RICH while purging [FIXED]

I have a 2002 Dodge Dakota 3.9L that I could use some help with. It came in for low power and lack of acceleration while cold. Once warm, it would run fine. Initial test drive confirmed the complaint, and shortly after, the vehicle became a NO START. A clogged CAT was quickly diagnosed, and replaced. The exhaust system has 3 Catalytic Converts. One for each bank and a third one, downstream of the "Y" pipe. Both upstream banks were clear. However, on Bank 1 the "honey comb" had been eroding away on the downstream end, and collecting in the third CAT.

New "Y" pipe assembly, with all three CATs, installed. Runs great. Data looks good...until EVAP Purge kicks in. Cold start up and highway cruising, data looks good. However, after warm-up, when EVAP Purge kicks in at idle, LTFT starts to dive...-20ish%. STFT hangs around 0 to -5,-7%. The more EVAP Purge, the richer it goes. Oxygen sensors cycle as expected. I checked the charcoal canister and it doesn't seem to be flooded. I wondered if an EVAP vent valve that was stuck shut could cause this. My search for the vent valve lead me to the Leak Detection pump/system, which I am not real familiar with, and is the only thing (that I can think of) that I haven't checked. After theorizing about a stuck closed vent valve, I notice that the gas cap doesn't fit properly. When questioned, the customer stated that he has replaced the Filler Neck to the fuel tank.

Any thoughts?

I can upload a .vsm file of a cold start-up test drive, if anyone is interested.

Does it set rich codes? I've never knowingly watched trims during purge, but I hear the valves clicking away under the hood all the time, so it with make sense that 1) I've seen it and 2) it didn't result in -20% fuel trim.

I'm a little suspicious of the DIY filler neck.
Is it difficult to fuel up?

Monde wrote: Running rich during purging is normal, isn't it? Does the truck has any drivability problems when that happen?

This is well beyond the accepted +/- 10% Total Fuel Trim. I haven't noticed any drivability issues, since the CATs have been replaced......UNTIL I put gas in it, as Noah's response suggested. The first start up, after fueling up (only $3.50), it coughed and sputtered for a few seconds.

Noah wrote: Does it set rich codes? I've never knowingly watched trims during purge, but I hear the valves clicking away under the hood all the time, so it with make sense that 1) I've seen it and 2) it didn't result in -20% fuel trim.

I'm a little suspicious of the DIY filler neck.
Is it difficult to fuel up?

It hasn't set any codes, yet. Thanks for the fuel-up suggestion. I hadn't thought about putting gas in it. :blush: I ran up to the gas station and, sure enough, the pump kicks off, right away, if the nozzle is fully inserted. Pull the nozzle out a little, and it will fill.

I'll post back with what I find.

I would have thought a soaked canister too. I know some manufacturers provide a weight spec for you to know if it's too heavy.

Some vehicles with leak detection pumps have the vent normally closed, which totally threw me off working on a volt a year or two ago. It opens up when you push the fuel door button in the car.

Are you getting any evap codes?

Monde - the vent valve should open during purge to draw the vapor into the intake with fresh air, so it should be lean, unless the vent doesn't open, then it would draw a vacuum and i guess could suck fuel? I thought it would be rich too until this was pointed out to me in a class.

What does the fuel tank pressure look like while this is happening?

Nissan Technician

I didn't get a chance to get back on this one, today. I did get it in the door for the morning, though. I'll post back, tomorrow.

I started out to remove the battery tray and power distribution box to gain access to the Leak Detection Pump, which is the vent for the charcoal canister. I removed the battery, and exposed the air filter and housing, which is the inlet source of fresh are. This filter connects to the LDP via a hose. This hose was twisted and kinked, blocking off fresh are intake.

Rather than continue on with pulling the battery tray (the twisted kink is under the tray), I disconnected the hose coming from the Charcoal Canister and attached the air filter, bypassing the LDP. After a long test drive to, finally, purge the canister. LTFT gradually started to fall and looks good, even at idle. When I sat down to make this post, LTFT was at -4.7%, and falling...(falling?...Rising?...:woohoo: ...It was getting better, closer to Zero :whistle:) , during 100% purge.

I've never had to work on a Chrysler EVAP system, before. This was a good learning experience, for me.