backfire through air box

[krazy kiwi]

im new to lpg i have a 3.9 d1 thats started to backfire through the airbox every now and then 3 times on a 100km trip how can i fix it or does it just need a tune up

[bee utey]

im new to lpg i have a 3.9 d1 thats started to backfire through the airbox every now and then 3 times on a 100km trip how can i fix it or does it just need a tune up

Almost certainly your spark plugs are not optimum for gas. They need to be 1 heat range colder than standard for petrol, and the gap no more than 0.8mm/0.032". 0.7mm is best. I recommend Bosch part no. WR7DC+ as being very good for standard engines on gas.

Timing sould be set at 6-10 degrees BTDC at idle. ( I set it at 10 for the 3.9) Plug leads should be inductive core (stainless steel spiral core) types and NOT tied together in a bundle. Rather they should be run with about 20mm air gap between them where possible.

Once you have done all that it will normally cope with lean mixtures without backfiring.

[krazy kiwi]

thanks i will give that a try

[Sideroad]

Thanks for the advice.
I'm having the same trouble and will give it a go. I'm running a 179 holden in a 109 2A.

[bee utey]

Thanks for the advice.
I'm having the same trouble and will give it a go. I'm running a 179 holden in a 109 2A.

Similar issues. If it's got the flat seat plugs use WR7DC+, if its the 202 head with taper seat plugs use HR8BC. Also the electronic dissy (blue motor type) upgrade is always worth while.

[It'sNotWorthComplaining!]

im new to lpg i have a 3.9 d1 thats started to backfire through the airbox every now and then 3 times on a 100km trip how can i fix it or does it just need a tune up
If you have had 3 back fires through to the Airbox, then also check you MAF, that's often how they end up dead, the little thin platinum sensor wire gets blown to smitherines. So running on petrol might not work too good, try running it on petrol and see if all is still ok.

[frantic]

You should also look at getting a spot to relieve the pressure before it reaches the airbox. In my old playdough we had a hole about the size of a 50c coin in between the airbox and the gas car/mixer that was covered by a thick airtight/fireproof sleeve that went all the way around the pipe. It would expand like a rubber stocking to take most of the pressure from the backfire and not damage the air filterbox, in the prado if the airfilterbox was opened, or one of the sensors in it was loose, your engine would not start and you would get more backfiring as a result! That is why when we got the newer playdough it was put on gas injection so never backfired while we owned it:D

[Sideroad]

Thank Bee Utey,
It has the 179 head but bored to 186; and is running the blue Elec. dissy. I will have to check the leads, they may be getting a bit old and were from before the gas conversion. I was running a touch fast at idle and I asked the mech. to adjust it. Now it back fires randomly over 80kph+. A 30 min run can get 0-3 back fires resulting in gas ring and filter being blown loose and damaging the top of carb. I now have the filter loose-ish so it is blown off only.


Similar issues. If it's got the flat seat plugs use WR7DC+, if its the 202 head with taper seat plugs use HR8BC. Also the electronic dissy (blue motor type) upgrade is always worth while.

[bee utey]

Thank Bee Utey,
It has the 179 head but bored to 186; and is running the blue Elec. dissy. I will have to check the leads, they may be getting a bit old and were from before the gas conversion. I was running a touch fast at idle and I asked the mech. to adjust it. Now it back fires randomly over 80kph+. A 30 min run can get 0-3 back fires resulting in gas ring and filter being blown loose and damaging the top of carb. I now have the filter loose-ish so it is blown off only.

The probability of a burnt out lead with these dissy's is quite high if you run the standard plugs with a large gap. Definitely worth putting new leads on.

[LRDV8]

Hate to say this but the mixer systems just don't work on the Disco's..... I have a 2000 model disco and had a mixer system installed about 4 years ago.

It started backfiring about 6 months after the conversion and basically kept happening on and off for the next 4 years.... had it tuned, cleaned, MAF replaced, coil packs replaced, leads, plugs .... you name it I tried it. Usually got better for a while then back to backfiring eventually...

Finally cracked the **** and had the mixer system ripped out and binned and replaced with a full injection system.... can't say how happy i am, not one issue since.

Wasn't cheap at $2750 but I got the rebate again (as it was over 4 years from the original conversion) so it was only about $1500 at the end of the day. I would have spent at least $2000 trying to fix the backfiring before finally cracking the ****s.

Good luck !!

[bee utey]

Hate to say this but the mixer systems just don't work on the Disco's..... I have a 2000 model disco and had a mixer system installed about 4 years ago.

It started backfiring about 6 months after the conversion and basically kept happening on and off for the next 4 years.... had it tuned, cleaned, MAF replaced, coil packs replaced, leads, plugs .... you name it I tried it. Usually got better for a while then back to backfiring eventually...

Finally cracked the **** and had the mixer system ripped out and binned and replaced with a full injection system.... can't say how happy i am, not one issue since.

Wasn't cheap at $2750 but I got the rebate again (as it was over 4 years from the original conversion) so it was only about $1500 at the end of the day. I would have spent at least $2000 trying to fix the backfiring before finally cracking the ****s.

Good luck !!
Hate to say this but mixer systems work on D2's (Thor's) so long as the plug gaps are put down to 0.6mm. Otherwise you overload the weakling coil packs and they die, with frequent backfiring. I have a few successful D2 mixer systems out there, never backfired in 3 years.

Granted injection is much safer and better. D1's aren't nearly the same problem on mixers, they are quite easy to prevent backfires on.:)

[Sully]

Hate to say this but the mixer systems just don't work on the Disco's..... I have a 2000 model disco and had a mixer system installed about 4 years ago.

It started backfiring about 6 months after the conversion and basically kept happening on and off for the next 4 years.... had it tuned, cleaned, MAF replaced, coil packs replaced, leads, plugs .... you name it I tried it. Usually got better for a while then back to backfiring eventually...

Finally cracked the **** and had the mixer system ripped out and binned and replaced with a full injection system.... can't say how happy i am, not one issue since.

Wasn't cheap at $2750 but I got the rebate again (as it was over 4 years from the original conversion) so it was only about $1500 at the end of the day. I would have spent at least $2000 trying to fix the backfiring before finally cracking the ****s.

Good luck !!

Where in Melbourne did you find someone to install an injection system for $2750? That's a good price.

[landrover dave]

Where in Melbourne did you find someone to install an injection system for $2750? That's a good price.

The only reasons lpg backfires are running too lean and poor spark. Have run lpg for years and no backfires if tuned correctly. Maybe your system wasnt installed or set up properly.
There is a set of tanks you can get that fit under the sills and hold 35l usable per side. You dont have to have a cradle as they have mounts welded to the tank set, and of course there is no need to touch the std petrol tank. Speak to Sean at Roverparts 1300760125.

[bee utey]

Toyota 100 series land Cruisers run those 35 litre sill tanks with welded-on brackets. I can't see how they would fit on a D1. Pictures please? Ground clearance would be compromised badly. The 19 litre APA ones lose 50mm clearance as it is.

[johnvig57]

l've found with 96 3.9 on gas is very finicky
leads and plugs have to be spot on , timing too
l had a 4.1 cortina '76 on gas for 20 years super reliable easy and cheap to fix and after the dizzy was re-jigged to 10% BTDC from the normal 6% there was hardly any difference from pertol heaps of power
with the landrover however!
l've found that the vaacum lines had tiny cracks at the ends and this affected
the backfiring
two airboxes later had a cheap after market air filter($15)
as to fuel economy 300 kms oer 70 ltrs city 350kms highway
thanks for sharing info very helpful

[Kelli]

could where you get your lpg from make a difference? mine seems to backfire more if i get my lpg from the big w servos


or am i just imagining that

[bee utey]

could where you get your lpg from make a difference? mine seems to backfire more if i get my lpg from the big w servos


or am i just imagining that

Not impossible, I have had plenty of people report running issues with different brands of autogas. Autogas is a mixture of different gases, the suppliers aren't all using the same. However if it backfires repeatedly there's something not right with your vehicle's tuning.

[Gremlin]

Very interesting about all this backfiring. Mine (98 D1 3.9) has had a couple of backfires (3 from mem over 6mths). Firstly thanks for the advice on the plugs and I'll check those out shortly, but have no idea what I'm looking for with the leads. Secondly I was given a new (none LR) MAF and was wondering is it just a case of plug-n-play or do they have to be calibrated? Lastly I've heard the Woolies/Coles LPG is not the best and filling up from ELgas or Supa Gas is by far the prefered option. Lastly my system is 6yrs old and like some others here, I'm most interested in this '$2,500 system' and being able to claim the rebate again. What's the deal there? Oh, P.S.....I love my disco, quirky or not :D

[bee utey]

Very interesting about all this backfiring. Mine (98 D1 3.9) has had a couple of backfires (3 from mem over 6mths). Firstly thanks for the advice on the plugs and I'll check those out shortly, but have no idea what I'm looking for with the leads. Secondly I was given a new (none LR) MAF and was wondering is it just a case of plug-n-play or do they have to be calibrated? Lastly I've heard the Woolies/Coles LPG is not the best and filling up from ELgas or Supa Gas is by far the prefered option. Lastly my system is 6yrs old and like some others here, I'm most interested in this '$2,500 system' and being able to claim the rebate again. What's the deal there? Oh, P.S.....I love my disco, quirky or not :D

Bosch have a good lead set in their catalogue for the D1. It can also be done with individual leads from a Bosch ignition lead merchandiser if your auto store has one, a slightly different fit but does the job.

Don't know about the MAF, it either fits or it doesn't.

The rebate is currently only $1250 for fitting a new system, I wouldn't bother, just spend the money on yours. I don't think you can claim two rebates on the same vehicle in any case.

[Gremlin]

Sounds pretty sweet to me and thanks for the info. I was pretty sure you couldn't have two bites of the cherry with the LPG rebate, still if someone was lucky enough to get it, then half their luck :D

Also I love the urban myth about leaving the D1 on petrol (:( guilty as charged) overnight.

Hopefully the new MAF might solve the other problem I have on petrol at the moment. The o'l fella will start up on petrol fine enough and when I switch over to lpg he runs like a dream. However, should I switch back to lpg, acceleration is a no go. If I gently squeeze the pedal, then back off a smidge, squeeze again, I can slowly increase my speed and I do mean, slowly. Try and ask for a bootfull and forget it, it just wants to die in the arse as though it's flooding. Which really makes the petrol tank a good for nothing, heavy lay-about free loader who's enjoying a free ride at my expense.

Cheers, Gremlin

[bee utey]

Hopefully the new MAF might solve the other problem I have on petrol at the moment. The o'l fella will start up on petrol fine enough and when I switch over to lpg he runs like a dream. However, should I switch back to lpg, acceleration is a no go. If I gently squeeze the pedal, then back off a smidge, squeeze again, I can slowly increase my speed and I do mean, slowly. Try and ask for a bootfull and forget it, it just wants to die in the arse as though it's flooding. Which really makes the petrol tank a good for nothing, heavy lay-about free loader who's enjoying a free ride at my expense.

Cheers, Gremlin

You mean switch back to petrol? That is easy to fix. Your MAF is fed by the same 12V wires as the injectors. When you switch off the injectors your engine ECU goes into limp mode until you switch off the engine and restart on petrol. Check there is 12V at the MAF, at the brown/orange stripe wire, while it's running on gas. Then what you need to do is cut the brown/orange stripe 12V wire to the MAF, and connect the MAF side back to the always-powered side of the injector-cut relay. A common mistake for less experienced gas fitters.

[Gremlin]

Oooops and yep, I meant going over to petrol. With regards to the 12v to the MAF solution, the Impco system has been on the D1 since 1996, so would this solution still be applicable to mine Bee-Utey? I've only owned the wee beasty since Feb this year and its only done 175k.
Cheers :D

[bee utey]

Oooops and yep, I meant going over to petrol. With regards to the 12v to the MAF solution, the Impco system has been on the D1 since 1996, so would this solution still be applicable to mine Bee-Utey? I've only owned the wee beasty since Feb this year and its only done 175k.
Cheers :D
Just do the test, the wiring is essentially the same for all RRC's and D1's from 1989-99. If there's power at the MAF while on gas then something else is wrong. Just I've met this one too often and its a fast fix.