Advice on CJ 6-258 Engine Restoration: Injection vs. Swap -
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post #1 of 10 Old 07-16-2017, 04:39 PM Thread Starter
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Advice on CJ 6-258 Engine Restoration: Injection vs. Swap

Hi folks,

Been awhile since I have been on this forum, so long that I had to create new account (can't remember old email). Anyway, I have owned my 1981 Jeep CJ5 since 1990 and it was my daily driver thru college and beyond for several years. It has a 2.5 inch lift as its only major mod. As many of you, I constantly had carb issues with the stock I-6 258 engine... and tried several Weber solutions and even a Ford carb conversion from Ebay. The last one was so bad that I could never get the engine to run right. She has now been sitting for about 5 years since she last ran. Although the reason for not running is more of a carb issue, both the engine and tranny were very tired and really were in need of a rebuild.

Luckily, I have approval from the wife to finally throw some money and time at my Jeep to get her running again. Thus, I am willing to start at the basics and do it right. My question is shall I go with fuel injecting the stock inline 6 and get it rebuilt or just go with one of the more common Chevy 6 cylinder swaps? I have a buddy that did the latter (along with a matching tranny) and he swears by it. However, I was always eyeing that fuel engine kit, new distributor, computer, etc. to eliminate my carb issues and part of me likes that route since it will keep it closer to stock.

One factor that may impact the route I take is that I will likely have to pay someone else to do this. Although I could have probably handled the fuel injection conversion myself, the engine rebuild/swaps are beyond my capability and to be honest I just don't have the time anymore to do any major work like fuel injection conversion. Is the cost in labor/parts for both similar if a shop were to do them and if so, does that make one excel over the other?

What are most doing now? Would love to read some pros and cons about fuel injecting/rebuilding stock engine vs. entire new engine/tranny swaps. In the end, I am not looking for a huge performance gain with a new system. I am looking more for reliability, safety, and off-road function. I don't want a drag racer (have another vehicle for that). If a engine swap/tranny is significantly better performance/reliability wise then I can overlook the cool factor of having a more stock setup. If there are any recent posts on this topic feel free to share the link.


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post #2 of 10 Old 07-16-2017, 05:18 PM
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Unless you already have a built engine lying around the garage, rebuilding your stock engine and upgrading to FI will be cheaper, faster, and probably a lot less headache. With both engines, you have the cost of the rebuild that will be more or less comparable between the two. With the swap, you also have the cost to adapt the engine to the frame and the transmission to the transfer case. Both of those can add up. Not to mention adapting your wiring harness to the swap engine harness.

I went through two engines before settling on my current 4.3L V6. The stock 2.5l was way underpowered and one of the previous owners swapped in some weird carburetor that I was never able to identify. Engine #2 was a free 258 with a flat cam that a buddy gave me. I installed a cam and lifter set, new bellhousing and input shaft to mate it up and away I went. I never had any complaints about the HP or torque, but the 10 MPG if I was lucky got old quick. I had the 4.3L and complete wiring harness lying around, so I tried that. I like it. My B-I-L installed an MPI kit on his 258 and that performs just as well as my V6. He claims 18-22 MPG (suspect IMO), I get 15-18 mpg. (He bought a chopped up stock wiring harness and manifold off eBay. I spliced it all back together and identified the wires he needed to hook up. Time consuming and a pain, so I don't do that work anymore.)

With most of the fuel injection kits, the average jeep owner should be able to do it themselves. HESCO used to make MPI conversion kits, but I don't see them on their website anymore (probably because new factory parts are no longer available, but eBay still has a bunch). They do have the MPI wiring harness and the balancer kits.

I would recommend swapping the 4.0L head onto the 258 lower end. Get the head, intake/exhaust manifold with throttle body, distributor, and computer, then buy the harness, crank trigger balancer kit, and new sensors. HESCO does still have the MPI wiring harness and the ballancer kits. (I have seen whole Cherokees with the 4.0L HO engine go for $200 on Facebook and Craigslist, so getting all the parts shouldn't be an issue if you shop around.)

Oh, in my experience, if a shop charges $100/hr for regular repairs, then customization will be $200/hr or will take twice as long as it should. Jaded? maybe. But such has been my experience.

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post #3 of 10 Old 07-16-2017, 06:14 PM
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Hello APMS2017, maybe I can be of help as I am doing the exact same research right now. My main concern was the transmission, I didn't want to have to swap it out and didn't want to re-adapt the Dana 300 to another transmission. Nor did I want to have to change mounts and drive shafts, so the V8 option was not in my book unless I did the GM 4.8 and then I would still be on the hairy edge of killing the transmission.

First, by far the simplest and easiest is the swap to an aftermarket EFI kit. The Howell system comes to mind, they use an older GM two barrels Throttle Body Injector system (TBI) unit and the ECM 1227747, the 747 is probably the most popular ECM to use, robust and was used in all kind of GM vehicles so it is a tried and true system with all factory parts. A little clean up under the hood and away you go. That said, you still can get parts with ease. So for about $1300 you can be up and running. Power brakes could be an issue as the original air cleaner lid will be way to small for the TBI opening.

Now, the GM V6, you want the 90 degree not the 60 degree. Tons of them out there and pretty dirt cheap. What you want to look for is the RPO code LU3. Quick search on Ebay and you' find tons of drop outs, complete motor, from head to toe and low milage for around $600-800. You'll need fly wheel,$300 and clutch $200 and bell housing $400. I have an email out to one of the vendors who supplies the V8 with a standalone ECU and wiring harness, so I am waiting to see what that runs for a V6, if they will do it.

Pros and cons. The EFI kit uses a lower fuel pressure so fuel pumps are not a problem. Its also a batch fire Manifold Absolute Pressure system so its not going to be perfect, but pretty good and far better than a carb. Older tech on the motor for the straight six, its a tractor motor. But it will be far more original which is what a lot of folks really want for a DD thats to be mainly street and light trails. I do notice the more original the higher the selling prices are.

The V6 will shift the engine weight back further giving you a better center of gravity and improve handling. HP increases will be around 60HP, torque is not a lot more, but is on a flatter curve through the RPM, better all around performance. You'll need the high pressure fuel pump in the tank, cooling purposes and probably a 20 gallon tank, things keep adding up in cost.

Thats just a start, hopefully other will chime in
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post #4 of 10 Old 07-17-2017, 05:55 AM
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I have a 258 with a Weber 32/36 DGV (Manual choke). I bought an assortment of jets to fine tune. Bought a Summit HEI distributor, added an electric fuel pump and got rid of the stock manual fuel pump. So, I do not have any computers to worry about, get 15-17 mpg, run 60 mph @ 2400 rpms. Still (generally) looks stock but runs much nicer. Re-jetting the carb is a little aggravating but doesn't take more than an afternoon of adjusting.
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post #5 of 10 Old 07-17-2017, 12:33 PM Thread Starter
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Great ideas guys. Thanks so much for the info. I am really leaning toward just getting the Fuel Injection kit for my 258 and getting her rebuilt. I may even try to do the install myself but I doubt it will run perfect even if I do all the injection work correctly. But I guess it could save me a few bucks and then take it somewhere to do a engine rebuild and give me some options with the transmission as well. I know at one time the Howell system was the way I was leaning. Sounds like that is still the best choice. Dryseals, lets trade some notes as well and let me know if you have some posts or links that have helped you with your decision process.
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post #6 of 10 Old 07-17-2017, 01:28 PM
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Have you thought about doing a 4.0 swap? No need to change motor mounts or bell housing. Look for a 92-95 4.0 from a wrangler and it's pretty much a drop in (well, nothing is ever that easy, but it's pretty simple) and you get MPFI built in.
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post #7 of 10 Old 07-17-2017, 01:37 PM Thread Starter
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Sounds like something to look into but would have to deal with emissions, etc. to make it work with my year model (of course I would need to do the same if I went with a newer Chevy V6). I would definitely need to get someone that has done that before to do it. But this is good info and gives me some options to discuss what I should do with a good shop.
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post #8 of 10 Old 07-18-2017, 11:45 AM
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Having done several 258 EFI conversions, including Howell kits and DIY setups, you're money ahead to find a 4.0 and swap it in. It's more work than an EFI kit, but the results are worth it. The 4.0 would not require adapters to bolt in to your frame or to the rest of your existing driveline. It's a well documented swap on the web.
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post #9 of 10 Old 07-19-2017, 12:49 PM Thread Starter
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Hi, thanks for the update. Do you know of a good link that documents the 4.0 swap... even a good thread here to get me started. Thanks!
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post #10 of 10 Old 07-19-2017, 03:54 PM
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Here's a good place to start...

California 4.0 OBDII Engine Swap
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