Archie0979

Problem with air in fuel system

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I have had the car a couple of months (Avensis 2.2 D4D 2007) and had a fair share of issues mainly due to poor servicing. My main problem is that I have had injector problems. All the brass washers have been replaced as no. 4 had severe blow by. Injector 4 was also replaced as the blow by was so bad it had badly damaged the injector. I know that no.2 has been replaced in the past which just leaves no. 1+3 are still originals. My mechanic has assured me that all the injectors are working as they should now. Mostly the car runs perfect the only issue I have is if the car is sitting any length of time I get air in the system. The annoying thing is that it does not happen all the time. It seems to be worse when it gets really cold and also when I get down to 1/4 of a tank or less. This might happen only once every 2 weeks (approx.). The symptoms are the car is very difficult to start. If I continue cranking the car it will eventually start. Now when it happens I immediately hand prime the filter housing priming bulb. What I notice is that to begin with it is completely soft. Within 3-4 pumps it goes solid and when I turn the car over it starts first time. Once I have it going I can immediately turn the car off and try to start it again and it starts like a dream. Also when the car is up to temperature I have no issues. Since it is starting with no issues when warm I am hoping this rules out a possible issue with a leaking injector? I have checked all my fuel connections and have no visible signs of a leak. There is no smell of diesel in the engine bay. I have a new fuel filter and I have also replaced the fuel filter housing. has anyone else experienced similar issues and found the cause of this as I am running out of ideas? 

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As your thread title suggests, & the various facts as you've detailed, I think it's definitely air in the fuel line.  This used to be the curse of the older generations of diesels, which relied on the injection pump sucking the fuel all the way from the tank.  I no longer run a diesel, but I thought that modern diesels, with having injection pumps developing higher pressures, also had a low lift pump close to/inside the fuel tank.  The introduction of the pump close to/in the tank ensured that if a little air did get into the system, it would get purged out as soon as the low lift pump was energised.

You're unlikely to see any fuel leak, or smell, as it's air getting into the fuel line, and allowing the fuel to run back towards the tank.  Unfortunately air is a lot more searching in finding a leak point, than is diesel fuel (or many other liquids for that matter).  In addition to closely examining the joints, check any rubber hoses for signs of deterioration, and also scrutinise the priming bulb itself.  I've read in the past of a priming bulb being the culprit.

The fact that the problem's resolved by squeezing the primer bulb, and also your observation that it seems worse when the tank fuel level is low, all point to what I think is a correct diagnosis on your part.  Alas I don't think it's always easy to track down.  Have you disturbed any fuel hoses in changing such as the fuel filter.  Old fuel hoses harden slowly with age, and object to being disturbed.  I've had a split develop on the inside of a sharp preformed bend in a hose line - it did not like me disturbing it!

In the past, the standard reply to your problem was to smear over every joint with grease, to ensure a good seal.  I never had to resort to this.

I'm making my comments with unfortunately having no knowledge of the diesel engined Avensis.  Good luck - not the sort of job you really want to have to sort out in the winter, especially so far north in Aberdeenshire.

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Thanks for your response. It makes me feel a bit better knowing that you think I'm on the right track. It always seems to happen like clockwork, exactly when I have 1/4 a tank or less. As far as I know this car does not have a low lift pump hence why I experience this issue. The priming bulb is part of the fuel filter housing and you are correct that this is a common failure but I have replaced this part. Since replaced the problem is better but still not completely solved. I guess I can only but keep looking until hopefully I find a leak.

Your right it's not great weather to be working in lol. It's currently -5.

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Well at least you know to keep the fuel tank well filled.

Somewhere there might be a non-return valve (maybe part of the primer bulb?), and I'm not sure if some injection pumps had such a valve at the inlet from the fuel tank - my memory is casting back a few years now 🙁

Maybe you'll have to resort to the grease method.  At least should be quick to apply.  Thick grease best, with the idea being that smeared all around a joint, it doesn't allow the air into the fuel line and permit the fuel to run back to the tank.  Tempted to suggest the higher joints may be more suspect, in that there's a higher relative pressure encouraging the air into the fuel line.

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