P0301: Missing on Cold Start

Bratch

Bratch

TJ Enthusiast
Supporting Member
Joined
Jan 22, 2018
Messages
113
Location
OKC
Our Jeep threw a P0301 last weekend, it’s been parked since then but I got to take it out today.

It’s has always needed to prime the engine to get it to start easy, I’ll turn the key to run three times and then it’ll turn over. I suspect we have a bad check valve but haven’t inspected it.

This morning it started a little harder than normal, and then had a pretty rough idle for 15 or 20 seconds and then smoothed out. Ran smooth and normal on the 4 mile drive to the park, power and responsiveness seems to be normal. Took the dog for a 45 minute walk and when we got back to the Jeep it started right up on the first turn with no priming. We set in the parking lot for a couple minutes and the idle was nice and smooth. The drive home was completely smooth and normal.

I’ve read @CodaMan detailed thread and there are so so many angles to look into. Any advice on places to start with the information that it only seems to be rough/missing on a cold start for a few seconds?
 
Any unusual noises on first startup? I've got what I believe to be a sticky lifter that ocasionally causes symptoms similar to yours. But you can hear a definite clatter when it happens..
 
Your problem describes the symptoms of a bad check valve inside the fuel pump. I'd replace the fuel pump itself, which is located inside the fuel pump assembly, with a Bosch like is available on Amazon etc. Don't replace the entire module with an aftermet Airtex, Spectre, or store brand or you'll be sorry within about a year when those tend to fail.
 
twistedlv said:
Any unusual noises on first startup? I've got what I believe to be a sticky lifter that ocasionally causes symptoms similar to yours. But you can hear a definite clatter when it happens..
Click to expand...

It’s had a rattle from the engine on start up for a couple minutes that goes away. It’s been that way for the 2+ years we’ve had it.

Jerry Bransford said:
Your problem describes the symptoms of a bad check valve inside the fuel pump. I'd replace the fuel pump itself, which is located inside the fuel pump assembly, with a Bosch like is available on Amazon etc. Don't replace the entire module with an aftermet Airtex, Spectre, or store brand or you'll be sorry within about a year when those tend to fail.
Click to expand...

It’s been on my to do list, I need to go ahead and order the pump so I have it on hand if I get a nice weekend to pull it. Is there anyway the fuel pump could cause it to show a P0301 CEL?
 
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