Misfire after switch over.

[57jam89]

Hi all
My car was converted over 4 years ago and I've done 80k since but has a very bad misfire after switch over (happens about 3 times a week). It runs fine up to it switches over to gas when misfires badly (only from a cold start), if i switch it back to petrol then back to gas it's fine. Also then it switches over fine but i floor it within 5 minutes it misfires.
glued up injections, could this be the problem? Thanks

[Gilbertd]

Injectors, spark plugs, coil pack? Do you have OBD and is it showing a P030x code?

[57jam89]

Hi, once when it misfired bad i didn't switch it back to petrol and kept it running as long as possible to try to get a pending fault code but couldn't.

[57jam89]

Also fitted new spark plugs and a few coils which I've been slowly over the last few mths been moving around all 6 cylinders but hasn't made any difference to the misfire

[Brian_H]

if its done 80k on gas and never had injector cleaning done, it may be worth giving it a try. Without knowing which ecu you have fitted, it may be beneficial to get hold of a lead and the software for it, as some have a dedicated cleaning program you can access from the software. The KME Nevo definitely does have it if thats whats fitted. That might also give you a better idea of whats going on at the same time as you can access a few other bits of info in the software (and switch cylinders between fuels, which might help further if you suspect a dodgy injector).

Can you see fuel trims with the diagnostics you have? Any difference between gas and petrol used?

Alternatively get hold of Simon and ask him what he recommends if its the Skyline in your signature.

[57jam89]

Yes it's the skyline which simon installed but can't get hold of him.
Yes it's KME system so i will look into what you suggest.

Thanks

[LPGC]

I see I haven't replied to Simon's last Whatsapp message from 17th May in which he told me he's started a new job working 12hour days including weekends with no phones allowed at work. In our most recent message before 17th May on 6th May I advised the problem could be glooped injector(s) but there were other possibles and we were going to have a chat on the phone which never happened. If we can't have a chat I'm happier messaging on forum so I can use a proper keyboard rather than using my phone's keyboard for Whatsapp or Txt messages, though it might still be better to have a chat.

Other possibles would include ignition parts as suggested above by others and worn/broken injector(s) as opposed to just glooped, or a reducer that's pushing incorrect pressure...
If a vehicle runs poorly on first switchover but will run OK on gas if switched while it is running it can be because the reducer is allowing a little liquid gas to be vaporised all the time (even when vapour pressure exceeds the reducer's pressure setting) due to it's inlet jet being slightly stuck open, this can lead to high pressure in the vapour lines which can be too high for injectors to open against during initial switchover. Replacing worn / broken injectors would be an inlet plenum off job because the injectors on Simon's Skyline are individual (not on rails) and are fitted below the inlet plenum with very short pipe runs to spuds.

I'm not a fan of cleaning fluids but having individual injectors can ensure that cleaning fluid gets to selected injectors because the fluid can be put into the feed pipe(s) to selected injector(s). Should first check reducer pressure, including initial (no engine load) pressure, and find out which injector(s) / cylinder(s) have the problem.

KME also has an injector checking facility (diagnostics / injectors test), it's results are not definitive but are another tool in the box for checking injectors especially if repeated tests all point to the same injector(s). Should be noted that before running the injectors test any offset dialled in to calibration (such as a 0.1ms addition on bank 2 etc) should be cleared to zero or the injectors test results will reflect more/less flow from injectors that have the offset dialled in.

[57jam89]

Hi simon,
Thanks for replying. I posted my problem on here because i do remember you saying in the past you preferred using your laptop and not your phone.

Thanks for information but I'm a bit lost on what to try 1st.

Cheers

[LPGC]

No probs Simon.

I forget if you have an interface cable and software for the KME system and/or an OBD scan tool compatible with your car? To diagnose and fix the problem either would be a great advantage, both would be a massive advantage. If it comes to changing injectors, which would then mean a check of calibration would be in order, you might really need both.

if you have the software and interface cable for the gas system, first check pressures... When you first start the engine on a morning what is the gas pressure reading? If you click on the 'open gas solenoids' button while the engine is running on petrol does gas pressure hold steady or does it slowly increase? Then when the engine is running on gas does it run better if you switch any single engine cylinder back to petrol?

Of course we could arrange a date for you to bring it to me for sorting.

Cheers, Simon

[57jam89]

Hi Simon.
Connected software and there's no option to open solenoids or switch gas injectors off 1 by 1.
So the only thing i can do is read gas pressure- engine running cold start = map .31 and psys .61 which turns to 1.30 after switching itself to gas, map stays around .31.

It also does always smell of gas after switching to gas on a cold start (inside car) and warn idle in neutral feels like a misfire but in drive fine. No fault codes in cars ecu.

Thanks

[Brian_H]

Hi Simon

The attached screenshot should point you in the right direction if its the Nevo system you have (KME do other systems and can't see which one you have but suspect its the Nevo)

Click cylinder numbers to switch betwen petrol and gas, the other bit circled on the righthand side does the valves

Download of Nevo software here > https://kme.eu/kme/en/download/#oprogramowanie if yours is Nevo but doesn't look like that

If your using the mobile app, then I don't think its possible to switch cylinders using that. At least I've never found a way to do it.

If you can smell gas its obviously leaking somewhere, if you can track that down that will probabbly answer where your problem is. If you can't smell it prior to trying to switch over its got to be somewhere after the vapouriser that you have a problem. KME will normally try to prime the system first so you may see pressure going up a few seconds before switchover. It may be worth trying to get the system to swtich over so the system is pressurised and then shut off the engine, and then see if you can track any leak down (easier without noise of the engine etc). I think the valve open override might help there as well.

[LPGC]

Hi Simon.

When the software is connected and you're looking at an appropriate screen in software there will be 7 round circles upper right side of the screen just below the picture of the interior switch, clicking the left one allows you to manually switch the solenoids open/closed whenever you like, clicking any of the others allows you to switch individual cylinders back to petrol when it is running on gas.

Edit - My post crossed with Bri's, Bri has shown another way to achieve the same thing when in the diagnostics screen. The circles I was talking about are just under where it says 'Off-Line' below the pic of the switch and can be accessed from most screens.

Pressure jumping from 0.61 bar to 1.30 bar when the solenoids are open may point to a leak on the low pressure rubber lines between the reducer and injectors, or less likely to an injector that's stuck open.

[57jam89]

Update- can't connect software to ecu.

But since the weather has warned up it hasn't misfired on switch over.

[Brian_H]

What lead are you using? Looks like you have the right type of lead (as you've given pressure readings above that you must have got via the software?) Could be a driver issue with the usb type leads, pin come out of the connector, or the lead itself has failed. I'd start by checking device manager on the laptop to see if any problems are being shown there first. It may also be worth checking the com port assigned to the cable, I'd expect a low number but its possible its set it to something odd, though I would expect the kme software to find it anyway even on a high com port number (other older software would only look at com1-4). You can change the assigned port from device manager if its gone and set it to something that may be a problem. Can also sometimes help to delete the device entry from device manager, unplug the cable, plug it back in and let it detect it again.

[57jam89]

Update- i got the software connected up today and open the solenoids and gas pressure doesn't drop and can't smell gas anywhere around pipes etc.
Waited and watched gas switch over but unless it misfires switching over there was no point in turn any injections on/off.
It doesn't misfire if it's idling on switch over.

[LPGC]

I should have a copy of your current calibration/settings but to make sure can you save your calibration and email me the file? I'll have another look at it and see if there's anyway I can adjust to prevent problems during cold switching, if I make any changes I can email you the revised file back for you to upload to your ECU.

[57jam89]

I should have a copy of your current calibration/settings but to make sure can you save your calibration and email me the file? I'll have another look at it and see if there's anyway I can adjust to prevent problems during cold switching, if I make any changes I can email you the revised file back for you to upload to your ECU.

Hi Simon, thanks. I've increased the switch over temp to 35c and it only misfires occasional now so it's ok for the moment.
What temp did you set the elgrand to switch over?

I may in the near future change cars and was thinking of a jaguar xkr which would be a 2006 -09 with the 4.2. v8 supercharged engine not the later 5.0 direct injection engine. Any problems with doing this car?
Thanks

[LPGC]

Thanks for the update Simon.

I usually set customer Elgrands to switch at 25 or 30C. But if reducer temp falls below 25C while calculated engine load is above 20% or gas temp falls below 0c while calculated engine load is above 20% they will momentarily switch back to petrol until temp(s) increase or engine load decreases. Calculated engine load is more of an abstract figure than a meaningful figure and in practice the engine might have to be making more than about 70bhp before calculated engine load exceeds 20%... And would normally expect the system to switch back to petrol momentarily only in cold conditions and only if the driver boots it while the engine is still in the early stages of warm-up, it will never momentarily switch back when the engine is warm.

The 4.2 supercharged engine in the Jag is almost the same as the engine in the 4.2 supercharged Rangerover, same soft valves and needs an electronic lube system, needs a petrol return fitting, is fussy regards fuelling, etc. But I've done loads and get great results. One difference between the Rangerover and Jag versions is there isn't as much clearance between the charge coolers and cam covers on the Jag, so it's a bit more work to get manifold spuds in the correct position and route injector pipes than it is on the Rangerover. And the engine bay is smaller (for fitting the reducer etc).

[57jam89]

Hi Simon, update - I'm now lucky it doesn't misfire!
I now have to switch it back to petrol and wait until coolant temp gets to around 60c before switching back to gas.
Sometimes it may switch over ok but if i lift my foot off the throttle within a five minutes it misfires again.

I think i may have to buy a new set of lnjectors and try to get up to you to setup again.

Thanks

Update- today has has been the worst ever. Cold start, misfire the moment it switched over, switched back too petrol and left for a minute or so when switched back to gas and again misfires. I had to do the above 5 times before it run ok on gas, by this time i had been on a motorway for 5 minutes on cruise control and engine temperature was 82c.

[LPGC]

Could be the injectors or could be a fault with the reducer that sees pressure rise too high before the gas injectors kick in. Cold injectors are less likely to be able to open and meter gas properly at high pressures than warm ones. Or could be something else.

May have to play it by ear because I have 2 vehicles booked in to convert every week until at least mid-January, I will get time before then but I won't know well in advance when I'll get time... E.g. I'll likely get time on some of the Fridays but won't know until mid-week if I'll get a job finished before the Friday.