister filled the new purge solenoid with charcoal. If I can figure out how to attach a picture I will post how the charcoal looks like. Hopefully this will solve error code 31. I will keep you all updated.
 
Discussion starter · #14 · (Edited)
After work yesterday I decided to drop the tank to replace the vapor hoses and tee vacuum fitting. Dropping the tank wasn't hard but I definately did not do this as smooth as the Rokmen guys on youtube. I also decided to buy 12 feet of 3/16 fuel/vapor hose because I suspected that the steel vapor lines were clogged (after dropping the tank and removing the vapor hose from the I steel line I blew air into the vapor line attached to the canister and it was almost impossible for air to pass through it). I spent 29 dollars on 12 feet of 3/16 vapor/fuel line, 3 feet of 1/4 vapor/fuel line, and vacuum fittings. The 1/4 vacuum lines on the tank were dry and rotted and when I would squeeze them on both ends I could see cracks(same when to for the short 3/16 line). I cut and replaced them and attached a new tee vacuum fitting cleaned everything up and connected the tank back up. Last thing I did was place a straight vacuum fitting from the line on the canister to my new 12 foot vapor line. I did not remove the steel vapor line and used it as an anchor for my rubber vapor line through the use of zip ties. I have driven 30 miles and no check engine light. Hopefully this fixed the problem but I should find out in the next 20 miles or so. Jeep runs/sounds great and it idles very well. Oh yeah, I forgot to mention, I had a brain fart with the red retaining plastic clip that holds the connection for the fuel pump. Not sure if it was because it was raining on me(bad luck) or if I was just tired. Anyways, I was finally able to insert the clip by pulling the connections a little closer together and pushing the clip through its slot. I'll let you all know if I solved this annoying problem.
 
Discussion starter · #15 ·
Long story short, check engine light came back on after 30 miles. I bought a new purge solenoid from Autozone since I could blow air through the new one I bought through rock auto. I think it had got damaged with the old canister pushing charcoal through it. Now the CEL came off. I hope it stays off. The following is what I believe caused error code 31(incorrect purge flow):
1) bad canister- replaced with another from the dealer($40)
2) bad purge solenoid- replaced with rock auto ($25), replaced again w/autozone ($40)
3) clogged/cracked vacuum lines- replaced at autozone($30)

How I checked the above parts
1) noticed charcoal leaking from canister
2) blew air through the purge solenoid which means it has a leak
3) blew air through vac lines which was very hard and noticed numerous cracks at the ends of the line(bought 12 feet of vac line to bypass preformed steel line that was clogged)
Hope this helps someone with the same problem.
 
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citadeltango26
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