4.0 fuel injection on a 258

[grand_wag_85]

Looking to throw a 1990 Renix head and fuel injection system on a 4.2L I6. I will be getting a 4.2 short block and have a 1990 4.0XJ with a seized crank at my disposal. It's all going into an 82 J10. I would like to use as many parts that I already have on hand as possible but will do whatever it takes to make it all work.

Will the 'ECU' be able to handle the extra 0.2L? Also, what all wiring will need to come out of the XJ in order for me to swap the fuel injection system over? I plan on running an AX-15 but the XJ that is donating the parts has the AW4, will this cause trouble or is the tranny on a different computer than the engine? Can I run the 4.0 distributor on the 4.2 or is that apples and oranges? If I remember correctly there is a hole in the tranny bellhousing for the CPS, I'm guessing I will need to run a 4.0 flywheel rebalanced to a 4.2 or does the balancing not matter on this setup?

I'm assuming that the alternator will need to be swapped as well.

Fuel pump wise can I mount an external pump on the frame rail or does it have to be in the tank.

Anything else I might have overlooked? I'm sure I will have more questions.

Thanks for the help!

[ThisGuyUKnow]

cjoffroad.com has a section soley dedicated to putting in 4.0s and 4.0/4.2 hybrids you may want to post up there as most the tech will apply to any 258 powered vehicle.

This is exactly what I want to do with my 4.2l in the girlfriends cj but I still have a huge project left on my wagoneer.

[grand_wag_85]

Thanks!

[cu4whln]

SO - a few answers of sorts..

The dist will work. Parts are very interchangeable between 4.2 and 4.0L

The ECU will not care if you run a manaul. The AW4 had a seperate cotroller. The ECM will set a fault, but it will not affect the basic engine running situation.

As for the CPS - Not sure if the flexplates swap? I would think so - but you'll have to find that info somewhere else.

Mopar makes a CPS relocation kit for the SBEC based system. I am not sure if this is compatable with the RENIX sysytem. Bacically, they machine a front damper with windows that send the signal. The CPS mounts off an adapter bracket on the oil pan. I run that on my 258 with fuel injection. [ I have an extra V-belt damper with bracket if you find that will work ]

Mopars injection kit is based on a 95 YJ setup. I just pulled all the engine harness, it goes all the way back to the t-case speed sensor, then tank to run the fuel pump. Use a factory manual toi trace wores/colors. The Mopar kit even has the same colors as the production YJ !

Good luck - This was the best engine upgrade ever for my CJ - I run a 4.0L head on a 258 btw.

[ThisGuyUKnow]

dumb questions but: is the only difference in the 4.0 HO and the standard 4.0 the design of the head? Are there any solid figures on how the 4.0 head affects the output on a 258? Were the HOs offered as an option or was it the standard engine after a certain year? And finally if you were planning to junkyard a MPI would you get better performance by finding a HO head and mating it to the 258 over the standard 4.0?

[addicted]

dumb questions but: is the only difference in the 4.0 HO and the standard 4.0 the design of the head? Are there any solid figures on how the 4.0 head affects the output on a 258? Were the HOs offered as an option or was it the standard engine after a certain year? And finally if you were planning to junkyard a MPI would you get better performance by finding a HO head and mating it to the 258 over the standard 4.0?

The Renix head has higher intake ports then the 258 head for improved flow into the cylinder. The 4.0 has even higher ports for even better flow, but they are basically the same. The 258 head has a nasty 90* angle before the intake port turns down into the cylinder. The H.O. allows the air to flow into it on a downward angle without any turns.

I haven't seen actual figures but it doesn't mean they aren't out there.

The H.O. engine was the only 4.0 after '90 it was introduced for the '91 model year and replaced the Renix 4.0 in the XJ and MJ and the 258 for the YJ.

Yes, you would get better performance from a H.O. swap then the Renix.

[1983 j10]

the ho also has a better fuel system and inproved intake manifold and exhaust manifold. and the 4.0 was also offered in the mj and yj.

[addicted]

the ho also has a better fuel system and inproved intake manifold and exhaust manifold. and the 4.0 was also offered in the mj and yj.

YJ didn't get the 4.0 until '91 when the H.O. came out

[grand_wag_85]

YJ didn't get the 4.0 until '91 when the H.O. came out

Yes the YJ had the 258 thru 1990 *but supposedly* you could special order a 1990 YJ with a Renix 4.0. The Renix motors were used in XJ's and MJ's from '87-'90 but you could order a super late built '86 with a 4.0. The 4.0 High Output was redesigned again in either '97 or '98 IIRC.

cu4whln-I would love to see a picture of that damper setup on your CJ.

[1983 j10]

yes thats what i ment.

[Cecil14]

Given the choice I would go for the HO system over the Renix setup any day. Reason is simply popularity. There are a TON of HO vehicles and support out there...support for the Renix setup is pretty slim as it was on around for ~3 years.

With that said, either system should work fine for you. Just grab everything you can from a donor vehicle if possible. All the sensors should move over just fine AFAIK. If you're using an AX-15 the CPS should bolt to it just fine.

As for the ECU...I know the AW4 had a separate computer up to '96 (I believe it was merged with the introduction of OBDII). On my HO setup I simply pulled the wires that went to the trans controller. There was only 3 or so I think...TPS, VSS, and power, I believe. I would bet the Renix computer is real similar. My HO computer isn't "aware" of the auto computer at all, no codes or anything. The signal from the sensors was simply split to both computers.

Alternator is kinda your choice. The 4.0L alt is externally regulated (through the ECM). I went serpentine on my stroker but did not use the 4.0L alt. They're expensive and I don't like the remote regulator. I first ran the stock 10SI then upped to a CS-144. Either can be made to work with a serpentine pully and a few home made brackets. If you do go serpentine you'll need this spacer:

http://hescosc.com/shop.asp?action=details&inventoryID=45565&catId

This thread may help on your alt choice...not exactly the same situation but similar:

http://www.ifsja.org/forums/vb/showthread.php?t=113645

Fuel pump, again, is pretty much your choice. Not sure what the PSI requirements of the Renix system are (~30PSI maybe?). I know the HO system requires ~38-45PSI. The fuel rail I got ('94 XJ) had the pressure regulator on the fuel rail. In tank pumps tend to last a lot longer as the fuel in the tank keeps them cool and primed. External high pressure pumps are pricey (so are in tank high press pumps). I've heard good and bad experiences with external pumps...I chose to go internal and upgraded to a 42gal suburban tank at the same time I did my FI upgrade.

Feel free to ask any other questions you've got. The wiring is really the most intimidating part...get a good wiring diagram and take your time. It's really not that difficult.


aa

[ThisGuyUKnow]

ok thanks for the clarification on the HO. Cecil i know you and I have talked this issue to death

Another dumb question I have been curious about is how does the distributorless setup on the later 4.0s work? i kinda picture them like putting a faux dizzy stem in the place where the dizzy originally would have been Haha

[addicted]

ok thanks for the clarification on the HO. Cecil i know you and I have talked this issue to death

Another dumb question I have been curious about is how does the distributorless setup on the later 4.0s work? i kinda picture them like putting a faux dizzy stem in the place where the dizzy originally would have been Haha

That is exactly what it is. It is a sensor much like the pick-up in the distributor only now it is known as the cam sensor. It is used to tell the PCM where the cam is in it's rotation and to drive the oil pump.

[Cecil14]

Yup...exactly what Simon said. It still spins just like the dizzy did. The computer takes that reading and triggers the coil packs accordingly. I was contemplating trying that on my HO setup...but I don't believe the earlier computer has the leads to trigger the individual coil packs like the later ones do. Probably something that can be done with a megasquirt setup, though, if I ever get that far. On the HO type computers there was only one coil so it just sent that signal each time it gets to a cylinder (6 times per cam revolution). The dizzyless setup gives each coil a whole revolution to re-saturate...so you get a LOT stronger fire on each cylinder.


aa

[grand_wag_85]

Lots of good info here!