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90 Cherokee 4.0 No spark

9

90XJCherokee

NAXJA Forum User
Location
Sherwood
Hi, I have a 90 Cherokee 4.0 5 speed 4x4 Ive replaced the following, Distributor Cap and rotor, Ignition Module, Ignition Coil, and all plugs and wires. No spark. Idk what to do now that Ive replaced the whole ignition system, and still nothing. There is 4 relays on the passenger side that im not sure about. Iknow one is the fuel pump relay but idk if any of the others have to do with ignition. I took the cap off and cranked it over I know the rotor is turning. There is a spade prong that comes out of the coil that im not sure about I dont see any lose wires that could possibly go to it. Can anyone help me out? is there something that Im missing here? Could it be the ECU or a sensor? I had no check engine lights on before this happened I was just driving down the road and It died.
Thanks everyone
 
Does your CEL come on when you turn the ignition to On? That light indicates the ECU is working correctly and the light is operative. Have you looked into your CPS sensor?
 
Crankshaft position sensor is a primary suspect. Without input to the computer from this very important engine management sensor, you will not have spark and you will not have fuel going TO the fuel injectors.

Here is how to verify the crank sensor on your vintage. Good luck!
---------------------------------------------------------------
Renix (87-90) Crankshaft Position Sensor Testing and Adjusting

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, 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 crank sensor directly from the Jeep dealer for best reliability and longevity.

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 it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
 
The CPS or its wiring is bad. If the wires are OK, the CPS is bad. Look up the modification for moving the new CPS closer to the flywheel or flex plate before installing a new one.

Also I suggest getting either a dealer CPS or the standard products brand from Rockauto.com (made in Italy not China). The other aftermarket ones made in China have been bad out of the box lately.

There is one thing you can try first since yours is a manual transmission. The CPS has a magnet and is nown to collect magnetic dust from the clutch and stop working, so try cleaning it first, with compressed air....
 
birchlakeXJ said:
Crankshaft position sensor is a primary suspect. Without input to the computer from this very important engine management sensor, you will not have spark and you will not have fuel going TO the fuel injectors.

Here is how to verify the crank sensor on your vintage. Good luck!
---------------------------------------------------------------
Renix (87-90) Crankshaft Position Sensor Testing and Adjusting

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, 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 crank sensor directly from the Jeep dealer for best reliability and longevity.

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 it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
Click to expand...

Tom, you need the latest revision.

Renix CPS Testing and Adjusting
　
　
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, 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.

　
　
Revised 01-26-2013
 
Thanks guys Ill try it tomorrow. I appreciate it. I love my Jeep I wish it was an HO though. I Know this is way off topic but would it be easy to convert it by swapping the 91-95 Head I think its a 7120 Casting number, chrystler MPI,Intake and the HO ECU/PCM Wiring harness or should i just buy a whole new HO engine? Because Ive been researching Performance parts and 90% of the aftermarket performance parts like the Throttle body spacer for example(just throwing it out there) says years 91 & up meaning H.O.
 
Last edited:
Take it from someone who has been there since 1987. HO stands for Highly Overrated. I can get a REnix to run just as strong as an HO. HO only had 8 more HP than the latest generation of Renix like yours, and it was only in the higher revs. Not a bit more torque.

Like this: PC307 CPS from RockAuto. advances the timing. Have a new headpipe built and re-routed eliminating the restrictive "crush" there. Bigger throttle body from www.strokedjeep.com. Later model injectors from some supporting vendors.
 
Cruiser54: "Have a new headpipe built and re-routed eliminating the restrictive "crush" there." I would like to do this....any details on how to reroute it? Where should it run?
 
4xBob said:
Cruiser54: "Have a new headpipe built and re-routed eliminating the restrictive "crush" there." I would like to do this....any details on how to reroute it? Where should it run?
Click to expand...

My muffler shop guy makes them and installs them. If you have 3" or more of lift, you don't need to re-route it. Less than that you do. Basially, since you have a Renix Jeep, the headpipe comes off the manifold and then makes a 908 turn toward the rear. Have the pipe made with two 45* angles or thereabouts to get it up and away from the front driveshaft. Your butt dyno will notice the change in power.
 
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