HELP!!!!!!!!!!!!!!!!!!!

[john hoy]

I'm going nuts!!
Have a 1998 Disco 1 on dual fuel
It has developed the habit of backfiring through the air cleaner when on LPG
It is fluffy on take off although recently it has at times done the same at higher speed
I have replaced coil, plug leads, spark plugs new distributor
On petrol it can fuffy on takeoff but it pulls well.
Earlier on in my ownership it was faultless.
From what Ive read it could be a blown head gasket however there is no sludge in either sump or rocker cover and no cooling water loss
It idles perfectly but once away from idle my headaches begin.


I also own a 71 p6b rover on club plates which is spending more time as the daily driver than the troublesome disco.


Anyone got any thoughts?
Cheers John H

[justinc]

Tim8ng? Should be up around the 12 to 16 btdc mark for gas in a low comp v8.

Jc

[bee utey]

1. which spark plugs
2. what plug gap setting
3. what idle timing
4. what brand of ignition leads
5. what kind of "new" distributor
6. what rotor button
7. what have you done about the ignition module
8. what type of ignition coil
9. what kind of gas system?

Ignition module replacement thread:

http://www.aulro.com/afvb/technical-chatter/96950-lucas-ignition-amplifier-replacement-bosch-024-a.html

[john hoy]

Firstly thanks JustinC
Now Bee Utey
1. which spark plugs NGK 5 something [colder than normal as recommended to me
2. what plug gap setting 0.88mm
3. what idle timing 12btdc
4. what brand of ignition leads supa cheap
5. what kind of "new" distributor ebay special [$153 - no brand name though]
6. what rotor button as supplied with dizzy
7. what have you done about the ignition module as supplied with dizzy
8. what type of ignition coil bosch
9. what kind of gas system? broemo {Italian came with truck - I replaced the mixer quite earlier on when it was installed}
I set out doing this replacement stuff as the fault became evident after running perfectly for quite some time and suddenly this.
I've restored cars, built engines and this really has me beat.
For the first time in my life its booked into a lpg specialist this Friday as ivew run out of ideas
Love the truck but right now she's wearing me thin:(

[bee utey]

Which part number Bosch coil? Bosch sell zillions of different ignition coils, some OEM, some repackaged Chinese junk, also there is a huge difference between points coils and electronic coils. Swapping one for another is real baaad. Land Rover OEM Bosch coils are good, they rarely need replacing unless physically damaged.

12 degrees BTDC at idle is fine.

Check the clearance between the rotor button tip and the dissy cap by laying the rotor sideways inside the cap and lining up the carbon brush. The gap to the contacts should be well under 1mm, less is better so long as the cap is a tight fit on the dissy body and can't move sideways. Cheap caps and rotors have slop everywhere. Some cheap caps are sold in Lucas boxes but are total crud because of sloppy manufacturing tolerances.

Cheap no name brand ignition modules are short lived experiments in extreme frustration, the OEM Bosch BIM024 module in the conversion thread goes well compared to Lucas fake copies.

NGK plugs should ideally be a 6 heat range, gap should be 0.7 to 0.8mm.

Get a multi meter and measure the resistance of the longest plug lead and report back. Readings of under 2000 ohms show crap quality.

[350RRC]

Leads should be Bosch induction.

Supercheap do sell them. Mine have been in for over 130,000. No probs.

DL

[Tins]

Dunno about Discos, but Falcons were notorious for backfiring, and blowing the plenum off, if there was a vacuum hose off.So, I'd check all the hoses, as well as what everyone else says.

[Roverlord off road spares]

What was wrong with the old dizzy? Maybe re install it and see if the problem is still there. Cheap aftermarket dizzys are not the best quality. Some Aftermarket Rotors are also the cause of miss firing
You say it idles ok but once under way the head aches start.
Could be an ignition break down. Cheap aftermarket caps can cause cross arcing, apparent when a load is put on it.

[john hoy]

Thankyou all for your suggestions.
Valuable lesson to share.
I purchased an aftermarket dizzy on ebay listed as suitable for 3.5 and 3.9's.
Once at my mechanic's today all became clear.
The advance curve was not remotely near spec
Once off idle the advance was way off the mark.
I'm currently running with vac advance disconnected until I decide what I'm going to do
Moral of my tale - let the buyer beware!!
I now have one very sweet running disco again

[Roverlord off road spares]

My old Disco1 v8 ran sweet with a Scrorcher Dizzy system from Performance ignitions in Nunawading Vic , it ran a custom designed dizzy made from Holden and ford parts and used an electronic bosch coil, other who have installed them were also happy, but it was around $600.

[350RRC]

Leads should be Bosch induction.

Supercheap do sell them. Mine have been in for over 130,000. No probs.

DL

Yeah I'm quoting myself but I wish to elaborate.

With various non LR vehicles in the past silicon leads just seemed to fail, obvious firing on 6 or 7 cyls only, even with relatively new leads.

The local garage had a lead tester they loaned me and I found that half their new ones failed on the rack. They thought it was a bit funny too. All silicon.

Somehow or other I ended up with a set of these Bosch leads in my RRC pos that runs points through a MSD thing that drops the voltage across the points to sweet fa. A bit like peasant level electronic dizzy, except I can go back to points only in the boonies if something goes wrong just by removing 3 wires.

What changed? No more genuine Bosch dizzy caps cracking and carbon tracking (20,000 k's regular max). No more backfires...... my pos is always started on lpg, Same NGK plugs in for 130,000 with no loss of anything, especially money.

Sure they're black and skinny, sure they're cheap, sure they're not sexy but they are doing the job they should be doing, very well.

cheers, DL

[john hoy]

Thanks for that info. I may yet spend the $600
Just to update I took the bob weights from the old dizzy and put them in the new one.
Have to say the build quality of the old one is far superior to the new one.
Anyway once installed it runs well on gas but quite fluffy from take off with petrol
I'm going to now swap the vac advance form the old dizzy to the new as perhaps the advance might be a little out.
If that fails I'll be off the performance ignition. I had a dizzy done for my old mgb which was excellent

[john hoy]

My old Disco1 v8 ran sweet with a Scrorcher Dizzy system from Performance ignitions in Nunawading Vic , it ran a custom designed dizzy made from Holden and ford parts and used an electronic bosch coil, other who have installed them were also happy, but it was around $600.

Scorcher dizzy fixed everything
Thankyou All for your thoughts
John

[john hoy]

Ended buying a scorcher dizzy from performance ignition and all my ignition issues died a sudden death.
Runs perfectly on lpg and petrol HOWEVER lately when on petrol it appears to starve for fuel. If you boot it; it dies and splutters in the exhaust pipe. If you open it up gently it goes reasonably ok.
Fuel starvation? blocked filter, water in fuel, faulty MAF as a consequence of one to many misfires, fuel pump [it does seem a little noisy at times]
What do people think?