Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Fuel System Not Holding Pressure

Chris, without fuel pressure, the engine will not start no matter what the ECU "thinks". (wry smile) After all, no manner what the ECU programming it cannot create what is not present.
namely pressurized fuel in an unpressurized system, BTW, I often clarify my thinking by remembering that one needs two elements for combustion, (outside of air) and they are fuel and a
spark. No combustion means one or both are missing.

If there is a leak in the fuel system, difficult starting will logically commence, depend on how fast that leak. EFIs can leak from an anomaly anywhere in the entire fueling system. Assuming
the leak has not been genteel enough to express itself with a polite petrol puddle on the floor coming from a hoses, pipes or junctions. (The MMC diagram shows there are too many of
those for a purist's tastes) but that is an old MMC tradiition A cost saving that increases risk and hassles, IMHO.

If no puddlet, then pressure leak would be:

1. forward of the pump through an injector (s) (which the hired technician denied). Nothing visible
2. backwards from the engine showing the element stopping backward fuel flow malfunctioning. Nothing visible. Please trust me when I note that something that malfunctions is a sure sign
that it could do so again and for all M3Ws with the same components. Good to know what component is amiss but if can be solved better for 2-3 pounds...while keeping the errant part...

If a simple check valve or clamp prevents rearward flow in the supply line, that will hold pressure for a LONG time. It can be used diagnostically or as a permanent fix. Of course, one can
change part by expensive part to see which one had an apparently breakable check-valve included, but testing first is always wisest, especially when it is not invasive and costless.

I shall watch this thread with interest from the cheaper seats from now on.

gmg

Yes it does in this instance and also in many other fuel injected modern cars.
The arrangement in the M3W is that fuel flows from the pump in the tank to the engine then flows to the filter (which also contains the pressure regulating mechanism) and from there flows to the tank. Incidentally the description of the item #15, the short pipe between the filter and the tank is "Fuel Filter To Tank" which is a specific and correct description.

I can assure you gomog, your diagram is incorrect. The unfiltered fuel goes from the pump, to the injectors and then back the the filter/regulator, finally returning to the tank. It seems the wrong way round, filtering the fuel after the injectors but this is Morgan we are talking about 😁.

Gomog, I think you have somewhat misunderstood what I have been saying.

Firstly I fully agree with Bunny, Red Three and Planenut that the published fuel system diagram is wrong. The fuel flow is from the pump to the injectors and returns via the fuel filter.

When the fuel pump fails it can sometimes initially provide the required 58psi and so the engine can start but the pressure rapidly falls away leading to the engine spluttering and stopping.

So, back to the original post, if they have access to a Schrader valved fuel pressure gauge check the pressure is 58psi and holds whilst trying to start the engine and for a minute or so afterwards. Somthing like Fuel Pressure Gauge


Alternatively replace the fuel pump again.

I don't think Red Leader received a reply to his question regarding when the pump was replaced was it replaced with a new original Land Rover pump or a proper Walbro?. If it was a Land Rover or cheap "Walbro" knock off then we know these pumps fail some much quicker than others, also was the pump installed correctly? I would start with the pump and it's connections all as stated previously.

That's ok Chris. (mona lisa smile) The great thing about mechanics is reality invariably rules. One of us will proven wrong anon. I am willing to believe that the MMC diagrams from their two parts books,
along with their detailed parts description and my own understanding is incorrect M3W are different. https://www.ls1gto.com/threads/walbro-255-pressure-bleed-down.323614/.

My guess was that the multi-purpose pump-sender-strainer houses a check valve (which has failed as so many of them do). Does anyone of you have that assemblies maker and model? Easy to check then
(PUN!). Is this the one? https://morgan-kent.com/product/fuel-pump-m3w/ It's unavailability suggest that this is a common failing.

My WALBROs never came with a check valve. It is good to hear from you that to know that they do now. I will keep searching to find one.

gmg

That is the fuel pump, original fitment 93-98 Land Rover Discovery, p/n WFX101020, and yes prone to failure in both M3W and Discovery’s which is why it is recommended to replace the pump with a Walbro unit.

The Walbro GSS342 we use for the M3W does not have a check valve.

The pressure is maintained in the system by the constant flow from the pump to the restriction that is the pressure regulating valve in the fuel filter. If there is a one way valve in the pump assembly it is a particularly rubbish one but some pressure does stay in the system for quite a while after the pump has shut off and the initial drop from operating pressure. Can't say I feel like stripping the assembly down far enough to see if there is something hidden in the plastic...and even with the dedicated non-return valve I fitted between the output of the pump and the engine on my one, once the pump is off the pressure falls away fairly quickly, and yes, I do have a good fuel pressure gauge on my dashboard.

Then I can stop searching. Ty.

Do either of you have the maker/part# of the regulator?
Interesting. Some of those identical vehicles, with the same pumps, came with check valves and some did not. Can it be that some had redundancy built into their fueling systems pressure and some did not? In both cases it
suggests that there is another feature that could hold pressure. Normally, it is between a check valve and the regulator. Here is a generic EFI fuel pressure diagram..first I found on a 2 second internet search, It, like all others I find,
matches the MMC and their part task descriptions. (the rrows are not mine) I am going to search out what the poor 93-98 Disco people did when they had the same problem.


That isnot how EFI is ideally supposed to work, but the such vehicles will function. It takes over a day for my EFI system to lose much pressure. BTW, I too fit fuel pressure gauges to my Morgans, into the FSE
fuel pressure regulator's blanked off and unused side. I also wired my fuel pump differently, so, after long periods, I can run the pump and the pressure up before trying to start the car.
May I suggest you call FSE a super fuel pressure regulator manufacturer in the UK. If you get the right guy (not all are) he can cross reference the regulator you are using using and suggest a replacement. You will have a
much better and easily repairable component. That will might give you a sharper acceleration and allow you to determine whether you have the best pressure for the most fun. If not, merely set it to stock. In all cases, you
have a better quality and the manufacturer is at hand.

BTW, are you are aware of the symptoms of a faulty fuel pressure gauge?

Thanks for you help here. I am having fun.