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Still bucking and dieing

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I am running out of ideas in what this could be. I've done all the renix tips. And you guys have helped alot. But the comanche is starting a new problem. On my way to work last week and this week. It died going 60 down the highway. Both times were about 20 miles into the trip. It starts back up and does fine. So today it died going down the highway. It started back up no other problems. Leaving the parking lot after work it died and started right back up. But then it bucked and surged quite a bit coming home at about 60mph. It's a 90 4.0 auto I'm going crazy trying to get all the gremlins worked out of this truck

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I was saying that I had a fuel tester on the truck I tested the regulator and pump. All my numbers were good. I will try again and see if there's any changes. I tested the fuel system about 6 months ago. I was wondering I'd there was something I might of missed 

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It's hard enough to diagnose a shut off remotely, an intermittent one impossible, keep plugging away checking the fuel pressure when it does it, keep the tester with you, also, if you have a spare coil swap it and see if problem returns, but still does sound like fuel starvation, maybe an injector going bad as well.

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If there was a previous thread related to this, I missed it.


This is exactly how my cherokee acted when the crank position sensor was failing.  Random dying but would always start right back up.  then one day It didn't start right back up.  CPS was failing.  Replaced and all is well.   

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Easily tested. And check the wire routing. 



CPS drill mod

CPS location

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. CPS bolt socket

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  • 3 weeks later...
1 hour ago, cruiser54 said:

Shoulda gotten a check engine light for the oxygen sensor on a 97. 

The check engine light is what ultimately triggered that told us to check the O2 sensor.  It was a very sporadic issue, dealer changed many parts and tested many things over the years trying to fix it.  As soon as we changed the O2 sensor the problem was fixed.

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In this case, might not be a bad idea. There are some crappy pumps out there. Try to stick with Bosch or Delphi. The issue could be as simple as the split/boogered internal fuel pump hose though. They weren't engineered for our ethanol fuel. 


I would suggest you do my fuel pump ground upgrade no matter what. 

Injectors? Here: trevor.skankfootracing@gmail.com



The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, XJ-Body-Ground.jpg?resize=300%2C162and behind the driver’s taillamp on an MJ.

Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture.

Locate the black wire on  the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire.1-fuel pump ground MJ

Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.1-fuel pump ground mj-002Solder the connection. Tape it up and reinstall the split loom covering.1-fuel pump ground mj-003

At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces.1-fuel pump ground mj-004

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