Hard starting since service?

[pyro225]

So Range Rover 4.2 sc - all been running fine for the last couple of years with flashlube etc…

Anyway it was overdue a service so I did the oil and filter and the two gas filters (have two regulator) and noticed one of the vacuum lines going to the MAP sensor was split. Changed that reset the adaptations, went for a long drive on petrol to set the baseline and switched over to gas the next time I used it… so far so good.

He lies the problem if gas has been used on a previous journey the car barely starts from cold or warm 3x cranking usually - I never had this issue until after servicing. If I run on petrol it seems ok for the next start…
I put the vac line from the regs into a glass of water to see if there are bubbles when off there aren’t so imagine they are ok.

Also I noticed the gas switch is lit up but as soon as you crank it goes off and doesn’t come back on until either the car starts or you lock and unlock then try again?

It’s a king system, and luckily I have another car running the same system I took a backup of the config and swapped the control units and still the same problems with starting and the switch which I can’t help but think are linked but maybe my memory is failing and it never lit up? I’ve also tried another map sensor from the other car to no avail…

I should say if you run it on gas it runs ok but you risk it being a nasty start by doing so…

Any ideas?

[LPGC]

There are quite a few things that could cause this, I'll list some.

A reducer diaphragm leak could see gas enter the engine when it is off but you've tested for this.
Still, a leaky injector would also see gas leak into the engine when it was turned off.

Repairing the vacuum hose to the map sensor would have the effect of changing fuelling when running on LPG - The King ECU monitors gas pressure and manifold vacuum to calculate effective gas pressure (gas pressre minus manifold pressure, some systems call this delta pressure). If the vacuum leak is only to the pressure sensor (not to the pressre reducer) the ECU will incorrectly read lower than actual delta pressure, which will have the affect of richening the mixture when running on LPG, which could have the effect of steering fuel trims more negative, which could cause starting problems.

The car will be fitted (or should be fitted) with either/both a physical petrol fuel return / petrol fuel pressure emulator. If a physical fuel return allows petrol pressure to fall when you've been running on gas it will take some cranking to start on petrol (will just crank until there is petrol pressure again, then it will start).

if you run for a while on petrol and switch to gas just for (say) 30 seconds before turning the engine off do you have the same problems? The answer might help rule out fuel trim issues, fuel return issues, leaky gas injector issues... Wouldn't expect fuel trims to change much just running on gas for 30 seconds but there'd be the same quantity of gas that could leak into the engine and any fuel return solenoid is either not opened (when running on petrol) or has been opened during running on gas (if opened some will stay latched open even when the power is off until fuel pressure falls away, the wrong type of solenoid to use for a fuel return).

[pyro225]

Thanks -

I can answer a few questions - so it was setup when new and obviously the vacuum line wasn’t split so replacing that and resetting the adaptations hopefully would rule that out?

Regarding fuel return yes it has a physical one but this weekend I’ve ruled that out. I put a new fuel filter in (without the holes for the return) and it is back to stock now with the return line off.

I’ve then permanently left two cylinders running in petrol to make the system not throw up a fault for fuel pressure. I’ve also changed it to switch over to petrol above 3k too just to rule out any other things.

Went for a drive all seemed well..then a hard start again about 4 hours later …

Where would you go next?

My next two ideas were you 30 second idea and also the reverse go for a ride and just after swap back to petrol?

Cheers

[pyro225]

It started ok not great but ok after 30 seconds on petrol at the end - in the absence of time to try and tackle your idea potentially about an injector I have disabled a whole bank now and I’ve also set it to return to petrol at 1100rpm and also above 3000rpm.

If this still yields nothing I will swap the banks…

Any thoughts?

[pyro225]

Right update… so with one bank off and return to petrol on idle and above 3k it still was a hard start next time.

I then swapped the banks - still hard start.

I then cleared the adaptations again - still a hard start.


Then cleared again and ran for 20miles on petrol to set them again, then switched into gas for 30 seconds before switching off - still hard start!


Then drove on petrol and left for a few hours started lovely so definitely gas related but not sure what to do now?

[hitman2]

I had something similar, turned out to be the solenoid valve at the reducer had worn through the seal and was passing gas to manifold, maybe pull the plunger and inspect the seat?

[pyro225]

Can have a look was it ok on petrol though?

[LPGC]

If there is a leak in a reducer diaphragm or if you have a leaky LPG injector, when you've been running on LPG and turn the engine off gas continues to enter the engine inlet manifold through the leak. Then when you try to start the engine it gets gas and petrol instead of air and petrol so it won't start until you've cranked it for long enought to pump all the gas from the inlet manifold out of the exhaust and the inlet manifold contains air.. at which point the engine will get air and petrol and start.

[pyro225]

Ok… any idea how to check if it’s the reducer or injectors likely to leak? How does it get into the manifold if it’s the reducer? Through the vacuum line?

[pyro225]

I do have two reducers T’d together so could I just disconnect power to the solenoid for one?

[pyro225]

I have found I have a bad lpg injector. currently its switched off and running petrol on that cylinder but have ordered a replacement hopefully somehow that's braking things

[pyro225]

Never summarised this - the new injector loved the issue… for nearly a year but it’s back… this time there is not one obviously bad one and I’ve cleaned them all with carb cleaner to no avail. Diaphragms seem fine as no bubbles when taking the vacuum line into water so tempted to get 4 injectors and swap them bank to bank

[LPGC]

The hard starting issues are back?

I'll have mentioned a few other things it could be above, things such as calibration, fuel trims, fuel return, etc.

If it seems to be hard starting because gas replaces air in the inlet when it's switched off and you can't find a leaky injector or reducer (diaphragm), have you checked pressure in the feed pipes to injectors when the engine has been switched off for a while? Reducers can develop a problem where they continually allow a small amount of gas to flow which can over-pressurise the lines when no gas is being used like when the engine is turned off, then if the pressure gets too high injectors or diaphragms might leak but you wouldn't find a leak before the pressure gets so high.