james.peralta

Hey everyone. I was hoping I could get some advice on where to start on diagnosing and issue I've been having with my XJ (97, 4.0L, AW4, 215k miles). I did a good amount of research on the forums as well as a run down of a few diagnostic tests I could easily do. Trying to figure out where to go next.

So, here is the issue. And I am not sure these are all related or not. My jeep has been idling rough for quite a while. It started throwing a P0301 code for cylinder 1 misfire, and P0700 for transmission control system (MIL request). It seems to idle the worse when its cold. Somewhat frequently, the CEL will disappear and it will seem to run a little better after driving 20+ miles on the freeway, but it has never disappeared on me just from driving around town. This issue has been happening for a few months at least.

The second issue just started this last week. It died on me suddenly at a stop light, without showing any signs of sputtering or extremely rough idle. I threw it in neutral and it started right back up. The operating temp was maybe at 170 degrees when this happened, I had just started driving. Then it happened twice a few days later. Again at an idle in a parking lot, and then driving through a parking lot at 5mph. Both times, I threw it into into neutral or park, and it started right back up. on this occurrence the jeep had been sitting for about 1.5 hours since I had last drove it, and was basically cold. The last two occurrences happened yesterday, out on trail. I left the jeep idling while airing my tires back up. without any sign of a rough idle or sputtering it just died. It started right back up. the jeep was at full operating temp this time. On my drive back from the trail on the same day, at freeway speed and full operating temp, the jeep died again. I put it into neutral while coasting at 70mph and it took a while cranking this time to start back up.

On seemingly random occassions, the jeep will take a long time (10-15 seconds maybe) cranking over before it finally starts up, or I stop cranking and give it another try and it starts up. This has been happening for a year or so.

lastly, my fuel mileage has seemed to suffer a little.

So far, within the last year or so, I have done spark plugs, distributor cap, plug wires (all connections with dielectric grease), a compression test (with good results, slightly high in 2 cylinders), I've cleaned my IAC within the last few years and the jeep has only been driven maybe 15k miles max since then. I have a new battery, and just got my alternator and starter tested. all grounds and battery connections are good. I'm probably forgetting some things here as well.

Tomorrow, weather permitting I am going to do a fuel pressure test. I'm leaning towards my Crankshaft position sensor (CPS), cam sensor, or a possible fuel issue like the pump or the filter.

Sorry that was so long winded! Where would you guys start at for diagnosing purposes? What would you lean towards being the issue? Do you think that the rough idle and suddenly dying while idling or driving are all connected? Thanks in advance!

Very Red XJ

This is my drill, because I'm bad at guessing - get your shop manual. Assuming your air filter is clean, spark plugs, cap & rotor and wires are good, check for dangling wires grounding. The wires coming up from the O2 to the fuel rail wiring harness are a good place to start. Then open your shop manual and test your sensors: the temp sensor, idle solenoid, MAP and TPS. In my experience, the crank position sensor is good - or you stranded by the side of the road - but test it anyway. If they are good and your throttle body is clean, move to the injectors: clean them and test the resistance for each one. You can pull them and usie a 9v battery to produce a click unless it's defective.


The pins are for the wires

Testing restance in cleaned injectors

Legendslayer

My knee jerk reaction is the fuel pump because you said some days it takes a couple seconds to crank and its been like that for a year...
the thing about a fuel pump is its not gonna all go bad at once, it'll just get worse and worse
The fact that you said it turned off mid drive and at the gas station and didn't stall out like a choked engine or bad sensor makes me think the ballast resistor.

good pressure is important in complete clean fuel combustion, Low pressure is probably causing sporadic misfiring despite new spark plugs. you also mentioned you lost MPG

All points to fuel delivery or combustion

When it takes awhile to turn over, turn the ignition on and let the fuel pump build pressure for a couple seconds then turn the key and see how fast it turns over.
if it works near instantly every time after building pressure, you know what the problem is then


check the ballast resistor on the driver side inner fender(IF YOU HAVE ONE; MY 93 DID, WHEN IT WENT BAD MY JEEP RANDOMLY DIED) controls fuel pump cuttoff voltage,
Then id move on to injectors/fuel rail like the post above mentioned.

cps/cam sensor are same thing i don't think you'd be reliably turning over your jeep for over a year if that were going bad.
IAC controls your idle, so unless your idle is lower than 700rpm or higher than 1000 move on

wildmustard

Check the Crank Position Sensor. My '93 XJ started to die at random. Engine would just quit, but start up again right away. Even just pop it into neutral, hit the ignition, and keep on rolling. The Crank Position Sensor is on the top of the transmission, slightly to the drivers side. Replace it from underneath. Have to let it get good and cool and then bear hug the tranny from the bottom. A single 10mm bolt, I recall, and a clip connector. Don't drop the bolt into the tranny!

james.peralta

Update: Thank you for the responses everyone. At the time of writing the initial post I already ordered a MOPAR CPS, so I figured I would try that first. So far it hasn't died on me again, but I have only taken it on a short test drive and let it idle for about 20 minutes. I also ran a fuel pressure test. My fuel pressures are good, but my fuel check valve is shot, I am losing pressure very quickly after I shut down the jeep off. I'm sure this is what has been causing the long cranking time for the most part. Although it does seem to run a little better with the new CPS, it stills sounds like it might be misfiring. I'll have to wait and see if the CEL comes back, but I plan on doing more follow up diagnoses on the misfire/rough idle/bad fuel economy. Thanks for your help everyone, and I will still be coming back here as I go to follow up on these suggestions and update everyone. Any additional ideas are always welcome!

Very Red XJ

Certainly, just please let us know when you actually find what caused the problem

lawsoncl

Could be an injector leaking down too. Pinch the fuel line from the tank and see if the pressure still drops.

Very Red XJ

if you get to test and remove the injectors, you should replace the "o" rings around them before putting them back in - they are available at most parts stores

wildmustard

If changing the fuel injectors, and o-rings, be sure to lube the o-rings. Fuel, especially 'modern' ethanol-laced gasoline, is very dry. That, and the aluminum fuel rail, destroys o-rings. I used petroleum jelly (Vaseline). The real-deal would be o-ring specific stuff - Molykote.