Jon Weywadt
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« Reply #45 on: October 16, 2009, 10:32:21 am » |
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Of course, the vaccuum is pushing down on the remaining body of fuel and not sucking it as I had thought because of the air intake whilst removing the filler cap.
No, you were right the first time Titus. As the fuel is consumed, it should be replaced by air. The intake of air you hear is an indication that this is not happening, and the vacuum created is trying to stop the fuel pump drawing fuel, although the pump is strong enough to overcome it. My parts list shows a two-way valve in the filler neck near the top connected to a breather tube. It sounds as if yours is blocked.
All cars that I have dealt with (at least later models) develop a vacuum in the tank as the fuel is consumed. Letting air into the tank creates a real risk of, at some point, reaching an explosive air-fuel vapor concentration. This can not be a good thing.  At any rate, the fuel pump should be able to easily overcome the vacuum and provide fuel to the carb(s). What I find most annoying is that the nearly horizontal hose, from the filler cap to the tank, results in fuel sloshing out before the automatic cut-off of the pump can activate. On most other cars the steeper angle allows fuel to trigger the pump cut-off mechanism before it reaches the brim. |
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« Last Edit: October 31, 2013, 03:30:53 pm by Jon Weywadt »
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davidewanprice
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« Reply #46 on: October 16, 2009, 01:16:17 pm » |
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On my car there is no Vaccuum of air as the filler is removed ... On my new Fiesta there is a massive release when taking the cap off..
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roy4matra
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« Reply #53 on: January 06, 2017, 03:54:34 pm » |
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Of course, the vaccuum is pushing down on the remaining body of fuel and not sucking it as I had thought because of the air intake whilst removing the filler cap.
No, you were right the first time Titus. As the fuel is consumed, it should be replaced by air. The intake of air you hear is an indication that this is not happening, and the vacuum created is trying to stop the fuel pump drawing fuel, although the pump is strong enough to overcome it. My parts list shows a two-way valve in the filler neck near the top connected to a breather tube. It sounds as if yours is blocked.
Yes, Peter is quite right, and as the fuel is consumed and the level drops, air should be drawn in to replace the fuel otherwise the resulting vacuum will oppose the fuel pump trying to pull the fuel from the tank. This vacuum can be so strong that with the old metal tanks they would actually collapse inwards. During my working life I have seen this a number of times and had to replace the tanks on a few cars. In each case the car had been brought in with the statement that the fuel gauge was not reading correctly. Yes the tank collapse had restricted the gauge sender from operating correctly!! Fortunately the 'plastic' fuel tank fitted to the Murena is strong enough that it doesn't collapse inwards, but it is not good to have such a strong vacuum being created in the tank since this puts a greater strain on the fuel pump. Since the fuel cap should be non-vented, to prevent fuel dribbling out though it and down the bodywork, there has to be another means for air to get in, and this was provided by the small hose connected to the filler pipe which needed a valve to prevent fuel spilling out when the tank was full. So if you get a vacuum created in the tank then this valve must not be allowing air in and needs attention. Regarding the list now at the top of this posting, the only real design/material flaws are the semi-trailing arms which corrode badly; and the fuses/circuit board and connectors, where the connector terminals crack reducing the positive contact to the board causing arcing which burns the contact surface. Also relays should have been used between the radiator fan motor and switch, and the electric window motors and switches. All the other items on the list are not really design faults but simply items that fail through natural wear and lack of adequate preventative maintenance. So whilst it is useful to point these out to new owners they are not design faults. Matra got most of the car correct mainly as it was a development of the Bagheera so had had a number of years prior testing and correction. One item missed from the list is the necessary checking and periodic replacement of the engine stabiliser bushes on the 2.2 models. If excess movement of the engine is allowed because of worn stabiliser bushes, then the exhaust will eventually break. Roy |
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« Last Edit: January 06, 2017, 04:09:33 pm by roy4matra »
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