strange running problem

Post by **cheshire190e** » 28 Jul 2008 02:01 pm

Hi everyone, I have had my 340 for around 6 months now. When i bought it i was told the fuel guage was dodgey and since i have had the car it always seems to cut out when it reaches the quarter line.

I had a look when my car cut out to see if i could sort the sender unit out and hopefully fix the guage but when i removed it from the tank there was still loads of petrol left.

Now i have a strange problem which i just cant get my head round. The car is fine from a full tank but when it gets to around quarter on the guage the car starts to kangaroo as though its running out of fuel.

At first i thought it could be fuel lines but the fuel is going into the carb fine. I have checked the breather pipes too and they are clear.

Does this sound like an electrical problem? something to do with the ignition timing im starting to think.

Also when i was looking around the breather pipes i was wondering what the plastic tank in the right hand side of the boot is for? its always empty is this just a breather tank? if so could there be something blocked inside, causing a vaccum and stopping fuel from flowing propperly??

Any help would be much appreciated, cheers

Matt

Post by **Ronnie** » 28 Jul 2008 04:43 pm

Your fuel pump is on the way out - when the tank's full, the extra pressure on the fuel line from the higher level helps it pump through. When the tank is low, the pump has extra work to do and cant cope.

Website · Post by **antiekeradio** » 28 Jul 2008 08:06 pm

I'm totally with Ronnie on this.

another thing you might check out are the rubber hoses at the top of the tank; when these become porous the fuel pump sucks in air/petrol mixture instead of pure petrol.

if the hoses are still of the fabric covered type, you should replace them without further investigation...

The plastic tank near the filler is the fuel expansion tank. This prevents overflow caused by heating of a fully filled tank.

the expansion tank will not be filled during fill-up, because of a small orifice that connects it to the tank.

if the fluid level in the tank starts rising after fill-up, this goes so slowly that it can be accomodated in the expansion tank. the overflow will only start to leak once the expansion tank is full; which almost never happens.

Post by **cheshire190e** » 28 Jul 2008 11:32 pm

agh right, well I had a new fuel pump in for the MOT it just had so can't be that, I will change the pipes though. Cheers guys, there anything else it could be?

Thanks

Matt

Post by **Chris_C** » 29 Jul 2008 09:17 am

When you do change the fuel lines mate, you want to be doing the flexible ones both under the bonnet (i.e. to the fuel pump) and the ones from the solids to the tank. Don't bother replacing them with fabric covered ones again, change them to the same diameter fuel injection hose, lasts a lot lot better.

Post by **cheshire190e** » 29 Jul 2008 09:52 am

well i have just gone to check the fuel lines and all of them have already been replaced.

All i know now is its not the pump or the fuel lines.

Its really strange i just dont seem to understand why it would cut out when it gets to quarter, sometimes it can be abit more than quarter and sometimes just under.

im really struggling to think what it could be but its so annoying

Post by **Ronnie** » 29 Jul 2008 10:07 am

Well, if it's not the pump giving a low output, then it has to be resistance somewhere in the fuel line like a partial blockage somewhere

Sounds like the previous owner has tried to fix this already by replacing all lines. Time to check what hasn't be replaced. Only way to get to the bottom of it is to inspect every part systematically.

The other possibility is that the new pump is a duffer, why did you have to change it for the MOT and where did you get it from?

Post by **cheshire190e** » 29 Jul 2008 10:12 am

The pump i fitted was a new one from unipart and i had to replace it because the old one was leaking and spitting fuel out.

The reason im unsure wether its a blockage is it only happens when its near a quarter full, and if it was a blockage wouldnt it happen more irrationally?

Also when it cuts out there is still fuel in the inline filter before the carb so i dont think its lack of fuel....

Post by **jtbo** » 29 Jul 2008 12:59 pm

Maybe fuel pickup and filter in fuel tank is worth to check?

Amount of fuel should really not effect any other component than just fueling, imo.

Post by **Chris_C** » 29 Jul 2008 01:36 pm

For comic amusement, and just to be certain, try taking the fuel hose off the carb, put the end in a jam jar, and crank it over for 15/20secs. That way you can confirm whether fuel is coming through (though if you have a full tank atm, this won't help, but do it when you find it's cutting out).

It's the only sure fire way to rule out the fueling problem, even if the hoses have been replaced, I had a set of cloth covered ones perish after 6months of being on the car, and you've owned it that long

Post by **cheshire190e** » 31 Jul 2008 01:10 am

i checked, i thought i did but i dont actually have the cloth covered fuel lines, they have been replaced to newer solid ones, there is still fuel when it cuts out because the inline filter is still full, all i can think of is electrical or a vaccum

Post by **jtbo** » 31 Jul 2008 05:07 pm

But is there fuel in carb when cutting out does occur? Top plate of carb should be rather easy to remove, just needs bit of fiddling with choke lever and ventilation lever, twist so that ventilation lever gets loose and then choke lever needs to be pulled a tiny bit and top plate comes free (of course before anything you need to remove screws) be careful not to use force as float arms can bend. There you should see two pools filled with petrol, if empty then fuel is not passing trough from inline filter to carb.

Problem can be then dodgy fuel pump, clogged fuel hoses between pump and carb, or then that cylinder shaped bottle if 1.7 ever had one? Oh yes and there is filter in carb too, just need to unscrew that hose connector from carb where fuel hose connects. If this filter is installed wrong way, car runs quite badly and cuts out a lot.

Vacuum and electric should not be affected by amount of petrol in tank, at least I fail see how those could be connected at all.

Post by **morgan105** » 04 Aug 2008 03:17 am

Fuel tank transmitter float could be bent out of shape if someone has had a play with it in the past and could be touching the bottom of the tank at quarter reading. Had it happen on a old car of mine I bought and is easy to do if not carefull when transmitter is removed from the tank just to bend the float rod slightly downwards.

morgan105

Post by **fig roll** » 04 Aug 2008 03:41 am

have you tried starting it with the petrol cap off? i know its a long shot but worth a try...