Intermittent Starting Problem (and lack of power at take-off)
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Overlanding
Joined: Nov 2017
Posts: 15
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Okay, all is well that ends well! Just thought I'd give an end to this story now.
Td5 in the driveway, started - engine running rough and a lot of whitish smoke coming out the exhaust. Wanted to rule in/out fuel supply problem and breather issues, so switched off the ignition and opened the fuel flap and then opened (removed) the fuel filler cap. Started her again - perfect, running as smooth as a diesel can run and no smoke! Pumped the accelerator - still smooth and no smoke! Perfect running again! Yeah!
Sierrafery explained that the fuel filler cap acts like a two-way valve, which presumably vents diesel fumes when the tank pressure gets too high (warm days) and allows air into the tank headspace when the tank pressure drops while fuel is being drawn.
All explained now? If you start her in the morning she starts first time as there is no vacuum in the fuel tank headspace; as the fuel gets drawn out of the tank a slight vacuum then develops in the fuel tank headspace and the fuel filler cap does not allow air to move into the tank to extinguish the slight vacuum. So, if you try and re-start her again soon after the slight vacuum has formed you have trouble starting - I guess this is why she at least started okay after being left alone for a while (slight vacuum is "extinguished" with the passage of time). The rough running, engine rumble, and copious exhaust smoke were all due to diminished fuel supply I guess by virtue of the fact that there wasn't enough suction-side pressure on the fuel pump?
Anyway, waiting on the new genuine filler cap. Might cut open the old one to see why it stopped working!
Td5 in the driveway, started - engine running rough and a lot of whitish smoke coming out the exhaust. Wanted to rule in/out fuel supply problem and breather issues, so switched off the ignition and opened the fuel flap and then opened (removed) the fuel filler cap. Started her again - perfect, running as smooth as a diesel can run and no smoke! Pumped the accelerator - still smooth and no smoke! Perfect running again! Yeah!
Sierrafery explained that the fuel filler cap acts like a two-way valve, which presumably vents diesel fumes when the tank pressure gets too high (warm days) and allows air into the tank headspace when the tank pressure drops while fuel is being drawn.
All explained now? If you start her in the morning she starts first time as there is no vacuum in the fuel tank headspace; as the fuel gets drawn out of the tank a slight vacuum then develops in the fuel tank headspace and the fuel filler cap does not allow air to move into the tank to extinguish the slight vacuum. So, if you try and re-start her again soon after the slight vacuum has formed you have trouble starting - I guess this is why she at least started okay after being left alone for a while (slight vacuum is "extinguished" with the passage of time). The rough running, engine rumble, and copious exhaust smoke were all due to diminished fuel supply I guess by virtue of the fact that there wasn't enough suction-side pressure on the fuel pump?
Anyway, waiting on the new genuine filler cap. Might cut open the old one to see why it stopped working!
Last edited by Intestinalworm; Jun 21, 2018 at 08:02 PM.
Thread Starter
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Overlanding
Joined: Nov 2017
Posts: 15
Likes: 0
New L/R genuine fuel cap was fitted and the diesel Td5 engine is just perfect now - starts first time every time, no engine rumble or rocking, no white smoke, great throttle response and much more power than before! Hard to believe the fuel cap was the culprit!
Over and out.
Over and out.
Baja
Joined: Aug 2013
Posts: 5,845
Likes: 368
From: Near Bordeaux, France
New L/R genuine fuel cap was fitted and the diesel Td5 engine is just perfect now - starts first time every time, no engine rumble or rocking, no white smoke, great throttle response and much more power than before! Hard to believe the fuel cap was the culprit!
Over and out.
Over and out.
It also sounds as though your fuel tank breather pipe may be blocked with crud.
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