s1 3.8 Solid State Fuel Pump

[Heuer]

The SU AUF 300 range of high pressure pumps (as used in the 4.2 cars) are designed to provide approximately 140 pints of fuel per hour at a point about 3 foot above the level of the tank. It is thus capable of supplying fuel at this rate when ascending the most severe gradients likely to be encountered. The fuel pressure is about 3.8psi static and 6psi pulsed. The SU AUF 700 series of mechanical pumps produce a constant fuel pressure of 6psi. Both of these are designed by SU to work with SU's. The new electronic in tank pump has a bypass valve set to 2.5psi.

I have a SU AUF 300 in my OTS and use a Filter King pressure regulator set to 2psi. Looks almost exactly the same as the stock item with the benefit of adjustment:

[rswaffie]

The new electronic in tank pump has a bypass valve set to 2.5psi.

SNG told me that too - however both pumps I got from them fire it out at about 5psi (as shown in my earlier post in this topic. I have to use a Malpassi to get it back to just under 3psi to stop the carbs flooding.

[Heuer]

The SU's should take 5psi without problem but the higher pressure can cause leaks if the carbs have faults. Sensible move to fit the Filter King anyway.

[johno560]

Hi
SNGB shouldn't have confused the 3.8 with the 4.2 since the 4.2 is not using the submerged pump. Their comment about there being no fuse in the standard harness is completely incorrect and and on a subject concerning electrical equipment submerged in a petrol tank I think this is highly irresponsible.

I am also concerned about the likely increased pressure causing carb flooding and from the posted comments it seems that the expense of an additional regulator is almost inevitable to be sure of reliability.

My own conclusion is that this replacement is not "fit for purpose" as a direct replacement for the Lucas 2FP pump and SNGB should be advising S1 buyers that they need to change the fusing as well as add a pressure regulator in order to achieve roadworthy reliability.

Cheers

[Heuer]

You can always fit a SU AUF 300 pump a'la the 4.2 cars - all the parts are available from SNGB.

As I have said the SU's (new, in good working order or professionally restored) can handle 6psi without problem. The car wiring can handle the extra 3.8A without problem. I have the new pump in my FHC and it has worked perfectly since installation and I did not change the fuse or put a regulator in line. Over pressure fuel would not cause the SU equipped engine to 'flood' but the SU's can 'leak'. Fuel can leak in two ways:

1. from underside of a jet
2. from a float chamber

These are caused by a leaking float needle valve, punctured float or incorrect fuel level all of which are maintenance related. The SU's have overflow pipe's to drain the fuel away safely in the event of this condition

So, in summary, your conclusion is not "fit for purpose"! Some clarity on fusing from SNGB would be helpful though.

[rswaffie]

I’m going to politely challenge some of the statements made about why flooding occurs, based on my own experience with the 3.8 solid state submerged pumps.

1. My carbs were all professionally rebuilt, the only original parts retained were the brass floats as they were deemed good.
2. From the moment the pump fired up, fuel leaked out of at least two of the overflow pipes and up through the jets, and over the bridge. The needle valves, arms and pins were all checked and found to be fine.
3. The ‘fingers’ gap, based on the round bar setting in the manual were validated.
4. Pump on, Still the same flooding pattern.
5. New floats of the latest non-leaking material installed.
6. Still the same flooding pattern.
6. Discovered the higher than desirable pressure from the pump, added regulator to bring it down to just under 3psi.
7. Pump on, No more flooding.

I agree that the extra pressure may well cause an overflow from the pipes, but I firmly believe that the outflow from these pipes at 5psi is not enough to prevent fuel also being forced up the jets and over the bridge as well.

This is purely based on what i encountered over a very frustrating 4 week period of troubleshooting what was ostensibly needle valve/float problems.

[Heuer]

I have asked Julian to look at this thread and come back with his thoughts.

[Heuer]

From Burlen:

"Assuming that the float height setting is correct, the normal cause of flooding is a small amount of dirt (i.e. rust) lodging in the float needle valve, preventing it from closing. Fuel continues to fill the float chamber, eventually overflowing or ‘flooding’. The cure is to remove the float lid and clean out any dirt from the fuel line/needle valve and reassemble. The main cause of dirt in the fuel is from residue or rust in the fuel tank. A temporary fix would be to fit an inline filter but a clean tank is the only real solution.

Another cause of flooding, often mistaken for an over high fuel pump pressure, is caused by air trapped in the float chamber. When fuel is fed into the float chamber it rises and the float shuts off the needle valve. If, however, the chamber air vent is blocked, the fuel rising compresses the air in the chamber and fuel is forced out of the jet at pump pressure.

There are several different methods of venting the float chamber, from a simple hole in the lid to overflow pipes, all of which can be blocked in various ways. If in doubt, loosen the fixing of the float lid just enough to allow air to escape and see if this cures the problem. If it does, then hunt down the blockage and remove."

The current electronic in-tank pump is from a XJ6 S2 made by AC Delco and includes a pressure regulator. If I find the specs I will post them here.

[nichmoss]

Interesting comment from Burlen about the trapped air and how to diagnose that - thanks.

I've had one of the SNG pumps in my 3.8 for about 8 or 10 years and never had any issues. Did they change the design recently? I've not measured the fuel pressure or current draw but I might check the latter as I'm sure that I just run standard fuses.

[johno560]

SNGB returned a replacement pump back to me and I've had a good dialogue with them.
They now acknowledge that the spec of their pump is outside of the original Lucas 2FP, both in terms of supply pressure and current drawn, but it seemed that they had not been drawn to this conclusion previously.

I checked the pump which SNGB sent back and it has a static delivery pressure of just in excess of 5 psi and the the static current ( engine off) current is 3.3 amps rising to around 4 amps with the engine running. so for the time being I am continuing to use my old Lucas 2FP and SNGB are sourcing a Filter King plus some 7.5 amp fuses which they will send me.

I understand that some users have said they have had no problems with previous SNGB pumps - so have they changed the design - maybe. When I spoke with them, they informed that it could be that the pump design has changed to meet new E10 fuel standards

SNGB tell me that they are continuing to look into this along with their pump supplier and hope to develop a pump configuration winch is closer to the original Lucas 2FP spec.

Cheers

[rswaffie]

For the record, I pointed out the increased flow pressure to them in Aug last year, when I had all the issues with flooding when I installed their pump and I posted their response in this topic. They insisted it was to spec. Until I installed a Malpassi regulator to reduce it to 2.8 psi, it continued to flood the carbs. I probably wasted weeks of my time and unnecessary expense in getting the car up and running because of this.

[christopher storey]

I often wonder how many of these flooding problems are caused by misassembly of the float chamber securing nut and the slotted washer. It is odd that this is not referred to in the Burlen quotation, but if the slotted washer is not placed next to the lid (** I hope I've got that the right way round ) the chamber becomes airlocked and/or slightly pressurised which then causes fuel to rise in the jet

** Just checked and I have got it right