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no fuel pressure when pressing fuel rail valve?

B

bboyes

NAXJA Forum User
Location
australia
Hey guys this morning my 95 xj wouldn't start, it turns over fine just wont fire up.
I can hear the fuel pump prime when the key is turned but should there be pressure when i press the valve on the fuel rail??? the most i got was a small dribble after priming the pump 3 times...
any help appreciated thanks!!
 
Your engine needs approximately 31 psi of fuel pressure to start. If you can hear the fuel pump running but you have no fuel pressure at the fuel rail, you have 1 of 2 things happening.

1. A completely clogged fuel filter (located on the frame rail on the drivers side)
2. A failed fuel pump
 
The prime fills up the fuel rail but really doesn't build much pressure (kind of a small squirt, then dribble). The fuel pump kicks in again while the motor is cranking. No pulse signal from the CPS and the fuel pump won't pump. I'd check for spark while cranking, no spark and no fuel pressure *while cranking* and it is most likely the CPS.
 
I have a similar problem. I have a 1991 Laredo with a 4.0L. It had been sitting a while (several years) and the tank and pump were totally shot, so I replaced them both, flushed the fuel lines, replaced the fuel filter, flushed the fuel rail and cleaned the injectors.

The pump will prime when I turn the key, and the engine will start, but it idles rough, surges then dies. I checked for pressure at the rail, and there is none with the engine off. I checked for fuel flow at the rail, and it passes the liter-in-a-minute test. I jumped the fuel pump relay, and the gauge shows about 12-14 psi but drops to zero when I remove the power.

To my thinking, there is only four places where the fuel could go: (1) back to the tank via a leaking regulator. I eliminated this by removing the return hose and plugging the return outlet on the rail with my finger and got the same results. (2) into the engine via leaking injectors, but I don't suspect this because the engine starts right up indicating that it is not flooding, which it would if you squirted a lot of fuel into the intake. (3) onto the ground, but there are no signs of that. (4) back into the tank via a bad fuel pump. As I said earlier I just replaced the pump. Do they go bad right out of the box?

Any suggestions would be helpful. I really don't want to drop the tank again, since it is half-full of gas.

Thanks
 
birchlakeXJ said:
Your engine needs approximately 31 psi of fuel pressure to start. If you can hear the fuel pump running but you have no fuel pressure at the fuel rail, you have 1 of 2 things happening.

1. A completely clogged fuel filter (located on the frame rail on the drivers side)
2. A failed fuel pump
Click to expand...

Or 3) a failed vacuum actuated fuel pressure regulator on the fuel rail. (I think the 95 still had the FPR on the fuel rail? I could be wrong)

Or 4) a bad rubber hose from the fuel pump outlet in the tank to the steel fuel line in the flange assy.

or 5) a clogged fuel filter on the pump suction side in the fuel tank starving the pump.
 
HellCreek said:
I have a similar problem. I have a 1991 Laredo with a 4.0L. It had been sitting a while (several years) and the tank and pump were totally shot, so I replaced them both, flushed the fuel lines, replaced the fuel filter, flushed the fuel rail and cleaned the injectors.

The pump will prime when I turn the key, and the engine will start, but it idles rough, surges then dies. I checked for pressure at the rail, and there is none with the engine off. I checked for fuel flow at the rail, and it passes the liter-in-a-minute test. I jumped the fuel pump relay, and the gauge shows about 12-14 psi but drops to zero when I remove the power.

To my thinking, there is only four places where the fuel could go: (1) back to the tank via a leaking regulator. I eliminated this by removing the return hose and plugging the return outlet on the rail with my finger and got the same results. (2) into the engine via leaking injectors, but I don't suspect this because the engine starts right up indicating that it is not flooding, which it would if you squirted a lot of fuel into the intake. (3) onto the ground, but there are no signs of that. (4) back into the tank via a bad fuel pump. As I said earlier I just replaced the pump. Do they go bad right out of the box?

Any suggestions would be helpful. I really don't want to drop the tank again, since it is half-full of gas.

Thanks
Click to expand...

Yes bad pumps are common especially airtex. Use only Mopar-Jeep or Bosch pumps imho. The fuel line on the pump outlet could have come loose in the tank? Did you check the ground and the voltage to the pump?
 
Thanks, Ecomike. That's what I was afraid of. As I said, the flow test was good, It just doesn't build pressure or hold it. What's your take on Delphi pumps. They work great on Broncos. In fact, that's what is recommended on the Full Size Bronco forum.
 
How full is your tank. The hose from the pump to the outlet pipe sometimes comes loose. All seems fine with a semi full tank, but as soon as it goes down a bit, things quit.

Clamp off the return hose and see if you get pressure/start. If so, most likely the regulator is bad.

You may not have pressure after you turn off the key if the one way valve in the pump is bad, but that should not keep it from starting, just keep it from starting as fast.
 
Hi, Tom,

My tank is half-full. My fuel lines (both) are plastic and steel, so no clamping. I did remove the plastic return line from the fuel rail and held my finger over the fuel rail stub. I still only got about 14 psi. I removed my finger from the stub and there was no leakage. Besides, I replaced the pressure regulator with a new one, because I also thought that was the problem. I am guessing that the check valve in the pump is bad or the rubber elbow has blown off.

Thanks,
Tom
 
You either have a plugged filter, a bad pump or the hose in the tank is loose.
 
Since you hear the pump prime, it is not likely that the pump is the problem, but you never know. Check the fuel filter first because it is the easiest. After that you have to deal with pulling the fuel pump assy to check both the hose and the pump.

Look at the bright side, you aren't doing it on some dusty trail or mud bog.:rolleyes:
 
Hi, Cruiser,

The only problem is that I need the complete assembly and not just the pump. I have not been able to locate a Bosch complete assembly. Does anyone know who has these?

Thanks,
Tom
 
I don't think Bosch builds a sending unit. worst case scenario. Buy a used sending unit from jy or part out and install the bosch fuel pump into it. That is your best bet.
 
I was hoping to return the Spectra Premium pump assembly to O'Reilly's and get my money back on the lifetime warranty, but since I need the sending unit, I guess I will have to keep it and replace the Spectra pump with a Bosch. I would have bought the Bosch at the get-go, but, as you say, they don't have a complete assembly.
 
I pulled the Spectra "Premium" pump from the tank, and the rubber hose was just sitting on the pump outlet - not over it. The hose clamp was installed at the factory about 3/4" from the end of the hose, which is beyond the length of the pump outlet tube, which allowed it to blow off under pressure. Definitely shoddy workmanship. If it had been installed properly, the pump might have lasted for years - who knows. At any rate, they are getting this one back. Thanks for the help.

Tom
 
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