tabacka

Dear Phootbag, I have the hunch (your last input) you may be someone capable of answering a few of my questions about the physics of the Fuel Tank System Pressure Control (see thread #16 and #18, here). Would you, please, reply either way so I would not be wondering any longer (whether or not you could) or if I have missed an opportunity to learn...

Thanks. -- tabacka --

night

1456 = if two way valve has gas in it, change valve and solenoid and be done with it.

phootbag

EVAP systems can have internal leaks, external leaks and component malfunctions. There are two types of tests that are performed to check an EVAP system for malfunction. 1. The ECM runs the self diagnostic function. 2. The human runs his/her own diagnostic test. These two diagnostic test are going to be very different.

The ECM tests the system in a very complicated way. If you have a LOT of time, you can perform the test in the same manner the ECM does. However, I prefer to diagnose these systems my own way which takes about 10 minutes once all the appropriate tools are in place.

The way the ECM tests the system is pretty irrelevant. You will not be able to recreate the conditions the ECM uses for it's test. Throw it out the window.

Also, if you use the factory service manual for testing the system, you will need about ALL DAY. Throw the book out the window.

Step one. Foget if the DTC is tank side or canister side. Doesn't matter. ( Next post.... )

phootbag

The system is essentialy two cavities joined with a valve assembly ( 2-way bypass ) and each cavity vented through a solenoid valve ( purge and canister valve ). The tank side of the system has the fuel tank pressure sensor.

The 2 way valve is a rubber diaphram held by a spring against an orifice. The orifice leads away from the spring to the purge valve. Which means, vacuum from the purge valve cannot effect beyond the diaphram. The 2-way valve is actually a 1-way valve.

The 2-way valve has the bypass solenoid valve attached to it. This valve can "bypass" the 2-way valve and open the tank side of the system ( along with the FTP ) to the purge valve.

The Canister Vent Shut valve is used to close the other end of the system during diagnostics. The valve is normally open.

( Next post )

phootbag

I work at a dealership and have access to a factory scan tool. This allows me to operate the solenoids via ECM command through the scan tool ( HDS ).

Apply vacuum to the purge valve while the valve is deactivated. This is to make sure the valve holds and doesn't leak. Apply vacuum to the purge valve while activated to make sure the valve allows vacuum to pass. I've seen a venturi effect during vacuum that causes the valve to shut.

Close the Canister Vent Shut valve ( activate it ). Leave the Bypass valve closed ( off ). Activate the duty cycle of the Purge valve ( activate it ).

Apply vacuum to the system through the Purge valve and monitor the FTP. If the FTP value falls, indicating vacuum reacing the sensor, the 2-way diaphram or bypass valve is leaking. This is one way you can have an internal leak in the system causing a DTC.

Open the Bypass valve ( activate it ). Leave the Canister Vent Shut valve closed ( activated ). Open the Purge valve ( activated ). Apply vacuum to the system.

phootbag

The FTP value should fall, indicating a vacuum in the system. Increase the vacuum until the FTP reaches between 1.7 and 2 volts. Unplug the Purge valve connector causing it to shut. This should seal the system and allow you to monitor the FTP for potential leaks. Since most malfunctions are the result of a failed monitor component, you should be looking for a considerable change in FTP value. If the vehicle is old and may have cracked vacuum lines, you may be looking for a much smaller leak, which could be more time consuming requiring the use of a smoke generator or pressure instead of vacuum combined with soapy water or a 5-gas anaylzer.

If the FTP did not fall in the last step there may be a HUGE leak which doesn't allow you to draw a vacuum, a faulty Bypass solenoid or Bypass solenoid driver circuit in the ECM which prevents vacuum from reaching the FTP.

If FTP did fall and hold, open the Canister Vent Shut valve by removing the command. The FTP should rise back to atmosphere ( 2.5 volts )

phootbag

If the FTP value does not return to atmosphere, the Canister Vent Shut valve may be stuck closed. Which, again, shows that a failure of a monitor component can cause a DTC.

There are other sources of internal leaks. I believe the overfill valve has a diaphram that can rupture and cause an internal leak and set a DTC. Though, I've never seen one that failed naturally. The only one I found was caused by a technician who supplied pressure to the diaphram and busted it.

If you are without a scan tool that can activate solenoids the only thing you cannot do is confirm ECM driver commands to the solenoids since those are done while driving and the monitor is running. Good luck predicting when that happens.

You can substitute the FTP reading on the scan tool with a multimeter. It displays voltage and will show you what you need to know. You can use a fused jumper wire to supply power and ground to the solenoids to operate them.

phootbag

I have performed this test with perfect success. I have never had a comeback and have diagnosed everything from leaking fuel tanks to fautly ECM driver circuits.

The system seems extremely complicated but if you can figure out what to ignore and what to do, you can diagnose them with great ease.

I've had quite a bit to drink, so I hope all that helped. I'll probably read it tomorrow and say, "WTF?" lol

topshot-rhit

I hope you're still following this thread.
Knowing that it must pass p1456 for it to get p1457, at what point in your excellent debugging posts above does the 1456 test complete and test for 1457 start?

I have a 2002 Civic with 178,000 miles that has been getting p1457 the past few weeks. I've cleared the code several times now. It has fired again in a few days or as little as one day (seems to be getting faster). All short city trips. I'm guessing leak in the canister or vacuum hose getting worse? Which components should I focus on?

I don't need this for emissions in my state, but am going on a major summer trip and don't want the CEL on to mask a potentially significant issue.

Sagero

I'm diagnosing p1456 on a '98 Accord LX 4cyl. Don't have access to the Honda manual, just Haynes. Can you tell me where on the car the 2 way valve and solenoid assembly is located?

Lost Again

You could buy one for ~$27 - this is for a CD shipped to your house. For ~$22 you can download it.

Sagero

I'll download it.
Thanks!

Lost Again

"automanualsource dot com" is pretty good.

Johnny_9

Good Video to understand the system