Hello all, I'm thinking about replacing my 258 with a 4.0. Yes I did a search of the site but I didn't find all the info. I need so please lend me a hand. I want to install a carbureted 4.0, or maybe put a Howell on the 4.0 that's going in so I don't care about the wiring harness. Also I want to transplant as much as possible from the 258 to the rebuilt 4.0 long block. But does the 4.0 have a serpentine belt? Will I have to replace the harmonic balancer to use the alternator that went with the 258? Will that throw the crankshaft balance off? Do the 4.0 and 258 use the same water pump? Chain cover? Flywheel and clutch? Can you stick the 1bbl or 2 bbl intake and exhaust manifold from the 258 onto the 4.0? Is the pilot bushing outer diameter still the same? Are the motor mounts the same or can I build an adapter or throw in a spacer to make up the difference? Can I still stuff a mechanical fuel pump back into the side of the 4.0 where I assume there is now a plate? Will the 258 temperature and oil sending units work on the 4.0? Will the bell housing between the 258 and T5 mate up to the 4.0? Can I use the distributor from the 258 on the 4.0? What else am I missing? I want to avoid surprises. Your input is appreciated!
eprobe1
Joined
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10,682 Posts
You can drop in the 4.0 complete with all ancillaries but without the injection manifold.
the issues you then have to run it in carbs are:
The 4.0 distributor is fixed, you need a 258 distributor swap. Two minutes work.
The mechanical fuel pump will not work as there is no lobe on the camshaft in a 4.0 for it. Buy a $10 solenoid type furl pump, ideal for a carb.
The alternator on a 4.0 is controlled by the PCM. You need to fit an external regulator. Needs a bit of research because it is not obvious
If the 4.0 is from an XJ Cherokee the water pump will put the fan off centre. replace water pump with Wrangler unit, inexpensive
You will need to fit the 258 manifold to the 4.0 head.
It is all doable but you end up with an engine on carbs but designed for injection. The Mopar MPI is the best injection out there for a Jeep 4.0, a great dry manifold system. Most people do this swap in order to get the MPI fitted.
the issues you then have to run it in carbs are:
The 4.0 distributor is fixed, you need a 258 distributor swap. Two minutes work.
The mechanical fuel pump will not work as there is no lobe on the camshaft in a 4.0 for it. Buy a $10 solenoid type furl pump, ideal for a carb.
The alternator on a 4.0 is controlled by the PCM. You need to fit an external regulator. Needs a bit of research because it is not obvious
If the 4.0 is from an XJ Cherokee the water pump will put the fan off centre. replace water pump with Wrangler unit, inexpensive
You will need to fit the 258 manifold to the 4.0 head.
It is all doable but you end up with an engine on carbs but designed for injection. The Mopar MPI is the best injection out there for a Jeep 4.0, a great dry manifold system. Most people do this swap in order to get the MPI fitted.
Joined
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10,682 Posts
Eprobe, do not let me put you off.
I think it is a great idea!!!!! And the extra bits I identified will not cost you much or take much time to alter.
It is just that I would go the extra 22 yards, 3 weeks of pain and $500 to get the MPI. I have it on my XJ Cherokee and the difference with a carbd 258 is exciting.
I think it is a great idea!!!!! And the extra bits I identified will not cost you much or take much time to alter.
It is just that I would go the extra 22 yards, 3 weeks of pain and $500 to get the MPI. I have it on my XJ Cherokee and the difference with a carbd 258 is exciting.
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