Hi everyone,

I have a 1996 Jeep Cherokee with 252,000 miles and it has a misfire that shakes the Jeep. The idle is steady no check engine and I have new ignition, spark plugs, wires, distributor cap, rotor, maf sensor, throttle body sensor, no vacuum leaks, new header with gasket, new injectors, new air filter. Today, I was checking the fuel pressure and when it’s on it flutters from 42 psi to about 51 psi. When I shut it off it stops at 49 psi and it’s stays pretty steady. My issue is that I spent like 10 minutes releasing the fuel from the clear fuel line on the fuel pressure test kit from autozone and bubbles came out and never stopped coming out. Any ideas what it could be. I may need to do more diagnostics but maybe somebody here can point me I’m in the right direction.

 

Error

 

I gotta take a minute to give you

We sure get tired of people who think repairing a car is about throwing parts at it until it works right. We've seen people throw a couple of grand at a problem and never do one bit of actual troubleshooting It's sure nice to see someone who takes a rational approach for a change! Kudos!


That's not good. That's probably your misfire source.


That part is good.


And that part is NOT good. That was while the engine was running, correct?


Sounds to me like your pump is strong, but it's sucking air occasionally. If there were a leak AFTER the pump, you'd have a fuel leak, instead of sucking air. That suggests to me that it's a problem with the intake into the pump - somehow it's sucking in air. I can't quite picture how that could be, though.

Let's see what other folks have to say.

 

I think the next step would be shooting the Parts Cannon at the fuel pump. Faulty check valve.

 

Although what means "pretty steady"?

Try measuring it after a period of time.

Regardless, I think you're looking at pulling the fuel pump.

 

yes, while the engine was running.
thanks for your input.

 

k

I watched it for 15-20 mins and went from 49 to around 47 psi. Thanks for your help.

 

Sorry but I'm confused. What is the clear line connected to? One end is obviously the gauge, the other end?

The spec of fp is 49.2 psi +/- 5 psi. If yours drops to 42psi, then look for any kinks in the lines running back to the tank. If they all look good, then as others suggest, your pump is suspect.

 

Hi, the clear tube is the one that releases the fuel pressure from the gauge and fuel comes out through it. I attached a picture to reference.
thanks for your help.

 

When you hook the tester to the Schrader, the black tube is full of air and may be the source of those bubbles. I don't think you can definitely say there's air in the system itself. Yet.

 

Did you check compression?

 

While it's shaking, pull the plug wires one at a time to see if you can identity a particular cylinder(s) as the culprit(s).

 

I don't think it's the fuel pump. I'm gonna throw out some back of the book stuff like CPS/CKS is out of sync or the timing chain jumped (rare, but if teeth or a chunk of gear breaks off it happens).

 

OK, that's what I wanted to verify. As Dave said, that's likely air trapped in the gauge line you released by pressing the button.

When I check for a "missing cylinder", I pull the fuel injector connector off. Less risk of getting zapped.

Also your '96 is OBD. I read that the CEL is off, but have you read any codes to see if any are pending??

 

i agree that sounds like a timing issue maybe a cylinder injector is coming in and out.. check the wires rule it out..

the compression test is not a bad idea and so easy to do on them