Fuel System Problem - pressurised / vapourised or What?

[Ian Anderson]

Ok what I know

GT40 Rover3.9Efi Hotwire Mad cam (JE102)
2 tanks through a 6 way valve to Red Top, to Swirl, to 6 way valve return to tank, Swirl to Bosch HP pump to fuel rail to Swirl. Fuel tanks are in the side sills and the fuel pumps are mounted at lowest level of chassis in the engine bay.

Engine bay is at rear of car so no airflow until moving fairly quickly
Rad at front with long pipes with twin fans etc.

Temp gauge says 86 -90 degrees normally and when stationary gets to 93 ish when fans cycle and temp drops to about 90 and repeats.

Drive on the road at reasonable speed and everything is fine car goes well.

But get caught in traffic and at 20MPH for a while and the car will eventually die!

It seems to manage to stop the pump that delivers the fuel to the swirl pot

Pull over and leave it for 5 minutes and it all primes up again and off we go again.

So the tanks are sealed (no bleed to atmosphere) so could the heat in the engine bay be warming the fuel to the point where it will cause the vapour to pressurise the tank to the point where the Facit Red top thinks it should stop?

Could it be something else - I'll fit new in line filters tomorroy to try that but the ones on have less than 1000 miles. - I'll also clear out the mesh in the Facit inlet.


All ideas welcome

thanks
Ian

[katanaman]

confused here if your tanks don't have a breather then how can you pump the fuel out of them? There has to be a breather of your tanks will go into vacuum and fuel will stop flowing. Or do you mean you have breathers but there are one way valves on them?
Either way I cant see it being pressure that's stopping the pump. Even if it could do it I cant see there being that much pressure in the tank anyway as your removing fuel all the time. The fact the pump and engine stops should mean the pressure gets higher as no fuel is being used. More likely to be the pump that's failing due to heat or something in the pump circuit.
I guess just to prove the point when it happens you could open the fuel cap which by your theory the pump should start instantly.

[ramon alban]

But get caught in traffic and at 20MPH for a while and the car will eventually die!

It seems to manage to stop the pump that delivers the fuel to the swirl pot

Pull over and leave it for 5 minutes and it all primes up again and off we go again.

Ian

Ian, I dont know whether this applies to your problem or not, but it may be similar to a Hot Start Problem caused by Fuel Vaporization.

Please bear with me and read this explanation that applies to the Rover V8 fuel injection system and see if any of the circumstance could apply to your entirely different setup, particularly some of the solutions offered.

http://www.vintagemodelairplane.com/pag ... art01.html

[Eliot]

confused here if your tanks don't have a breather then how can you pump the fuel out of them? There has to be a breather of your tanks will go into vacuum and fuel will stop flowing. Or do you mean you have breathers but there are one way valves on them?

Yes - could you clarify this point..

[Ian Anderson]

Marki

No breathers and no one way valves - sealed tank once the fuel cap is put on. (I believe this is how all modern cars are forced to run to stop hydrocarbons getting into the atmosphere)

On my Fiat this was really noticable by a whoosh of air when you pull in to a filling station after a drive!

I can leave the caps off (under the GT40 "pretty" items) but under braking with long thin tanks the fuel sloshes forward and will escape so probably not a good idea.
See http://www.gt40s.com/forum/race-track/1 ... crash+test
That's scary stuff!


Now when blasting down the road at 70 mph the car is using a load more fuel than then bumbling along at 20 so perhaps at that speed the fuel tank will go into vacuum and with voporising fuel the tank would pressurise.

I can hear both bumps in normal use
The low pressure Facit clicks away continuously
The HP pump emits a high pitched whine

When this problem happens I can still hear the whine but not the clicks so hence I thought the facit was stopping it's pumping due to high pressure.
Perhaps the pump is failinf due to high temp - I can't tell as it all starts working again after a few minutes.

One last thing when it is ready to start I have to energise the ignition3 /4 times to have the 3 second pump and then I can hear the fuel pump go from CLICK CLICK to click click - at that time it will restart (this would then refill the swirl pot)


Ramon
Yes it sounds like that and the temperatures under the "bonnet" with the the high up exhausts etc is pretty high.

But I can hear the HP pump running so that sunds fair.

I also have a Bosch HP pump on the system not a Rover part but it is fed from the ECU fuel relay so perhaps according to this there is a reduced voltage - do you know if this is the case in a standard 1990 loom?
If so probably time to fit a direct feed to the pumps to see if that will help.

thanks for the help time to keep looking fo the answer.

Or is it time to fit say 2 x8 inch fans in the engine bay to move the air?
With all the electrical stuff I'll need a much larger Alternator just now!

Ian

[katanaman]

modern cars have a one way valve in the fuel cap to let air in but not out. If your caps don't have that then I think we have found why your leaning out under power as your tanks are going under vacuum. I didn't mean run the car with the caps off I just meant when it stops open the cap and equal the pressure.

Cant see the pic by the way as you need a membership.

[Ian Anderson]

Ok so if there is no valve fitted and the tank goes into vacuum will it stop a Facit from running? I would have thought not (Probably cause it to race as it would be in a non fuel state) but on the outlet side of the pump backpressure (carb fills) will stop it pumping until more fuel is needed.

Perhaps I am wrong on this - been wrong many times before!

It's a good day here so time to get under the car and do some mods!

IAn

[JSF55]

Just a couple of pointers...... is the battery losing charge when u sit in traffic witht he fans running causing the ecm to overfuel? most modern cars have carbon filter do da that takes the fumes from the tank and feeds it back into the engine at sometime, never looked into it my self, and howcome thers no baffles in the tanks? i would have thought they would have been foam filled if they are that unsafe.... i haven't seen it either !!

[Paul B]

Marki

No breathers and no one way valves - sealed tank once the fuel cap is put on. (I believe this is how all modern cars are forced to run to stop hydrocarbons getting into the atmosphere)

On my Fiat this was really noticable by a whoosh of air when you pull in to a filling station after a drive!
Ian

You've got to have SOMETHING to let air in, else your motor will stimply stop running once you have a certain level of vacuum in your tank.

The woosh when you take the top off your Fiat is merely the pressure difference built into the breather system, ie the spring that holds it closed. It'll only be 1 psi or less, else you'd never get the cap of the tank.

[ihatesissycars]

Moder cars do have a breatehre but not of the converntional type to atmospohere, I can't remember what it is they have now but its possible something to do with engine vac or similar but it lets the tank breath but nothing goes to atmospohere.

[ihatesissycars]

I'd bet on overheating fuel.

WIll holman had this once in his V8 capri, stuck in traffic the fuel would overheat and the pump would get noisey and then stop.

It was due to the return from the fuel rail going back to the swirl pot and not the tank which caused the fuel in the pot to get very hot rather than be cooled by the fuel in the tank.

[ramon alban]

[quote="Ian Anderson"]
Ramon. Yes it sounds like that and the temperatures under the "bonnet" with the the high up exhausts etc is pretty high.

But I can hear the HP pump running so that sunds fair.

Ian, If the fuel rail is getting SO hot in slow traffic or when Stationery, then it is the fuel rail where the fuel moves slowest allowing it to vaporise right there. I never realised it may vaporise when the car is actually running, but that would depend upon just how hot the system gets, i guess

So the pump may still be running full bore yet all it is really doing is sending COOL fuel back to the tank.

Only when you allow the engine bay to cool sufficiently is the fuel going become liquid again.

I also have a Bosch HP pump on the system not a Rover part but it is fed from the ECU fuel relay so perhaps according to this there is a reduced voltage - do you know if this is the case in a standard 1990 loom?

I can only speak of 1986 SD1 loom where there is a series pump resistor to limit the pump voltage to about 8-9 volts, this was only to reduce pump noise, because the pump had sufficient pressure at the lower voltage.

Or is it time to fit say 2 x8 inch fans in the engine bay to move the air?
With all the electrical stuff I'll need a much larger Alternator just now!

Possibly, but what if you could have a channel of COLD air from outside the engine bay directed at the fuel rail. It may be easier to imagine than to perform.

[quote]

When Rover had to solve their SD1 Efi problem in the late 1980's the solution was purging of the fuel system, the fuel pump ballast resistor was by-passed, thus supplying direct battery voltage to the pump with consequent increased output. That raise the pressure in the fuel rail to 50 psi sufficient to richen the already weakened mixture and to cause the fuel to reliquify due to Boyles Law.

None of this directly helps you because I never found the Rover cct diagram for their solution but it explains the problem and their solution.

Further more I have no idea if this problem ever occurred on later versions of the Rover Efi system such as yours.

One thing for sure, It seems that your engine bay may be getting considerably hotter than the engine bay for the original application.

[Ian Anderson]

Ok

Fuel filter was really 5H1TTY muddy with some metal bits in it - presumably from the manufacturing of he tanks

So I fitted a new one and also tested and tightened a number of jubilee clips on the fuel system

Went for a fairly long hot drive at slow speeds and she ran perfectly.


So perhaps I'm lucky and it was just the filter restricting the fuel flow allowing it to overheat and then stop.

Time will tell - need to do a load more miles

Ramon yes the fuel rail and plenum get really hot - exhausts curl up mext to rocker covers then above the Renault Transaxle behind so lots of heat source. At speed the side scoops move enough air to keep it cool but at slow speeds it seems to not like it - strangely enough at idle it will run for ever!

Battery getting flat - don't think so and the meter is reading 14.5 volts at anything over idle - even when fans kick in. It also starts first time every time on the key. (72 amp hour battery Rangie spec)

Thanks all for the ideas and assistance- if it fails again I'lltry opening the fuel caps and listen for the whoosh - easiest thing first - if that doesn;t work - perhaps the fan to keep air moving in the engine bay

Cheers
Ian

Next thing - how can I keep myself cool inside at slow speeds - the heat soak into the cabin is high! Thats what you get when you run a race car on the road! Perhaps I'll loose some weight in the sauna!

[ramon alban]

Fuel filter was really 5H1TTY muddy with some metal bits in it - presumably from the manufacturing of he tanks

So I fitted a new one and also tested and tightened a number of jubilee clips on the fuel system

Went for a fairly long hot drive at slow speeds and she ran perfectly.

Well Ian, thats what I like about these forums, someone asks a really complicated and long question.

Three or four people come up with equally complex or off target replies.

This leads to an "intelligence dance" where the answers get refined.

Then the originator comes up with the simple solution eg: changing the fuel filter.

Well "I'll go the the foot of our stairs".

Just goes to show that you were going to come up with the solution all by yourself, I reckon.

But then all the profferred solutions seemed to be somewhere on the right track ie the fuel was not getting thro in the correct mixture. It's just that you happen to be the cleverest to come up with the simplest solution.

"I haven't had so much fun since our pet pig ate my sister!"

Now, regarding the excessive cabin temperature?

[katanaman]

as for fuel rails getting too hot why not insulate them and stop them getting hot in the first place.