Rough running sorted but now an issue with LPG

Hi Everyone,

I replaced the Coil and HT leads on my 1999 disco v8 this morning, in an attempt to cure a rough running issue, which i had from when i picked it up last week. She was running badly on Petrol and LPG (similar symptoms), the rough running was poor idle, lots of hesitation and bogging down.

Swapping these components has transformed the drive. It pulls well and he hesitation is done which is great, however there is now a new issue.

After the swap i took the disco our for a test drive and was pleased with the results. I tested on both Petrol and LPG and didn't see an issue. During the drive (on LPG) there was an unexpected backfire (noise came from the engine) and it wouldnt rev. I swapped back to petrol and all was well and got some no problem.

I noticed a ticking noise from the engine when i returned hope (like a playing card in spokes). I did some more checks and found the HT leads on 5 and 7 were loose! I've reconnected these and the ticking has gone which is good however, when trying to run on LPG the engine is all over the place.

If i swap from petrol to LPG at idle (with some revs to stop ist stalling), the engine wont rev over 3k. Under load when driving the revs drop and the engine nearly dies.

On petrol there is no issue at all. I'm assuming the back fire was caused by the HT leads coming loose (my fault), but im a little unsure as to why we have the LPG issue. It seems off that the disco ran (albeit badly), on both Petrol and LPG, but now all is well on Petrol the LPG is poo.

The Distributor cap has been replaced recently by the previous owner and checking it this morning there is no discernible damage or pitting so that seems fine.

I've got some new plugs which i'll get replaced shortly (checking the gaps obviously), but im a little concerned as it was running before and now isnt, could the backfire have damaged something on the LPG system?

Sorry for the long post!

what is the lpg system??

if good on petrol i would be looking at lpg system not ignition..(though lpg could be showing up ign weakness)

Sorry should have said, its a Single Point Romano system

I had similar rough running, backfires under load etc on LPG and switching to NGK plugs cured the problem. theres a lot to be said for decent plugs.
I also fitted a new coil and leads from simonbbc since owning the car, this has transformed how it runs. When using LPG you need the best ignition components.

Completely agree with Johndregg: LPG needs a really decent spark.

It took me ages to get my V8 running properly, and it's still a bit weird. I found the biggest difference i made to mine was replacing the spark plugs for NGK items. Gapped at .7mm, which has made a huge difference.

One question- is it possible to adjust the timing on your LPG system? On some it's possible to plug it into a laptop and adjust. If you're certain your engine is timed correctly, and your ignition components are good (Including coil and rotor arm), that would be my next step.

But then again, i'm very new to V8 ownership and have a lot to learn!

Im rather embarrassed about the solution to the problem! I was out of LPG! The Gauge reads full but the tank was almost empty. That said with the new coil fitted with leads its running much better. I'd purchased some plugs which were apparently correct, but according to my mechanic are the wrong ones. He checked the ones in there which seemed pretty new and in good condition, for now he's re-gapped them to .7mm and its running like a champ!

NExt job is to fill it with LPG and gauge how many miles i can get!

Glad it was a simple fix! Happy motoring.