Thread: Disco backfired this morning on gas :( What to do?

YA, the black plugs could either be burning oil or excessive fueling, ( Unburnt Fuel). If your MAF was faulty it can run rich. they are expensive to replace.
I've tried the expensive magnacore ones and was disappointed with the insulation rotting from engine heat. So I replaced them with Bosch Black leads. B8026i They come in a set of 8 and are custom lengths for your Disco. By a set that's for your car, that way you'll have them all fitting nicely.
To throw a spanner in the works, I found NGK plugs run very good in mine, Your Vehicle:
1993 - 1999 Land Rover Discovery 3.9L V8 22DSpark PlugPart No.Plug GapRecommended PlugBPR5ES gap 0.8BPR5EIX
But since you run on Gas get the BPR6ES and gap them to .09 for better spark for gas

As a general rule is a wider gap better for gas is it?

What was the deal with the different "s" ratings on the plugs, I still don't get that and I've tried to figure it out from the net.

I got the timing light hooked up properly and it looks like timing is set to that white mark which was 2 BTDC...by the sound of it if I change the tune to 10 deg and put new plugs and leads that should hopefully make a significant difference. Though I still don't know why the tune just went out likethat in the first place after that torrential rain storm. (checked all the plugs and dizzy and no moisture), I haven't been game enough to try it on gas again after that backfire the other day. There was actually a very small hose which looked like it had cone off the back of the air filter box that I put back on today when inoticed it, didn't make a difference though.

Originally Posted by Young Angus

As a general rule is a wider gap better for gas is it?

What was the deal with the different "s" ratings on the plugs, I still don't get that and I've tried to figure it out from the net.

I got the timing light hooked up properly and it looks like timing is set to that white mark which was 2 BTDC...by the sound of it if I change the tune to 10 deg and put new plugs and leads that should hopefully make a significant difference. Though I still don't know why the tune just went out likethat in the first place after that torrential rain storm. (checked all the plugs and dizzy and no moisture), I haven't been game enough to try it on gas again after that backfire the other day. There was actually a very small hose which looked like it had cone off the back of the air filter box that I put back on today when inoticed it, didn't make a difference though.

A slightly wider gap gives a bigger spark, which is better to ignite the LPG.
The different numbers are the heat range, one is hotter and one is colder.
The "S" is the standard NGK plug and the "X" is the iridium.
The timing is not really tuning, it's engine crank timing so it is in correct sequence with the opening and closing of Valves.
Check your vacuum advance unit by sucking on it and see if it holds vacuum by sticking your tongue on it , if after sucking the air out and holding your tongue on it and it grabs your tongue the vacuum is holding ok.
I had a problem once where my timing was stuck on approx 25 deg, it turned out to be a broken vacuum advance unit and the timing plate actuating lever was stuck in that position. As for yours it maybe either the dizzy holding nut was not tightened before causing it to shift or someone played with it,

Ahh cheers, I'm still wondering about those Bosch plugs though and all the different ones that are available.

Do I get the WR7 or the WR9 ones since you guys recommend WR7 but the Bosch handbook recommends WR9?

It looks like I'll have to hunt around for a set of leads for my car because the supercheap I went to yesterday didn't have them in stock. Anyone know who sells that particular Bosch lead set?

Any good recommendations on a tool to use for setting the gap? Or should I just grab whatever can get a grip on the end and pull/push it to set the gap without breaking it?

I've heard of the MAF but I don't know what it is yet. Is it a computer part or something I can look at under the bonnet myself to see if it's working?

You might have to experiment with gap. I found the stock lucas ignition system is slack on spark compared to Australian Bosch gear so you open the gap more than for petrol and it cant jump...in fact I found a slightly narrower gap helped on LPG - ie helped make up for the fact that LPG is harder to ignite and hte ignition system was lack lustre even with all new parts To give you an idea if you put a purpose built test plug on a lead and look at the spark, then go lift the bonnet of a similar year commodore (or even earlier - I had a VH....) and check the spark with the same test plug...that will answer most questions about the Rover spark. I have tried the spark off other Rovers off the same era and they are fine for petrol but struggle with LPG.

Cheers

The book says a different number because it is for petrol. You are running gas so a colder plug works better. just get the NGK BPR6ES from super cheap if that"s handy for you as they stock them and work fine.

On gas the plugs should be running clean and not black. Keep a check on the oil level in case it's burning oil. You said you have been running on petrol for awhile since the back fire, this could be causing black plugs if it's running rich. The MAF may need adjusting for petrol but it is not used on gas. Once people convert to gas they seem to forget about petrol and have the set optimum for gas.

Try running it on gas again and see how it goes. I have had gas on lots of cars and they can sometimes back fire out of the blue for no reason (Dam Commodores). May be it got some water in some where and now dried out. Change the plugs and leads and see how it goes.

Just drive the car and stop worrying, it will wreck the experience.

Originally Posted by Young Angus

Ahh cheers, I'm still wondering about those Bosch plugs though and all the different ones that are available.

Do I get the WR7 or the WR9 ones since you guys recommend WR7 but the Bosch handbook recommends WR9?

It looks like I'll have to hunt around for a set of leads for my car because the supercheap I went to yesterday didn't have them in stock. Anyone know who sells that particular Bosch lead set?

Any good recommendations on a tool to use for setting the gap? Or should I just grab whatever can get a grip on the end and pull/push it to set the gap without breaking it?

I've heard of the MAF but I don't know what it is yet. Is it a computer part or something I can look at under the bonnet myself to see if it's working?

Did you ask at the service counter at the rear of the stores, they are usually happy to order anything in for you. A deposit is required and it usually takes a couple of days to get in.
Plug gaps are set using a feeler gauge, only cost around $10 for a complete set.

No disrepect intended, but it seems your basic mechanical knowledge is a bit limited judging by your posts , it might pay to get some one mechanically minded on the tools to help you and show you how to do the basic things, just in case you break something and then have to spend more $$$$$$$.
Google can be your friend too. do a search on the how tos. like setting a spark plug gap, I found this in .22 secs of searching
Results 1 - 10 of about 327,000 for setting a spark plug gap. (0.22 seconds)
[ame="http://www.youtube.com/watch?v=lk70oyUEftY"]YouTube- NGK Spark Plugs - Tech Video Spark Plug Gap[/ame]

and How to Set Spark Plug Gaps: Changing Spark Plugs | eHow.com

Haha cheers guys, my mechanical knowledge is definitely limited compared to you guys but now that I'm living out of home and have lots of bills I'm needing to save money on things like car work so I'm trying to do it myself. I did a few things on my old car which was fine like replacing a brake booster, plugs and leads, but I never set the timing myself and I know it's something that if you muck it up it isn't a very good thing.

I just ramble a bit but I also like trying to do things myself if I have the time and my Dad and other friends are very mechanically minded so I've grown up around a lot of it...just never really attempted some things myself. So instead of asking them more questions I'm asking you guys so thank you for all the input it really is very appreciated