v8 efi viteese will not idle and seems permanently off a couple of cylinders. have checked spark at all plugs and seem ok. starts pretty good in this state but bloody horrible to drive, including backfiring in the exhaust, any ideas ?

Hi,
What condition is the engine in?

Could be many things, but is the camshaft lobes worn? whats the mileage?

low milage, and a very quiet engine. will try to get compression test done tomorrow, and see from there. thanks

Are all the injectors firing?

A quick check for this is (engine OFF, ignition ON) to remove the connectors
to the 8 injectors, then try reconnecting one at a time and quickly press
the accelerator. The ECU still tries to enrich the mixture when the throttle
is opened quickly, even with the engine off. You should hear the injector
'click' as it opens.

all injectors seem to be firing, plugs replaced, leads checked for crossfiring etc, new rotor arm and cap, compression good at 175 - 180lbs in all cylinders, have upped idle speed just to gain idle but is definitely off 1 or 2 pots all the time regardless of rev range. now have to look at dizzy i think. or any ideas ?

Bearing in mind the tests you have already done, with the engine running, if you remove one spark plug at a time it should be possible to tell which cylinders are not firing because disabling the non firing cylinder will make no difference to the way the engine runs.

If you have sparks on the discovered cylinders then it may be down to a fuel blockage in some injectors because you say that you heard all the injectors clicking.

If it turns out to be the injectors they can be tested/serviced in the workshop according to some notes on the PDF to be found here:

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or you can replace them or they can be professionally cleaned.

New Theory.

Now as to the backfiring in the exhaust this indicates unburned fuel/air self igniting when the hot gasses from other cylinders are exiting. That would indicate that you have do have a spark problem on 1 or more cylinders.

OR

one of the injectors is stuck open (yet still clicking) so the flooded cylinder does not fire but the fuel/air in the exhaust system is self igniting.

For ignition problems dont overlook the ignition amplifier which can go wonky before it completely gives up the ghost.

Good luck

many thanks , it was two injectors, both to the rear one on each side, clicking slightly but obviosly when replaced with two that were clicking upon full throttle with a heavier clonk, hey presto.many thanks once again, especially to jrv8 who supplied the parts and said he would put money on the injectors being faulty. cheers.