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

I have a friend with an M3W that is not holding fuel pressure. He replaced the fuel pump and also the fuel filter. He now reports the fuel system will hold pressure for about 40 seconds and then returns to zero as measured on the Schrader valve. Clearly, there is a leak in the system somewhere.

My M3W had similar symptoms before I found a crack in my plastic fuel pump assembly and once I replaced the pump all was well again. Does anyone know any problem areas besides the pump plastic where these systems lose pressure? Those crazy plastic clamps at the fuel line connection points come to mind but I have seen them hold pressure fine when in poor shape also. I actually replaced my fuel system with a Morgan Customs unit so I am no help with weak points on the stock fuel system.

I have been told there is no fuel smell or puddling of fuel for obvious clues to where the system is leaking. My friend's car will now not start because it cannot hold the pressure necessary for the fuel injectors to function.

Any ideas here?

Could be a leaking injector. Have them check for excess fuel in the intake manifold. If there is no external evidence of fuel anywhere, then it pretty much has to be an issue within the pump or one of the injectors.

That is great advice. I believe his car has over 20k miles and a tired or bad injector is a serious possibility here.

It could be anotehr defective fuel pump.

Alternatively, when the fuel pump was changed was it for another MMC or the upgraded Walpro? In either case if the internal plastic pipes are not secured by a suitable fuel line "jubilee type" clip then it can come off and the pump just circulates fuel in the tank.

Updates: My friend found a leaky injector. He is looking into having them cleaned or overhauled now. I will post up the results as well if his issue is resolved. Thanks again!

They're not too expensive, so it's probably easier just to replace it rather than having it refurbished?

From Alternative Parts List:

o Injector Nozzle. The part # is 0280156198, Bosch, typeB
o Alt.Injector Nozzle Bosch 0280155788

Updates - my friend had the injectors serviced and the technician said "I doubt these are your problem." Injectors were reinstalled and still no start. However, the car is making a new sound: "a clicking sort of gurgle from the motor end when raising the pressure and again when the key is turned off." My hunch is wherever the gurgling sound is coming from is the leak or compromise in the fuel system but I thought I would post up here for any ideas.

I think if it were a leak you would have smelt petrol by now.

Recheck that the fuel filter is the right way round as that includes the pressure control valve.

If that's OK I would suspect the new fuel pump has an internal leak as there have been instances where a pump pressurises the system OK but after a few seconds the pressure drops away. A(nother) new pump or Walbro upgrade should sort the problem.

www.mtwc.co.uk/wp-content/uploads/2020/09/5-Speeder-fuel-pump-replacement-April-2020-update.pdf

It is probably the pump, especially if he went with a cheap no name one.

But still worthwhile to verify presence of fuel in the cylinder (pull a spark plug or remove air cleaner) and check for spark. If neither is present, then suspect the crank position sensor.

Also, you haven't given information on how this no start situation first occurred. Did it fail while running? Just refuse to start one day?

If I muse a bit, I would guess this is a generic problem, not one specific to the vehicle. Intank pumps (does the M3W have one too?) All almost vehicles use them days. They are dirt cheap for manufacturers but are often forced to do different tasks. Intank pumps, ideally, should have two filters, but sometimes don't. One outside of the tank which is rarely changed and another (the important one) which is attached directly to the pump inside the tank and is never changed.


Wise and messy. Ideally, there is one on intank pump one, or should be, as well. Walbro demand it. The pump filter comes with the purchase. Inlinbe filters and check valves come with an arrow showing the direction they should be installed...with the fuel flow TO the engine.

Pressure control valve? You mean the regulator? I think you are very close. (Not to worry, I couldn't care less about nomenclature..try dealing with many nations every day!) I think the key here may be a check-valve. It fits all of the symptoms and input from the friend and his technician. Some fuel pumps have internal check valves and some do not. With those that do, their check valve (a simple device the prevents fluid from flowing backwards) often fails as so often happens when we ask a device to do multiple tasks. (fuel gauge sender//float/ pump.. ), Without a functioning check valve, fuel, after the engine and the pump turned off will leak backwards until the system it is unpressurized. Add to that the fact that modern electrical pumps are now wired [b]not to function[/b] until the engine turns and not simply the ignition key, so he has no way of bringing the fuel pressure up before starting the car. Not good for the starter or the car. (I re-wired my car to avoid that).

It is a simple matter to buy an inline check valve off ebay, Halfords or Amazon.co.uk. Merely make sure it fits your friend's fuel line size. As his fuel system is unpressurized any way, installation will not be too messy, especially if he has two needle nose vice-grips and merely squeezes the fuel hoses before and after the spot he chooses to install the valve.

BTW, this thread caught my eye as my own Walbro, was mentioned. They do NOT come with internal check valves, or didn't the last time I bought one. I have been using this part for 22 years on my big bad Plus 8. However, that Walbro now comes in a version that is both intank and external, I used it for 16 years as an internal pump and now for 8 years as an external pump....after trying out 3-4 much more expensive external pumps. High price does not always mean the object of your purchase is best for the task chosen. That old saw lost its factual basis 20-30 years ago.

Actually. I have found this Walbro is more sensitive (wow!) to burn out IN the tank than when installed out of OUT of it...the opposite of what we are told. Though internal pumps run cooler..being submerged in fuel, when fuel runs low this model pump will burn out in moments. One can more easily avoid that with an easily accessible external installation and well- placed check valves. For the moment, your friend should NOT run up long steep hills (seriously) unless he wishes to chance rolling back down, stalled. I plumbed my check valve just before the external pump (upstream from the pump flow).

But that will be a trick with an intank pump. And if he has an intank pump, he should stick with it present. An image could help us determine aplacement. How about a compromise?Just a short length after his fuel hose exits the tank. As you can see from the images of the device, it will only add an extra 6mm hose length after both sides hoses are fully pushed on and clamped. In the most perfect world, we should have fuel filters before and after a high pressure pump...ditto for check valves with EFIs. I am not going to tell you I do that, we all merely should. At this point a check valve is a 2-3 quid way to diagnose his issue, if not cure it.

I usually swap in one part at a time (Luddite taught me that most vital rule) starting with cheapest when in doubt. A repair modus is more important than the fix itself. And this one, even if only adds redundancy, is wise. There is no law that forces us to retain unreliable systems at all costs. The sign of unreliability is when any component or a system fails. If it happens once, it is a certainty it will happen again, likely when you least want it to.

Have I mixed everyone up?

gmg