So the engine blew a rod on my 86 740 and I put the block from an 86 240 in it and it won’t start. Is there any difference between 240 and 740 blocks. Is there any different sensors that would prevent the engine from starting? I put my 740 head on the 240 block. Would I be able to run the 240 dist wiring on a 740 harness? Am VERY stuck and need assistance

 

There should be no difference in the blocks. The heads, yes, the 240 has a front distributor, the 740 rear mounted one, but you swapped those even though you didn't have to, my 940 has a front mounted distributor like a 240--many '93-'94 940s do. The harness, hmm, there may be some differences there, how do they look side by side?

 

they look exactly the same side by side I believe. Which connector on the wiring harness would I need to splice into so I could run the Hall effect wires from the 240 dist to the 740 harness. Where does the 240 and 740 get their crank and cam signal from

 

The 240 also has a Hall sensor in the distributor... like the 740... Just compare the two harnesses, splicing the Hall sensor coaxial cable is tricky but it should be OK, just insulate it well...

 

there’s no Hall effect connector attachment on the 740 dist. I found where the connector would have been on the 240 dist had it not been cut off. I don’t remember disconnecting a sensor from the 740 head when I removed it

 

An '86 740 with B230 should have a Hall sensor in the distributor, at the base, the Crankshaft Position Sensor started in 1990... If it doesn't, well, I don't know... Post some pictures of the original distributor.

 

I have a CPS in my 89 740 gl.

 

Well, OK, late '89... generally what they list for 1985-1989 distributors is a hall effect ones... Point is, a b230 has a CPS or a Hall effect distributor...

 

CPS is a crankshaft or camshaft position sensor?

 

B230 motors don't have camshaft sensors, (~89+) some have crank position, top rear of engine block looking at a shutter wheel on the flywheel.

 

so my 86 would have a camshaft sensor right. On my old engine it had a spot for the crank sensor but it was never plugged in

 

None of the LH systems used for the 240, 740 or 940 had camshaft sensors (well, maybe the dual cam version with which I am unfamiliar). Crankshaft position sensor started in '89 with the introduction of the LH 2.4 version of the fuel injection. 740 turbos in '89 still used LH 2.2.

 

The crank sensor fits in a cutout in the top of the transmission bellhousing - if you had an empty hole in the top of your bellhousing - that transmission came out of a later car. If you are talking about that unused sensor kinda halfway down on the right side looking like it might point toward the flywheel - that is not used in any car - maybe during manufacturing it's used.

And as others have said the b21, b23, and b230 engines (4 cyl, overhead cam, aluminum head, steel block) do not have cam sensors. Either there is something in the distributor to tell the Ecu/Icu where the engine is or there is a crank position sensor. Both front/block mount, (under the thermostat housing) and cam mount (on back of head) distributors on cars with a crank position sensor are empty inside - other than a rotor button.