Evap System Test

Post by **MrAl** » 10 Jul 2017, 12:13

Hello there,

1998 v70 non turbo.

I was wondering if anyone knows how the 'system' tests the Evap system for leaks.
It must have to pressurize it somehow right? If so, what does it use to pressurize the system.
If it does it some other way, how does it do the test?
I'd like to find out more about this with as much detail as possible.

Thanks much,
Al

Post by **abscate** » 10 Jul 2017, 14:39

There is a gory detail write up here somewhere. Short version it uses engine vacuum to put negative pressure on the tank, then watches how fast it bleeds back up to determine leak rate and likely failed components.

This is one of the reasons it is so damn sensitive...the P2 went to a pressure pump which is much better. My VW and BMW complete the test with the car shut off which is really a much better way

I'll try find and link

Post by **sleddriver** » 10 Jul 2017, 15:01

Search on PO 455 Gross Evap leak

Post by **jreed** » 11 Jul 2017, 05:01

This thread: viewtopic.php?f=1&t=27538
is a good starting place for identifying the components that are likely to fail.

Post by **abscate** » 11 Jul 2017, 13:52

Here is a link to ME7 testing in gory detail. Please make sure the children are in bed before reading...

Link to PDFs on ME7 Evap testing protocol

https://www.volvoclub.org.uk/tech/fuel_ ... 0-RFLS.pdf

(fixed link)

Post by **MrAl** » 12 Jul 2017, 05:07

Hello again,

The trouble code i had at one time was PO442 "small leak detected".

So it uses the engine vacuum to check the Evap not the secondary air pump?

Steve:
The link you posted does not work. I think it is because the entire link got truncated.

Thanks for the ideas, i'll be reading some more now.

Post by **abscate** » 12 Jul 2017, 10:17

DO a search on that string above - the link is also in my Maintenance thread, for the 1999 V70T5M Nautic Blue model

https://www.volvoclub.org.uk/tech/fuel_ ... 0-RFLS.pdf

Post by **cn90** » 12 Jul 2017, 20:11

This is the way I understand it: VACUUM.

- Normally, when the engine runs, fuel is being pumped away ---> engine, this creates vacuum in the system.
The EVAP valve (located near the left fender) serves 2 purposes:
a. One-way valve allowing atmospheric air to enter, but it does not allow air to escape (anti-pollution).
b. There is a shut-off valve used for testing purpose.

- Also, there is a purge valve to vent fuel vapor into the intake manifold.

- So, when the car needs to test the integrity of the system, this is what happens:
a. Engine runs and there is vacuum in the intake manifold.
b. The purge valve is opened for a fixed amount of time (to allow fuel vapor to enter the intake manifold), during this period:
c. The EVAP valve is shut off, i.e., air is not allowed to enter the fuel tank.
d. Now the fuel tank is under vacuum b/c the purge valve is opened (vacuum is created by the intake manifold ---> fuel tank), the vacuum sensor on top of the tank will compare its readings against known values, let's say minus ___ inches of Hg.

Now, let's say an EVAP hose is broken or you forgot to put the gas cap back on, there will be no vacuum in the tank during the test period after a start, so the computer will log an error code.

I think the thread below has very good info:

1998 V70 AWD P0455 P0440 P0442 Fix with Photos
viewtopic.php?f=1&t=63069

Post by **cn90** » 12 Jul 2017, 20:16

Below is a generic video, but this is very instructional:

Post by **erikv11** » 12 Jul 2017, 21:16

MrAl wrote: 12 Jul 2017, 05:07 Hello again,

The trouble code i had at one time was PO442 "small leak detected".

So it uses the engine vacuum to check the Evap not the secondary air pump?

Steve:
The link you posted does not work. I think it is because the entire link got truncated.

Thanks for the ideas, i'll be reading some more now.

The SAS pump has a very limited and very specific function, for pumping some pre-warmed air from the near the exhaust manifold into the intake (either at startup or when idling, for a test run of the pump). It has nothing to do with the EVAP system.