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Unread 05-10-2012, 11:43 PM   #1
dustinslaton
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Difference between 89 and 91 4.0L?

I'm finally about to start restoring my 89 Jeep Cherokee Laredo. It's going to be a daily driver, and stay pretty much stock except for a few toys (2" lift, tire rack, etc.)

My question is about the changes that happened to the 4.0 in 1991 resulting in about 14 more HP. I read that the main change was added multipoint fuel injection. I'm not a big mechanic, so I don't know exactly what that means. Can you help with that?

Was there any other significant change to the 4.0 that year, or any year after that which would make it worth upgrading the motor/components as I'm doing the rebuild? The engine is solid, and ran fine when I parked it 6 years ago aside from oil seal leaks.


Thanks for your help.

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Unread 05-11-2012, 12:21 AM   #2
USAXJ
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Multipoint fuel injection just means each cylinder has its own injector. The main differences were intake and compression I think. Jeep changed the intakes several times throughout the years. Wikipedia is a good source info about the changes.
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Unread 05-11-2012, 12:28 AM   #3
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Quote:
Originally Posted by dustinslaton View Post
I'm finally about to start restoring my 89 Jeep Cherokee Laredo. It's going to be a daily driver, and stay pretty much stock except for a few toys (2" lift, tire rack, etc.)

My question is about the changes that happened to the 4.0 in 1991 resulting in about 14 more HP. I read that the main change was added multipoint fuel injection. I'm not a big mechanic, so I don't know exactly what that means. Can you help with that?

Was there any other significant change to the 4.0 that year, or any year after that which would make it worth upgrading the motor/components as I'm doing the rebuild? The engine is solid, and ran fine when I parked it 6 years ago aside from oil seal leaks.


Thanks for your help.
1987-1990 was pre-OBD ("RENIX", after the control system used.)
1991-1995 was OBD-I
1996-2007 was OBD-II. OBD-II may be further divided into "early" and "late" - "early" OBD-II used the #0630 head, while "late" OBD-II used the #0331 head and distributorless ignition.

The 6-242 has always had MPFI, there's no such thing as a carburetted 6-242 from the factory.

The primary difference between RENIX and OBD is the location of the intake ports in the cylinder head - RENIX has exhaust and intake more or less on the same line, while they were raised slightly for the 1991 Model year. This reduced the angle that the intake charge had to turn through (slightly,) which made the intake port flow more efficient. This can be seen when comparing the raw flow numbers of the RENIX and #7120 (1991-1995) head for the 6-242.

Internally, the engines are otherwise (mechanically) identical. There were some small revisions (graphite coatings on the piston skirts, addition of a main bearing cap brace) in later years, but they're not that significant on a stock engine.

While the "High Output" (OBD-I/II) engine may have had a higher peak output, the RENIX generates its peak output (both torque and horsepower) at a slightly lower crankshaft speed - making those values more useful. People get too tied up in the peak values (marketing tends to depend on that...) without looking at the overall output curve - and it's more important to know the overall output curve than peak power (trucks also tend to be mismarketed by horsepower ratings - it's torque output that's important, and peak horsepower output will always be above 5200rpm anyhow, which makes it relatively too high to be useful.)

If you want more detailed information, it's been done to death - usually by me...
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Unread 05-11-2012, 07:11 AM   #4
cruiser54
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5-90 is right on the money here as usual.
The peak horsepower gains in the HO were primarily due to a 58mm throttle body versus a 52mm throttle body on the Renix and a better flowing exhaust manifold. I'm sure the intake ports helped somewhat but I'm not prepared to give the head ALL the credit.
The 14 HP figurre between the two series of engines is rather large. It's more like 8 HP from the last generation of Renix. From 1987 to 1990, ECU changes added HP fro 173 to 182 on the Renix.

FWIW, I've done the Renix to early HO swaps and they're super easy. Some things to watch out for but no big deal.
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Unread 05-11-2012, 10:28 AM   #5
dustinslaton
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So it sounds like it's not really worth the trouble, and may even be beneficial to keep the 89 setup since it's got better the HP in the lower RPM range?

I'm definitely a fan of NOT changing things unless I have to. I just wish they had a few more bolt on options for pre-91 models.

Now that I know what to look for and terminology I'll do some searching on here and web for Renix and OBD. Thanks guys!
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Unread 06-22-2014, 09:58 PM   #6
PNWxjJeeper
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Quote:
Originally Posted by cruiser54 View Post
5-90 is right on the money here as usual.
The peak horsepower gains in the HO were primarily due to a 58mm throttle body versus a 52mm throttle body on the Renix and a better flowing exhaust manifold. I'm sure the intake ports helped somewhat but I'm not prepared to give the head ALL the credit.
The 14 HP figurre between the two series of engines is rather large. It's more like 8 HP from the last generation of Renix. From 1987 to 1990, ECU changes added HP fro 173 to 182 on the Renix.

FWIW, I've done the Renix to early HO swaps and they're super easy. Some things to watch out for but no big deal.
could you tell me more about the swap? i am currently dropping a 91 engine in my 89 cherokee and am wondering how to do the intake swap. how do i hook it all up to the renix? and i also have an 02 intake that i got super cheap. will that work on the 91 engine and hook up to the renix?
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Unread 06-22-2014, 11:40 PM   #7
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Quote:
Originally Posted by PNWxjJeeper View Post
could you tell me more about the swap? i am currently dropping a 91 engine in my 89 cherokee and am wondering how to do the intake swap. how do i hook it all up to the renix? and i also have an 02 intake that i got super cheap. will that work on the 91 engine and hook up to the renix?
Ask and you shall receive:

Cruiserís HO into Renix Swap

This swap is easier than some will lead you to believe, generally those who have never done it. Those of us who have done it, like myself, will share with you the things that need to be done for a successful swap. Just think of it as swapping in a long block.

The HO and Renix have some differences but none that canít be overcome very easily.

Any HO engine from an XJ or ZJ through 1999 can be used. One running change was that the rear of the head was no longer drilled and tapped for the temperature gauge sender beginning in the 96 model year. The sender can be relocated to the threaded hole in the thermostat housing taken from the HO engine. Youíll have to extend the wire to that location. Some brave souls even drill and tap the HO head for the sender.

You will be using the intake and exhaust manifolds from your Renix, along with all your sensors and wiring. Since the intake ports of the HO are slightly different, you use the Renix gasket. Exhaust ports are identical.
You will need to use your Renix distributor as it is different than the HO because they use different fuel management systems. The flywheel or flexplate from the Renix must be used so your CPS gets the correct signals. The valve cover from the Renix allows you to keep your CCV system intact and requires no modifications.

The HO block will have a plug in the coolant galley on the driverís side of the block, closest to the front, which needs to be removed so your Coolant Temp Sensor can be installed in itís place just as it is on the Renix. It requires a 5/16Ē square drive or a modified 3/8Ē drive that has been ground down to fit. Do this before installing the engine.

As for the knock sensor, which is located just above the oil pan on the driverís side of the engine about mid way, all the blocks Iíve seen are threaded for it. If not, Iíve heard they may be drilled but not tapped. Tap the hole if thatís the case.


Revised 03/28/13
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 06-23-2014, 06:38 AM   #8
Zapa
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I haven't tried any HO Jeep, but I'm delighted with how my 89 Renix performs.
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Unread 06-23-2014, 07:21 AM   #9
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I haven't tried any HO Jeep, but I'm delighted with how my 89 Renix performs.
Yep. Spend a little time eliminating glitches and potential glitches and they're fine.

That's how my Tips evolved.
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 06-23-2014, 11:27 AM   #10
75SV1
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Some people say that the Renix gets a bit better MPG than the HO. While there are more stuff out there for the HO, the main accesories can be had for the Renix with a bit of searching. I didn't find a performance coil for one though. When I had mine running, I didn't think it lacked for power. I do have two '98 Cherokees. I haven't driven the one much. The other the trans slips a bit. Both Autos. My '88 Comanche is MT. I'd say as much power in the driving RPM range as either '98.
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Unread 06-23-2014, 01:40 PM   #11
PNWxjJeeper
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Quote:
Originally Posted by cruiser54 View Post
Ask and you shall receive:

Cruiserís HO into Renix Swap

This swap is easier than some will lead you to believe, generally those who have never done it. Those of us who have done it, like myself, will share with you the things that need to be done for a successful swap. Just think of it as swapping in a long block.

The HO and Renix have some differences but none that canít be overcome very easily.

Any HO engine from an XJ or ZJ through 1999 can be used. One running change was that the rear of the head was no longer drilled and tapped for the temperature gauge sender beginning in the 96 model year. The sender can be relocated to the threaded hole in the thermostat housing taken from the HO engine. Youíll have to extend the wire to that location. Some brave souls even drill and tap the HO head for the sender.

You will be using the intake and exhaust manifolds from your Renix, along with all your sensors and wiring. Since the intake ports of the HO are slightly different, you use the Renix gasket. Exhaust ports are identical.
You will need to use your Renix distributor as it is different than the HO because they use different fuel management systems. The flywheel or flexplate from the Renix must be used so your CPS gets the correct signals. The valve cover from the Renix allows you to keep your CCV system intact and requires no modifications.

The HO block will have a plug in the coolant galley on the driverís side of the block, closest to the front, which needs to be removed so your Coolant Temp Sensor can be installed in itís place just as it is on the Renix. It requires a 5/16Ē square drive or a modified 3/8Ē drive that has been ground down to fit. Do this before installing the engine.

As for the knock sensor, which is located just above the oil pan on the driverís side of the engine about mid way, all the blocks Iíve seen are threaded for it. If not, Iíve heard they may be drilled but not tapped. Tap the hole if thatís the case.


Revised 03/28/13
ok so i shouldnt use the 91 intake? ive herd that there are conversion plugs that you can buy so that the wire all works together. that way the ports match up and everything. is this true? and ive also herd that the 02 intakes are supposed be way better. but ive also herd it takes power away. Im just confused from all the different answers lol.

All the other info was very very helpful. Thank you so much!
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Unread 06-23-2014, 01:50 PM   #12
75SV1
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As for the 00-up intakes, some made a bit more HP and some lost a few. At least from my memory for various post. There is one article that claims say 20 hp or more gain. It was with a dyno sheet. But, there was a lot of changes made at once and the dyno runs were not on the same day.
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Unread 06-23-2014, 05:24 PM   #13
cruiser54
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Quote:
Originally Posted by PNWxjJeeper View Post
ok so i shouldnt use the 91 intake? ive herd that there are conversion plugs that you can buy so that the wire all works together. that way the ports match up and everything. is this true? and ive also herd that the 02 intakes are supposed be way better. but ive also herd it takes power away. Im just confused from all the different answers lol.

All the other info was very very helpful. Thank you so much!
Use your Renix stuff. There are no adapter plugs, They are 2 different injection systems.

The later intake is not worth the effort and expense.
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 06-24-2014, 07:08 AM   #14
75SV1
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Hesco does make some adapters and 'kit' :
http://www.hesco.us/products/7902/40...adapter-640177

I think $$. Some bore the Renix TB to 60mm. My thought is that with the basic upgrades, Header/exhuast, bored TB, cold air intake, ignition upgrade, you will see a good power and possibly MPG increase. My Renix got better mpg than my HO.
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Unread 06-24-2014, 07:23 AM   #15
cruiser54
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Let's de-bunk the HO deal:

HO myth buster


Renix in 90 made 182 HP. HO in 91 made 190 HP. That's 8 HP difference.

HO only made more HP than Renix at higher RPMs and not a bit more torque. HO had 58 mm throttle body versus a 52 mm throttle body on a Renix and also had a better design header. See where I'm going with this?

The whole 8HP was not mostly from the head, but from the bigger TB and better exhaust manifold.

Put a 60mm TB from www.strokedjeep.com on your present head, eliminate the "crush" in your headpipe with proper re-routing, and go for it.

HO stands for Highly Overrated.
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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