KClight01

OK, I just installed a new crank sensor. There was a little bit of residue on the end, not sure what it was. I compared the ohms readings and the old one seems to be bad or going bad. I installed the new and did the ecu reset, not sure if that was needed but I figured I would do it since I have both new cam and crank sensors now. Runs good as always, seems good so far. I just shut down and now am going to wait an hour since the engine is hot now, and see how it cranks, hoping for a good start.

Well no good. It did the long crank and stall but then started right up on second try. I just am going to have to accept that I can’t fix this.

Mr.T

No doubt it's a difficult and frustrating problem.

I'd bet that whatever it is will eventually fail completely, or at least set a DTC -- Then it will be easier to figure out. Suggest scanning it regularly, and note if the symptoms change, especially with temperature. Waiting isn't giving up, sometimes it's the best troubleshooting route to take.

Stay in touch, quite interested in what it turns out to be.

Mr.T

I've an idea to try:

Since you're able to replicate the failure, set it up for the same test, but add another battery in parallel with jumper cables in the usual manner. The voltage will run higher during cranking with two batteries, see what happens.

KClight01

I am trying to "let it go", but as it gets closer to the weekend, I start thinking of more things to try. I like your battery idea, but my battery less than year old and tests good and cranks strong. I have a good 2/10/60 amp battery charger/starter that I could hook up before the "hot start" and see if it makes a difference, not sure if that would hurt the battery though (adding amps to a good battery). I also plan to try flooring the gas pedal during a hot start, to see if it makes a difference if you go straight to crank. I also need to hook up the pressure gauge again and verify pressure over time to see if it could actually be a leaky injector or fuel pump check valve. I still would find it hard to believe since the fuel pump is less than month old and my fuel trims are perfect. Wouldn't it show rich fuel trims if leaking injector? My vacuum pressure reads good and is steady which should indicate a strong engine. So, I keep going back to electrical. I checked the ground cables, sensors, sensor wires, and even bypassed the fuel pump relay which is faulty on some Jeeps. All were good, and it still did the extended crank after hot sitting engine. Another interesting thing is that it always seems to start fine if you wait a couple of seconds before cranking (like 2 chimes worth), then it seems to start right up every time. And it also starts right away after first crank of the day. If it is losing pressure, why would it crank fine on the first crank of the day? Maybe I will find answers to these questions one day.

Mr.T

It sounds like electrical-electronic to me too.

The jumper cable to another battery idea is a simple way too increase voltage during cranking and see if it makes a difference. If it did happen to work, then you could narrow down whether and where voltage was too low, or what device is abnormally voltage sensitive.

The key-on wait to start and it's OK is very interesting, but I can't think of a reason for it ???

KClight01

Some more data today, Battery tested good at ~12.7v, 12.6v key in, 12.5v acc, ~11.5v during crank. I checked the IAT and ECT sensors with a scanner and compared to readings with infrared thermometer. Everything seemed ok. ECT temp was close. IAT didn't match ambient at start, but the engine was still warm, and hard to get a good reading of inlet air. I checked the grounds again, and even had a jumper cable ready to go from the battery to alternator to see if it made a difference. I played with the ignition at with the key in different positions and watched the voltages. I could hear the fuel pump. One thing I noticed was a faint sound like a relay clicking off, when I had the key in the ACC position (the first position when the door chimes). It sounds like its coming from behind the steering column somewhere but may just be traveling and it sounds that way. Could this be a clue? Does your jeep have a sound like that with the key in the ACC position? From more research, most check the J13 WCM fuse, but I have never had the "no start" condition. Could it still be that fuse or relay acting up when warm? I still plan to test fuel pressure, but Jeep has been getting a lot of use today so I did not get much done. It never did the long crank, but it's probably because of all the key cycling I did. I really didn't replicate the condition today.

Mr.T

Mine has a periodic click type noise with key in acc too. Might be the e-throttle or the evap purge solenoid. Doubt a bad fuse would behave the way you described, but strange things can happen.

KClight01

New info, latest theory. On a whim I decided to look at the relays, I looked at the starter and ASD relays. I noticed the leads on the ASD relay had slight charring or oxidation, I cleaned very gently, I also swapped the starter relay with the fan relay. I went to crank (cold start) first crank of the day without delay and it did the extended crank. It has never done that before during the cold engine (first start) condition. This was either a fluke or it proves that it's related to one of these relays I messed with. I then swapped the fan and starter relay back, and so far, it has started right up every time, (4 different times). So, I am wondering if whatever I did either helped reseat the relays or the little bit of cleaning made a difference, or maybe all just a coincidence.

Mr.T

Hope that's it, it sounds like a good theory to me!

KClight01

Well still no good. I can't explain why it seemed to start good after messing with the relays. I mainly was getting second hand information which may not have been accurate. I went ahead and ordered a spare relay and swapped it. I also bench checked the relays by checking resistance and applying power and verifying it clicks and closes the circuit. All the relays checked fine. The "load" side leads look slightly discolored, but I don't think that is my issue anymore.

I had a full day with the Jeep so I took video with phone of different times. I would post if I could figure out how, but all you would see/hear is the engine/starter turning strong for several seconds before it fires up.

1. cold engine (no pause turning key) - started after a few revolutions, tach seemed to have a slight delay compared to revs, but not sure
2. warm engine (~5 mins wait, no pause turning key) - started right up, no delay, the tach still seemed to lag behind, the engine started right away but the tach didn't really move up until after it seemed to start)
3. warm engine (~1 hour wait, no pause turning key) - long crank, ~5 full seconds of revolutions, the tach looked like it started for a sec but then dropped to zero, then went up when engine started. Turned engine off, went to start again and it started right up, no delay.
4. warm engine (~15 mins wait, no pause turning key) - long crank ~5 secs

I also played with the CAM sensor position just for grins, I marked it, then moved it up slightly. It did a long crank, almost faster than usual. I then tried pushing the CAM sensor lower closer to my mark, then it started right up. I am not sure what to make of this yet, because it was back to doing the long crank the next day after it was sitting warm. I might see if I can lower it more, then spacer is gone I am sure so I will need to back off based on my mark. I don't feel like it's the sensor though, I think as long as the sensor is good and within the tolerance, you are fine. I am not sure about the crank sensor though, even though the sensor is new, my symptoms still seem to match a crank sensor issue, since the tach stays at zero during the long crank. I still need to check fuel pressure, but I really think its electrical. I have a feeling the coil and plugs are not getting spark during the long crank, maybe due to the PCM, which could be cutting power through the ASD relay because it isn't getting a good reading from the sensors. I have read that after an extended crank the computer might bypass the sensors, not sure, just more theories right now...