YACNS issue (Yet another crank/no start issue)

[DavidG91]

I'm reluctant to post a new thread since several others report similar issues.

I am the original owner of a 2005 Liberty KJ 3.7L.
For several years, it has sporadically failed to start when warm after being off for 5-30 minutes, but not when immediately restarting it.
Sometimes, it's months between occurrences and sometimes it's several times a day. Last week it was several times, almost every time the engine was warm. The engine cranks but the idle is low and goes up and down for a second or two, then it dies, and does that again and again. If I feather the gas pedal when starting, I can sometimes get it to start. If I wait an hour or more it will start.

I replaced the Idle Air Control Valve but that didn't fix it. I checked the fuel pressure and it was in spec starting running and after turned off (but the issue did not occur during the test). Once when the issue was happening, I took off the fuel line pressure test cap, and there was pressure there. This issue persisted even after getting a new Jasper engine. I just replaced the camshaft and crankshaft position sensors.
I guess I'll see whether the issue recurs.

 

[KJowner]

Usually the crank angle sensor, they don't like heat when they get old.

 

[DadOSix]

Fuel pump.

Next time it does this, cycle the key on and off a few times before trying to restart. This process will build fuel pressure.

You could also check the fuel pressure with a gage.

 

[DavidG91]

Fuel pump.

Next time it does this, cycle the key on and off a few times before trying to restart. This process will build fuel pressure.

You could also check the fuel pressure with a gage.

I had tried cycling the key to increase fuel pressure but that didn't let it start.
Just waiting 1+ hours or (sometimes) feathering the gas pedal would make it start.

I'll pay attention to whether I see the issue again with the new sensors.

 

[blackhawk]

If I were You I would check the fuel pressure in ralentí and in the road! Sometimes you got a good reading in ralentí but not in the road in different scenarios

 

[DavidG91]

There are no codes displayed with the key cycling nor saved for a later scanner, but are there any real-time scanners that I could keep in the vehicle and connect when/if it happens again that might show any useful real time data?

 

[DavidG91]

I still sporadically see the crank no start issue on a warm engine even with the new sensors. The Delphi crankshaft position sensor failed after a few months causing stalls, check engine light and threw codes. I put back in the original and it works again (no check engine).

 

[klc]

There are no codes displayed with the key cycling nor saved for a later scanner, but are there any real-time scanners that I could keep in the vehicle and connect when/if it happens again that might show any useful real time data?

Maybe a Scanguage?


ScanGauge
https://www.scangauge.com

 

[DavidG91]

I haven't tried the scan guage or other tools. The local auto zone did not see any codes after the issue occurred and there was no check engine light.

I did just order a new Mopar camshaft position sensor to replace the Delphi brand I got a while back, which did not fix this intermittent start crank issue. It will go along with the original crankshaft position sensor I had to put back on when the replacement Delphi crankshaft position sensor eventually failed badly and caused stumbling and a check engine.

Maybe this replacement Mopar camshaft position sensor will fix the issue but I don't have much hope.

 

[DavidG91]

The replacement Mopar camshaft position sensor did not fix the rough crank no start issue. I'm going to re-replace the underneath crankshaft position sensor from the original Mopar that I put back on after the Delphi one completely died after a year with new warranty replacement Delphi one.

Any other ideas? The piñata start issue is really annoying!!!

 

[DavidG91]

Maybe fuel pump? I ran a test on it a few times when I did not experience this intermittent issue and saw the pressure stay where it should as long as it should, but maybe when the issue is happening there's insufficient fuel pressure?

I don't want to spend $950 on a new fuel pump installed unless I'm pretty confident that will fix the issue....

 

[James Akemon]

Mine ended up being the ignition switch was cracked and wouldn't make contact when hot

 

[DavidG91]

Interesting. I just replaced the ignition switch actuator when it cracked and freely turned but didn't start, but saw the rough starting issue both before and after that, intermittently for years. (https://www.jeepkj.com/threads/key-ignition-actuator.78834/post-821365)

 

[DavidG91]

I followed the fuel pressure leak down test here https://www.slideshare.net/slideshow/jeep-liberty-2002-2005-fuel-system/45717461, while the system was working/starting and saw the pressures were good, it immediately rose to 55+ with the key on, 56-58 while running, and stayed above 50 for well over 10 minutes after turning it off and removing the key, while the spec just says it should remain above 30 for at least 5 minutes.
I guess I'll keep the loaner pressure test kit in the jeep to test when the start issue happens again.
I guess it could be the relay or the pump or the filter or....

Can you think of any issues with keeping the pressure gauge attached to the fuel rail test port while driving the jeep normally? (With zip ties to keep it from flopping around)

 

[ikuo78]

No DTCs have been output, right?
Since it's not very reproducible, it seems like it's difficult to find the cause.

Have you checked the fuel trim values with a scanner?
Especially the long-term ones.
It seems that LTFT is used for hot starts.
LTFT is calculated from the O2 sensor values while driving.

For reference, I've attached a description of the sensors read by the PCM in real time at the start and the relays used.

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