Hot weather hard start = fuel press regulator?

[SCM]

I just replaced my fuel lines again including adding barbed fittings to the hard line-to-rubber hose connections and installing MansiSpeed fuel injectors.

I ran a fuel pressure test to check for leaks and, while I have no external leaks, I do get a few PSI of pressure drop over 5-10 minutes.

On really hot days, when I'm parked in the sun, the van will struggle to start if it's sat for hours. It will crank and sputter and stall unless I feather the gas pedal for a few seconds until it idles correctly. This is very occasional but it has gone on for years.

It seems to me that the FPR may be allowing my fuel pressure to bleed down under those conditions resulting in the hard start.

Does that seem likely?

Why would it only happen on hot days and not all the time?
_________________
'91 Westfalia GL Automatic (GTA "Turbo" Rebuild w/Peloquin) and 2.3L GoWesty Engine

[4Gears4Tires]

A hot start issue is a a shut off and turn on in less than 30 minutes. If it's sat for hours the engine shouldn't be hot anymore.

Does it start if you turn the key, let the fuel pump prime fully and then start? Does it make a difference if you turn the key on and off repeatedly priming the fuel system?

I don't think the fuel system should lose 10psi in a matter of minutes. Maybe check your injectors too.
_________________
'87 Syncro
Ferric Oxyhydroxide Superleggera Edition

[valvecovergasket]

[4Gears4Tires]

[valvecovergasket]

[SCM]

[MarkWard]

Starts fine cold, so that rules out the fuel pressure drop as the problem. Cold engines need more fuel than hot engines. I would describe a hot start no start if I had pulled in for a fill up after 200 highway miles. How does it do in those situations?
_________________
☮️

[SCM]

[MarkWard]

Stretch diagnosis. Do you carry a spare coolant temp sensor for the ECU? It may have a bad spot where it works ok at ambient or full temp, but maybe not so much middle temps. An ohm meter could confirm, but is a bit of a pain to setup.

If you have a spare sensor, it's easy enough to plug it in hanging loose and see if the engine starts. Also, I'd be interested in how the engine runs with the oxygen sensor disconnected. You won't hurt anything running it disconnected and it will give you insight to how the engine is actually starting and running.
_________________
☮️

[Vanagon Nut]

Do the Mansi injectors allow more fuel out per pulse than the OE injectors?

I'd be curious if, under certain conditions, there's a mismatch between a value at a sensor, e.g. coolant temp sensor, and the amount of fuel injectors allow out when turning engine with starter. ("cranking" engine).

Get a helper to sniff the exhaust as engine is cranked and after it starts? The rich smell should be obvious and one might see smoke as well.

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Howesight]

I think the symptoms, plus the drop in residual fuel pressure, sound like an interal leak. There are only three sources - - the fuel pump check valve, the injectors, and the Fuel Pressure Regulator.

When leaving the van parked after it has first been brought to operating temperature in high ambient temps, if you have an internal leak, then the residual fuel pressure is not sufficient to do its job - - preventing vapour lock. The injectors are located in a fairly hot area and when the residual fuel pressure drops below spec, fuel vapourizes in the injectors and bubbles up to the highest point of the fuel hose(s). On a hot re-start, it takes a lot of cranking to operate the injectors long enough to remove the vapour bubbles. Running the fuel pump will not clear these vapour bubbles and will only push fuel through the FPR and to the return hose and back to the tank.

Sadly, the under-hood temps in my turbocharged Audi cars are high enough to really boil the fuel and also ruin the FPR (similar design to the Vanagon, different fitment) prematurely, so I am familiar with the vapour lock problem and the most common solution on these cars - - replacing the FPR. The fuel pump check valve was never the cause, but you must test for the source of the internal leak as it might be the cause of the loss of residual pressure in your Vanagon.

It is possible that an injector is leaking. In that case, not only will you get some vapour lock in the fuel lines, but the affected cylinder will also be "flooded" with the raw gasoline. If all cylinders were flooded, the usual way to clear the excess fuel is to crank the engine with the accelerator floored. Because of the lengths of fuel lines in the Vanagon, the vapour lock takes more time to clear for some cylinders than for others.
_________________
'86 Syncro Westy SVX

[SCM]

Thanks everyone, you gave me some good ideas for diagnosing the problem the next time it happens. If it happens at all.

To be clear, I just installed the new injectors on Friday and haven't used the van since last fall. If injectors were the issue there's a good chance I won't experience the problem again.
_________________
'91 Westfalia GL Automatic (GTA "Turbo" Rebuild w/Peloquin) and 2.3L GoWesty Engine