LPG misfire [Archive] - Australian Land Rover Owners

Utemad

13th December 2009, 09:15 PM

Hi all,

Is there anything with an LPG setup that could make it feel like a massive misfire other than ignition problems?

My MY95 Disco1 is having issues with LPG that feels like a massive misfire. When cold it runs fine but as it warms up it starts to misfire and then gets worse until it is undriveable on LPG. Although it feels like a misfire it doesn't backfire at all like I would expect.
If you switch over to petrol it runs perfectly.

I recently (<300kms) changed the rotor button over for a new Bosch one as I accidentally broke the old one. The Bosch one looks exactly the same as the old one. The dizzy cap is aftermarket too but I swapped it for a new genuine one I had today (no difference). Old cap and rotor had been in there and trouble free since I bought the car 70000kms ago so due for a change anyway.
I'm going to get hold of a genuine rotor button just in case it is that as people seem to not like the aftermarket caps and buttons for whatever reason. So long as it isn't a crazy price.

The leads are Gasmaster and I haven't checked their resistance yet but will do.

Thanks

Lotz-A-Landies

13th December 2009, 09:30 PM

The only thing that I will say is that quite often, LPG fitters don't move the PCV hose when installing the LPG. Ideally the PCV port should be moved from the plenum chamber inlet, to somewhere between the LPG mixer ring and the air-cleaner. You should also make sure the flame trap is clean and working.

When the engine is new you don't get any ignition flame bypassing the rings, as the engine gets older you can get flame into the crank-case and this flame runs along the PCV tube back to the inlet. If there is LPG in the plenum you get ignition of the LPG in the plenum often blowing apart the air cleaner box.

On my 4.6 you can see the blanked original PCV port (in-line with the orange oil filler cap), to it's right the LPG mixer ring on the plenum and (following the green line to) the moved PCV port to the RHS of the LPG mixer.

https://www.aulro.com/afvb/images/imported/2010/04/1705.jpg

Utemad

13th December 2009, 09:57 PM

The LPG fitter did move that hose and plumbed it into the engine side of the AFM housing by tapping a new hole.
However I just recently blocked that off and have vented my engine to an oil catch can.
I wanted to see how much is coming out and so far it is bugger all.

LandyAndy

13th December 2009, 10:24 PM

Give your plugs a check/clean.
Also,under cover of dark with the mojo running use a spray bottle mister and spray the leads lightly,it will show any leakage of spark from the leads or dizzy cap.
Goodluck
Andrew

mike 90 RR

13th December 2009, 11:32 PM

I'm going to get hold of a genuine rotor button just in case it is ....... So long as it isn't a crazy price.

Yep ... It will be a crazy price .....

Try to borrow one if you can

whitakerb

14th December 2009, 12:20 AM

Sounds to me that your HT leads are crossed somewhere. It is a known phenomenon that L.P.G. will reveal any slight electrical issues, and will get worse as it warms up..

CAUTION: Failure to route the leads correctly, as shown, can cause cross firing between cylinders five and seven, as can be seen by the firing order 18436572. When cylinder 5 is at T.D.C. on the power stroke, cylinder 7 is at 90 degree before T.D.C. on the compression stroke ready for ignition. If the plug leads for these two cylinders are routed parallel in adjacent clips, HT current to number 5 plug will also be induced in number 7 causing combustion of the mixture in number 7 cylinder to occur 90 degrees B.T.D.C. and again at T.D.C. It is for this reason that the correct clipping of the plug leads is observe to avoid the possibility of severe damage to the engine. (Quote from Land Rover Discovery Workshop Manual)

I don't have a scanner, so I cant upload the lead arrangement as shown in the book, but perhaps someone on here has the resources to post up a pic?

Hope that helps,

Ben

Utemad

14th December 2009, 06:54 AM

My leads aren't run the best. But they never have been and never caused a problem before. I'll sort them out though when I check their resistance.

I'll play with it again tonight.

Utemad

14th December 2009, 05:35 PM

What do people use to separate their leads?
My lead separator thingys are all broken (be careful when you remove your tappet covers!) and didn't fit these bigger leads anyway.

Would covering them in split tube where they touch be effective isolation?
No doubt the heat would destroy the tubing eventually.

LandyAndy

14th December 2009, 09:31 PM

The spray bottle mist will show you where you where your leads are breaking down.If nothing shows at idle,set the revs at 2000rpm and try again.
WORKS A TREAT;););)
Andrew

Utemad

14th December 2009, 09:41 PM

I didn't do the mist thing but earlier today I removed all the leads one by one and tested them. All were between 1 and 2 ohms. So I covered them all in split tube (coil lead was already done).
I re routed the leads too. Much neater now and no. 5 is nowhere near no. 7 anymore.
Took it for a for a 6km drive and it shows no symptoms any longer :)

I really thought it wouldn't be ignition though. It never once backfired. Before I replaced my spark plugs about 5000kms ago it backfired multiple times and it wasn't nearly as bad as this was.

Hopefully it is cured.

Thanks for the tips. I should have routed them properly originally I suppose.

Utemad

19th December 2009, 08:57 PM

Ok although it ran fine on my test drive and was fine yesterday, it wouldn't run properly on LPG again today. Idles fine on LPG and runs fine on petrol but never backfires.
I'm going to assume that the LPG filter is clogged (or something else in the line) and therefore can't supply enough LPG.

I've closed the tank valve and I'm going to take it in for an LPG service now that I work nearby to where I had it installed. Won't be til January sometime so til then it is running on petrol for me :)

Utemad

6th January 2010, 11:34 PM

Well well well. I'm going to say that it is definitely a spark issue now.

Driving home just now on petrol and stopped at a servo for some more. Went to start it and it wouldn't. I eventually got it started and it ran like crap with a misfire. Sometimes it idles fine and other times it will barely idle. Taking off from a standstill you need to slip the clutch to keep it running but once the revs are up it is ok.
That is the opposite to the LPG though. LPG idles fine but won't drive without a massive misfire feel.

I'll check the leads out tomorrow night with the water in a spray bottle thing.

This has all happened since I changed my rotor button for a Bosch one and maybe it is a coincidence but surely it should at least run. As said earlier it looks like it is the same one that came out.

Not happy Jan.

mike 90 RR

7th January 2010, 12:05 AM

This has all happened since I changed my rotor button for a Bosch one and maybe it is a coincidence but surely it should at least run. As said earlier it looks like it is the same one that came out.

Not happy Jan.

Lucus / Lucus / Lucus

:D

disco97

7th January 2010, 01:03 PM

one thing i learnt never run a Bosch button or in 2 to 3 months you will have problems. lucas is best and at $30ish ts worth it in the long run my last one was 10 years old lol

bee utey

8th January 2010, 02:43 PM

A Bosch box will be marked "Bosch packed" meaning its actually a chinese cheapie. Use genuine manufacturer's content only!

Utemad

9th January 2010, 05:33 PM

Well I ordered a Lucus rotor button from Karcraft yesterday. Should fix things I think. Although I do wish I had just bought one in the beginning.

justinc

9th January 2010, 06:53 PM

Justin,

The possibilty that your distributor module could be breaking down is high, after stopping at the servo heat soak can play a part in module/ spark breakdown. Since the current hot weather is a constant also in this scenario I would also consider this aspect:)

JC

Utemad

9th January 2010, 07:16 PM

Thanks JC. I've previously moved that to the inner guard and mounted it to a heatsink. Been that way for a while but still a possibility.

Utemad

9th January 2010, 07:21 PM

I actually glued my old rotor button back together. Not sure if I mentioned that already. I refitted it yesterday and it actually runs better than with the new one. Not perfect but enough of a difference to make me think it is the rotgor.

justinc

9th January 2010, 07:28 PM

Yup, having to break them apart to get them off the shaft is pretty well the only way sometimes:o

Brings tears to your eyes knowing how much they are worth:(

JC

bee utey

10th January 2010, 02:25 PM

Yup, having to break them apart to get them off the shaft is pretty well the only way sometimes:o

Brings tears to your eyes knowing how much they are worth:(

JC
It is a little known fact that distributors should have a drop or two of oil under the rotor button every 6-12 months. To stop the little nylon clip from pulling off sometimes you need a screwdriver to hold down the mechanism. If everyone did that service they would last forever!

Utemad

10th January 2010, 07:48 PM

Hi JC. I'm thinking I might just change the module anyway if they aren't to pricey. At least have it on hand for when it needs doing.

Do you just use a generic one?

The reason for my broken rotor button wasn't due to it being stuck on the shaft. I was doing something that I can't even remember which entailed taking the distributor cap off. I later tried starting it but had forgotten to refit the cap. The rotor hit the cap and shattered :angel: The cap was fine though.

Utemad

11th January 2010, 07:29 PM

Ordered a Lucas rotor button from Karcraft on Friday and it was delivered to my door on Monday. That's pretty good. Just standard mail too.

Fitted it and test drove it. Still pretty warm here in Brisbane. Idled fine. Drove fine on petrol and on LPG. Switched it off at the shops and restarted it 10mins later or so and it started up straight away.

Hopefully this is a long term fix.

I rang REPCO and priced an ignition module. They only had a listing for a Fuel Miser unit (CM476) and it cost $169.
I thought you could just buy a generic Bosch 5 pin unit but he said there was no such thing.

A Bosch box will be marked "Bosch packed" meaning its actually a chinese cheapie. Use genuine manufacturer's content only!

Just checked the packet the Bosch part came in and it said 'Made in the UK'.
It looked identical to the trouble free part that I broke but it certainly didn't work the same.

camel_landy

12th January 2010, 06:07 AM

LPG is very harsh on the HT system as it requires more 'ooomph' to make the fuel burn. On top of that, the V8 is quite fussy about the quality of HT components...

So, I'd suggest you invest in the best quality HT leads you can find as well as a good quality set of spark plugs.

HTH

M

bee utey

14th January 2010, 06:43 PM

I rang REPCO and priced an ignition module. They only had a listing for a Fuel Miser unit (CM476) and it cost $169.
I thought you could just buy a generic Bosch 5 pin unit but he said there was no such thing.

I did another module conversion today, I should remember to take pictures! The module I use is a Bosch BIM024 module, it has 4 terminals and it must be earthed via a good heatsink. I usually pay around $60-80 trade. Also they can be lifted from any Bosch HEI distributor which has the little tin cover next to the cap, e.g Holden VC-VH, Falcon XE-XF. If I get around to taking a pic or 2 tomorrow I might post them up.

Utemad

15th January 2010, 05:52 PM

I did another module conversion today, I should remember to take pictures! The module I use is a Bosch BIM024 module, it has 4 terminals and it must be earthed via a good heatsink. I usually pay around $60-80 trade. Also they can be lifted from any Bosch HEI distributor which has the little tin cover next to the cap, e.g Holden VC-VH, Falcon XE-XF. If I get around to taking a pic or 2 tomorrow I might post them up.

Thanks for that. I'll look up that part. :)

bee utey

22nd January 2010, 08:59 PM

Finally did it, look under my post: lucas-ignition-amplifier-replacement-bosch-024 in technical chatter

HBG650

28th April 2011, 07:16 PM

Hi Utemad, did you solve your LPG miss fire issue. I have a 1997 Disco that this has just started happening to as well. Runs OK on petrol, but miss fires when warmed up on gas. I have rebuilt the gas convertor, replaced the filter. New plugs, ignition module and coil. leads are about 1 year old. I'm sure it is an ignition issue. What did you find?