I replaced the fuel pump on my white 96 2WD 4.3L about 3 months ago. The Delphi pump solved the no start issue and after testing the fuel pressure at the fuel filter inlet, or right after the pump it shows + 70 or higher and it holds this with the pump not running. I have replaced the spider on another 96 (red) blazer so I have some "on the job" experience with how most of the fuel delivery works on these. That being said back to the white blazer, at the shraeder service port I get a dropping pressure down to 40psi or lower when doing the key on test. I know that a leaking injector or a leaking regulator could be the problem with the pressure drop. What I am unsure of is the fuel return line and what it connects to as the culprit as the possible problem. I was about to remove the intake manifold and I suddenly realized that I was unsure of the operation of this fuel return line in the fuel delivery system. I have done both lower manifold once and the upper twice on my other 96 Blazer so it seems I should know more about the return fuel line but duh...could someone please enlighten me as to the operation of the return line. That is the other smaller tube into the spider block. Affect on drive ability is that at idle the engine is rough to very rough however it hasn't died. As soon as you give it gas it accelerates and runs perfectly and seems to not be using excessive fuel. Thanks for your help.

 

Sorry bit of a tough read.


Are you asking if the return line is the cause of your FP drop down?

 

Sorry for the hard reading, I should have read what I wrote. I verified that the pump has very good pressure at the fuel filter (out of the fuel pump)and it holds it and does not bleed off. At the Shraeder valve it varies between a bleed off from 63 psi to 40psi or lower in 3 to 4 seconds after performing the key on pump energize test. I know that there are several ways fuel can leave the injector block, one being the unlikely possibility of an actual crack in the plastic it is made of. Normal ways would be through the injectors or through the pressure regulator. The engine runs very good through acceleration, without missing and does not seem to be using excessive fuel. The pressure bleed off is not normal but apparently the pump is able to pressurize for a normal engine "start". Is there a place to plug the return fuel line such that this could be eliminated as a possible source for the pressure being lost. That would just about eliminate all other possibilities other than "under the upper intake manifold".

 

No not really. It's a straight unblocked line back to the tank. You need to pull off the plenum, I think if it was blowing out you would smell raw fuel.

 

Fuel in the return line to the tank is from the fuel regulator, right? I need to take the upper manifold cover off and check the fuel regulator.

 

My 95 blazer is doing the exact same thing. We had just replaced the pressure and return fuel lines inside the intake in June of last year. Talking to a couple of mechanics one said it could be the regulator and the other said it could be the whole spider itself. You wont know until you take the upper manifold cover off where the leak is coming from. Just hope its the $50 regulator and not the $250 spider.