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PostPosted: Wed May 06, 2015 4:31 pm 
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Hi guys,

I'm just looking for some advice on my car. It's a 2003 bmw e46 3 series with 131k on the clock. I've recently had it converted to gas - Romano system.

Over the last 2k since the conversion it mostly runs fine apart from an intermittent misfire on acceleration. This has slowly become more frequent and never generates a fault code. I've also never noticed an issue on petrol.

I talked to the fitter about it at my 1000 mile service and he took for a test, he said he though that it was most likely a problem with the ignition system as the gas setup seemed fine.

Do you think the fitter is fobbing me off? Or does this sound like an ignition issue?

I fitted new spark plugs before the conversion.

How would I go about diagnosing the fault?

Any advice appreciated.


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PostPosted: Wed May 06, 2015 6:22 pm 
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Ignition could well be the problem. What type of plugs did you fit?

Romano can have issues with freezing under load on higher power engines and that could also be your issue. If that is the issue Romano normally resolve it by adding a small amount of petrol under load to reduce the amount of work the reducer is having to do and also help with ignition

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PostPosted: Wed May 06, 2015 8:39 pm 
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Thanks for getting back to me.

I fitted NGK Iridium IX plugs, do you think they would work ok with LPG?

The fitter said it might be the coils because gas is harder to ignite, but he was just guessing... I understand that in theory, but is there any way of confirming this before I fork out for 6 new coils?

The system is supposedly rated up to 350bhp, my car is 237bhp, do you think it could still suffer freezing? It tends to be light acceleration that it happens, if I thrash it then it tends to be fine.

It's bad enough now that I can usually generate the fault by trying to accelerate from a slow speed in a high gear.


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PostPosted: Thu May 07, 2015 12:44 pm 
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In the first case, I would pull the plugs and look for signs of tracking on the outside of the ceramic.
Also have a careful look at any smallbore pipe from gas injectors to manifold - sharp bends or pinches may have slowly collapsed a bit more in use.

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PostPosted: Thu May 07, 2015 1:49 pm 
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Are you getting misfire just coming off idle, or from light load? M54b30 engine? Auto or manual?


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PostPosted: Thu May 07, 2015 2:59 pm 
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Since it's only done 2K since the conversion and the problem has always been present, just gradually got worse - Why not take it back to the fitter again, this time asking him to identify which cylinder(s) are misfiring and find the reason for it... coll packs and plugs can be ruled out by swapping them about etc..

Wouldn't be his responsibility to pay for plugs / coil packs if these are found to be at fault but given the circumstances he has some responsibility to help you get this sorted.

Simon

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PostPosted: Thu May 07, 2015 4:29 pm 
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@rossko - thanks I will add those to the list of things to check :)

@e301988325i - it's M54B30 engine with a manual gearbox - misfires can happen coming off idle or say if I am cruising at a set speed and then try to accelerate - however it is usually at lower speeds (20, 30, 40) - I don't think it has ever happened on the motorway

@LPGC - I may well take it back, but it's a bit of a trek to the fitter so I would like to hear other people's opinions as well so that I feel well informed before I go there - I am fairly mechanical and I usually do my own servicing/repairs so I would like to try and get my head around the problem myself if I can! :)

There are no misfire codes stored in the OBDII memory which is why I was wondering if there is another way of checking the coils, it's difficult to swap around coils when you don't know which cylinder is having the issue...


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PostPosted: Thu May 07, 2015 6:28 pm 
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Sounds more like a throttle response problem.

It could be as simple as adjusting the enrichment or it could be down to the position of the injector nozzles. The other thing with AEB is the RPM freezing causing misfire issues but the installer should have spotted that

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PostPosted: Thu May 07, 2015 7:10 pm 
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I'll put a boat load of money that the separate idle air supply has been ignited in consideration to nozzle placement.


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PostPosted: Thu May 07, 2015 7:18 pm 
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I'm trying to find the diagram of the idle air supply circuit.

It's a long read but see this thread:

viewtopic.php?f=28&t=10450


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PostPosted: Thu May 07, 2015 7:25 pm 
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The green inlet flow is accurate and reflects how close the port opens to the inlet valves.

Image


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PostPosted: Thu May 07, 2015 7:39 pm 
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@classicswede - He did play with the enrichment last time I was there, but it didn't make any difference to the misfires
- It does sort of feel like a throttle response problem, I know that you can get similar symptoms on this engine from failing cam sensors, but I thought they usually throw a fault code


@e301988325i - Interesting, that is a possibility, although I hope its not the case, I did try and make sure I went with an installer with experience of these engines... my symptoms don't seem to match yours mind, It doesn't seem to lack power, in fact there is no noticeable difference in power between petrol and gas, just an occasional, noticeable miss... I don't have an engine light on either and it idles exactly the same on petrol and gas...

So in your diagram, where should the injectors be placed?


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PostPosted: Thu May 07, 2015 9:01 pm 
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The diagram is a schematic, it wouldn't be great for pointing out where injector nozzles should be placed.

@ Dai, great minds think alike, only I didn't say as much lol..

@ e3301998325i, you meant to say ignored? That crossed my mind too, and I'm sure it did Dai's too.

@ Welshman, even without OBD codes the installer might switch cylinders back to petrol to see if the fault occurs on only certain cylinders. I doubt coil packs are the issue, as has been said before it could maybe just be a plug problem, if the installer is a long way away you might try re-fitting the standard plugs or cheaper NGK equivalents, I don't usually see problems with standard plugs on this engine. One of the most common complaints from customers with converted vehicles is 'Problems started after I had it serviced including the spark plug change'...

Simon

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PostPosted: Thu May 07, 2015 9:52 pm 
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Sorry, my question was unclear, I understand that the diagram is a schematic... what I want to know is with that schematic in mind where should the injectors be placed?

I plan to whip the cover off at the weekend and have a look so it would be good to know what a position for the injector is on this engine.

I'm confused, the misfires don't happen on petrol as far as I am aware... I thought the LPG ECU worked in tandem with the original ECU to the point that the original ECU thinks it is still running the engine, so you don't need to be running on petrol to get OBD info?

I don't have the original plugs anymore, are NGK Iridiums no good for LPG then? Why do you doubt the coils could be the issue?


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PostPosted: Thu May 07, 2015 11:18 pm 
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Injectors should be placed where the gas outlet position will facilitate gas mixing with the airflow and getting into the cylinder under all conditions. The diagram doesn't show such a position but such a position is possible low down near the port end of the manifold.

You might post a link to a pic of the injectors on your install?

The original ECU does think it is still running the engine under all conditions. Problem is that unless the LPG system is installed and set up in such a way that it accurately copies the fueling that the engine would receive on petrol (only replacing petrol with LPG), problems with fueling are introduced, problems with fueling are problems in their own right but on top of that the petrol ECU will probably pick up that there is a fault and this could lead to further issues. Someone might design an alternative fuel system which has the petrol ECU believing it is running on petrol when actually it is trying to run on milk - never going to work but the petrol ECU would nevertheless still not know it wasn't running on petrol! For the LPG system to work properly it must have appropriate components, installed in appropriate locations and appropriate calibration.

These days most manufacturers fit platinum plugs as they last much longer running on petrol than the cheaper old skool nickel plugs. Supposedly platinum plugs don't offer the same longevity advantage on LPG and might have a similar life to nickel plugs - given that info would you want to pay several times more for platinum over nickel? Iridium offers the same long life advantage of platinum plugs but for LPG applications too, so now iridium is looking like the plug to go for for LPG applications even if they cost as much or more than platinum - Except it isn't always possible to buy iridium replacements for platinum or nickel plugs that match the original plugs spec. Plugs have many characteristics - electrode design, electrical spec, thermal spec, etc. My car's plugs are a real pain to change, so if I thought iridium plugs or LPG specific plugs would be a great advantage I would have fitted them... but I fitted nickel plugs and would probably also have rather fitted the manufacturer recommend platinum plugs rather than iridium! I like to check my plugs occasionally anyway, even though they are much more difficult to access than those on your BMW. As said, never had a problem with original fitment plugs on a BMW.

I doubt coil packs will be an issue because - although I know some installers reckon 'weak' / 'weakening' coil packs can cause problems, in my experience if a coil pack is causing a problem then it is most likely going to cause a problem on both LPG and petrol, any difference in performance between the 2 fuels probably not so much due to the coil pack itself but more likely due to the connection between the coil pack and the plug (the long bit maybe with a spring that sits on the plug not making a good connection - usually able to confirm with a visual check). The spark might jump between an old corroded spring and the plug so the plug might still spark on petrol, but maybe not on LPG. Only rare cases.

Individual coil pack / plug failings should be easily identifiable by your installer, would say plugs more likely an issue than coil packs, LPG setup just as likely and maybe more likely. Would really think it your installer's responsibility to put his finger on the issue and put his money where his mouth is - How about 'Hello installer - if I change all the plugs and coil packs on your advice and if it fixes the issue I'll pay for them, it it doesn't fix the issue how about you paying for them?'.

Simon

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Last edited by LPGC on Fri May 08, 2015 11:23 am, edited 1 time in total.

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PostPosted: Fri May 08, 2015 5:30 am 
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This is not actual mine photo , but that's how I got mine done similar , same engine(m54b30), with no problems.
Image


Get error codes , then you can see what cylinder misfires and go from there.

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PostPosted: Fri May 08, 2015 11:28 am 
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Thanks, that's really helpful.

I plan to check over the plugs and coils for any obvious problems at the weekend, I will also check over the position of the injectors in the manifold and post a picture.

I will also talk to the installer about looking at the car further, I need to talk to him anyway as my filler neck seems to be a little bit too narrow. The cap can be a bit stiff to remove, and some filling guns don't want to come back out either.


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PostPosted: Fri May 08, 2015 11:39 am 
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Similar to how I fit spuds on this engine. They look to be the long threaded type spuds - long thread spuds are probably good for getting gas into idle airflow but might reduce flow ability of the manifold runner a bit (thereby decreasing peak power a little), I've had no problem with short threaded spuds fitted in this location.

Let us know how your spuds are fitted Welshman?

Regarding filler housings - there are some cheaper copies of the 70mm filler housings available, I've tried them and not been impressed, problems include those you've mentioned, especially if the housing isn't fitted onto a completely flat panel (and there aren't many completely flat panels on vehicles) and caps falling to bits. Some suppliers only sell the cheap copies, better suppliers ask 'Do you want the original type or the cheaper copy type? We sell the cheaper type only to look competitive against other suppliers prices in the eyes of those that don't know better'. To which a good installer should reply 'I've tried the cheaper type, only ever send me the original type please, not worth saving a couple of quid and thereby causing a problem for the customer or myself'...

Simon.

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PostPosted: Sun May 10, 2015 6:27 pm 
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Well I had a good look this afternoon.

I couldn't get a decent picture of the spuds as there was too much stuff in the way, however I could see them well enough to confirm that they are positioned in the same way that the ones in hardcorepit80's photo are positioned.

There's some slight yellowing on the ceramic of a couple of plugs, but not bad enough that I could conclusively describe it as tracking. On a couple of the coils the upper rubber section has deteriorated a lot and has large cracks in it, the boots however look ok.

I have some cheap software that gives live data but annoyingly not misfire information and there is still no fault code. Maybe it's time I invested in some better software...

Interesting what you say about fillers, presumably that's the problem with mine, it's mounted in the bumper so it's definitely not in a flat panel!


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PostPosted: Mon May 11, 2015 6:27 pm 
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welsh_man187 wrote:
@e301988325i - it's M54B30 engine with a manual gearbox - misfires can happen coming off idle or say if I am cruising at a set speed and then try to accelerate - however it is usually at lower speeds (20, 30, 40) - I don't think it has ever happened on the motorway


This low load transition is fundamental as the ICV supplies air for up to 15% of engine load not just at idle, therefore there's still a significant pocket of 'stationary' gas waiting to be gulped down upon initial throttle increase. As can be seen in this picture this hole continues directly to the valve therefore it's not viable to get the LPG nozzles directly into the low load airstream.

Image

LPGC wrote:
The diagram is a schematic, it wouldn't be great for pointing out where injector nozzles should be placed.

@ e3301998325i, you meant to say ignored? That crossed my mind too, and I'm sure it did Dai's too.

Simon


Simon, yes ignored, autocorrect typo. Also agree reference stock BMW plugs, it's not a bad place to start renewing them all as certain types don't bother changing 5 & 6 as they're a PITA to get to.

@hardcorepit80 – your lpg nozzles are placed much closer to the head than mine were.


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