Low Output 4.0 Modifications
Hello everyone! I’ve got a 1987 Cherokee that I race in some local 4x4 races that I’ve been trying to get a little more power out of. My plan right now is to put the HO throttle body with a spacer/adapter on, and I put some injectors out of a triton 5.4 out of an old expedition.
Im looking for any other worth while and some what easy upgrades that I can do to the engine. Any info on other engine parts I can take from other engines including the HO 4.0 would be great. Or just any smart modifications.
Thanks for the info!
Im looking for any other worth while and some what easy upgrades that I can do to the engine. Any info on other engine parts I can take from other engines including the HO 4.0 would be great. Or just any smart modifications.
Thanks for the info!
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,579
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Renix 60mm throttle body from Leigh Performance Machine.
Bigger than HO and no adaptation needed. http://strokedjeep.com/
Remove the 2 crush spots in the exhaust. One in the headpipe. One where the exhaust goes above the crossmember.
Advance your CPS and increase its output while you're at it. CRUISER'S MOSTLY RENIX TIPS

Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS itself as shown in Figure 2 as Connector A, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from NAPA or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8″ from the stock 5/16″, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
Another little tip to save tons of aggravation is to stick a bit of electrical tape to your 11mm socket and then shove the bolt in after it. This reduces the chances of dropping that special bolt into the bell housing.
And I have to throw this in!!!!!
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 a 58 mm throttle body versus a 52 mm throttle body on a Renix. That’s 20% more air available through the HO throttle body. The HO also had a better design header. See where I'm going with this?
It’s only a 4% horsepower increase…..
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 manifold using the Renix head, eliminate the "crush" in your headpipe with proper re-routing, and go for it.
HO stands for Highly Overrated.
__________________
Bigger than HO and no adaptation needed. http://strokedjeep.com/
Remove the 2 crush spots in the exhaust. One in the headpipe. One where the exhaust goes above the crossmember.
Advance your CPS and increase its output while you're at it. CRUISER'S MOSTLY RENIX TIPS
RENIX CPS TESTING AND ADJUSTING
OCTOBER 30, 2015 SALAD 131 COMMENTS

Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS itself as shown in Figure 2 as Connector A, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from NAPA or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8″ from the stock 5/16″, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
Another little tip to save tons of aggravation is to stick a bit of electrical tape to your 11mm socket and then shove the bolt in after it. This reduces the chances of dropping that special bolt into the bell housing.

And I have to throw this in!!!!!
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 a 58 mm throttle body versus a 52 mm throttle body on a Renix. That’s 20% more air available through the HO throttle body. The HO also had a better design header. See where I'm going with this?
It’s only a 4% horsepower increase…..
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 manifold using the Renix head, eliminate the "crush" in your headpipe with proper re-routing, and go for it.
HO stands for Highly Overrated.
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