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PostPosted: Sun Oct 29, 2017 9:39 pm 
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Got a 2005 Vauxhall factory fit dual fuel necam koltec car, that now only runs on LPG. Starting is a struggle when cold, but will get going on LPG then once warmed up will run fine. But switching to petrol will cause it to splutter and cut out. Only code is P0170 (fuel trim). Have checked fuel pump, plenty of pressure coming through.

TBH we don't run it much on petrol, so I suspect stale petrol is gumming something up. With it running fine on LPG I'm inclined to dismiss engine and consider something fuel line related on petrol side.

Any ideas? Injectors? Where does the LPG cross over with the Petrol side on this engine? Does it share the 4 injectors and fuel line with petrol? Reckon it'll need taking to an LPG specialist or is it likely to be something a regular local garage may be capable of?


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PostPosted: Sun Oct 29, 2017 11:06 pm 
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Arfa wrote:
Got a 2005 Vauxhall factory fit dual fuel necam koltec car, that now only runs on LPG. Starting is a struggle when cold, but will get going on LPG then once warmed up will run fine. But switching to petrol will cause it to splutter and cut out. Only code is P0170 (fuel trim). Have checked fuel pump, plenty of pressure coming through.

TBH we don't run it much on petrol, so I suspect stale petrol is gumming something up. With it running fine on LPG I'm inclined to dismiss engine and consider something fuel line related on petrol side.

Any ideas? Injectors? Where does the LPG cross over with the Petrol side on this engine? Does it share the 4 injectors and fuel line with petrol? Reckon it'll need taking to an LPG specialist or is it likely to be something a regular local garage may be capable of?


Most regular garages would struggle with an aftermarket system - The necam systems wiring is even more strange so won't help any. Taking it to the right specialist might get it fixed, others would recommend swapping the whole front end out to solve it.

Given the age its probably the GSI type with injectors rather than the older EGI with a distributor, you have a seperate injector for gas mounted somewhere on the inlet manifold (one for each cylinder). Injectors shouldn't gum up normally on this kind of system as they are used to start the engine in the first place, so are getting a fresh shot of petrol through them.

I'd suspect its more likely than anything that you might have a bad connection for the power to the petrol injectors - at least on my EGI (though this was on a Ford/Tickford conversion rather than the Millbrook Vauxhall ones) the petrol positive feed was controlled by the lpg ecu (cut to allow running on gas) - Either its not receving the feed in the first place due to a break somewhere in the feed, or the lpg ecu isn't passing it back when switched back on. Some investigation with a multimeter should tell you that.

When you checked for petrol pressure where did you check?

Only other thought I'd check (as its easy to do to rule out) is if you are getting gas leaking from the vacuum point on the reducer - this would allow the manifold to be flooded with gas, the lpg side might have adapted to it (there would be less leaking with gas running anyway as the pressure would be lower, once switched to petrol the pressure held in the system has only one place to go as the injectors are closed). There is a small hose leading from the reducer (probably a vg392 unit) to the inlet manifold, either pull it off the reducer or other end and check if theres any pressure there - if there is you need to replace the diaphragms in the reducer to stop the leak.


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PostPosted: Sun Oct 29, 2017 11:08 pm 
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Also there used to be a load more info on here from PJPJ about these systems, unfortunately his hosting appears to have removed it now, I've got a copy of it if its any help to you. Drop me a pm on here and I will find a way to get it to you.


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PostPosted: Mon Oct 30, 2017 11:05 am 
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>When you checked for petrol pressure where did you check?

My uncle did this, wasn't present, but I believe we confirmed pressure at a fuel hose in the engine bay.

As for checking stuff with multimeter, be good to do this before taking to a garage. I'll see what diagrams and info Brian can provide to help me out here.


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PostPosted: Mon Oct 30, 2017 10:36 pm 
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I've got your pm. Will sort it tomorrow once I'm back home.

I'd check that vacuum hose first though. The difficulty starting May be down to that as well as lack of petrol running.


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PostPosted: Sat Nov 04, 2017 5:37 pm 
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How do you get it to start on gas when the engine is cold? Which prompts a daft question - Are you sure you're not thinking it's running on gas when it's running on petrol and vice/versa?

Would think you'd check fuel pressure on the rail(?) and that was OK?

There may be a black box beside the LPG ECU (could be behind passenger side headlight). The box effectively performs some of the switching functions between gas/petrol and they're known to go wrong. But the petrol ECUs on Vauxhalls of around that year are known to go wrong too. Could be the beginning of a lengthy diagnostics process.

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PostPosted: Sat Nov 04, 2017 9:57 pm 
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LPGC wrote:
How do you get it to start on gas when the engine is cold? Which prompts a daft question - Are you sure you're not thinking it's running on gas when it's running on petrol and vice/versa?

Would think you'd check fuel pressure on the rail(?) and that was OK?

There may be a black box beside the LPG ECU (could be behind passenger side headlight). The box effectively performs some of the switching functions between gas/petrol and they're known to go wrong. But the petrol ECUs on Vauxhalls of around that year are known to go wrong too. Could be the beginning of a lengthy diagnostics process.


With foot to floor and an awful lot of cranking over. Has been starting eventually, though today was first time it ran flat and need a jump start to provide enough cranking.

Once running, on what I assume is LPG, it runs fine. But when I flip the dash switch that normally switches it to petrol, the revs fade away and it dies within about 3-4 seconds.

TBH I've not had chance to investigate it much myself, but plan to tomorrow. Though my expertise is limited, probably just be checking for any obvious dodgy connections, so will likely end up taking it to a local LPG specialist.


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PostPosted: Sat Nov 04, 2017 10:09 pm 
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Arfa wrote:
LPGC wrote:
How do you get it to start on gas when the engine is cold? Which prompts a daft question - Are you sure you're not thinking it's running on gas when it's running on petrol and vice/versa?

Would think you'd check fuel pressure on the rail(?) and that was OK?

There may be a black box beside the LPG ECU (could be behind passenger side headlight). The box effectively performs some of the switching functions between gas/petrol and they're known to go wrong. But the petrol ECUs on Vauxhalls of around that year are known to go wrong too. Could be the beginning of a lengthy diagnostics process.


With foot to floor and an awful lot of cranking over. Has been starting eventually, though today was first time it ran flat and need a jump start to provide enough cranking.

Once running, on what I assume is LPG, it runs fine. But when I flip the dash switch that normally switches it to petrol, the revs fade away and it dies within about 3-4 seconds.

TBH I've not had chance to investigate it much myself, but plan to tomorrow. Though my expertise is limited, probably just be checking for any obvious dodgy connections, so will likely end up taking it to a local LPG specialist.


The thing is these will not start on gas - they start on petrol and switch to gas (the EGI i had would take at most 10 seconds to switch if it was really cold, usually a couple of seconds). either its managing to run on petrol (possibly not on all cylinders?) when starting and then switching, or something else is going on there.

Note that a manifold flooded with gas will stop it starting - The first LPG car I drove would do that (not my car, and didn't know any better at the time) but it would take a lot of cranking over before it would start if switched to gas when switched off, even overnight it would still struggle to start in the morning. Same would apply with switching back to petrol from gas, the pressure inside the vapouriser will bleed off down the vacuum line to flood the intake until the pressure runs out. In either case removing the hose from the vapouriser will tell you if thats whats going on, equally a leaking gas injector could cause same to happen.

Also bear in mind a lot of installers will be of the mindset of rip out the front end and replace with something they are more used to if the lpg side is suspected of being the cause, as in most cases they won't have any info on the Necam systems. Given if its the injector type that new injectors aren't available off the shelf (alternative ones exist, but to replace them is around the cost of a new front end anyway) this is understandable, but something to be aware of before you go down that route.


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PostPosted: Sun Nov 05, 2017 11:59 am 
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The best way to confirm what fuel it's running on is pulling off an injector connector... You think it's running on gas, so disconnecting a petrol injector shouldn't affect running.

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PostPosted: Sun Nov 05, 2017 12:26 pm 
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Not got very far today, bit colder out, struggling to get the thing started. Had it running briefly (on what I believe is LPG), pulled vacuum hose off vapouriser (yep VG392). Spluttered briefly, but kept going. Definitely a draw on hose from manifold. With hose off, flipping switch to petrol still caused engine to die and still no better at starting. Now have flat battery on a charger slowing progress.

FWIW, when trying to start on first turn over it feels as though it almost catches, then dies away and then cranks over for ages. Indicative of it getting flooded?


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PostPosted: Sun Nov 05, 2017 6:19 pm 
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Arfa wrote:
Not got very far today, bit colder out, struggling to get the thing started. Had it running briefly (on what I believe is LPG), pulled vacuum hose off vapouriser (yep VG392). Spluttered briefly, but kept going. Definitely a draw on hose from manifold. With hose off, flipping switch to petrol still caused engine to die and still no better at starting. Now have flat battery on a charger slowing progress.

FWIW, when trying to start on first turn over it feels as though it almost catches, then dies away and then cranks over for ages. Indicative of it getting flooded?


Possibly. Your not interested in the vacuum from the manifold side, it's if you have gas leaking from the vaporiser that's what might cause you issues. Note that a stuck open injector on the gas would cause same to happen though.

The most common thing to have happen with the petrol side is for the pump to fail due to running dry. Wouldn't normally be seen on a petrol car as it would obviously just cut out and stop the pump, on gas it wouldn't do so, think you've ruled that out with testing pressure though.

Next time you get it running once it's been stopped check the pressure on the output hose. After a couple of hours check it again. If there's no pressure left there it's leaking somewhere.

If it is getting flooded you should smell it. Either take the intake hose off and see if you can smell anything near the throttle area, or check the exhaust.


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PostPosted: Sun Nov 05, 2017 7:50 pm 
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Brian_H wrote:
Possibly. Your not interested in the vacuum from the manifold side, it's if you have gas leaking from the vaporiser that's what might cause you issues. Note that a stuck open injector on the gas would cause same to happen though.


Did check the other side on vaporiser, nothing obvious coming out, but couldn't check it when I switch to petrol - died to quickly.

Brian_H wrote:
The most common thing to have happen with the petrol side is for the pump to fail due to running dry. Wouldn't normally be seen on a petrol car as it would obviously just cut out and stop the pump, on gas it wouldn't do so, think you've ruled that out with testing pressure though.


My uncle said he checked this side, believe he checked pressure at the bleed value on engine (on fuel line I think). Could this be confused with gas pressure? He's got years of normal mech experience, but no LPG.


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PostPosted: Sun Nov 05, 2017 10:43 pm 
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I would expect he would be able to tell difference as gas would come out as vapour, petrol would be liquid. Easiest thing would be to pop off the fuel feed to the rail, and put something to catch what comes out, get someone else to cycle the ignition a couple of times and check you get petrol out. It should give you a short spurt of petrol each time.

Best done outside away from any ignition sources though.

It might be an idea if the petrol is really stale to empty the tank and put some fresh fuel in. You can use the tank pump to empty the tank if you remove the fuel pump Relay and connect the two pins for the switched side together. Best to use a fused connection for that, I use an online fuse holder with spade connectors on the wires To do that. Then just break into the feed side of the fuel system somewhere convenient and arrange something to catch it. I've used large bore hose to slip over the end of the connector at the fuel rail for that.

If you suspect fuel is bad changing the filter if it has one might be an idea at the same time.

You might be able to feed the fuel rail with fresh fuel in some way to prove this if you'd prefer,


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PostPosted: Mon Nov 06, 2017 9:31 am 
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Above I mentioned the black box, when running on LPG this should prevent any fuel trim problems being logged since one of it's functions is switching the lambda voltage that the petrol ECU sees between actual lambda voltage (when running on petrol) and emulated lambda voltage (emulated to continually steer petrol fuel trims to zero) when the engine is running on LPG; It also performs other functions such as disconnecting petrol injectors. So, if this box is working correctly the P0170 must have been logged when running on petrol (because fuel trims should be steered to zero when running on gas anyway)... Either the P0170 was logged when the engine was running on petrol, which could point to a MAF problem (since the LPG system doesn't use the MAF as input) or the black box isn't working properly. If the black box isn't working properly in that respect, perhaps some of it's other functions aren't working properly either. The P0170 could potentially cause starting problems on petrol just by itself, a broken MAf could cause starting problems just by itself. If the engine will continue to run on LPG the lambda probe itself must be working properly, as in not contributing to the P0170.

Definitely worth checking for petrol pressure again, can do that by just depressing the schraeder valve on the rail itself (bit like a tyre valve) while someone cranks the engine, fuel should squirt out. Seen lots of converted Vauxhalls with failing petrol pumps, sometimes they can be made to work again at least for a short while just by banging on the underneath of the petrol tank.

Have you tried squirting a large dose of easy start into the manifold before trying to start it?

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PostPosted: Tue Nov 07, 2017 8:30 am 
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OK, rewinding, revisiting prior assumption, checking fuel incoming again. Just to confirm is this the petrol bleed/decompression valve on the fuel rail?

https://www.dropbox.com/s/hub2ddtdakbto64/2017-11-07%2008.16.39.jpg?dl=0

The black cap on the lower bit sticking out towards right of engine?
Just removed this, and tried cranking engine whilst switched to petrol - nothing came out? :-/

Have ordered a petrol syphon too, will try draining petrol and replace with fresh, in case it's bad/stale etc.


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PostPosted: Tue Nov 07, 2017 8:49 am 
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If it's the right bit there should be a schrader valve inside that cap. Like the ones on the tyres. You'd need to press that inwards to release anything. You will probably need someone else to cycle engine while you do it.

Pictures a bit close for me to tell, as long as its on the end of the fuel rail that should be it.

Can you hear the pump running when switching ignition on?


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PostPosted: Tue Nov 07, 2017 9:37 am 
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Aldo you will probably struggle with the siphon to get it into the tank - Its far easier to pull of the feed to the rail and pump it from there, you just need to identify the fuel pump relay and remove it, replace the load pins with a piece of fused wire it will then keep running.

You just need enough suitable hose to get from wherever you get the fuel coming out of into a suitable container.


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PostPosted: Tue Nov 07, 2017 9:56 am 
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Edited pic, arrows points to bit I checked fuel at. Unscrewed to reveal an open pipe, no valve as such. Yep, someone else cranked engine for a bit whilst I tried to catch anything - nothing came out. Hard to say if I could hear fuel pump, lot of other noise, cranking and whirring elsewhere. Pump is situated in tank in rear of car, I'll have a closer listen tonight.

Was hoping the siphon would give me an easy way to initially inspect fuel - could try it in my motorbike to confirm if good or not. Kit also comes with tonne of flex hose to help me with your plan of trying to drain it with fuel pump, from fuel rail. As for fuel pump relay, I'm guessing that'll be in one of the boxes on right of engine bay (there's a couple full of relays and fuses) - I'll try and pinpoint it from Haynes manual.


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PostPosted: Tue Nov 07, 2017 1:20 pm 
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Arfa wrote:
OK, rewinding, revisiting prior assumption, checking fuel incoming again. Just to confirm is this the petrol bleed/decompression valve on the fuel rail?

https://www.dropbox.com/s/hub2ddtdakbto64/2017-11-07%2008.16.39.jpg?dl=0

The black cap on the lower bit sticking out towards right of engine?
Just removed this, and tried cranking engine whilst switched to petrol - nothing came out? :-/

Have ordered a petrol syphon too, will try draining petrol and replace with fresh, in case it's bad/stale etc.


I don't think stale petrol will be to blame, the 1/4 tank of petrol was well over a year old till I ran out of gas the other day, it still ran fine. When I had a "factory" fit lpg combo I think the fuel in the was well over a year old as it came with a full tank when I bought it and I never used it other than when it was started from cold when it ran for possibly a minute before auto switching to lpg.
I don't think there is anyway to force a start on gas.


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PostPosted: Tue Nov 07, 2017 3:31 pm 
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I can't see it being stale petrol tbh, and not being able to force start on gas with cold reducer temp was what promoted me to suggest that it might be running on petrol when it's thought it's running on LPG.

Arla - been pointed out a few times that you need to depress the schrader valve, just like you would to let air out of a tyre by pressing in the middle of a tyre valve (not enough just to remove the valve cap lol!), there's like a pin sticking out in the middle, press it in using something like a screwdriver (perhaps wider and less sharp than a screwdriver because you don't want to miss the pin, bend it or stick into the other workings of the schrader valve) while someone cranks the engine. If there's no valve and it's just an open pipe, fuel should be flowing out at high rate if the petrol pump is running, there's no chance it could run on petrol if it's just an open pipe... but it won't be an open pipe there'll be a schrader valve in there. If you had one you could even use a tyre/schrader valve removal tool to unscrew the schrader valve and connect a bit of pipe (other end of pipe into a petrol can) to see if the petrol pump is at least pumping but pressing the valve pin is probably a better test because if there's enough petrol pressure it should squirt out when you press the pin (you wouldn't see the same effect of pressure from an open pipe in a container of petrol but an open pipe in a container of petrol container can give a better idea of the pump's flow rate.. we might do a flow test if your engine ran lean on petrol at 5000rpm flat out but we're more concerned with pressure here).

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