Member Since: 02 Apr 2014
Location: Windhoek
Posts: 8
Disco3 4.4 V8 Fart noises at fuel cap due to vacuum build-up
Hi
My South African 2007 disco 3 v8 appears to have a problem on the evap system. The evap system collects fuel gasses in the charcoal canister and releases to engine just after throttle body, via the evap purge valve, located centrally behind engine, close to the firewall. The charcoal canister is located behind the electronic park brake module and mounts to its bracket.
Mine creates a vacuum at the fuel cap, so it is hard to open cap with engine running. This makes a fart noise from fuel cap as air is sucked in. It is worse when it is hot -ie over 30C and can cause irrigular idle and even the engine to stall sometimes on extended idles. No problem whilst driving, only when idling.
Thus far, I replaced fuel cap and my indie replaced pcv valve. I also removed the charcoal canister, blowing through all pipes and canister pipe connections to make sure nothing is blocked. Pipe to purge valve is clear up to throttle body (after disconnecting pipe from throttle body), so valve appears to be open with engine off.
Only breathing pipe to fuel tank I cannot test on pipes. The atmostheric vent connector on canister is almost blocked when blowing - nr 2 in sketch below. Must all connectors on cannister be open when blow unto? Can the cannister be cleaned in someway?
Cannister only appears to be Wtb000303 for around 100GBP - must still confirm part nr from vin & get local pricing for Namibia. Per google, problem appears to sometimes have been resolved by replacing the evap system charcoal canister in some instances.
Anyone else maybe had the issue? The purge valve is very expensive to replace as appears to only come with full pipe kit, so around 400GBP. Part nr MAP500100.
Google mostly points to WTR500020 - pump leak valve when searching for purge valve, but this is an USA/ Canada version only as this is mounted on the charcoal canister. The evap system is slightly different on North American LR3 version that has pump leak detection system and filter added.
Last edited by Bennvdm on 14th Mar 2023 9:24 pm. Edited 2 times in total
14th Mar 2023 6:13 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10364
you can test the purge valve by disconnecting the pipe from it to the rear of the car.
disconnect the electric connector to the purge valve
start the engine
it should idle ok.
apply 12volts to the purge valve (get wires +- the correct way round, else internal diodes can be damaged and valve killed)
If the purge valve is ok, it should open and the engine should stall or idle worse
Is one end of the charcoal canister open? (I know on USA models this is blocked by a valve)
14th Mar 2023 8:47 pm
Bennvdm
Member Since: 02 Apr 2014
Location: Windhoek
Posts: 8
Thanks Pete. I have an iidtool so will see if it allows me to activate purge valve from it with cannister to purge pipe disconnected with engine running. The purge valve sits in a very hard to reach place, so easier to disconnect at cannister. Purge valve appears to be pwm modulated from engine ecu on neg side. Can reach connector to disconnect, but will be difficult to run wires to valve whilst still mounted to bell housing
I fixed my initial post, atmospheric vent connector 2 only allows a little air to pass when blown on the canister, so might be my problem. On pipes, all pipes other than tank vent pipes are open when blown into.
On North American versions, the dmtl pump unit connects to cannister at connector nr2 location and has its own filter close to the fuel cap.
I have not removed wheel arch cover yet to see how cannister atmosphere vent pipe ends or is connected to fuel filler, but has no filter per the diagrams. It is easy to blow air through the pipe though, so does not appear blocked.
Last edited by Bennvdm on 15th Mar 2023 12:01 pm. Edited 1 time in total
14th Mar 2023 9:39 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10364
It is normal that air will be restricted if you try and blow through a charcoal canister.
It contains a honeycomb like material.
14th Mar 2023 9:57 pm
loanrangie
Member Since: 18 Jun 2017
Location: Melbourne
Posts: 600
Why would you open the fuel cap with engine running ?
15th Mar 2023 6:15 am
Marshall8hp
Member Since: 05 Dec 2022
Location: Townsville
Posts: 32
I had a similar problem on my P38, so I vented the fuel filler neck. No more issues and no tank vacuum.
Just put a small hole in the filler cap, job done.
Flack
15th Mar 2023 9:52 am
Bennvdm
Member Since: 02 Apr 2014
Location: Windhoek
Posts: 8
My issue is ingress of dust. It is my week-end / holiday car and used to tow offroad caravan, so 60% of use is gravel or offroad conditions and 40% tar roads. Almost none of our national parks have tarred roads.
I only open the fuel cap with running engine when using air compressor to inflate tires etc or inflatable mattress pump etc to prevent engine from cutting out. It was more of a test to see if it is a vacuum or high pressure. Worried that extended vacuum conditions might damage the fuel tank.
Police/ officials at road blocks or border crossings are also worried about the sound coming from the fuel cap. It can become a problem on big intersections with long traffic light waiting times, but luckily those are limited in Namibia. It was a problem in Cape Town though, with engine stalling just when traffic light turns green or driving in rush hour traffic jams.
The Iidtool unfortunately have no Engine ECU output controls on V8 petrol - only appears supported on the Diesel. I will try to reach purge valve, but will likely have to remove the bonnet to do so. I will 1st remove wheel arch liner to check how breather pipe is connected at the top.
15th Mar 2023 10:50 am
Bennvdm
Member Since: 02 Apr 2014
Location: Windhoek
Posts: 8
Can a malfunctioning purge valve cause vacuum buildup? Surely the vacuum is created by the purge valve opening, but should be filled through a breather pipe.
Blocked purge pipe or malfunctioning purge valve should create DTC P0441 per my manual, but I have no DTC’s or dashboard lights.
Per some googling, the purge valve only can be bought as fomoco WTV500080, but can only find chinese 3rd party valves or used valves. Appearently some Jaguars used the same valve as the V8 4.4 is AJ-V8 Jaguar designed.
Member Since: 02 Apr 2014
Location: Windhoek
Posts: 8
My purge valve appears to be stuck in open position, as pipe is fully open when disconnect at cannister up to intake connection.
Can you clean it if stuck open? I likely also still have a blocked breather pipe somewhere that causes the vacuum. I will try to check over the weekend.
Member Since: 15 Jan 2016
Location: GL
Posts: 10364
At idle the engine will be sucking on the tank !
Seams to be linked to your problems.
17th Mar 2023 3:36 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10364
I doubt you will be able to service/clean it.
You could try hitting it with a screw driver handle, see if it closes.
But if it's stuck once, it will stick open again. But good to prove the issue
18th Mar 2023 11:04 am
Bennvdm
Member Since: 02 Apr 2014
Location: Windhoek
Posts: 8
I managed to eventually remove the valve with pipes conencted. It is a no go to try and just remove the valve alone.
Valve appears to function normally with 12v applied. Closed with no power and fully open with 12v applied. Resistance is 20ohm, so also in 13-30ohm range as per generic purge valve testing guidance.
Maybe screw driver taps changed something, but it had no effect on my fuel cap vacuum and idle problem.
I will heat the pipes a bit with a heat gun to disconnect and then clean valve with some maf cleaner.
20th Mar 2023 7:38 am
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10364
Bennvdm wrote:
My purge valve appears to be stuck in open position, as pipe is fully open when disconnect at cannister up to intake connection.
Is this still the case? or another leak in the pipe ?
20th Mar 2023 6:34 pm
Bennvdm
Member Since: 02 Apr 2014
Location: Windhoek
Posts: 8
Thanks. Good point - found pipe to not seal properly onto connectors and valve with only push in connectors, so I fitted hose clamps. Now seals properly again.
Might explain why line appeared unblocked with previous checks.
I will try to check breather behind tank filler hose over the weekend. Need to remove inner wheel guard housing for access.
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