87 RR gas problem

[Jhonno]

Hi Folks
Hope someone can through a little light on this problem on this problem for me, first a little background info it is an 87 3.5 dedicated gas, still has all efi components except air flow meter, previous owner said it was destroyed by backfire, when I picked it up had to fit a new convertor, as it was positioned on the left hand skirt close to the exhaust I fitted a heat shield, the mixer is an impco 200. There has been the occasional back fire on startup, just recently it has started to be quite difficult to to keep running whilst in gear at lights etc, if it stalled it would start instantly. A few days ago my son managed to run it out of gas (gas guage decided to read full all the time) in the proccess there was numerous backfires, now it cold and hot starts immediately, idles at 1000 smoothly, engage drive or switch on the air con revs drop till engine stalls, approx 5/10 secs, if you switch off the gas the engine may start after about 15 secs of continual engagement with throttle wide open, but usually you have to prop the diaphram in the mixer open a little and leave the gas of until she fires. there is a high pitched whistle at idle, placing a finger in the mixer air intake near the block the noise ceases, no change in engine revs.
Any feedback on this problem would be greatly appreciated, it is driving me nuts.
Thank you

[DeeJay]

Primary cause might be an air leak somewhere, maybe vacuum hose?
Secondary cause might also be spark plug leads or plugs themselves, or a combination. It appears though that the engine is not getting correct mixture via air ratio.
Bear in mind also that you can get dodgy LPG sometimes, its rare, but I reckon I copped a bad tankfull with only the second fill after my County was converted. If the mechanic was'nt away on holidays, it would have gone back to them, but a new fill seems to have cleared it away.

[POD]

Any chance you may have popped a hose off the plenum somewhere with the backfiring? Have a good look at every hose you can see- can't quite recall which ones used to pop off on mine when I had backfire problems for a while a few years ago. The air bypass pipe and the stepper motor I think. However if this is the case with your engine, it sounds like possibly one of the small hoses, perhaps the fuel pressure reg vacuum hose at the rear of the plenum.

[V8Landy]

I would check for a vacuum leak first check the hoses for cracks or splits. I would pull out the stepper motor and clean with carbie cleaner. change your plugs and leads maybe a new dizzy cap and rotor. Get your mixtures right and all should be sweet:eek: