Talk Morgan Forums Morgan Sports Cars Morgan Aero 8, 2012< Plus 8, SuperSports, Coupe & Aeromax Hot start .... vapour lock

The digitally controlled world is full of "wonder," and is one of the reasons I am so fond of my Trad.... Though admit that it too has a rudimentary digitally controlled anti theft device... Sigh..! Though at least there is a little led that extinguishes to let me know the "key" has unlocked the device, Jeez it even seems to send some beeps through the Mog`s speaker system when initially deactivated.....Sigh.

I remember a friend who was an assistant service manager at a Nissan dealership telling me in the late 90`s that activating the door handle to initially access the car caused an inordinate amount of electrical processes to begin, only one of which was to prime the fuel system....

Perhaps taking some degree of the wonder out of the process by checking the fuel pressure... Given after 20 mins one might expect that the system might be likely to loose much if any pressure...and if it did, I might then be thinking the fuel pressure release valve set point....? But then I have zero hands on knowledge of working on modern EFI systems, and am using no more than logic, flawed or otherwise...

At least your battery, starter motor and alternator are getting a good work out till you hopefully manage to resolve the issue...?
Fingers crossed.

I would be investigating further into the fuel supply line, it sounds to me as if a non return check valve has failed and is letting the fuel bleed back or evaporate before the high pressure system or even in the high pressure side - relay or valve failure is where I would be looking.

My Plus 8 will take an extra turnover if conditions are extremely hot such as we experienced recently and evaporation has taken over under the bonnet and this normally ties in with me needing 1 Ltr of water to drink..

Latest - I've fitted the aux cooldown fan with a capillary thermostat strapped to the fuel rail.

If I set it to 55C it stays off whilst driving the car .... and kicks in when the car has been shut down after about 3 minutes.

Slight problem, It stays on for about 40 mins whilst the engine cools and I think its drawing about 15 amps - so possible flat battery issues on really hot days.

I've adjusted to 70C and it still kicks in on shutdown .... waiting to see how long it stays in for at this setting.

Next up, Ive ordered a fuel pressure measurement kit (surprisingly cheap @ £25). There's a schrader valve test point on the fuel rail so I'll be looking for about 70psi engine running and paying particular attention to pressure decay on shutdown.

What I can't explain is that it starts on the nail when cold but cranks for ages when hot.

If it were a faulty check valve (apparently there's one as part of the in-tank pump unit) then why only a problem when hot ?.

Hols now for a week - I'll be back on the case on my return.

BTW, have you done a diagnostic scan? But nothing you have mentioned is too serious, IMHO. Nothing to fret about..though fretting about one's Morgan is a hobby.

I am not as sure as you are as to the cause. Yes, vapour lock is a common reason for hesitation in starting a hot EFI engine. But I have found it is more often a leaking injector. They both create a temporary situation where insufficient fuel and fuel pressure slows a start as the fuel pump brings the fuel rail back up. Also, a hot engine is harder to start than a cold one as the internals have expanded, tightened and the starter must work harder because of it. As Luddite suggests, modern engines are made to run ever hotter.

There is a cure for leaky injectors. Clean, refurbish or replace the leaking guilty injector (s) which implies you find which it is. Cleaning is often effective and can be accomplished in situ by professionals. They detach the fuel feed and replace it with a cleaning solution that flushes and unclogs. Low mileage car injectors are especially vulnerable. And storage gums them all up. The cost for professional cleaning in situ in the UK, according to search engines, is 150£. I clean mine yearly at the start of my mogging season, no point in doing at other times and notice a difference. I learned to do it at home as that is more convenient. One merely needs the right interface to the fuel rail and a can of injector cleaning fluid made for the purpose.

Of course, a true injector specialist can do the best job with the injectors out of the car and create a report on each injector flow and its spray pattern. If you are looking for perfection, buy 16 injectors from a break-up yard, send them to an expert to refurbished them and test Then chose from them a set of 8 with the closest matching flow rates and patterns. If you choose, you can then sell the rest for more money than the entire process cost.

BTW, a rad fan should run for no longer than 5 minutes after the hot engine is turned off More runs the battery down and definitely pre-age it. In many cases, I have told moggers, to power the fan from the ignition switch. The reason for running a few minutes after the engine is merely to protect other components (plastic!!) from a too hot engine bay. Did you have melting components?

Lorne

Hi Lorne,

Thanks for the reply. The car has had a fairly odd life so far. Bought new by a collector and registered in 2019, it had only covered 140 miles by 2024 (I dont think he ever drove it). It went to the next owner in 2024 and he drove it to Devon and France (once) before hurting his back dinghy sailing and then not driving it again for some time. Fast forward to a month ago (Early Aug (2026) and it arrived to me with 2040 miles on ..... it's like brand new, but spent plenty of time idle for fuel to congeal etc.

It put the EMS light on on the way home, after much faff I realised generic OBD scanners etc dont work - so it went to Ledgerwood for a proper scan. The EMS reported to a failed exhaust cam sensor, so I put 2 new ones on and it reset itself after 5 drive cycles. There were a few other codes showing - tank fill level and crankshaft sensor signal, all cleared and the EMS light has stayed off for 800 miles.

I always like to get my vehicles "just so" when I first get them, so there's been a very intensive flurry of activity - dealing with various niggles, upgrades and adjustments and at the same time getting up the 1st few rungs of the Morgan learning curve (This is my 1st Morgan). Fuel injectors are one of the things I sell for a living, I've got a flow test rig for producing matched sets and an ASNU cleaner. I've also been running on Vpower since I got the car with the theory it helps remove deposits etc.

I'm planning to work through the problem logically, next up will be fuel pressure tests - Injector cleans / replacements & check valves if I find leakage. There's definately something not quite right with the way it starts at the moment even if it does run perfectly once going.

Regards, Richard

Another nugget of information

The Morgan part no for the fuel pump in-tank assembly is MPS08751 (no 37 / Page 24 in parts book)

Marked on it are

BMW 7243975-17
Bosch 0580200331
R97517424220

Update 15 9 26

Another busy day tinkering with my Car (I love doing this though - really !)

Fuel pressure guage arrived. I see roughly 48 psi on "key on". Stable at 52psi when running, BUT fairly rapid decay to zero on shutdown - roughly 10 to 15 seconds.

My interpretation - Leaking injectors or Failed non return valve on the fuel pump unit

I'm hoping its the latter (ever the optimist !). I think I can test this by pinching off the main fuel feed pipe from the tank and seing if pressure holds (If yes, non return If no, injectors). Just got to figure out how to do this with the tools and access I have (no car lift sadly).