2 injectors not firing

[paul mc]

My 3.5 V8 Efi flapper runs lovely on LPG but not on petrol. When idling on petrol it hesitates severely when the throttle is applied.

I pulled all of the HT leads one by one when running on petrol to check which one was mis-firing and sure enough 2 cyliders were missing, the middle two when viewed from the drivers side of the engine bay. I plugged each injector plug into a spare injector and they were not ticking, which suggests to me that a pulse is not being sent to these injectors.

Does anyone know what could be causing this and what I can do to fix it?

I also pulled each HT lead while running on LPG and all 8 cylinders were running properly.

Thanks,

Paul

[Ally V8]

From long ago memory isnt there a resistor pack on the LH shock tower that feeds the injectors ? Many years ago I seem to remember these having corroded terminals resulting in misfires... Silver box,bit smaller than a fag apcket.

[V8david]

Test for the above ^^^ in the tech archive, flapper diagnostics.

[Cynic-al]

Depending on what test equipment you have available see if there's a signal coming. From memory its a 3v sinking pulse? I had loads of resistor packs but I think I've dumped them all now as I've been having a clear out .

I've had the pins corrode off in the injector & plug before as well but the plugs are cheap if you need to replace, I know I've got some of those kicking about.

Although very crude and makes people cringe I've tested injectors before by pushing the hose pipe over the end and applied a voltage for a short period.

[FridgeFreezer]

Resistor pack is very noddy indeed, check the pins are OK. There's no injector signal as such as the ECU grounds the injector pin (with the resistor pack supplying volts to the other pin) to complete the circuit and fire the injector, would show up as an AC voltage across the injector. A low-wattage bulb or "noid" tester (an LED with an injector plug on it) will show you if there's something happening.