Fuel Pump Or Maybe Cps?

[MmMBurritos]

Last night while I was driving for over 20 minutes or so out and of nowhere I immediately the motor shuts off. After a couple cold starts it began running and seemed to drive fine. Later when I went to start it, again it would not start (cranks but does not start) until after a couple cold cranks. This morning it started right up just fine and I can hear the fuel pump running.

 

My guess is electrical either with the CPS or the Pump. Checked grounds and tested CPS properly (I think) and everything seems to check out. I'm also curious if the cold/dry at night as opposed to much warmer daytime temperature might have any effect.

 

Where is the fuel pump exactly on a 1988?

 

For the life of me I cannot seem to find it. Is it in the fuel tank? I confused the starter for the fuel pump and I'm a little embarrassed asking this since google isn't helping. Will continue to source the issue but any advice would help

[jimoshel]

It is in the fuel tank. It can be removed without removing the drive shaft but for the trouble just remove the drive shaft. Makes it a lot easier.

[Geonovast]

Do a fuel pressure test.  Also, before you tackle the pump, bypass the ballast resistor to see if there's any effect, also change out the fuel filter (easy and cheap)

 

Very high likely it's the CPS.  Even dying CPSs can ohm out just fine.  Cruiser has a slight modification that can help with a dying CPS, but it should still be replaced and not relied upon.

[ftpiercecracker1]

Do a fuel pressure test.  Also, before you tackle the pump, bypass the ballast resistor to see if there's any effect, also change out the fuel filter (easy and cheap)

 

Very high likely it's the CPS.  Even dying CPSs can ohm out just fine.  Cruiser has a slight modification that can help with a dying CPS, but it should still be replaced and not relied upon.

 

 

:agree:    Hit it right on the head Geonovast.

[MmMBurritos]

the CPS seems new, however the harness is looking ragged and I'm also concerned over the fuel pump harness.  Any idea where I could find either?  I've checked Rock auto and Jeep 4x4 but havent seem much.

[cruiser54]

The CPS harness can get burned by the exhaust if not routed properly. I have a photo of how to route it but I suck at posting photos on CC. TEST the CPS output.

 

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