My car is a 2003 XC90 – D5 Euro 3 (154k)
In the past couple of weeks I have been getting an ECM-6805 Boost Pressure fault. The car has always suffered from the popping sound from the oil filler cap which I’ve never got to the bottom of. However MityVac readings in the past were always pretty good – steady 25+ inHG measured at the TCV (aka engine mount control valve)
However when I now check the vacuum it has dropped significantly. Its now down to 15 at best and flickering …. but I’ve seen it lower.
I’ve recorded this video to try to show the issue. I know that my engine mounts are leaking so they have been taken completely out the loop. In the video the mityvac is connected to the rubber hose that would normally lead to the input of the engine mount control valve.
However since the video was made I have connected the mityvac directly to the Vacuum pump and getting the same poor readings.
Timeline
0 – 36 secs – engine start and showing the poor vacuum reading
37 secs – I disconnect the quick connector for the brake servo at the back of the vacuum pump. Vacuum falls to 0 as I would expect
42 secs – Brake servo port on vacuum pump sealed with my finger. Vacuum rises to a good steady reading
53 secs – Repeat . Finger off. Vacuum falls. Finger back on Vacuum recovers.
60 secs – Finger off. Replace servo hose quick connector. Vacuum build back to the poor reading.
At this point I thought I was homing in on a leaking brake servo or its pipework and possibly an expensive replacement.
However I have performed the following tests on the brake servo circuit:-
- Connected the mityvac to the servo hose at the inline check valve (engine side) and pulled a static vacuum on the servo. I could pull a max vacuum of 20 inHG but no more.
- Ive also removed the check valve and pulled a similar vacuum on the servo.
- For both tests I left it 15 to 20 mins and in that time the vacuum does not drop at all.
With my limited knowledge this gave me some reassurance that the servo at least seems ok. Would you agree?
With regard the vacuum pump:-
- I attached the mityvac directly to the brake servo port on the vacuum pump. With the engine running a steady 30inHG is recorded…. And the vacuum holds when the engine is turned off
- I connected the mityvac directly to the small secondary port on the vacuum pump used for the (Boost solenoid / engine mount control valve and as predicted I see a very poor reading . With the engine switched off no vacuum is maintained on this port. Is this correct?
- I also noticed that even though the mityvac clear pvc hose was only connected for a short period for the test, a noticeable amount of oil was present. Im assuming that isn’t right!?
My view is still angling this towards being a failure of the pump but only because I cant see anything wrong with any other components.
What I don’t understand however is that even though there are no faults identified with the brake vacuum side, I get a poor reading on the small port on the vacuum pump with the brake system connected, but if i remove the brake system connection and plug the large port with my finger, the small port then records a good vacuum.
Any thought on what could be causing this problem?