another AFM post!

[shakes]

I apologise if this has been asked before, infact I'm sure it has I just cant find it.

a mates '88 classic running the flapper style AFM...

changing from gas to petrol the car occaisonally backfires
twice now its backfired bending the AFM and basically stopping it from running on petrol. the car is fitted with the scuba tanks and the trick electric changeover switch... this could be part of the issue ie: putting petrol in before gas is completely gone.

he's basically trying to avoid forking out $400 for a new AFM for the car to backfire again!

What options have we got in regards to getting a different style of AFM/throttle body thats fairly easily adapted in terms of wiring and tuning? (more importantly one that wont dislike things as much as the standard one does) and/or stopping the car having the occaisional misfire?

sorry again if its been posted up before.

Cheers

Simon

[Loanrangie]

Unless the lpg controller is faulty it wont cause a backfire, on an efi car the switch over from petrol to lpg and vice versa is instantaneous and there will be no residual fuel left - carby lpg cars are opposite. Best bet is to fit a anti backfire gizmo between the mixer and afm so if it blows again it wont crap the afm. I would get your mate to check all the ignition system components and the timming as this is what causes backfires.

[shakes]

thats whats killing us, recently timed. new plugs leads cap etc
cleaned gas mixer new diaphragm pulled all connections off and cleaned with "contact cleaner" seems to be running perfectly on gas and petrol and as powerfull as a tired 3.5 gets.

what are these anti-backfire gizmo's you speak of? real estate in the engine bay is at a premium

Simon

[subaman]

I have an anti back fire protector on my rangie and all it is is a peice of pipe off the intake after the afm with a heap of holes drilled in it. It has a stubbie cooler over it. When you get a large backfire it blows the cooler off instead of damaging the afm. It works good but last time it happened I did not have a spare cooler so had to use some tape to get me home.

[Loanrangie]

LPG mixture must be way out, i have never had an lpg backfire on either of my rangies in the 6 years of running lpg ?

[POD]

G'day, have been looking at this forum for a while and this thread finally prompted me to register. I have an 88RR and had problems with backfiring a while back, repaired my AFM many times and replaced it once, despite having a stubby holder backfire valve as described.
Make sure all your ignition electrics are in first class condition- route all your low tension ignition wiring as far away from the high tension wiring as possible. Separate all your HT leads as much as possible. Check the integrity of the flexible harness to the ignition pickup inside the distributor.
Alternatively, throw away your AFM and fit an aftermarket EFI system like I did. All the thing does is get in the way of incoming air anyway.
Another possibility- sticking inlet valve.

[RaginRover]

The flap will be jammed forward on the housing of the meter, take the intake apart and gently pop it back into place from the front. That will get it running on fuel again

As for the backfiring - don't accelerate when swapping over, I always try and run it down a hill and switch over.

Tom

[shakes]

loanrangie - its not the LPG thats backfiring, its not the petrol thats backfiring... its the changeover that seems to make it backfire, and again it very rarely happens. Unfortunatly when it does... it pops an intake hose off or blows the afm.


Ragin rover - both times its blown its actually bent/twisted the flapper bit just slightly causing it to jam, can still run on gas no drama's by opening it fully like you said

POD - somehow my tinar$e mate scored a COMPLETE motec computer loom and manifolds sensors etc to suit for nothin amd a 3.5 hi-comp off someone else (again free and perfectly good) but as the car is still his family's daily until around xmas we're back on a better AFM option than whats in there?

Simon