Evap gross leak. Curious canister vent symptoms

[rnettleship]

I decided to troubleshoot the P0455 code from the rear of the vehicle forward. I pulled the canister vent solenoid and it bench tested fine using a battery charger as the power supply. It sealed completely when 12v was applied. I then turned the engine on and tested the plug and got 12+ volts across the 2 leads.

This is where it gets strange...

I plug the solenoid in and nothing happens. I figure it must be the leads in the plug being spread too wide so I mess around with about a dozen times and nothing makes the solenoid work so I decide to cut the plug out of the harness with pig tails and bench test. Connect the leads to my batter charger and the solenoid works fine.

Re test the wires in the harness and get 12v.

Connect plug to harness and nothing. With everything plugged in I test across the leads and get 0v. Unplug the solenoid and get 12v.

If I separate the ground lead from the harness and simply ground to the frame the solenoid works.

My understanding is the vent solenoid is triggered by the ground so I can't just ground to the frame or the vent will be closed 100% of the time the key is turned on.

So..... Seems like a bad/weak ground to me. Any other ideas out there? I guess my next step is to trace the wires back to connectors and see if I have corrosion as the cause.

 

[JUST4FUN]

Most gross leaks are the gas cap gasket just from wear from fillups

 

[rnettleship]

Any EVAP system experts out there??? P0455

I changed the gas cap - did not fix

I pressure tested the system from the purge management valve under the hood after first closing the canister vent valve by manually putting 12v and ground to it and the system easily holds 1# psi with no perceivable leak down. I tested from the hose fitting that goes down the firewall as I do not have a connector for the test port on the purge valve. My understanding is the system check requires it to only hold .5# psi (3.48 KPA * .145 PSI conversion factor = .504#) At 2# psi I can hear the gas cap vent off the extra pressure. Unless I'm missing something this tells me I have no leaks in any hoses, connections or vent valve.

When I drive the car and watch the purge valve start to open I can see vacuum forming in the tank via the fuel tank pressure sensor. Vacuum will slowly pull down to -.3 psi with purge valve at 100% duty cycle for at least 10 seconds. When the purge valve closes (0% duty cycle) the FTP sensor slowly returns back to 0.

When the PCM calls for the integrity test I see the canister vent valve go to 100% (Closed) as well as the purge valve (open). The FTP sensor does not go past -.2 psi and the system gives up after a few seconds and I get the P0455 pending code. At the next cycle it will confirm and I get the check engine light.

I hate to throw parts at a problem but my best guess is that the purge valve is leaking when it opens. I can bench test with it closed and it holds vacuum on either side of the valve but I have no way of cycling the valve open and testing it. The only other thing I think it can be is that the lead to the canister vent valve is not providing a solid ground at 100% duty cycle which could leave the canister vent valve partially open. Again, another thing I have no ability to test without a tool that would allow me to command the valves open/closed via the PCM. One last possibility is a faulty fuel tank pressure sensor although the values are changing under the conditions you would expect to see a change.

Purge valve - $80
Canister vent valve -$100+
FTP - $?

Any advice?

 

[BAD RONALD]

I feel your pain with this code. I have an '04 E350 5.4L throwing PO455 that is not gas cap related. It is an intermittent condition, pretty much only once or twice during the summer on a hot and humid day. Doesn't matter if the fuel tank is near empty or near full.

The van also has an intermittent difficulty refueling. It seems to me that the problems are related as an apparent vent issue is preventing the tank from accepting fuel at more than a trickle from the gas pump. Twenty minute fill-ups happen on occasion and the problem is not with the pumps at the gas station. I've been chasing this for a couple of years now. Damned intermittent gremlins.

I hope you find a solution to your problem. Please post your findings.

 

[rnettleship]

I finally gave in and bought a new purge valve as I was 99% sure it had to be that. Now I'm back to square 1. Since I have 2 valves I decided to take the old one apart to see how it works. There is a small vacuum port that has constant vacuum applied. At rest the vacuum is allowed to pass through a port and essentially not do anything. When the PCM calls for purge it begins top pulse a valve in that port to gradually apply the vacuum to a diaphragm which connects the large intake manifold vacuum source to the vent pipe going back to the tank.

This is where it get's really odd. When the pcm calls for the valve tp purge I can put my finger over the valve and cause it to completely close which applies max vacuum to the valve. Within 2 seconds I will get -.6 psi in the tank and that's with the canister vent valve open. Driving down the road when the pcm calls for the integrity check with the canister valve closed I can only pull -.2 and it gives up. My original thought was the valve not directing enough vacuum to pull down the expected level of vacuum in the tank.

At this point I need to get the vehicle through inspection so am going to try to manually open the valve via a hose run into the passenger compartment so I can cause the purge valve to open fully and have the pcm see the -.6 psi during the integrity check. IF that clears the code I will immediately go to the inspection station and get my sticker.

 

[rnettleship]

1 step closer. Although my canister vent valve bench tests fine and has 12v to it when the key is on it is not closing when the PCM calls for it. I have been tracing the wires from the rear of the car and first had some damage to the wiring harness just in front of the r/r wheel. I traced it up to a connector under the air cleaner and put a jumper wire across the connector and grounded it under the hood which does make the valve close. I added a toggle switch inside the vehicle so when the PCM calls for 100% canister vent closed I can throw the switch and force a ground. So far I have gone through 2 test cycles with no code. If nothing else this will prove the integrity of the system and that it does not leak and the valves work. Tomorrow I'm not going to throw the switch and see if the problem was really just a bad connection or not. If I get a code than it will isolate the problem between the connector and the PCM.

 

[Bedrck47]

print attached

 

[Bedrck47]

Evaporative Emission (EVAP) Running Loss System Monitor
The Evaporative Emission (EVAP) Running Loss System Monitor is an on-board strategy designed to detect a leak from a hole (opening) equal to or greater than 1.016 mm (0.040 inch) in the EVAP Running Loss system. The proper function of the individual components of the EVAP Running Loss system as well as its ability to flow fuel vapor to the engine is also examined. The EVAP Running Loss System Monitor relies on the individual components of the EVAP Running Loss system to apply vacuum to the fuel tank and then seal the entire EVAP Running Loss system from atmosphere. The fuel tank pressure is then monitored to determine the total vacuum lost (bleed-up) for a calibrated period of time. Inputs from the engine coolant temperature (ECT) sensor, intake air temperature (IAT) sensor, mass air flow (MAF) sensor, vehicle speed sensor (VSS), fuel level input (FLI) and fuel tank pressure (FTP) sensor are required to enable the EVAP Running Loss System Monitor.

Note: During the EVAP Running Loss System Monitor Repair Verification Drive Cycle a PCM reset with key on, engine off will bypass the minimum soak time required to complete the monitor. The EVAP Running Loss System Monitor will not run if the key is turned off after a PCM reset. The EVAP Running Loss System Monitor will not run if a MAF sensor failure is indicated. The EVAP Running Loss System Monitor will not initiate until the Heated Oxygen Sensor (HO2S) Monitor has completed.

The EVAP Running Loss System Monitor is executed by the individual components of the EVAP Running Loss system as follows:

The function of the EVAP canister purge valve is to create a vacuum on the fuel tank. A minimum duty cycle on the EVAP canister purge valve (75%) must be met before the EVAP Running Loss System Monitor can begin.
The canister vent (CV) solenoid will close (100% duty cycle) with the EVAP canister purge valve at its minimum duty cycle to seal the EVAP Running Loss system from atmosphere and obtain a target vacuum on the fuel tank.
The fuel tank pressure (FTP) sensor will be used by the EVAP Running Loss System Monitor to determine if the target vacuum on the fuel tank is being reached to perform the leak check. Once the target vacuum on the fuel tank is achieved, the change in fuel tank vacuum for a calibrated period of time will determine if a leak exists.
If the initial target vacuum cannot be reached, DTC P0455 (large leak or no purge detected) will be set. The EVAP Running Loss System Monitor will abort and not continue with the leak check portion of the test.

If the initial target vacuum is exceeded, a system flow fault exists and DTC P1450 (unable to bleed-up fuel tank vacuum) is set. The EVAP Running Loss System Monitor will abort and not continue with the leak check portion of the test.

If the target vacuum is obtained on the fuel tank, the change in the fuel tank vacuum (bleed-up) will be calculated for a calibrated period of time. The calculated change in fuel tank vacuum will be compared to a calibrated threshold for a leak from a hole (opening) of 1.016 mm (0.040 inch) in the EVAP Running Loss system. If the calculated bleed-up is less than the calibrated threshold, the EVAP Running Loss system passes. If the calculated bleed-up exceeds the calibrated threshold, the test will abort and rerun the test up to three times.

If the bleed-up threshold is still being exceeded after three tests, a vapor generation check must be performed before DTC P0442 (small leak detected) will be set. This is accomplished by returning the EVAP Running Loss system to atmospheric pressure by closing the EVAP canister purge valve and opening the CV solenoid. Once the FTP sensor observes the fuel tank is at atmospheric pressure, the CV solenoid closes and seals the EVAP Running Loss system.

The fuel tank pressure build-up for a calibrated period of time will be compared to a calibrated threshold for pressure build-up due to vapor generation.

If the fuel tank pressure build-up exceeds the threshold, the leak test results are invalid due to vapor generation. The EVAP Running Loss System Monitor will pass and complete.

If the fuel tank pressure build-up does not exceed the threshold, the leak test results are valid and DTC P0442 will be set.
The malfunction indicator lamp (MIL) is activated for DTCs P0442, P0455 and P1450 (or P446) after two occurrences of the same fault. The MIL can also be activated for any EVAP Running Loss system component DTCs in the same manner. The EVAP Running Loss system component DTCs P0443, P0452, P0453 and P1451 are tested as part of the Comprehensive Component Monitor (CCM).

 

[rnettleship]

Thanks Roxy1225.

I have the shop software and have been studying the entire evap system for the last few weeks. Here is my current situation:
When the PCM calls for the canister valve to close as part of the Running Loss System Monitor the canister valve is not closing as I never achieve the target vacuum. I can watch the Evap_test go to "Ready" and the EvapCV% go to 100 but the fuel tank pressure never get's below -.2. After several seconds the system gives up and codes.

With A toggle switch under the dash I can force a chassis ground on the lead for the canister vent. I tapped into the harness under the hood. When I throw the switch I get -.3 on the FTP sensor. The system moves to the small leak test by closing the purge valve and all is good.

Last night I pulled the connector off the PCM and did a continuity check between the PCM and the place I tapped into for the ground and that checks fine. No signs of water penetration or corrosion in the connector. My last thoughts on the matter are:

PCM not delivering a solid or any ground. I will check the ground leads from the PCM tonight.
Signal from PCM to canister vent is modulated similar to the purge valve. This does not make much sense to me as the canister vent is either open or closed. I would prefer to not drop $100+ on a valve just to find out.

 

[Bedrck47]

I am not sure how the system works. I just posted the previous information for you to read.

But check to see if the vapor management valve is working correctly.

kindly post your results as it will help others in the future