letsgomuddin

2001 XJ, wouldn't restart at the gas station. Wiggled the crank sensor wire at the sensor and it started. Drove it back to the shop and replaced the crank sensor. Now when I try to start it, it acts like the firing order is off and it pops and fights the starter. Besides a faulty new sensor, what else could be the problem? All I changed was the crank sensor, but after it wouldn't start I did put new plugs (old were junk) and a known good coil pack on it with no change.

Ralph77

Well I am going to ask the question that I always ask when we are talking about the CPS.
Cause hardly anybody tells you right at the beginning of their thread. LOL.
Where did you buy the CPS sensor?

lawsoncl

Yeah, quality matters here and it's not unusual to get a bad one right out of the box or have a new one die within months. Since wiggling the wire made a difference, I would thoroughly inspect the wiring harness. Pull the loom off if you need to. There has been a rash of people posting that turned out to be melted, chaffed, or flexed/frayed wiring where it goes from the engine to the firewall. The flexing is worse if you have 20-year old rotten rubber motor or transmission mounts. I've fixed a couple similar wiring issues this year.

letsgomuddin

Sensor is a high quality NAPA unit, used them before with zero issues. Scoped the signal wires for the cam and crank sensors and the crank sensor signal is erratic. Tried a good used sensor and it displays the same. Going to start chasing wires I guess.

letsgomuddin

Bypassed the harness entirely and have the crank sensor probed directly to ground, 5v, and the signal wires at the pcm. Still no start.

agreen

Take a step back real quick and do the basics again before you go too far in the weeds. Have you done a spark test?

letsgomuddin

I have weak erratic spark, but I've replaced the coil pack, cps, and ckp sensors.

BlueRidgeMark

Plenty of people have had problems with "high quality" aftermarket CPS sensors, including NAPA. That you have not had problems with the NAPA part before now is no guarantee that you have a good one this time.

Ralph77

Napa would be my first choice after OEM.
Could have something to do with the fact I work there though so.... LOL.
But when the time came I still went OEM.

Roler

I've never read anyone ever bypassing the CPS in an XJ..

lawsoncl

There was a service bulletin and kit for doing exactly that on the real old Cherokees. They used a different analog sensor which was sensitive to the extra resistance of going through multiple connectors, especially the C101 connectors. Starting with the HO engines, the sensor changed and puts out a nice 5-volt pulsed signal.

Roler

Good info
But would you be able to check the CPS that way, in the HO and up as well?

That would make it interesting since it's so often a suspected part. I'm not familiar with other method that the resistance measurements

letsgomuddin

Only reason I went NAPA over MOPAR is that I could actually get a NAPA one that day, MOPAR ones are a week out. For grins, I tries a different computer from a running XJ with the same results, so that rules that out. Going to start the tedious task of tracing every wire and ground today, JOY!

xxEuroBabexx

wiggle your fuel pump relay. did you install the CPS? Is is screwed in tight? Maybe it got chewed up after you installed it.

As far as NAPA or so called "OEM" parts go there are only so many people manufacturing this sensor in the world and NAPA uses just as many, and quite a few of the same, as everyone else. This isn't 1989 anymore. All that matters is "what is the return policy" and "how fast can i get a replacement".

My new CPS is the literal cheapest one I could get at autozone and it's fine.

letsgomuddin

Not a fuel pump issue as ive verified correct pressure at the rail, but thanks for the ideas