No start is vexing me!!!

Okay, I'm aware that there are many posts regarding no starts, but I've applied some of the info I've read to no avail. So, here goes:

1997 Cherokee XJ 4.0L HO Sport, AW4 auto, approx. 150k miles

Bone stock except for towing modifications (tranny fluid cooler, wiring for trailer).

The backstory:
Last year, went camping. Engine died suddenly, cranked but would not start. Had towed to repair facility, replaced fuel pump fuse and started right up. Techs could not find issue, ran the Jeep for an hour, did lots of electrical checks. $42 and sent us on our way. No issues for several months.

About three weeks ago, parked the Jeep, was running fine. A week ago, tried to start it, nothing. Replaced fuel pump fuse, cranked right up. 10 minutes later, dead. Replaced the fuse again, cranked right up. Died in about 5 minutes. Got frustrated, left alone.

Today, bought more fuses. Replaced fuse, cranked, ran for less than 30 seconds then died. Has not ran since. Got curious, tested fuse with multimeter, fuse was not blown. None of the previous fuses had blown. Started scratching head.

Tested the ASD, starter, fuel pump, and cooling fan relays, all checked out good. Popped them back in, still no start. Had dad-in-law switch ignition on with me standing over the fuel cap. Heard fuel pump cut on then stop, as should happen. Really boggled at this point. Jiggled shift lever, still no start.

Did some more reading in these forums, discovered CPS issue. Disconnected the CPS, used ohmmeter to check pins B and C. Checked on every setting, multimeter indicated open, as it should have. So, doubt CPS is bad. Now I am really stumped. I highly doubt the cap/rotor/wires are to blame because it ran great when it was parked. Where else can I look? Thanks!

Are you actually getting fuel? Check the schrader valve on the fuel rail to see if there is any pressure. Just because the pump is making noise doesn't mean its working.

If the fuel pump fuses have been blowing fuses, you have a problem that needs to be addressed. You either have a wiring short or a bad fuel pump.

Your symptoms sound like a bad CPS and similar to my recent experience. When cool, the CPS will test fine. Scrape up the cash (or borrow a good sensor) and replace the sensor. Post up your response. By the way, a dirty intake air controller has similar stalling symptoms.

Thank you so much for the quick replies! I will definitely try some of these. I'm hesitant to throw a CPS at it because it tested good. I don't want to throw away $60 some odd if it does not solve the problem, though I am tempted to try it. I'll check the fuel rail and pull a plug wire or two to check for spark.

The Jeep is used infrequently - mostly for towing and getting around in winter weather. I keep it at my in-laws' place (can't have 3 vehicles here at my house) so I can only get at it but so often. I will have an opportunity to mess with it in the AM but can't do too much because my wife wants me to go to a wedding with her (yuk). Can't get too grungy. I will keep you posted - again, thank you!

Testing for the crank sensor is often not conclusive. I've seen em test good and be bad.

If you buy, buy directly from Jeep. The extra $20 you spend on an OEM unit is so well worth the money. There are many people that have had problems with aftermarket crank sensors.

@mongolchuck: Pressed the Schrader valve. Got a quick, short squirt. Came out forcefully enough to splash against the air cleaner. Cycled the key on and off again, got another squirt. The only way to tell conclusively though is if a shop puts gauges on it. Again, time to spend money.

Next, need to check spark but volunteers to help are hard to come by here - they are working. Will let you know when I have the chance. Thanks for your help, folks!

Refault trace the FP issue. If the FP is blowing fuses- you have an issue to fault trace. Keep in mind you can have more than one simultaneous issue Often times one aggrivates the other.

If you are blowing fuses that means your are having an excessive current draw on the power side of the pump circuit. Either a pump motor going bad (yes a bad pump can still run and draw too much current), a short on the 12V line from the relay output to pump. OR short to power on the ground side of the relay circuit on the ECM side, OR a sticking FP relay.

The most common failures are the pump and pump relay. Here is a safe but not foolproof assumption. If replacing the fuse yeilds the vehicle to start and run until the fuse blows again you likey have a relay and/or pump issue.

The fact that it doesn't run now after blowing the fuse the carbon build up on the armature of the pump from wear or one of the windings is now open/permenatnly short- has likley gotten to the point where it won't even run to blow the fuse.

Thats not discounting you may not have a CPS/CKP sensor issue or something else. I would go and make sure you have 12V at the pump connector and a good ground at the pump connector- both can be had with a quick and dirty test light test. I perfer a DVOM test. With the DVOM you can see if you are getting near battery voltage to the pump say 11.89v to 12.3V or 10, 9, or less voltage which could point to excessive voltage drop across the relay.

If you find the pump is bad replace the relay- always a good idea and safe insurance policy. If you are luckily and its a relay then its a cheap fix. Excessive cranking by a failing FP can wear on the CKP/CMP sensors too or aggrivate other starting issues.

Fuel pump is not blowing fuses. I'm not sure if that repair shop knew what they were doing. I just took the plunge and purchased a $35 fuel pressure gauge. I have nearly 50 psi at the Schrader valve on the rail with the key on and engine off. That tells me fuel delivery isn't necessarily the issue. Now leaning toward ignition/computer/sensor issues. Fuel pump is getting power and I'm getting fuel pressure. Also smell gas from the tailpipe. So, either have flooded cylinders or some kind of system fault. I won't have a cranking assistant for a while so I can check for spark. Thanks for checking up on me.

Pull your plugs and check them.When was the last time you did a tune up on this?

Pulled the plugs. They don't look so hot. Pulled the fuel pump fuse and cranked the engine over some to try to evaporate some of the accumulated fuel. I don't think the spark plugs are the cause but they aren't helping. They were not wet but they smelled of unburned fuel. Have to give up on it for a while - wife wants me to go to a wedding. Yuk. Not sure if I'll get to it again tonight. I loved how easy the plugs were to access and remove. Didn't take 5 minutes. I'll pick up a set, but I won't be able to work on it again for a couple days. If any of you think of anything I haven't already, please let me know. Thanks for your help!

The symptom you describe (unexplained stalling and cranking not starting), point to the CPS. Every Cherokee will need a new CPS, the JEEP CPS lifespan is approximately 125-175,000 miles. Cheap "Lifetime Warranty" CPS have a much shorter lifespan and are not worth the troubles.

You can check for spark without an assistant. Pull the starter relay and run a fused (does not have to be fused, just a good idea.) piece of wire from terminal 87 and 30 and your starter will run.

Then you can watch for spark and run the starter at the same time, just make sure key is on/run position.

yea my TJ needed an ASD and CPS at the same time- it was cheaper to get a reman dist. with a new OEM quality Cam Sensor than the CPS by itself 70 and 65 go figure.

Hey everybody - finally had some time to wrench on the Jeep! Replaced plugs, no start still. Pulled a wire, checked for spark, no dice. Pulled wire off coil, checked for spark, nada. Scanned the computer, got codes P0122 and P1694. Figured I would clear the codes and try again. Then, code P0320 came up sporadically. Your thoughts guys?

Sounds like it is the CPS.

p0320 = Ignition/Distributor Engine Speed Input Circuit

You could check the wiring from the computer to the CPS.

CPS meaning cam or crank?

Crank

techedtchr said:

CPS meaning cam or crank?

Click to expand...

Crank.

birchlakeXJ said:

Testing for the crank sensor is often not conclusive. I've seen em test good and be bad.

If you buy, buy directly from Jeep. The extra $20 you spend on an OEM unit is so well worth the money. There are many people that have had problems with aftermarket crank sensors.

Click to expand...

I have had a brand new CPS test good, and be bad!!! The internal electrical connection was loose enough to work, test good, then loose contact and die, then test good again.