Engine misfire and stall on LPG

[Ilya]

I’ve recently put in new spark plugs (ER14YS Brisk Silver) and coils (Used Diamond Fk0140) in my Subaru Legacy Mk4 EZ30R engine that has also LPG conversion, following a constant check engine light.

Now when I cold start and then switch to LPG the car stalls as I move off, however if I start of on petrol and drive for a bit and then switch to LPG it’s fine. Is there a way of fixing that I can drive on LPG straight off?

Also, I’ve noticed that when I cold start on petrol and drive for a bit, I get a brief flashing check engine light on low revs such as while standing at traffic lights but it then disappears as I move on. It eventually seems to stop flashing all together or when I switch to LPG once the engine warms up. Any advice on how I can fix that?

Or if anyone could recommend a garage that knows about Subarus in west London? And should it be a garage that also works with LPG?

Thanks :/

[Judd]

Your car is behaving exactly as it should.

Car LPG systems are not meant to run from cold on LPG, the evaporator or whatever its called has water from the cooling system pumped through it, the system is only meant to switch on when a pre determined tempertaure has been reached, usually these are set when fitted so you cannot override the temp sensor ie switch to lpg before the temp is reached, and in any case switchover is normally fully automatic.

Haven't a clue why the check engine light is coming on.

Do you have a flashlube system fitted and do you keep it topped up, you should because LPG running on our engines without flashlube will cause valve seat recession without fail, if there is no flashlube system fitted then any decent LPG installer will fit one for you, not an expensive job at all, preferably an electronic system due to intake design.

Gas4cars at Woburn Sands fitted the system on our Forester, whether they would be prepared to work on yours i don't know, would depend on what make of LPG system is fitted, installers tend to have their own preferences in makes and all the software needed to program the system.

You might find an LPG pro here https://www.lpgforum.co.uk/

 

[Mr B]

Flashing engine light is misfire warning, either used coil pack/packs faulty and improves with some heat or similar issue with new plugs .

LPG requires far better spark than petrol thus any weakness shows up worse with LPG .

Would need know LPG system installed to know whether designed run from cold start or not, would assume is as most that can't auto run from petrol until receive suitable temp value point to allow LPG switching .

[Ilya]

Honestly not sure about if I have the flashlube system, I believe it does. Thanks for the forum, helpful as well.

Would you say I should always go a visit a garage that specialises in LPG when there is an engine issue?

[Ilya]

Not sure of the system I run but the spark plugs are not the original NGK that are recommended for the engine but the ones that are recommended for LPG as they are a level colder than the original ones. the coils have been replaced as well.

could that cause the engine light issue when I’m on petrol?

[Mr B]

failing spark is why light flashes.

Either don't like your plugs or they or coil pack faulty. Never assume new/replacement parts are not faulty .
Only plugs we use are Denso or NGK .

[Judd]

3 hours ago, Ilya said:

Honestly not sure about if I have the flashlube system, I believe it does. Thanks for the forum, helpful as well.

Would you say I should always go a visit a garage that specialises in LPG when there is an engine issue?

From the sounds of it the LPG system isn't at fault as by the time its warmed up and its running on LPG you say the light has gone out by then, or did i misread?

I don't think you need an LPG specialist, yet, you need someone competent with the right equipment to find out which cyl or issue is causing the engine light to flicker, someone familiar with Subarus would be best, but not essential i don't think at this stage.

Flashlube system will have a container, usually holds about a pint, of an oil which is usually clear or slightly amber in colour, genuine flaslube is amber but there are other makes miuch lighter in colour just as good, the container could supply via a small pipe to the inlet manifold by vaccuum, not ideal on Subarus, or it could feed into a small unit that pumps the fluid via one or several small bore pipes again into the inlet manifold itself, if you don't have a lubing system it would be wise to get one fitted, you can get kits and DIY this if you feel up to it if you have trouble finding an LPG pro.

When i fitted new plugs to the previous H6, also running LPG, they were OE spec NGK's but either Platinum or from memory more likely iridium so able to take the much hotter burn of LPG without degrading, never had any issues with them, nor with the NGK Iridiums the LPG shop fitted when they converted the present Forester.

When your H6 is ticking over is the engine smooth, it should be absolutely still and able to balance a full cup of coffee on top without spillage, my son and i went to buy an H6 once at a dealer, compared to my older H6 the one we looked at was running lumpy especially in tickover, the flashlube bottle was bone dry, suspect VSR was already an issue there, we walked rapidly away.

[Ilya]

Yep no flushlube, will look into getting one thanks.

as for the engine, it runs smooth on LPG especially once warmed up. In fact even smoother than on petrol. But at the start it does have rough idling when cold starting.

[Ilya]

Great thanks, I’ll have them all individually checked in this case then.

[Ilya]

 

Mr B. I’m going to change the spark plugs to the original NGK, but which should I use for a Legacy 2004 MK4 H6 EZ30 engine, with an LPG conversion on Dual fuel with petrol?

The original are NGK ILFR6B but as I understand for the LPG it’s better to have NGK LPG7 with the lower heat level? Would the LPG7 cause the same issue I have now when running on petrol?

And a question as for the torque, the NGK recommend 25-30Nm while I believe the manual said 21Nm when I change spark plugs last. Any advice?

[Mr B]

I'd go original NGK iridium and close the gap by about 0.15mm
As for torque 25Nm be sensible, most of torque relates to crushing the sealing washer so I take NGK remarks over subaru .