Random hard start, running rich

[bigpapaparker]

2004 Jeep lj, 4.0 42rle. Engine and things like that completely stock. 165k ish miles.

A couple times now after it sits overnight or longer. And months between incidents. Will crank fine but not for unless you give it throttle. Let off it'll die until it clears itself out. Definitely running rich, can smell the raw fuel coming from exhaust. No trouble codes, live data shoes acceptable numbers both short term and long term fuel trims. I believe all original injectors and fuel pump. I have not checked fuel pressure, it's a little harder deal than the older ones.So if I can't find anything with a scan tool, I'm looking for any advice.

 

[macleanflood]

Leaking fuel injector?

Does the fuel pressure drop over time as it sits?

I bought a set of injectors from Precision Auto Injector. Use the code Jeep for a discount.

-Mac

 

[bigpapaparker]

Leaking fuel injector?

Does the fuel pressure drop over time as it sits?

I bought a set of injectors from Precision Auto Injector. Use the code Jeep for a discount.

-Mac

Is that a likely culprit? Like I say, I don't have a good way to monitor pressure, but I can fashion something up, I think. How fast should pressure drop? And it's only a couple minutes of running to clear it out

 

[macleanflood]

You can rent or borrow a fuel pressure gauge from just about any auto parts store. Or buy from Amazon.

Your Jeep might not have a Schrader valve on the fuel rail. Racetronix makes an adapter for the quick disconnect fitting to 1/8" npt...you can then add a Schrader valve or a gauge.

Or buy a new fuel rail with a port... they're pretty reasonable.

Your pressure should remain constant. Only two things cause it to leak down... injectors or the regulator in the fuel pump.

My gut feeling is you have a leaking fuel injector since it backfires on start from all the fuel that leaked into the cylinder.

If it were mine I'd verify fuel pressure, replace the injectors, if you didn't have a Schrader valve get a new rail, and add DEI's heat shielding to your injectors to solve your next few problems.

-Mac

 

[bigpapaparker]

You can rent or borrow a fuel pressure gauge from just about any auto parts store. Or buy from Amazon.

Your Jeep might not have a Schrader valve on the fuel rail. Racetronix makes an adapter for the quick disconnect fitting to 1/8" npt...you can then add a Schrader valve or a gauge.

Or buy a new fuel rail with a port... they're pretty reasonable.

Your pressure should remain constant. Only two things cause it to leak down... injectors or the regulator in the fuel pump.

My gut feeling is you have a leaking fuel injector since it backfires on start from all the fuel that leaked into the cylinder.

If it were mine I'd verify fuel pressure, replace the injectors, if you didn't have a Schrader valve get a new rail, and add DEI's heat shielding to your injectors to solve your next few problems.

-Mac

View attachment 533044

Mine does not have a schraeder, and I do have that adapter from racetronix , but haven't got a gauge for it yet. It does not back fire though, like your saying. It just won't fire at all until I open the throttle, very much like a flooded engine

 

[bigpapaparker]

You can rent or borrow a fuel pressure gauge from just about any auto parts store. Or buy from Amazon.

Your Jeep might not have a Schrader valve on the fuel rail. Racetronix makes an adapter for the quick disconnect fitting to 1/8" npt...you can then add a Schrader valve or a gauge.

Or buy a new fuel rail with a port... they're pretty reasonable.

Your pressure should remain constant. Only two things cause it to leak down... injectors or the regulator in the fuel pump.

My gut feeling is you have a leaking fuel injector since it backfires on start from all the fuel that leaked into the cylinder.

If it were mine I'd verify fuel pressure, replace the injectors, if you didn't have a Schrader valve get a new rail, and add DEI's heat shielding to your injectors to solve your next few problems.

-Mac

View attachment 533044

Do you have a link for buying the fuel pressure schraeder valve that screws in to the 1/8 npt hole?

 

[macleanflood]

https://www.amazon.com/Earls-9616SVERL-Male-Schrader-Valve/dp/B01EKUFV90?tag=wranglerorg-20

 

[bigpapaparker]

https://www.amazon.com/Earls-9616SVERL-Male-Schrader-Valve/dp/B01EKUFV90?tag=wranglerorg-20

That looks like a tire schraeder, which is different than a fuel pressure schraede

 

[bigpapaparker]

well i have a fuel pressure gauge on now, it's reading about 42psi running. it drops down to about 32 psi after 30 minutes or so.

 

[macleanflood]

So either you have a bad fuel pressure regulator or you have a leaking injector.

-Mac

 

[bigpapaparker]

The fsm claims it needs to stay above 35 psi after 5 minutes. And it does that. Are you saying that is not good enough?

 

[macleanflood]

I might be wrong then.

-Mac

 

[bigpapaparker]

It does make sense that an injector could be leaking down intermittently, causing these problems. It has happened twice in the past 12 months or so.