2006 Liberty cranks will not start when warm but OK when cold

2006 Liberty cranks, starts, and runs perfectly when engine is cold.

If you drive 10 miles and turn it off and wait 5 min it will crank and not start. Wait 10 more min. and it will start.

I replaced just the fuel pump, not the entire assembly and it does the same thing.

Engine Running fuel pressure is 50 psi
Engine off, after running waiting 10 min., fuel pressure is 52 psi and gets a crank no start.

I can get it to start 3 different ways when I get a crank no start with a warm engine:

1) If I drain the fuel pressure from the fuel rail shredder valve the Liberty will start perfectly and run well.
2) If I let it sit for 15 min. or more it will start.

3) If I spray brake cleaner down the intake it will start.

Anyone have any ideas or next steps with troubleshooting?

Usually the cam or crank sensor fails when hot. Sometimes will post a CEL for the failing part so you need to read out the CEL codes stored....most common failure is the Crank Sensor.

Download the 2006 KJ-SM.pdf here....the bottom of the Index Page lists the CEL codes and tells you which page to go to for that code.

Section 8W has the wiring diagrams.

www.colorado4wheel.com/manuals/Jeep/KJ/

Thanks Billwill. I’ll check it out.

Well no luck. No CEL. I changed the cam and the crank sensors with Mopar replacement parts. It is doing the exact same thing.

Any ideas???

What CEL codes do you have?
Could be some other Sensor.

Is this a Gasser or a CRD?

There are no CEL’s. Just will crank/no start when it sits for 15 minutes after driving. It is a gas engine.

I swapped the ASD relay this morning. And then verified signals to PCM. I pulled relay and then put test lights between 30 and 87. Also a test light between 85 and 86. Both lights came on while cranking during no start. Also OHMed relay. All was good but still a crank/no start.

I verified spark and fuel injector voltage cycling during crank/no start also.

One shot of brake cleaner in the brake booster vacuum line that connects to intake manifold and it starts up and runs well

I am out of ideas

Sounds like a fuel supply issue.....these often do not set a CEL.

When you drain the fuel from the fuel rail shredder valve it seems to work.

Fuel pump/filter OK and not getting air into the fuel lines?

I am not an expert on gasser fuel supply problems so I will leave that to the real Experts here...I specialize in electrical problems!

have you checked/cleaned or swapped your injectors?

Took the Jeep to the local dealer this week. They could not figure it out for sure, but said when driving the fuel pressure drops to 35 psi. They think this low pressure when driving may allow fuel vaporization when Jeep is then parked after driving. They suggested changing the fuel pump assembly because it contains the pressure regulator and I only changed the actual pump.

New Denso fuel pump assembly comes Tuesday. I’ll post if it fixes the issue.

Replaced fuel pump assembly. After two days I have had no issues with the crank/no start. I believe the issue is fixed. Must have been the fuel regulator in the fuel pump assembly. Big thanks to Southern Jeep in Chesapeake VA for putting me in the right direction.

RodMac said:

Replaced fuel pump assembly. After two days I have had no issues with the crank/no start. I believe the issue is fixed. Must have been the fuel regulator in the fuel pump assembly. Big thanks to Southern Jeep in Chesapeake VA for putting me in the right direction.

Click to expand...

I think i have this issue just starting today, no codes, intermittent issue when starting the engine hot, it hiccups and seems to want to start but fails, can you link a part number of what you ended up swapping?