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Fuel Pressure Problems

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Old 06-09-2007, 01:25 PM
  #1  
1956_4x4
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Default Fuel Pressure Problems

Background - Engine is very difficult to start. Once started, it may die but will start easier the second time. Engine does not seem very responsive to throttle changes (this may be the way these engines are, I recently bought this vehicle and it wasn't running when I bought it...) Codes P0171 & P0174 (both banks lean) are being set by computer. There are no longer any vacuum leaks, the throttle body has been cleaned, IAC was outside parameters and has been replaced, MAF has been cleaned, coil pack has been tested, and plugs and wires have been changed. Most of this stuff was in dire need since the vehicle seemed to have limited maintenance during it's entire life....

Finally hooked up a pressure gauge to the fuel system and may have found the problem. Key on/engine off pressure reads "0". Start engine and pressure reaches "32". Shut off engine and pressure drops rightback to "0".

Is there not a relay that energizes the fuel pump for like 15 seconds with the key on/engine off? If so, where is the darned thing? Also, are these systems not designed to maintain pressure after the engine is shut down? I have the factory EVTM manual, but the shop manual is still "in the mail" and has not arrived.

I did a search and found 45-50 psi for key on/engine off and 35-40 psi at idle. Not too sure how accurate these specifications are for a 1995 3.8.


Smitty
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Old 06-10-2007, 04:43 AM
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jhodges10
 
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Default RE: Fuel Pressure Problems

I have a similar problem with my 5.0. It almost always cranks for a while then the second time I turn the key it starts right up as if it is building pressure the first time around. I also lose fuel pressure almost immediately. I've got a new fuel pump that I'm hoping to put on this week altthough I'm not sure it will solve the problem. I'll try to update you once I've done the work and let you know if it helps the issue.
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Old 06-10-2007, 11:40 AM
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1956_4x4
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Default RE: Fuel Pressure Problems

Ok. New bit of info on the problem. According to the manual, the pump is only to activate for 1 second when the key is in the run position and will stop if the key is not placed in the start position. So I hooked the pressure guage back up to see if I had just missed it. This time the guage jumped about 15 psi when I placed the key in the run position. The weird thing is that the pressure held. I cycled the key two more times and achieved around 35 psi ... and it held.

So I started the engine and the pressure held steady at 32 psi. When I shut the engine down pressure dropped back to "0". I cycled the switch to run and the pressure will bump up then drop right back to "0".

The manual actually gives me very little info on the system, so I have aquestion.
There is a chrome disk inline with one of the rubber hoses going to the fuel rail. Is this also a regulator or is it possibly some type of pulse dampner?

Between the manual and input I've received from people I think I've narrowed it down to the pressure regulator, fuel pump (or a check valve somewhere around the pump), or possible injector leak (I doubt this because of the lean condition, but it could result in a pressure drop.)

The manual gives no information on testing the regulator. Is there a way to actually test it? I'm not real big on shotgunning parts at a problem in the hopes of fixing it...

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Old 06-10-2007, 03:41 PM
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1956_4x4
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Default RE: Fuel Pressure Problems

Well, it's not the pressure regulator. I swapped mine with a friends car and my pressure problems stayed the same.

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