XJ6 & XJ12 Series I, II & III 1968-1992

XJ6, S-3, Fuel pressure Low

 
  #1  
Old 05-31-2014, 11:12 AM
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Default XJ6, S-3, Fuel pressure Low

Hi Guys,
Still fighting the fuel issues and appreciate all your help so far.

Fuel pressure at rail after warm up is 28psi (30psi cold). If I disconnect the vacuum line at the regulator, it jumps to 36psi. The vacuum is 17-18 inches on this line.
Dead heading the pump prior to the rail gives me about 75psi fuel pressure.

I plumbed around the fuel temp switch straight to the manifold and got the same readings.

I replaced the fuel regulator and got the same readings.

Could sure use some help.

Thx, Jim
 
  #2  
Old 05-31-2014, 12:04 PM
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The spec is 36 psi *while cranking*. Is that how you tested it?

My experience is that fuel pressure *while running* will vary from about 32-36 psi depending on load/vacuum

I'm not sure if the numbers you mention are low enough to be a problem but it sounds iffy to me

How is she running?

Cheers
DD
 
  #3  
Old 05-31-2014, 01:24 PM
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Thank you Doug for the quick response.
28 hot and 30psi cold while idling. A little fluctuation when working the throttle but quick return. Hard to tell about cranking.
The only time I see 36psi is when I disconnect the regulator vacuum line. Plugging the line has no change except the motor runs smoother. Normally it idles rough rough with some backfire during acceleration.

Thx, Jim
 

Last edited by jimwrye; 05-31-2014 at 01:26 PM.
  #4  
Old 06-04-2017, 03:19 PM
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Something new,...
Disconnect/plug the vac line and get instant, and constant 36-38 psi fuel pressure at all rpm's as well as in drive, key on. Never more, or less. Holds pressure for hours with the air bleed/check valve completely removed from system and engine off..
Pump deadheads close to 100 psi.
Filters show no sign of crud.
* Now,... Standing over the running engine, A/C compressor on, vac lines connected, engine idling really rough at about 600 rpm,... I accelerate quickly and the engine falters, hesitates for what seems like at least 30 seconds but the fuel pressure immediately jumped from 30 to 36ish psi. It apparently recognized the demand but acts like the advance is not working or ?

Could removing the California smog stuff have had any effect?
Now trying to run my A/c just made stuff worse.
Whatcha think guys?
 

Last edited by jimwrye; 06-05-2017 at 03:02 PM.
 
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