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Hi,
I had to disconnent the fuel rail when I was installing the LPG system and since I put everything back together again, the engine will take quite some cranking to fire up (on fuel).
Before it was instant. If I leave the key in ignition a couple of seconds it it much better, but still worse than before. Feels like the fuel rail is empty at startup.
I checked for fuel leaks at the rail but found none.
Did I miss something while re-assembling the rail ?
Is there a non-return-valve that can break ?
And do I need a special fuel pressure gauge to measure the fuel pressure at the schrader valve or can I take an air gauge...?!?
Any hints are appreciated,
Max.
EDIT: I just remembered that there seems to be quite a pressure build-up in the fuel tank, when I remove the filler cap there is a strong blow of air from the tank for several seconds...came up at a similar time, maybe it is related...?

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One thing that can cause difficulty starting on lpg conversions is if its leaking into the manifold either via leaky injectors or a leaky vapouriser filling throught the vacuum connection. It effectively puts too rich a mixture in the intake so it can't fire up until its pulled enough fresh air through to work again.

Pressure in the tank would suggest the evap system isn't working as well as it should, possibly stale fuel not helping there if its been converted a long time and the fuel been in there for an extended perioid. Though I've known to have petrol sat in the tank over a year without any major problems, you can sometimes notice if the fuel is getting old that it smells different when its running on petrol. A likely cause of problems is if the tank has been allowed to run low enough that the pump would run dry, causing it to overheat (on petrol the engine would cut out, on LPG it doesn't do that as its still getting fuel to the engine to keep it running). Best to keep at least 1/4 of a tank of petrol to avoid that issue happening as that gives you enough leeway to keep the pump cool and some spare just in case you run out of gas or have an issue that means you have to use petrol.

Don't know on the pressure gauge, never tried an air one personally. You probabbly don't want a tyre inflator type one though if thats what your thinking, a standard pressure check tool might be ok.

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GEMS has a pressure regulator on the fuel rail, at the back on the LH side (as seen from the drivers seat). It also has a vacuum hose that comes off the regulator and goes into a stub on the lower inlet manifold. It's well hidden down behind the throttle body and below the connector to the ignition coils. Fuel pressure should be there even after the car has been left standing but the pump will run for a couple of seconds when you switch on the ignition and then all the time the engine is turning. You can use any pressure gauge, tyre gauge will work fine (although it's probably a good idea to run it for a bit to blow the fuel and vapour out before using it to blow up your tyres).

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A rudimental check for gas leaking is to squeeze a rubber gas pipe to injectors when the engine has been turned off overnight, if it feels like there's pressure there probably won't be a leak, no pressure means the gas has leaked somewhere and in your case probably into the inlet manifold as Bri said.

If there's no gas leak and if the petrol system retains pressure then check LPG calibration because calibrating the LPG system too rich can cause negative fuel trims which makes the engine run leaner on petrol, including (in some cases) during cranking.

But since leaving a key in the ignition makes a difference it does point more toward lack of petrol pressure. What happens if you leave the ignition on a few seconds, turn it off, repeat a few times before cranking?

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From memory you have to leave the ignition off for more than 20 seconds so the ECU resets before the pump will run again.

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Marshall8hp wrote:

From memory you have to leave the ignition off for more than 20 seconds so the ECU resets before the pump will run again.

Ahh, my suggestion of turning the ignition on/off a few times before cranking won't help then (unless fuel pressure drops very slowly).

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The ECU cycles the pump when the ignition is turned on for two to five seconds, depending on the ECU build (one way to tell the difference, and no I don't have a chart of the time vs ECU :) ). It will then come on when cranking and running. Cycling the key will only turn it on first time, until the ECU re-sets, which, as noted is 20 seconds.

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Hi,
I ordered a fuel pressure gauge only to find out that it didn´t fit so I used the tyre pressure gauge and that worked fine.
Pressure was zero when I started, car had only been standing a couple of hours, there didn´t even come any fuel out of the shrader valve when I poked it with a screwdriver.
As soon as ignition was on, pressure rose to around 35 psi, when engine was running about 30 psi (or other way around). Opening the throttle increased the pressure. So I guess fuel pump is fine.
But as soon as I turned off the ignition the pressure fell to zero again within seconds. Did this repeatedly with always the same result.
So I guess some sort of non-return valve doesn´t work, apparently it is situated by the fuel pump....
Since getting to the pump seems somewhat complicated, are there any non-return valves that one could put into the system ?
Or any other ideas ?
BTW, what is that 90 degree-metal-thing on the right end of the rail ? Also looks like some kind of pressure reducer...?
Thanks, Max.

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The one on the RHS rear of the rail is a small accumulator, it is there to reduce injector knock. The unit on the LHS rear of the rail is the fuel pressure regulator.

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Checked my GEMS a few minutes ago. Fuel rail lost all pressure when I connected my pressure gauge, but turned the ignition on and it immediately jumped up to 40psi, started the engine and it dropped to 30psi but as soon as the engine started, stabilised at 35psi. Switched the engine off and it sat at 35psi for a good 15 minutes without dropping at all. So yours is definitely leaking somewhere.

As David says, the round thing on the input hose is to smooth out any surges in the fuel line. The pressure regulator is on the opposite side hiding behind the throttle linkage and excess pressure is fed back to the tank on the other hose. I'm assuming that if there is a one way valve, it will be inside the pump but if that had failed it would be a bit of a coincidence that it has decided to do it at the very same moment you have had the fuel rail off. You could try clamping the return hose and seeing if the pressure still drops, that would suggest the pressure regulator or a leak at the top of one of the injectors. The O rings can get pinched when you put the rail back on, but the leak should be obvious, you'll have fuel running out of the rail and flooding onto the top of the inlet manifold.

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Thanks for taking the time to check that on your vehicle !

I didn´t remove the fuel rail from the inlet manifold or the injectors at the time, just the fuel line connections at the accumulator and beside that, going to the pressure regulator. There are also no leaks anywhere, no smell of petrol either.
Could try to loosen and retighten those connections in case air does come in, but I guess at 35 psi there would be fuel oozing out if they weren´t tighty sealed.
The only thing that makes sense to me would be that the non-return valve in the pump died in a freak coincidence, I could order a separate one (they are cheap) and try to install it to see if that makes it better (where would be a good place to put it, it has connections for flexible fule hoses, and come in various diameters...?).