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Unread 02-27-2015, 09:03 PM   #1
RSWoody
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Engine ideas 1990 yj

I am currently running a 4.2 liter inline 6 in my 1990 yj. It has now power and I have already changed over to the motorcraft 2150 carb, and a HEI electronic distributor. SO.....what's next?? I really don't want to go to a V8 cause I know it will be a lot more work than I want to do right now. Is there a way to build my 4.2 to make it stronger?? Any and all information and ideas is greatly appreciated.

Thanks,

Jeepster

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Unread 02-27-2015, 09:33 PM   #2
Luuca
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Quote:
Originally Posted by RSWoody View Post
I am currently running a 4.2 liter inline 6 in my 1990 yj. It has now power and I have already changed over to the motorcraft 2150 carb, and a HEI electronic distributor. SO.....what's next?? I really don't want to go to a V8 cause I know it will be a lot more work than I want to do right now. Is there a way to build my 4.2 to make it stronger?? Any and all information and ideas is greatly appreciated.

Thanks,

Jeepster
Welcome to the forum RSWoody!

How long have you had it?
Did the power recently go away or has it always been like this?
How many miles are on it?
Have you run a compression test on it?
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Unread 02-27-2015, 10:09 PM   #3
mickcollinsb16b
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Put a 4.0 head on it with MPFI. lots of threads on how to do so and welcome to the #1 Jeep source.
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Unread 02-27-2015, 10:24 PM   #4
mike134
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I know that people/magazines were saying the Mopar MPFI upgrade adds 60-100 hp to the engine.

However, the stock 4.2L is a great engine and shouldn't really be bogging down much. You really need to figure out whether your engine is running properly before going through the expense of fuel injection (~$2000). We're really going to need more info from you, like tire size, gearing, service history/mods.

Take Luuca's advice and do a compression test.

Then take my advice and install a vacuum gauge: http://www.jeepforum.com/forum/f12/b...ealth-2841418/

The combination of these two tests will tell us about your engine health.

Do you live at high altitude? or did you purchase your jeep from a high altitude location?

In addition to this, I recommend making sure your maintenance is up to date (hopefully you do all of these regularly!): new Champion copper core spark plugs (not platinum!!!), plug wires, distributor cap (sounds like you've done this), new fuel filter, new clean air filter, make sure your air passage to the air box is clean and clear, rebuilt carb (sounds like you already installed a new one), oil, oil filter, differential fluid, transmission fluid, transfer case fluid, brakes (make sure a caliper or shoe isn't dragging!)

With all that said, I love my 89 4.2L MPFI engine!
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Unread 02-27-2015, 11:20 PM   #5
ShiJon
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Tire size and gear ratio? Alot of jeep owners find this is the best money spent if the combo is off.
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Unread 02-27-2015, 11:24 PM   #6
mickcollinsb16b
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MOPAR conversion for the 4.2 is a really good upgrade over pulse air electronic feedback stepped motor carb set up the 4.2 came with. But the head design ant intake manifold is no where as efficient as the 4.0. They typically run out of power at above 3k rpm with the fuel injection conversion. It's really expensive too. With the money spent you could do the full 7120 head with the MPI conversion.
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Unread 02-27-2015, 11:33 PM   #7
RedJeepster1
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Everyone will have their own opinions on this, but if you don't wan't a V8 and want more power, stroking the engine is always an option. I spent a little under $2000 when I was all said and done to bore my engine 30 over and stroke it. I also ditched my old carb and went with MPFI in the process. I had multiple spare engines and a donor Jeep with the 4.0 harness so that kept the cost down. I did the entire swap in a weekend, including rewiring everything for MPFI and switching to an ax-15 and 23 spline transfer case. Jeep was only off the road for 2 days and the difference was unbelievable. Its like driving a whole new vehicle, and when I open the hood, no one can tell I even changed anything. This is certainly not the only way to go, but its definitely a good option. Just my 0.02
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Unread 02-27-2015, 11:35 PM   #8
mike134
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Quote:
Originally Posted by mickcollinsb16b View Post
MOPAR conversion for the 4.2 is a really good upgrade over pulse air electronic feedback stepped motor carb set up the 4.2 came with. But the head design ant intake manifold is no where as efficient as the 4.0. They typically run out of power at above 3k rpm with the fuel injection conversion. It's really expensive too. With the money spent you could do the full 7120 head with the MPI conversion.
You do get the 4.0L intake manifold included with the MPFI kit.

I have heard the new 4.0L head helps a lot as well though, like you are saying. I'm actually not sure whether mine has that.
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Unread 02-28-2015, 01:30 AM   #9
mickcollinsb16b
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That post wasn't proof read. No other way to get the injectors on the motor without the log manifold.
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Unread 02-28-2015, 03:09 AM   #10
Chrisnvegas
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Although I have the 4.0 and love it, I would take a 4.2 any day. It's also a great six.
Assuming it is not worn, I would wake it up like I did on my (late) CJ7.

I put in a performance cam with all the fixins' (new lifters, pushrods, rockers, valve job ect) a header and performance Offenhauser intake and a Holley 390 4 barrel. It woke up and would pull pretty good to 4000+ rpm.
It also sounded great and got decent fuel mileage if I could keep my foot out of the secondaries.

It would just about keep up with a Fiero GT with two hot chicks (in the Fiero, not the Jeep unfortunately but I tried)
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Unread 02-28-2015, 04:52 AM   #11
roadyrob
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there are lots of good ideas already posted. as you already have the carb and ignition done I'd get a better cam and do some head work, either a 4.0 head or port yours and mill it to up compression. don't forget the exhaust, going to a 2 1/2" high flo cat and muffler will really help.
also, fill out your profile so we know more about your jeep, especially present gear ratio and tire size, if your running something like 33's and stock 3.07 gears then a gear change should be at the top of the list of mods.
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Unread 02-28-2015, 07:11 AM   #12
fishadventure
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Quote:
Originally Posted by RedJeepster1
...spent a little under $2000 when I was all said and done to bore my engine 30 over and stroke it....02
What pistons did you use?
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Unread 02-28-2015, 09:20 AM   #13
jsawduste
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Quote:
Originally Posted by RedJeepster1 View Post
stroking the engine is always an option. I spent a little under $2000 when I was all said and done to bore my engine 30 over and stroke it.
You don`t make a stroker by simply boring a 4.2.

Fish, I am on my 4th stroker build this year. Gathering parts today for another. Bulltear for stock ish or Diamond for everything.
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Unread 02-28-2015, 10:47 AM   #14
Luuca
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Makes no sense to look at the expense, time, and headaches of an engine or head swap if we have not verified the existing engine is dead.

IMO it may be something minor that restores adequate performance at a fraction of the cost. No offense to the OP, but I often feel that posts like these are less serious about an engine swap. I base this on having removed and installed over 20 engines in my lifetime an my knowledge that while not impossible for the average person, it takes a special type of person to be willing to do that much work at their home.

Posted via my pretentious iPhone.
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Unread 02-28-2015, 04:39 PM   #15
jsawduste
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Quote:
Originally Posted by Luuca View Post
I base this on having removed and installed over 20 engines in my lifetime an my knowledge that while not impossible for the average person, it takes a special type of person to be willing to do that much work at their home.

Posted via my pretentious iPhone.
Well said, and often overlooked till your in so deep there is no way out.

While I do plenty of stroker builds I do not remove or install engines, unless it`s my own junk. That`s been 8 years on this stroker.

To old, to impatient and not willing to extend that much effort.
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