Thread: AAArrrrrrrggggggggghhhhhhhh!!!!!!!!

Keep it on petrol mate. Sounds like a bad install for backfiring like that. Have you had an LPG vehicle before? Just be sure that you have absolutely no throttle on when changing from one fuel to another and wait a couple of seconds before applying throttle again. Helps to reduce the likelihood of backfire.

Hello,
I had a 97 Disco on gas, for 7 years. Had it backfire on one occasion, and blew apart the air cleaner box. I pulled over due to the noise. Repaired it with duct tape, and put in a Ford one. I think it was under 30 dollars. The reason was my spark plug leads were old. After replacing them (by recomendation from my mechanic) it worked fine again.
Good luck,

Ken

Originally Posted by Mark86

Hi JC no its not me i found that pic a couple of years ago do not no location i think it may have been in south africa iam having trouble resizing pics for my avatar got photos 19.5kb limit its the 80x80 pixel limit is the probem...

Mark

...bet you wish it WAS you every time you look at it!!!

JC

I have a 96 SI 3.9 V8 'Disco which I put on LPG shortly after I got it a year ago which is now running 100% reliably on gas (I know - I'm tempting fate by saying that!).

I had a few backfires initially which blew the top off the air-cleaner box and I've had to reform the clips a few times but it's still OK.

The backfires were due to 2 problems:

1. Old and dirty HT leads. Get new 8mm silicone HT leads and keep them clean. Clean the dizzy cap too. Run the engine at night with the bonnet up and the lights out to see where there is arcing - the cross-firing between leads is the killer. Rearrange the leads to ensure there are absolutely no blue sparks. (Do I need to say, best done with the engine stopped?)

2. Broken rubber elbow on the vacuum advance line from the plenum to the dizzy. This lets extra air into the plenum and the engine runs lean increasing the likelihood of a backfire. If the elbows are perished get a new line ($15 from Black Forest LR in Adelaide in Nov 2005) and make sure its not under tension when you install it.

Check the operation of the Mass Airflow Meter as described in the "Oxygen Sensor" thread. I was surprised to find the 'Disco will run with it disconnected entirely (my '88 Rangie wouldn't!) but it will be far from economical on petrol. You may well have got away without damaging it, but check that the voltage out of it varies with revs to be sure. Also, there is a stainless steel gauze on the front of the MAF which may well have blown out - check that. I'm now an expert in cutting a circle out of fine gauze and forming the big folded aluminium washer which holds it intact under the circlip. You'll get the knack.

Apparently some people cut a hole in the air cleaner cover and put a bath plug into it on a chain - it blows out in the event of a backfire and the clips don't get stretched. I haven't felt the need to do this (yet).

In the Rangie I had a back-fire flapper valve just upstream of the plenum but there's not room for one of those in the 'Disco, worse luck.

IMHO it's difficult for an LPG installer to make the engine backfire - it's more likely due to ignition problems as I've described.

BTW, I've recently fitted an Oxygen sensor into my exhaust at the last Y and put a stepper motor type power valve in the low pressure gas line with a closed loop controller. I've lost a smidge of economy as I had the manual power valve wound as lean as I could (about 190Km on 50Lt now instead of 200Km) but it works a treat. There is almost no difference in performance between LPG and petrol now.