Over pressure fuel tank

**GTS Dean** · 04-03-2023

I noticed after an extended road trip this weekend that my tank was not venting properly. I stopped for fuel at the destination and it belched out liquid. I drove home yesterday and immediately plugged in the DRB-3 and it is not indicating a stored fault. Looking at fuel trim pages, the purge solenoid duty cycle is steady at 7% at idle, but the tank was pressurized again. I would expect the solenoid to show some movement, but at idle - who knows?

I checked the fuel cap today and it tested good. It's got to be at the tank module rollover valve, the vapor recovery canister below the driver's headlight, or someplace in between.

Anyone ever have similar symptoms - and what was the fix?

**dave6666** · 04-03-2023

My bet is the rollover vent has malfunctioned or the hose to the canister from it has collapsed. I think the one labeled vent tube goes up to the cap area and is blanked off with the presence of the cap.

**GTS Dean** · 04-04-2023

I looked at the Emissions sticker on the toe box, then read the last section in the Service Manual. Somewhere between the vapor canister and the tank there is a check valve that I've never noticed before. I took a look at my '98 parts car which suffered moderate front end damage for clues. The radiator support and canister are gone, so it's a little confusing to figure out exactly what I'm looking at. There's a sticker on one of the lines near the Purge Solenoid that warns of applying no more than 1psi of pressure to the test port, but I'm not sure what the test port does. I guess I'll have to remove the fascia on my car to see how it all lays out.

**SA Heat** · 04-04-2023

Wouldn't it be easiest to check/replace the rollover valve first and go from there? Might save you from having to disassemble the front end.

**GTS Dean** · 04-04-2023

Yes, I'm going to start with the module because that's the last thing I touched with the new fuel pump install. I traded texts and a phone call with Dan Lesser about it. Hoping it's just a pinched vent line that wasn't oriented correctly. It's not something I look forward to, but I'm getting pretty skilled at fuel module R&R of late...

I stopped by the dealer and spent time with the parts manager at lunch. It appears the rollover/relief valve cross-references broadly and was used by many trucks from '88-'96+. With a few minutes of searching he was able to find a new valve and grommet seal for delivery late this week, or early next for around $50.

**goggles Pizano** · 04-07-2023

If they work, please post the part numbers.

**GTS Dean** · 04-14-2023

The valve is at the dealer, but still waiting on the grommet. In the meantime, I've been reading and watching some youtube segments on fuel vapor system operation and troubleshooting. I noticed yesterday that I cannot hear the Evap Purge Solenoid "tocking" under the headlight at idle. That led me back to the garage with the DRB-III later last night to run through all the solenoid actuator tests while the engine was off. Sure enough, it's dead. Now I have to determine whether it is the solenoid, or wiring. I think that starting in '99 or '00, they moved the evap canister and solenoid to the back bumper, opposite the battery.

**dave6666** · 04-14-2023

The solenoid is up front behind the front fascia on my '01. I replaced mine recently. Ordered it from Rock Auto. Turned out to be a PCM issue - mid year code change - so now I have a spare.

**GTS Dean** · 04-14-2023

Then apparently the solenoid remained up front and just the canister moved to the back. Makes sense that the bracket and wire harness didn't have to change.

**goggles Pizano** · 04-14-2023

Unplug the connector and put a meter on the connector pin 2 and chassis gnd. You should get 12V.
Then you can run the solenoid test with the meter connected to pin 1 as the PCM grounds pin 1.

Or you can just directly power the solenoid external and see if it clicks. 12V on pin 2 and gnd on pin 1.

**GTS Dean** · 04-16-2023

Thanks to the help of goggles the geeky Canuk engineer - the voltage test confirmed 12V on pin 2 and switching voltage on pin 1 after warmup. I pulled the purge solenoid out and it was packed full of tiny carbon granules that looked very much like stick gunpowder. After clearing it and plugging back in, it did not function. I popped in a new one from the parts store and it started "tocking" when warm and pulled a slight vacuum on the port from the tank to the canister as it should.

I'm not sure if my canister is junk or not. The center nipple was packed with activated charcoal, so I poured a couple ounces out and tapped it on the floor pretty hard several times to re-settle them. Does anyone know if I should change it out, or plug it back in?

**dave6666** · 04-17-2023

I would go with you need a new canister. There should be some type of filter or screen or mesh inside of the canister that keeps the carbon granules separate from the vapors. Yours has probaby deteriorated and fallen apart due to the likely polymeric material deteriorating. Heck, you probably even have plasticizers in your steering. I'd burn the entire car. It's the only way to be sure.

**GTS Dean** · 04-17-2023

Maybe I'll just burn the fuel system. Not worried about the steering because I have new seals and NEW hydraulic fluid - unlike your 15 year old horde full of leeched plasticizers.

**dave6666** · 04-17-2023

I looked at the parts book on my '01. Which I know is a little different than your blue/white car. It shows the basic components of the canister, purge solenoid, pump and filter. Looking at Rock Auto confirms this but there is also a vapor canister filter making it seem like that item is replaceable. I'll assume you would have noticed it by now if it was meant to be removed. Or if there was a spot for it and it is missing.

It looks like white plastic fuzzy mesh in the pics. Probably loaded with plasticizers. I'd burn the emissions system too. It's the only way to be sure.

Anywho the pump filter if clogged might slow the pump and make it unresponsive given the time limits on some of the actions. Doubt that's your fuel tank issue but you might want to look at that item as well. It should be on the pump.

**GTS Dean** · 04-17-2023

There is no filter on either my '96 or '98. But the '98 has some additional hose and a few tees for a 1psig max test port. Computer probably has a couple more OBD emissions code checks that the '96 doesn't. I think I'll get a new canister - they're only about $70 and I won't have to fret about it anymore.

**goggles Pizano** · 04-19-2023

Call or text anytime Dean. But i might not be able to answer right away as I am usually following Dave as it is safer because we all know he brakes only at 95% so I have to be alert. Plus he might be dropping plasticizers on the road or WD40.

**GTS Dean** · 04-19-2023

I did some searching and found a canister that looked like mine - both Dorman (#911-241) and Standard Motor Products (#3231) are used on '96-7 RAM trucks. The product page at Dorman had an email link, so I asked for dimensions around 4PM Monday. By 5, one of the sales engineers sent me a drawing to compare to. It matched within 3/8" on height and identical on all others. Ordered one on eBay Tuesday and had it installed after work today. Along with the new purge valve, it's running like a champ and picked up 0.5"Hg vacuum with no tank pressure. Still haven't gotten my rollover valve, but I'll pick it up when the grommet arrives and put them on the shelf.

I guess close to 30 years of bouncing around roads and tracks was just too much for the can and a bunch of carbon grains got up in the purge solenoid valve and plugged it. Incidentally, I can see all the way to the bottom cap thru the center nipple on the new can. I can blow thru either nipple on the new one with no resistance, while the old one is almost completely plugged.