I bought a 1997 XK8 with the engine and box down, I sourced a 4.0 engine from a 2001 XK8, the mechanic I used has put the 1997 cams and VVT gear in the new engine, changed the bottom casing as the 1997 had oil cooler pipes where the 2001 was just blanked off.

he's used the old inlet manifold injectors and throttle body , the problem is it won't fire on 8 cylinders, at the moment it's only running on 4

01 05

02 06

03 07

04 08

Front

Viewing the engine as above 1 and 4 are firing as are 5 and 7 he pulled the electrical connector form each fuel injection rail and the engine note didn't change when the above number were disconnected ie getting no fuel.

he timed the car up by removing the crank sensor and fitting a pin then locked the cams in each bank in turn as we only had one cam locking tool.

Basically all he's used from the new engine is the block and heads though he did just fit the cams ie didn't change any of the buckets or shims.

any idea why it'll start and run but only on 4 cylinders as i'm one step from pushing it down the hill with a lit rag in the petrol tank

 

wack, personally to me it is sounding like the engine is running in a protective mode. How is the engine coolant sensor reading on the motor. If this is reading hot (ie, higher resistance), the engine will attempt to fire every other cylinder and let fresh air run through the others by not injecting fuel into the cylinder. This is done to help cool the engine due to the cold air being let in.

The only other common thing that I can come up with is the ECU has a problem, and is therefore not allowing the signal to get to those 4 cylinders. This is where putting the ECU on a computer and watching the values displayed by the computer will tell you what is going on. You can't use a generic code reader to do this. You are going to need your mechanic to attach one of the $3000 readers.

Hope this helps. It isn't a ground issue as all of the injectors have individual power wires coming from the ECU and a single common ground wire.

 

the temp sensor is reading normal on the guage it's definitely working as the car won't start when it's low on water. I think you're correct re the scanner, the garage next door has a snap on scanner which cost £2000 so I think that's what we need.

Thanks for the advice