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Robert R
Robert R, ASE Certified Technician
Category: Jeep
Satisfied Customers: 4409
Experience:  ASE Master Certified, Jeep Certified
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2001 Cherokee 4.0 liter sometimes hard to start when engine

Customer Question

2001 Cherokee 4.0 liter sometimes hard to start when engine is hot. It sputters, misses and crawls along for half a block with gas floored, then engine takes hold and runs fine.
Submitted: 11 months ago.
Category: Jeep
Expert:  Robert R replied 11 months ago.

Hello, welcome and thanks for asking your question. My name is*****'m a Certified Auto Technician with 29+ years experience. I will do my best to assist you. please keep in mind that I may need to ask questions of you before I can answer. When you reply please feel free to add as much detailed information as possible pertaining to your concern.

What about the crank sensor? Have you tested or replaced the crank sensor?

Customer: replied 11 months ago.
no
Customer: replied 11 months ago.
Starts without a problem up to15 minutes after turning engine off. After 20 to 25 minutes it has trouble starting up again
Expert:  Robert R replied 11 months ago.

Sounds like a possible fuel pump issue, possibly the check valve or the pump is getting weak.

At this time, I Highly recommend to use a fuel pressure test gauge and run a fuel pressure test. There is a Fuel Pressure Test Port on the fuel rail that makes it easy to run a fuel pressure test. What you need to do is hook up the gauge, make sure no leaks, run the gauge up to the windshield and tape it there, carefully close the hood trying to not smash the fuel test hose (you might need to use something to help protect the hose ). Drive it and attempt to duplicate the concern. After the 20 to 25 minutes try to start it and check to see where the pressure is at when you try to start it. If pressure is the same as when it was running properly (40 to 50 psi) then the problem is NOT the fuel pump. If the pressure is less than 30 psi when trying to start it, the problem IS the fuel pump and it will need to be replaced.

Keep me posted and let me know if you have any additional questions...

Thank you,

Robert

Customer: replied 11 months ago.
Had fuel pump replaced last year but problem continued
Expert:  Robert R replied 11 months ago.

Where was the pump purchased? We see issues with some aftermarket units...

Keep me posted...

Thank you,

Robert

Customer: replied 11 months ago.
Fuel pump was purchased and installed by Big O Tires store.If low fuel pressure is responsible for the rough starts after 20 to 30 minutes, then how do you explain that it starts normally after an hour, or the first start each morning?
Expert:  Robert R replied 11 months ago.

I wonder where they sourced the pump at?? Big-O is a Tire store so they would have had to get it from their supplier. Do you have a copy of your invoice from Big-O to see if it is listed where purchased and whether it has a lifetime warranty...

If not able to get copy of invoice. My first recommendation is still to run a fuel pressure test to see if the new pump has failed...

Keep me posted...

Thank you,

Robert

Keep me posted...

Thank you,

Robert

Expert:  Robert R replied 11 months ago.

You stated: "If low fuel pressure is responsible for the rough starts after 20 to 30 minutes, then how do you explain that it starts normally after an hour, or the first start each morning?"[/U

I was leaning more towards a problem with the Crank Sensor but since you had the pump replaced with an aftermarket unit. I would recommend to test it first to make sure that it is not what is causing the issue.

From past experience I have seen faulty fuel pumps cause the same symptoms that you described. Normally won't cause a problem if you just shut it off for 5 minutes but for some reason sitting a bit longer the pump wont make enough fuel pressure to keep engine running properly. After sitting a bit longer, the pump cools off enough to run the vehicle normally. Or after the cooler fuel runs through the pump, it starts to make more pressure and run normally.

Keep me posted and let me know if you have any additional questions...

Thank you,

Robert