Crankshaft Sensor? Hard Startups

[Whelan]

Our 05 3.7L has developed a hard startup. Battery was replaced last summer, but all day it has a bit of a chug when turning over like it may not want to start. Sometimes takes a second turn of the key but it runs fine when started.

No codes, trying to diagnose if it’s a pump or a crank sensor. Would love any insights on what may be the culprit. Sensor seems easy enough to do quick and see.

 

[Billwill]

A bad crank or cam sensor should post a code...the fact that it runs fine would also suggest that the sensors are OK.

The fact that the engine chugs when turning over would suggest to me that you need to:

Check the battery terminals are clean and tight on both ends.
Check the engine grounding straps grounding the engine to chassis are clean and tight all ends.
Check the connections on the solenoid/starter are on tight.
Measure the voltage supplied by the solenoid to the starter with a multi meter while turning engine over....if very low then the solenoid may need replacing.

If you take a thick cable such as used on heavy duty jumper leads and clamp one end to the negative battery terminal and the other end onto the starter motor body and it then turn over nicely then it would point to one of the grounding straps/cables not being good!

 

[LibertyTC]

^ Good recommendations there Bill !
Any corrosion to terminals? If so definitely clean them up with emery cloth or wire brush & then tighten.
Even tho the battery is 1 year old, I would want to confirm the battery is able to pass a load test, & that the charging system voltage output is sufficient.
You could try trickle charging the battery overnight & if it starts easier the next morning, you know then battery should get load tested.
Another thought is to remove the serpentine belt to ensure all of the accessory pulleys are spinning freely, and not causing any additional strain, when starting.

 

[Whelan]

A bad crank or cam sensor should post a code...the fact that it runs fine would also suggest that the sensors are OK.

The fact that the engine chugs when turning over would suggest to me that you need to:

Check the battery terminals are clean and tight on both ends.
Check the engine grounding straps grounding the engine to chassis are clean and tight all ends.
Check the connections on the solenoid/starter are on tight.
Measure the voltage supplied by the solenoid to the starter with a multi meter while turning engine over....if very low then the solenoid may need replacing.

If you take a thick cable such as used on heavy duty jumper leads and clamp one end to the negative battery terminal and the other end onto the starter motor body and it then turn over nicely then it would point to one of the grounding straps/cables not being good!

Cold start this morning it cranked just fine with no issue.

As for the grounding straps, assuming I can just follow the negative cable around to locate or are there specific spot I can locate them? Just want to be sure I'm not missing anything, will definitely check all connections this evening when I'm doing the rear brakes on my fil Aspen.

 

[Billwill]

OK clean all the points with Emory cloth as suggested.
The negative battery lead can be traced from the battery down to the firewall.
The V6 gasser has two grounding straps I believe...one from the heads of each bank.

The 2005 Jeep KJ Service Manual section 8W has the wiring diagrams which include a locations section for the grounding points.

Index of /manuals/Jeep/KJ

Check if your fuel pump is running OK when you switch the ignition ON.

Put a voltmeter across the battery while turning the engine over. Voltage should be about 12.5 volts at rest and should not drop below about 9.5 volts at turnover and should be at about 13.4 volts while running.

 

[jeeplib05]

What about your spark plugs? Mine wouldn’t turn over at all so I changed them and it fires right up every time