The 'E' Type Forum

Hi.
1973 S3 2+2 LHD US import.
Engine is stuttering / coughing on hard acceleration, as in too lean mixture.
One of the carb diaphragm had a small hole, replaced all four. No difference. Oil level correct, ATF.
Adding choke did no difference. Raised all carb needles 1/4 turn. If any difference worse. Lowered them back 1/4 turn + additional 1/8. If any difference slightly better.
Maybe engine not getting enough fuel?

( Later found LH choke wire loose, so choke maybe had no effect )

So I decided to check fuel pump output, at least to eliminate one possibility.

Disconnected fuel pipe close to LH carbs and connected a pressure gage.
Pressure 4.4 psi, a little high.
Output around 100 liters / hour.

While at it cleaned out the Non Return Valve. When refitting it, I discovered it had been fitted the wrong way, effectively blanking off the return line. Testing NRV valve with air pressure and it ts working.

After refitting NRV checked again.
Pressure 2.8 psi. NRV acting as a pressure regulator.
Output still around 100l / h, as expected with free flow. NRV stayed closed.
Pressure downstream of NRV 3.2 psi, with fuel pipe reconnected to carbs.

Question is, is 100l / h enough?
Have not been able to find any Jaguar data.

Did some maths. My old Subaru diesel is consuming ca 6l / 100km. With full throttle uphill it is consuming almost four times that figure.
Cruising at 120km/ h the Jag is using less than 2l / 100 km, ( have an OD ).
2l / 100 km equals 96l / h at 120 km/h. Close to 100l / h.

Fuel pump. Have had the car for 5 years so I should have realized it before. It is not making the correct ticking sound. As in my 64 S type, were the ticking slows down as the carbs fills up. This pump is buzzing along a same rate, thought it was because of return system. But that was closed with NRV wrong way.
It is buzzing / pulsating, kind of diaphragm type?
Dug it out and it looks like a generic modern type. Not been able to find out what it is. It have some numbers printed. 19E and 52-3231.

Should not matter as long as 100l / h is sufficient.

Thanks in advance for any information.
Rgds Harald.
PS. For some reason not able to add images. The pump is cylinder shaped and silver, 7-8 cm diameter twice as long.

3.2 psi upstream (not downstream) of the NRV?
With all of yr fixes, is it still spluttering under hard acceleration? If so, maybe not the pump?
For how long are you hard accelerating? If the fuel pump is the problem, car shouldn't start to splutter until you've drained the float chambers ...
OEM pump capacity is reportedly 136 L/hr. 100 L/hr would empty yr tank in 48 minutes. That's some hard driving.

Hi.
Thank you.
3.2 psi are after fuel have flowed through the NRV, with fuel having no were else to escape. Ie the NRV are «stealing» 1.2 psi as fuel are flowing through.
Due to winter conditions with salted roads have not tested car after work as described. Hoping for a nice dry day or two. Have to wait until then.
The spluttering came after a few secs with pedal to the floor. If this is the problem, I think spluttering will start before the bowls are completely drained. Below a certain level problem will occur.
OEM is 136l/h, how much margin is there below that? Will not do anything more until able to do a test run.
And I found my pump on ebay. Specification there says 136l/h. I measured ca 100!

Powermax Universal 12v Electronic Fuel Pump

Rgds Harald.

Are you saying, there is 4.4 psi before the NRV and 3.2 after it when fuel is flowing back to the tank? Not stealing, enabling. NRV creates back (upstream) pressure. Because of the NRV the fuel supply to your carbs is ~1.2 psi higher than it would otherwise be. Fun thing to try, put a T in the fuel line before the NRV and mount the gauge so you can see it while driving. If the pressure stays above 3.2 the problem is somewhere else, probably vacuum leak.

Hi.
Thanks.
Have been a bit unclear.
4.4 psi into carbs, return line closed and engine not running.
2.8 psi into carbs NRV operating ( fuel returning to tank ) engine not running.
With a T in the return line I measured 3.2 psi in the return line. So fuel needs 3.2 psi of pressure to make it back to the tank. Theoretically should have had same pressure on feed side of NRV. Did not think about that so measured only once.

More useful and interesting to do this measurements while driving.
But I am trying to find out if I can rule out fuel starvation as a cause of problem. Thought maybe someone else have gone down this route and have some facts.

Most probable there is something else, and vacuum leaks can occur a lot of places.
And with winter time here in Norway might be some time before I get out of the garage. Checking vacuum hoses and connections in meantime.
Rgds Harald.