lumpy acceleration on LPG between 1000-1500rpm

[gussy]

I have a dual fuel ignition question...

A while ago I had my gearbox and transfer case rebuilt so I took the RR for a shakedown along the powerlines track here in WA. It was a good rebuild to say the least. It did go through some puddles though.

Almost immediately after this, I have noticed that when accelerating on LPG (especially at traffic lights) the engine feels quite lumpy/misfiring between around 1000rpm and 1500rpm.

I have figured out that the misfiring only occurs after the car has warmed up and only when it's running on gas. Since LPG systems need almost perfect ignition systems, and the issue occurs only after the engine bay is nice and warm, I was thinking solid state electronics issue. Do you guys think the ignition amplifier module needs replacing or is on its way out? Or am I barking up the wrong tree. I need to figure this out before Christmas as I'm driving across to Tasmania and I don't want any funny business on the nullaboor.

About three years ago, I replaced the ignition amplifier with another Lucas one for a similar issue, except that it was happening on both fuels and also stalling at the lights/ low RPM. So maybe this one is on its way out?

[gussy]

Here’s a picture of the Lucas amplifier module that I replaced the third party version with (bottom) 3 years ago https://www.aulro.com/afvb/images/imported/2017/11/1045.jpg

[bee utey]

I gave up years ago using those modules, they're marginal at best.

Lucas ignition amplifier replacement by Bosch 024 (https://www.aulro.com/afvb/technical-chatter/96950-lucas-ignition-amplifier-replacement-bosch-024-a.html)

Not to say that yours isn't working. Try undoing the distributor cap and leaving it to air in the sun for an hour after getting the engine warm. Use a hair dryer if no sun available. There may be slight traces of moisture condensing inside the distributor cap. Polish the cap inside and out with a soft cotton cloth.

[bee utey]

double post

[gussy]

I gave up years ago using those modules, they're marginal at best.

Lucas ignition amplifier replacement by Bosch 024 (https://www.aulro.com/afvb/technical-chatter/96950-lucas-ignition-amplifier-replacement-bosch-024-a.html)

Not to say that yours isn't working. Try undoing the distributor cap and leaving it to air in the sun for an hour after getting the engine warm. Use a hair dryer if no sun available. There may be slight traces of moisture condensing inside the distributor cap. Polish the cap inside and out with a soft cotton cloth.

Thanks @Beeutey! I'll give it a try after work today. I'll let you know how it goes! Otherwise I'll go for the amplifier module... I was thinking about doing your Bosch conversion a few years ago actually. Maybe this is the opportunity I've been waiting for.

Does this mean that oxygen & LPG is harder to ignite than oxygen & petrol vapour and consequently needs a cleaner spark? If my problem is failing ignition...

[FisherX]

My Rangie left me on the side of the road the other week for the first time. Not a biggy only took a couple of minutes to sort out. It was a bit of water on the ignition module plug. But I don't like people to see a Range Rover on the side of the road with the bonnet up [bigsad]. No good for any of us.

So prior to that I was having some issues with ruff idle and a miss every now and again that was probably fowled plugs.

So I didn't want that happening again so I fitted a MSD Street Fire ignition with the Tach adaptor to my RRC and it has sorted the little issues I was having and runns sweet as now. I've still got it on std 0 dec ignition timing but I'll be winding up the advance soon. You know advance till she pings and back off a smidge [thumbsupbig].

I don't mind sticking in MSD ignitions on older cars as they work great and it was the best modification I ever did to my sigma years ago.

Cost $220 for the ignition and $80 for the tach adaptor and took half an hour to fit. All the original stuff is still there so if it does happen to crap itself its a 2 min job to plug in the old ignition.


I was going to do a write up on it when I get some miles and a couple of tanks of gas through it and give some stats on the conversion.

Here it is fitted just next to the coil behind the left side headlight.

132877

and a youtube video on MSDs

MSD Ignition Controls - Playing with Fire - YouTube (https://www.youtube.com/watch?v=5LZuh0X7rtw)

[bee utey]

Does this mean that oxygen & LPG is harder to ignite than oxygen & petrol vapour and consequently needs a cleaner spark? If my problem is failing ignition...

Pretty much. A mixture of LPG and air takes a higher voltage gradient across the plug gap to ionise the mixture and initiate a spark compared to petrol/air. Momentary lean mixtures on LPG can be a real hazard to forwards motion due to less ionisation available. And retarded timing means a higher cylinder pressure at the point of ignition so 10 degrees BTDC at idle assists low to medium speed power.

Reduced plug gaps (0.7 to 0.8mm) helps a bit. The type of plug lead can cause odd running problems with LPG too due to resonances in the high voltage section.

[bee utey]

I knew a guy once who swore by MSD systems, gave me one to try in the wife's old P76. Worked well until it left her stranded by the side of a country road miles from home. It got a Bosch module soon after that and that never let her down. No doubt the newer MSD's would be reliable but the Bosch one works well as well under 1/2 the price.



My Rangie left me on the side of the road the other week for the first time. Not a biggy only took a couple of minutes to sort out. It was a bit of water on the ignition module plug. But I don't like people to see a Range Rover on the side of the road with the bonnet up [bigsad]. No good for any of us.

So prior to that I was having some issues with ruff idle and a miss every now and again that was probably fowled plugs.

So I didn't want that happening again so I fitted a MSD Street Fire ignition with the Tach adaptor to my RRC and it has sorted the little issues I was having and runns sweet as now. I've still got it on std 0 dec ignition timing but I'll be winding up the advance soon. You know advance till she pings and back off a smidge [thumbsupbig].

I don't mind sticking in MSD ignitions on older cars as they work great and it was the best modification I ever did to my sigma years ago.

Cost $220 for the ignition and $80 for the tach adaptor and took half an hour to fit. All the original stuff is still there so if it does happen to crap itself its a 2 min job to plug in the old ignition.


I was going to do a write up on it when I get some miles and a couple of tanks of gas through it and give some stats on the conversion.

Here it is fitted just next to the coil behind the left side headlight.

132877

[gussy]

My Rangie left me on the side of the road the other week for the first time. Not a biggy only took a couple of minutes to sort out. It was a bit of water on the ignition module plug. But I don't like people to see a Range Rover on the side of the road with the bonnet up [bigsad]. No good for any of us.

So prior to that I was having some issues with ruff idle and a miss every now and again that was probably fowled plugs.

So I didn't want that happening again so I fitted a MSD Street Fire ignition with the Tach adaptor to my RRC and it has sorted the little issues I was having and runns sweet as now. I've still got it on std 0 dec ignition timing but I'll be winding up the advance soon. You know advance till she pings and back off a smidge [thumbsupbig].

I don't mind sticking in MSD ignitions on older cars as they work great and it was the best modification I ever did to my sigma years ago.

Cost $220 for the ignition and $80 for the tach adaptor and took half an hour to fit. All the original stuff is still there so if it does happen to crap itself its a 2 min job to plug in the old ignition.


I was going to do a write up on it when I get some miles and a couple of tanks of gas through it and give some stats on the conversion.

Here it is fitted just next to the coil behind the left side headlight.

132877

and a youtube video on MSDs

MSD Ignition Controls - Playing with Fire - YouTube (https://www.youtube.com/watch?v=5LZuh0X7rtw)

those MSD ignition controllers look great. The difference in spark gap is huge. For now I will stick with a Bosch/Lucas replacement though! If I ever decide to restore the sports rover, that will go in! Thanks for the idea Fisher X

[gussy]

Pretty much. A mixture of LPG and air takes a higher voltage gradient across the plug gap to ionise the mixture and initiate a spark compared to petrol/air. Momentary lean mixtures on LPG can be a real hazard to forwards motion due to less ionisation available. And retarded timing means a higher cylinder pressure at the point of ignition so 10 degrees BTDC at idle assists low to medium speed power.

Reduced plug gaps (0.7 to 0.8mm) helps a bit. The type of plug lead can cause odd running problems with LPG too due to resonances in the high voltage section.

Are you suggesting that the issue could also be the LPG converter/vaporiser/reducer giving a lean mix to the engine @Beeutey? What system controls the converter? is it vacuum? or some mechanical part that gets fouled over time?

Angus

[bee utey]

Are you suggesting that the issue could also be the LPG converter/vaporiser/reducer giving a lean mix to the engine @Beeutey? What system controls the converter? is it vacuum? or some mechanical part that gets fouled over time?

Angus

Haven't the faintest what kind of converter you have, every one is different. On some brands of converter it is possible for water to splash into the balance line fitting. The weight of water against the diaphragm throws out its mixture delivery, usually making it rich. Vacuum generated by all parts of the inlet system change the mixture, you could even have a sopping wet air filter element. You could have even lost the security of the air cleaner case itself, causing the engine to run lean.

[gussy]

Noted. Thanks for all your help so far.


Haven't the faintest what kind of converter you have, every one is different. On some brands of converter it is possible for water to splash into the balance line fitting. The weight of water against the diaphragm throws out its mixture delivery, usually making it rich. Vacuum generated by all parts of the inlet system change the mixture, you could even have a sopping wet air filter element. You could have even lost the security of the air cleaner case itself, causing the engine to run lean.

[gussy]

So it turns out... after taking your advice @beeutey of letting the distributor air out when warm, that the distributor cap terminals are a little concave and the rotor edge has started to deteriorate. I'll replace them both and see how it goes! failing that, I've a new amplifier to pop in :D Hopefully in the next few days!

Is 3 years a normal lifetime for these lucas items?

133040

133036

[bee utey]

Original Lucas lasts longer than the Chinese rubbish sold in the pretty green boxes that you can buy these days. I've used genuine Bosch rotor buttons to fit XF Falcon, part no. GB864, as they are very close in the critical dimensions. They can be a bit tight on the dissy post though, rub around it with some wet and dry before you proceed.

[gussy]

If I were an electron, I know I'd have difficulty swimming through that corrosion in the cap. I think that was the problem. 7/8 cylinders running. I overthought the range rover's electronic system and initially missed the obvious... I'll take it for a test tomorrow. Looking forward to smooth acceleration and 8/8 cylinders firing like they should.
at least I have a spare amplifier now...
thanks for everyone's help. @beeutey I'll buy you a beer when we drive past SA after Christmas if you're keen. This is not the first time you've been a great help. Thanks.


133086

Original Lucas lasts longer than the Chinese rubbish sold in the pretty green boxes that you can buy these days. I've used genuine Bosch rotor buttons to fit XF Falcon, part no. GB864, as they are very close in the critical dimensions. They can be a bit tight on the dissy post though, rub around it with some wet and dry before you proceed.

[gussy]

All fixed! Pretty much ready to do the Nullabor after Christmas!