joey400ex

Jeep has been sitting since deer season last year, I was cranking it up every so often until the battery died (which I replaced last week). Buddy call me up last night to help work on his wife's car. I drive the jeep over, help him fix his wife's car and I go to leave the jeep will not fire up. The starter turns great but I just can't get it to crank up. So, my buddy had to drive me home last night. Before I start troubleshooting I wanted to get some tips I what I should check first.

I'm thinking change the spark plugs and wires and fuel filter. I wouldn't be surprised if it's the fuel pump but normally in the past my trucks would start cutting in out when the fuel pump would go bad. I will say the jeep was running great when I turn it off and then would not fire, so weird. Maybe a blown fuse also? Any pointers would be great, I've owned it for maybe a year so I have no idea when the plugs were last changed.

joey400ex

Buddy just called me and said it cranked up and he drove to my house with no issues? Guess I'll change the fuel filter and but some additive in it????

PatHenry

Could be CPS - When they fail they can cause crank no start when the engine is warm (though it sounds like it wasn't just shut off) and work when it cools down. However, I'd suspect that you have a wiring issue, shorting out or not making a connection. I'd start by thoroughly going through the battery cables, grounds and CPS wiring and verifying everything is in good condition and solidly connected.
It can't hurt to check the fuel filter and do a pressure test and check the fuel pump wiring as well.

joey400ex

Thanks for the response, I did just put and new battery so it may be a connection. What is a CPS?

PatHenry

Check the connections are tight and clean.

CPS == Crankshaft Position Sensor. It's a little sensor that plugs into the transmission bell-housing and uses a magnet to monitor the flywheel. If it doesn't send a signal to the Computer, the car will crank but not start. It is subject to thermal failure and only the Mopar brand can be trusted for replacement.

I think it fails primarily on automatic Jeeps since I've lived through over 700k miles without ever replacing one across 3 manual Jeeps, but it seems like an epidemic for folks having to replace them. The wires run near the back of the engine on the drivers side and sometimes they can come in contact with the exhaust which obviously isn't good.

joey400ex

joey400ex

Let it cool down for a hour and it fired right up. Did it several times and it cranked every time.

cruiser54

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.

joey400ex

Thanks for the tips, I did order a new CPS. Gonna just replace it, watch a few you tube videos but they did not suggest the tape just using grease. I will put it on in a few days. But I will also invest in a meter. Do I need to check the voltage once it won't start at normal operating temperature? I bought a CPS with good review but could find a mophar CPS.

cruiser54

Before you install it, do the drill mod.

Also, watch how you route the wires.....

HighOnLift

Does it start in neutral when it doesn't start? Worth a shot. My neutral safety switch has been bad for almost 10 years. On a full battery charge I usually won't have any issues. But when it's low or old batt,,, I must either put it in neutral, or kinda wiggle the shifter around in park until it starts.

Aecon

cruiser54

OCTOBER 30, 2015 SALAD 75 COMMENTS EDIT



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.

joey400ex

So..... I finally got around to replacing the CPS. And let's just say it made things worse. I did not use a mopar but a mid range one with good reviews. I installed the new with no issues other than hand cramping and a small work space. Fired it up and it starting running rough. So I turned it off and got a can of brake cleaner and sprayed it down real good. It fired right up and I took it for a test drive, was running great until I got to normal operating temperature then start running rough and I had to idle back home. I know there's a drill modification but I'm not sure if I even can get a drive up there and would need more direction on how that is completed........ But I rather just put in a new one without having to drill anything. Not sure where to go from here. I only use the jeep in my hunting woods 3 months out of the year. I will put the old CPS back for now, it at least runs until it's warm then won't crank. Any suggestions would be great.

cruiser54

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.