Fuelling Issues

[ESD1711]

Having some strange issues with my track car - hoping someone might have some ideas or have some previous experience of similar problems, as its got me scratching my head a bit.

Car is a VTS - which was recently reshelled in to a VTR shell. Everything was swapped over, fuel tank, return line - was all just taken from directly from the VTS and put in to the VTR.

I did a lot of road driving in the VTS shell and never once had an issue similar to those which I seem to be having in the new shell.

Basically, the car doesn't seem to want to run correctly with anything less than a half to 2/3 a tank of fuel in it.

On a full tank, it'll run absolutely fine - till it gets to a certain point and all of a sudden it no longer wants to rev freely under load and beyond 4k revs it has nothing at all.

Top it back up with fuel (takes just shy of a 20 litre jerry can to fill - so a little less than half a tank) - and all of a sudden it'll run just fine again.

Have checked the gauge using both the vtr and the vts clocks and both show the same value, which is backed up by how much it takes to fill it back up again so theres defo no fault there.

Changed a fuel filter and run some dry fuel through it to make sure theres no water / moisture in the tank.

Obviously for now I can run it just with a full tank all the time without issue, but that's just avoiding the issue and i'd rather get to the bottom of it than work around it.

So....... has anyone ever had anything similar? Or can any of the guru's on here offer up any suggestions as to possible causes?

Any help would be greatly appreciated!

[axsaxoman]

simple --you must have a leak on the fuel pump pickup piping inside the tank -so when level goes down -it sucks air not fuel .
OR there is no brether and you are creating a vacumn in tank as level goes down --would have thought you would hear a funny sucking noise when removing filler cap if that was the reason though-- so remove pump unit and look at it carefully.
It could be the pump is old and so weak it cannot lift the fuel =make pressure when tank not full-.

you sure its a VTS fuel pump?--1.4 pumps look the same but do not flow enough .you fitted ALL the correct fuel piping for the vts --EG a return pipe to the tank ?

[ESD1711]

Originally Posted by axsaxoman

simple --you must have a leak on the fuel pump pickup piping inside the tank -so when level goes down -it sucks air not fuel .
OR there is no brether and you are creating a vacumn in tank as level goes down --would have thought you would hear a funny sucking noise when removing filler cap if that was the reason though-- so remove pump unit and look at it carefully.
It could be the pump is old and so weak it cannot lift the fuel =make pressure when tank not full-.

you sure its a VTS fuel pump?--1.4 pumps look the same but do not flow enough .you fitted ALL the correct fuel piping for the vts --EG a return pipe to the tank ?

Thanks for the reply

I know that its 100% the fuel pump which ran in the VTS without issue - I suppose theres a chance that someone had changed it previously in the VTS for the wrong one, but like I say, i'd run the VTS as a road car for the best part of a year without issue so confident its the correct pump..... however, old / knackered could be a valid - no idea how long its been there.

All the correct piping from the VTS is there including the return line. As I say, the complete fuel system including the tank, pump, lines etc were all just lifted directly from the VTS and put in to the VTR.

Seems logical that the pump is going to be the source of the problem in one way or another though.

[ESD1711]

Had another look at this over the weekend and unfortunately don't think i'm any further forward.

Basically I've used everything from the VTS, and the VTS's fuel tank - there is only one line which is different which we used from the VTR and that is the line which is T pieced to the FPR on the VTR tank - the VTS one wasn't in very good condition so had just used the VTR one and blocked off the T-piece which would attach to the FPR on a VTR - given that on the vts that's just a straight pipe without a t-piece, I don't think blocking it off would have done any harm?

Other than that - theres nothing obvious. Have switched over to the fuel pump which was in the VTR previously. Will just need to give that a go and hope that its a problem with the original VTS fuel pump. Given that it ran for over a year in the VTS without any problems though - it would be a massive coincidence that it stopped working as soon as it was put in the VTR shell.

[axsaxoman]

then you have not swopped it all over to SAME as a vts --start by putting it all back to std vts -fuel reg on fuel rail on engine and no reg at rear with vts return system

[ESD1711]

Sorry John, I think you've misunderstood me - like I say, it IS all VTS stuff that's on it. There is only one hose which isn't VTS - that's the hose from the tank which goes to the wee white pressure release valve thing.

The hose I've used for that is off the VTR one, so it has a T-piece in it which would have gone to the FPR on the VTR, however, given that the FPR isn't there any more (as per VTS), I've simply blocked the part which would go to the FPR if it was there, which its not.

Aside from that one hose which goes (from memory) from the green connector on the top of the tank down to the white valve under it, everything is all from the VTS and setup exactly as a VTS would be.

[Chipwizards]

Then put it ALL absolutely the same as in a VTS.

Things very, very rarely change at the same time by co-incidence.

Q:- I have an issue with 'X', what can it be?

A:- 99% of the time, whatever you have changed since last it worked properly.

Q2, But I don't think it's that...

A2, then return it exactly as was and prove your theory.

[ESD1711]

Ok. Fairly certain from memory that the reason we didn't use the VTS line between the tank and the white valve was that the VTR one looked to be in better condition - fairly sure the VTS one had worn through.

Shall try dig it out though, or if I can find part numbers - renew from the green connector back to the white valve - i'm inclined to say if theres a problem its perhaps more likely to be with the white valve rather than the line itself.

Would there also be a benefit in changing the orange / red valve which sits at the engine side of the charcoal canister?

[axsaxoman]

that valve is a one way/two way partial pressure valve to stop you getting a vacum inside tank as you use fuel or to get rid of over pressure due to heat and return of fuel from engine and any vacum that the carbon canister valve could make
If you had a w/b lambda qauge on the car you would see if it is running lean when it has its problems -then you would know it is a fuel supply problem

[ESD1711]

w/b lambda seems a bit like overkill though - we're talking about a standard engine (barring exhaust and intake) run using a standard fuel system.

At this stage I'd really expect it just to be a turn-key jump in and drive it kinda car without having to worry about wide band lambda's and AFR's

Its due at knockhill this sunday, so will try and get the white valve from the old shell if I have time - failing that i'll just need to keep the fuel topped up after each session.

[craigyt]

Put the vts pipe back on and see if it works.

If it does order a new one

[Chipwizards]

You could also put a fuel pressure gauge on it.

You would also get an indication from the stock lambda using a suitable scan tool or a multi-meter. More than 0.45v (between the black and the grey wires) is richer than lambda 1 and less voltage is leaner.

At no point in the rpm range at FULL LOAD should it be less than 0.45v, it should usually be in the 0.8v range. If it's going lean enough for the engine to run badly it will show low voltage on the lambda.

[ESD1711]

Thanks for the suggestions folks - i'm gonna try and get the old breather pipe / pressure valve on it and see where that gets me.

[ESD1711]

GOOD NEWS!!!!

As suspected, when I went to look at the old pipe from the VTS shell, it was damaged with a hole worn through in it (i'm sure this was the reason we didn't use it first time around).

Rather than going to the hassle of dropping the tank to put on a broken part, I decided just to unplug the blocked t-piece on the vtr pipe.

Wasn't entirely sure what the chances are of fuel actually ever making it in to those pipes are (at least while the car is the right way up!!) - however, rather than take the chance with that - I just ran a new pipe from the t-piece to as high in the car as I could and had it venting to atmosphere out the top of the rear quarter window.

Not pretty, but for the sake of proving a theory it did the job.

Car ran flawlessly all day long at knockhill yesterday - didn't skip a beat and punched above its weight all day long.

Suggests to me theres perhaps a problem with the white valve itself although it sounds like the ball bearing is moving freely so not sure what else can go wrong with them - but for now i'll probably just tidy up what I've done and fine a more permanent home for the 'new' breather I've made.

Thankfully I can stop pulling my hair out for a while which is good - i'm running out of the stuff!