Back-firing 3.9

[dod51e]

Hi Guys,

The old girls is misfiring.  It occurs on both petrol and LPG and only when first started up and cold.  When it is warm there is no problem and runs fine.  My first thought was it was too lean on LPG.  This was checked and OK and still back firing, switched on to petrol and it still did it!  The back firing is through the exhaust and the inlet.....too advanced and too retarded?  Once eventually over about 2000 rpm or fully warm there is no trace of any misfire.

Your thoughts gentlemen please.

[Yoshi]

This happened to my series 3 2.25 petrol.  Same thing, started minor and just got worse and worse.

Turned out to need a new dizzy and all was fine after that!

ATB

Dan

[ben-dent]

Mark i would say it is the dizzy a mate had a 3.9 disco that did the same he replaced plugs, leads, cap, rotor arm, cat's Lambda's, and it still back fired, borrowed one of my dizzys and it fixed it,

[clbarclay]

Its not something daft like the nut clamping the dizzy isn't quite tight enough and the dizzy can be very slowly rotated by the vibrations, advancing the ignition too much.
Found the dizzy on a mates V8 wasn't bolted down tight enough and could be turned by hand. Probably why it died half way up a gully, 4 minuets before the pay &play site closed :lol:

[dod51e]

Thanks for the info guys.  I must concur following the advice that it must be the dizzy.  Had a look around for one and guess what... it's non of those listed!  It seems to be the later 35 limb dizzy but with a two spade connector rather than the three pin and definitely not the earlier two cable model.  Typical Land Rover.
Still, one on order now and hopefully I'll be able to find an adapter cable to fit (or make fit!!!)  [-o<

Cheers

[TwoSheds]

As well as wear in the distributor causing this sort of problem, wear in the timing chain is also a possibility. When you are fitting the new dizzy and you get the timing light on it, note how much the timing is 'bouncing about'.
With mine - still on the original dizzy and timing chain, the spark would occur anywhere within a 15^o range!  :-o

Rather than replace the distributor I went for Megajolt and - result! Rock solid timing and the engine runs as smooth as a smooth thing (well - a smooth thing that's 19 years old anyway) so I guess my timing chain isn't too bad - but I have seen horror stories about the condition of the original equipment - the RPI site has some good info at: http://www.v8engines.com/engine-4.htm#timing
Worth bearing in mind, but - don't let it give you nightmares ;)

Roger

[Range Rover Blues]

I'd love to know lots more about your megajolt conversion mate as I'm thinking of doing the same.

[TwoSheds]

I'd love to know lots more about your megajolt conversion mate as I'm thinking of doing the same.

If you do go Megajolt, you won't regret it! Smooth, perfect timing, great sparks, custom LPG curve and WATERPROOF!  :dance: :dance: :dance:

Your 'Click here for Spec' doesn't seem to work - do you run LPG? If not then MegaSquirt would probably be the way to go, but for me Megajolt is perfect.

When I have a bit more time I will put together a post on my conversion - but in the mean time, if you have any specific Q's or would like to pop up and see it, then drop me a PM (I would offer to come and meet, but it's not MoT'd, taxed or insured at the mo :( )

Rog

[Range Rover Blues]

Looks like the admin team finally got rid of the remains of the old site, so my spec and galeries are gone.

I might take you up on that at a later date, I havn't time for any projects right now that aren't part of my course :( but I've heard of megasquirt and megajolt before through classic Ford connections.  I wonder if a megasquirt could be coupled to my multipoint LPG system :-k

Just give me an idea, how did you attach the timing wheel? how much did it cost? how did you set it up?

[TwoSheds]

Just give me an idea, how did you attach the timing wheel? how much did it cost? how did you set it up?

Timing wheel is a Ford Transit - £15 new - and is simply clamped (using the thrower) on the back of the bottom pulley. There IS room ;)
Cost all together inc kit, EDIS ECU, TW, coilpacks and leads - probably £150 ish.
I just copied a known-good map, smoothed it and then set-up a 2nd map for LPG based on the petrol map with what I have read on the internet stuck on top.
Apparently MS can do multi-point LPG injection although I have not seen any details.

I will post pics of trigger wheel etc soon... promise!

HTH

Roger
p.s What course are you doing?

[Range Rover Blues]

PGCE in Engineering, I'm on the 1-year too so it's in at the deep end.