Fuel pump or CPS?

Been having extended cranking issues for a while now. Usually if the Jeep sits for more than 10 or 15 minutes. On the way to work today I was backing into my parking spot and the Jeep just died. No shuddering or anything before, just like i shut the key off. But after it died I noticed the tachometer was still sitting at idle rpm even with the engine off. Strange.

Tried to cycle the key with no joy. Listened for the usual fuel pump sound and nothing. Fuel pump isn't running. Swapped the relay with a known good one and again nothing. Also swapped the fuel pump fuse even though it looked good.

No CEL has popped up. At least it died in the parking spot I guess.

I'm leaning towards fuel pump but thought I read somewhere a bad CPS can also make for extended cranks and causing the fuel pump not to run.

Probably bad CPS if the tach is reading goofy. Could be as simple as making sure the bolts holding the sensor to the bellhousing of the tranny did not come loose either. With two people it is easy to manually run pump by jumping the relay and someone else turning the key.

testing the cps is always simple if you have a voltmeter. Here

My 92 had a weird plug so I wasn't able to test mine really well so I just replaced it after 200,000 miles and threw the original one in the back as a spare.

Good Luck

You should still hear the fuel pump run when you turn the key to "on". If you don't hear the fuel pump you could cycle the key on/off without starting a few times then check the valve on the fuel rail. If no fuel squirts out then there is something wrong with the fuel pump.

I just shot the CPS and it's reading 3.44 milliohms. From what I can find that means it is bad but doesn't account for the no fuel pump sound. I'll check the schrader valve when I get back to work. I just walked back to the barracks and got the motorcycle out.

Hello,
I would disconnect the CPS connector and turn the key to on without cranking.
If you hear the fuel pump then, go for a new CPS.

Good luck

Regards

Even when unhooked no fuel pump noise. I tried that when I was shooting it with the multimeter.

Have you checked the pressure on the fuel rail?

If not, fuel pump..

I don't have a fuel pressure tester. I did have a multimeter and the CPS tested bad at 3.44 milliohms. From what I was able to find. I'ma bout to walk out to take care of something and check the rail to see if I'm even getting fuel to the rail.

Welp I'm stupid. While the fuel pump fuse was good and the relay, I didn't check the "Start/Run" fuse under the dash, didn't think that would affect the fuel pump. 20 amp fuse. Blown out. Only had a 15 amp fuse on hand so swapped that in there for the time being so I could get it back to the barracks.

I already ordered the CPS so I'll keep that on hand incase it does go out instead of returning it.

Does make me wonder what made the 20 amp fuse blow out though. Fuel pump doesn't sound strained or louder than any other Jeep fuel pump I've heard so not sure there.

devildog0 said:

........
Does make me wonder what made the 20 amp fuse blow out though. Fuel pump doesn't sound strained or louder than any other Jeep fuel pump I've heard so not sure there.

Click to expand...

The fuel pump has a set of carbon brushes, sort of like
an alternator, that wear out over time. My guess is that
the brushes are worn causing high resistance in the
circuit, and blowing the fuse.

Might be worthwhile to install a new fuel pump, just for
peace of mind and to make it more reliable...

Well from what I can gather looking at wiring diagrams and reading other posts "fuse 11" is a common one to fail when some parts of the wiring harness start to chafe or when an ASD or Fuel Pump relay goes bad.

It handles power to the PCM, TCM, and the Fuel pump and ASD relays. The actual power for the Fuel Pump runs though it's own fuse in the PDC under the hood so this fuse only provides the power to the relay.

I checked all the chafe points on the underhood wiring harness and found nothing. Could also be a chafed harness to the NSS.

I'll have to get under there and check a few more wiring harnesses.