It's a used engine and we've done a compression test and all the cylinders are good. We've checked fuel, got new ignition leads, timing had been double checked.
If you are sure all the timing settings are all correct I would maybe consider less obvious things like the following areas in no particular order
Consider the possibility of a plugged fuel filter or partially plugged injectors, or a collapsed catalytic convertor matrix that is partially plugging the exhaust also ditto for a muffler collapse, possibly a major vac leak although I would expect idle would also be affected, check the throttle position; check the cable is opening the throttle valve completely, last if all else checks out maybe consider a jumped worn timing chain or miss timed cam.
A vacuum gage is very useful as it can help identify excessive exhaust back pressure and incorrect valve timing as well as vacuum leaks..
yep no vac leaks, throttle position is good, all fuel injectors plugged in, all sensors cleaned, new ignition coil, leads and dizzy cap/rotor, definite fuel pressure.
The misfires happen at both intake and exhaust when given throttle, the idle is good (albeit an inconsistent start).
Certainly a cam sensor is a possibility although your engine probably doesn't use a seperate sensor but uses data from the distributer sensor for that purpose, therefore the correct timing of the distributor is important.
In my experience crank sensors usually stop the engine when they go bad, the engine will often restart and run normally but the engine randomly stops again.
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ZJ Grand Cherokee 1998 4.0L engine replacement
