I've been calling around about the Mopar MPI for the 258. I have been told that they will only bolt on with a 1982 engine or newer. Is that true? and if it is true what is the diffrence between my 79 and an 82 or newer engine. Thanks

First off, I can't think of anything that would not allow you to use an earlier engine.

But, you definetely do NOT want the Mopar MPI. They should not even be allowed to sell those things.

The biggest problem is the pinging. After you spend $1600+ for the kit, folks will recommend you swap the head for 4.0. And that may help.

You would be way ahead to buy a good 4.0 and swap the complete engine. Those parts were designed to run together.

And with the money you save, go buy yourself a set of 38" SX's.:D

Originally posted by Bob/CA
First off, I can't think of anything that would not allow you to use an earlier engine.

But, you definetely do NOT want the Mopar MPI. They should not even be allowed to sell those things.

The biggest problem is the pinging. After you spend $1600+ for the kit, folks will recommend you swap the head for 4.0. And that may help.

You would be way ahead to buy a good 4.0 and swap the complete engine. Those parts were designed to run together.

And with the money you save, go buy yourself a set of 38" SX's.:D

basicly what I was gonna say

On early 258's with the cast iron intake, the exhaust manifold is bolted to the intake, to make the EGR connection.
All you need to do is swap in a newer style exhaust manifold with the tube style EGR connection.
Or use a header.
Have you looked into the Howell EFI?
Mine works great, is less$$$, less parts to swap.
I would do a complete 4.0 swap before I put the MPI on a 258.

Scrahara (CTjeepnut)

Originally posted by Bob/CA
First off, I can't think of anything that would not allow you to use an earlier engine.

But, you definetely do NOT want the Mopar MPI. They should not even be allowed to sell those things.

The biggest problem is the pinging. After you spend $1600+ for the kit, folks will recommend you swap the head for 4.0. And that may help.

You would be way ahead to buy a good 4.0 and swap the complete engine. Those parts were designed to run together.

And with the money you save, go buy yourself a set of 38" SX's.:D

Bingo! I was one of the unfortunate bastards that got sucked into this mistake. Thought it would solve all my problems. It only created more. It was a VERY dissapointing experience.

I eneded up selling it at a huge loss and threw a 5.7TBI chebby in and THAT DID solve ALL my problems. For about the same or less money.

I have a firend that put one in an 81 and an 82 neither ping, however all the 83-86s that I have seen ping like hell.:eek:

Let's get a few facts straight first...
1. Yes, you can swap an MPI onto your early head.
Reference: AMC 258 4.2L Block, Crankshaft & Head Casting Numbers (http://www.monsterslayer.com/jeep/258CastingIDs.htm)
2. No one has EVER said you should attempt an MPI swap on a tired 4.2 mill. Don't do it!
3. Most 4.2 folks who experience pinging problems with an MPI are running 1981--85 heads ... especially 1983's.
4. A 4.0 HO head swap WILL end pinging problems.
5. Those who always say "swap in a used 4.0 instead" are telling you to pay yer money and take your chances on someone else's junk.
6. A well built 4.2/4.0HO head/MPI mill will kick butt on ANYBODY'S stock 4.0.

I have two question. I have an SM420 bolted up right now to my 258. If I decide to swap in a 4.0 will my SM420 adapter work. I don't want to buy another adapter.

Forgetmysecondquestion. If I decide to buy a 4.0 head, whats the best year and what all will I need to do. I know I will need to fill in the water jackets sticking out.

My friend has $5k into his fresh 4.2 w/ mopar MPI. Professionally installed. And it pings running 92 octane w/ octane booster. If it does not run like they advertise it should, then they should not sell it.

Besides, he could of had a V-8.:D

I have about $1200 into my 4.0 swap, including AA bellhousing.

Mopar MPI does not have the output that the factory 4.0 has. Only a 20% increase. Sure a "well built" 4.2 will run good, but so will a "well built" 4.0.

An adjustable fuel pressure regulator and adjusting timing in the computer will usually cure pinging .

An adjustable fuel pressure regulator and adjusting timing in the computer will usually cure pinging .

A buddy of mine has tried everything. Adjusting the timing just changed the pinging from 40mph to 50mph. He did start with a fresh motor. Another buddies pinging was so bad he blew a hole in one of the cylinders of his fresh 4.2 after 7k mi.:flipoff2: 4.0 swap is the only way to go.:smokin: If you want more balls, stroke it!!!!:smokin:

By the way, if you install a Mopar MPI on a 4.2 the MPI stands for "multi pinging injection".:flipoff2:

ok for my XJ and for my Next project (CJ) I am building Strokers.
Get your hands on a older 4.0 out of a XJ that has the Renix system The older ones are better at not getting ping do to the knock sensor. (has MPI Already) and rebuild it using one of the Kits (I am doing the budget stroker but if I had to do again I would use the Accurate Power one. However Hesco and Clifford Make one as well. This will give you a Fresh 4.5 up to 4.9 Engine with MPI that is dependable.