1972 Granada Mk1 coupe build - Still going... 14-10-2024

Just a very quick question...

I received my lockable fuel cap, but to me it does not look vented in any way though I specified that when ordering.Seeing plenty of overflow evidence from the few drives without a cap means I don't want to return and reorder. On my previous fuel cap I had drilled a small hole, but I did feel that even with 2,5mm diameter, this would make the car smell.

So if i need to drill a hole again, how small may it be?

There is "no" real flow in the vent hole so yes, it can be small. But no matter how small, you will get the petrol smell.

The only "solution" is using a charcoal canister on the vent line.

Gustaf

Hi David,

Thanks for your compliments and for joining in!

A quick recap: I have a dual fuel pump setup. I use a low pressure (supposedly) high volume pump at the fuel tank end that supplies a swirl pot at the front of the car. This is setup as a feed and return so when the swirlpot is full, excess goes back to the rear fuel tank. From the swirl pot I have a high pressure efi pump feeding the engine and returning to the swirl pot. So basically two circles that share the swirl pot. The high pressure circuit is very capable of feeding the engine and has 8mm lines as the thinnest cmponents. The low pressure circuit has 6mm lines that in reality measure an ID of 5,5 mm at best. But during one of the few very hot weekends we had, I had fuel delivery issues.

Testing revealed a very hot fuel pump and swirl pot. The engine bay is pretty hot environment with a cosworth BOB engine anyway, but a lack of flow between the swirlpot and rear tank was found (only 450ml a minute!), which meant the fuel heated up too much as the same fuel was constantly recycled. Flow tests showed that with a fresh clear fuel filter for low pressure applications, the flow had doubled again to 850ml. Ever since the fuel pump temp has been a lot more normal, warm but not hot like before (you couldn't keep your hand on it then). So I may not even have a problem anymore as I had never had any problems with this in the 7 years to date that I'm running this combo. So it's not that the fuel pump experiences a pressure drop, it just does not seem to generate the expected flow (this particular model should flow 120L/H the supplier verified for me).

Still, ever since I've been paranoid about getting stranded on the motorway again, as I had some less than ideal places where I had to stop. Hence the activities and discussions on what all could be the cause. I figured it was due to line size, just not able to get the right volume flowing. In a final effort I removed the restrictive connectors, which turned out not to be very restrictive as the fuel flow remained almost the same. I can test a couple of things still: removing the filter altogether for one, which is relatively easy to achieve. Another fuel pump as a second thing.
At first I felt that if the elimination of the fuel filter would not improve the flow, I should up the line sizes, but I have to say that I'm leaning more and more towards buying a better/new pump. If a new pump still does not generate the wanted flow I can always up the line size afterwards. I also like the suggestion someone made before of using a second efi pump to feed the swirlpot, that will definitely mean a return flow will start running, as it is a lot more quiet than the current type. But the drawback for me is that the inlet of that pump takes a huge line 12mm at least if memory serves me and the tank output is only 8mm. The output side can take 6 as well as 8mm depending on the banjo used.

So maybe a good question to ask now is what would you guys do: Buy a better/new high volume low pressure pump and see if it helps or adapt somehow and use an efi high pressure pump (which I have lying around)?

As I'm using the Granada tank, the pump is external to the tank. This was the same on the MkI scorpio's. I cut the whole mounting plate and pump filter combo from one.

The pressure regulator on the fuel rail seems fine, that is, when there is fuel to flow the engine is getting it even on what acceleration etc. And the engine runs fine, just not when the fuel got so hot.


BTW: I was able to determine (form the supplier) my high volume pump should be able to flow 120l/h so with less than a liter a minute it is not flowing as it should for sure.

Yes, that test I will do this weekend as it is pretty straight forward!

"But seeing how sensitive the flow was to the switch from a dirty to a clean filter I'd hazard a guess that it (still) is a relatively large flow restriction." This is why I'm now more thinking about replacing the fuel pump. Only question is with what? The 120l/h one I have is considered pretty high volume. I haven't yet investigated seriously but a quick glance also shows many versions from 60-105l/m. Your math is very welcome, this shows that it is probably more worthwhile to do something about the pump than about the lines.

Yes, the tank is coated with an Ethanol proof product. The coating is stil looking awesome. Last time I had the sender out the filter was clear as new (only slight discoloration from fuel). This because the tank itself is simply very clean inside.

Also, when I changed the filter recently, well, the fuel came pooring out quite happily. That was a very steady and fast flow!

This pump has no filters, hence the carb/low pressure filter between tank and it.

Thanks for playing!

Well, quick and dirty:

With the filter removed and the gas cap off I now had a fat liter of flow in one minute.

With the gas cap on, it was exactly one liter in one minute.

I’m still not sure if my fuel cap is vented or not but I’ll take it for a drive and see if it hisses after a bit of driving.

I think though, that for now the total improvement from 400ml to a liter is good enough to try and see how the car behaves…

If I do still get in trouble on a hot day, I’ll update the pump.

One more question: The swirl pot, is it actually a swirl pot where the fuel flows "in the radius of the tank" to make the air in the fuel go away, or is it a catch tank to make sure you don't loose fuel pressure during hard cornering when/ if the fuel pickup tube gets uncovered?

/David

It’s sold as both catch tank and swirl pot but it’s just a small rectangular aluminium box with 6 ports.