 | Home > Technical > I know this sounds rediculous.......... |
 
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| Caterham Member Since: 06 Nov 2008 Location: Birmingham Posts: 6331   
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Is it possible that the engine could run differently on the lower half of a tank of fuel to the top half.
since new I've been convinced the car runs rough and smooth on / off with no real ryme or reason. However it would appear that it seems to run smoothly more often on the second half of the tank as opposed to the top half.......could it possibly make any difference what so ever. just thinking fuel returns - air in fuel - don't know just grasping at straws.  |
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18th Mar 2012 4:18pm |
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| cinstone Member Since: 29 Nov 2010 Location: Stourbridge Posts: 375 
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Blocked breather on the fuel cap???
Chris. http://shropshirelandrovers.freeforums.org 2015 Defender 90 XS SW & Helen, 1964 IIa. Previously 2012 Defender 90 XS SW & 2008 90 XS SW. Previous LR's: Michael, my 2008 Defender 90 XS SW. Machinas oportet intrare non capsicum annuum faveo |
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18th Mar 2012 4:22pm |
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| Caterham Member Since: 06 Nov 2008 Location: Birmingham Posts: 6331
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could it be ?
didn't know the fuel cap had a breather. thought they created a seal generally/ what have noticed and not really given it any consideration before is when I take the cap off water normally poor out of it? should or shouldn't they create a seal and could this really be a problem. thanks for the response cinstone - is this a wild guess / suggestion or do you have a experience on this matter?  |
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18th Mar 2012 4:32pm |
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| Caterham Member Since: 06 Nov 2008 Location: Birmingham Posts: 6331
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I was thinking - what the hell are you on......
I know in my excitement I miss the odd word out but ......what the heck. then the penny dropped - hmmm may be.
but does any of this have a bearing on the difference between 1st half of tank and second half? |
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18th Mar 2012 4:59pm |
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| Zagato Site Supporter Member Since: 08 Jan 2011 Location: Billingshurst West Sussex Posts: 5026 
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Water pouring out of cap
 Sounds odd Maybe buy a Defendoor covering cap for your filler recess!
"does this have any bearing on 1st half of tank and second half" Following on from what Chris is saying I suggested the fuel tank breather pipe but yeah it does sound ridiculous  
Somebody may know  |
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18th Mar 2012 8:24pm |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20820
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[quote="Zagato"]Water pouring out of cap
Sounds odd
After washing water in the key lock?? I've had it |
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18th Mar 2012 9:19pm |
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| Zagato Site Supporter Member Since: 08 Jan 2011 Location: Billingshurst West Sussex Posts: 5026
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Ah
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18th Mar 2012 9:20pm |
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| cinstone Member Since: 29 Nov 2010 Location: Stourbridge Posts: 375
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I've not took too much of a gander at the cap, but there seems to be two forms of fuel systems on vehicles these days.
Not sure on the exact technical names for the sytems, but one seems to be a sealed/pressurised system (as I've found on most modern cars. The other is the opposite, such as my old Moggie Minor and many motorbikes. From opening my Defender's tank when nearly empty I'm presuming it's of the old fashioned type in that the cap is just that, a cap and not "sealed" as it were. Now I don't know if the cap has a breather hole, or the tank has a breather pipe, but either way, if the breather is blocked you will get a vaccuum created, given time, and then fuel starvation. If you only fill the tank halfway there will be more air in the tank, so it would take longer to create the vaccuum and so you wouldn't notice the fuel starvation as soon. Not having a workshop manual for the Defender I'm clutching at a few straws here, but next time it does it with a full tank, stop and remove the cap. If you can hear the sound of air rushing in when you remove it the breather is likely to be blocked. Replace the cap and drive again. If the problem has stopped, but then comes back it'll sort of prove it. Sort of  .
Chris. http://shropshirelandrovers.freeforums.org 2015 Defender 90 XS SW & Helen, 1964 IIa. Previously 2012 Defender 90 XS SW & 2008 90 XS SW. Previous LR's: Michael, my 2008 Defender 90 XS SW. Machinas oportet intrare non capsicum annuum faveo |
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18th Mar 2012 9:46pm |
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| BigMike Member Since: 13 Jul 2010 Location: Lancashire Posts: 2253
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Suggest it's a fuel starvation issue really. Pickup is working harder as the fuel goes lower. So could be pickup issue ie dwarf in it, high pressure fuel pump or even egr problem.
If a tank issue you wont get a dtc but easy to rile out by putting a drum of diesel in the back and running pipes from the fuel pump to it. If all is well then your problem is definitely tank/pickup related When you undo the fuel cap is there a big whoosh of air? If so then tank breather |
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18th Mar 2012 9:48pm |
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| wslr Member Since: 18 Jul 2010 Location: Wellington, Somerset Posts: 581
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Someone better give Gaydon a call in the morning as they may need a TSB written on how to extract the dwarf from the fuel system on the Puma. |
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19th Mar 2012 12:26am |
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| cradgebank Member Since: 30 Dec 2008 Location: Nottingham Posts: 308
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Post edited, cos I was talking rubbish
Richard
Either a 90, 110 or 130. Discovery 5 Last edited by cradgebank on 19th Mar 2012 5:36am. Edited 1 time in total |
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19th Mar 2012 1:05am |
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| pannawonica Member Since: 21 Nov 2010 Location: Clackline Western Australia Posts: 568 
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Puma does not have a in tank fuel pump. High/low pressure pump is drven off the engine.
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19th Mar 2012 4:51am |
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| Caterham Member Since: 06 Nov 2008 Location: Birmingham Posts: 6331
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thanks guys for all the responses - although I'm still a little confused.
with the pump up front is it still worth me trying the barrel of diesel / disconnect of the tank ? as this will need to be a long(ish) term trial as the problem is intermittent.... 
just thought.....perhaps I should try running a 1/4 tank only for a while rather than filling up to see it that makes a difference (obvious really)> |
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19th Mar 2012 9:16am |
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| pannawonica Member Since: 21 Nov 2010 Location: Clackline Western Australia Posts: 568
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My Puma sort of does the same thing, however my theory is that it is heat soak of the intercooler. I have noticed that on 50 centigrade days this is more noticeable. I think the intercooler is minimal for engines needs. The truck drivers (owner drivers) tend to prefer driving at night, the cooler denser air actually save big dollars long haul east west. I do the same thing its a 1500km to the stealer for service. However due to warranty I cannot apply the Alive/Bas solution.
Maybe EGR issue, the operating strategy during warm up is zero, when engine temperature is attained the exhaust gases are recycled to differing degrees. |
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19th Mar 2012 12:25pm |
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