engine loss of power

[1hillbilly]

hi i have a 2000 gmc jimmy 300.000 km 4.3 vortec .starts ok, even when cold idle smooth but when I accelerate past 2000 rpm it has a complete loss of power. I bought a fuel pressure tester key on 2 seconds 60 psi when I start the vehicle and running 55 psi. I took it on a road test it stays at 55 psi and has a hard acceloration and will go to 60 psi ,and then starts to break up my first question is how can I block off the return line to the tank, there's no rubber hose in any of the connections just steel lines and hard plastic with push connectors, is there a plug that you can buy or any suggestions on how I can block off the return to see if the pump will build pressure to 75 psi to 80 psi will this will tell me whether the pressur regulator is faulty or the fuel pump needs to be replaced I have a manuel its a Haynes for chevy blazer gmc from 95 to 2004 it says with central sequential fuel injections (csefi) key on engine not running it should be approx 55-61 psi the engines running at idle it should decrease through 3 to 10 psi according to this manual i am within range but i have read on other posts that it should be 60-65 would you say that my 55 psi reading is okay? or should it be 60-65? also when i blocked the return line should i get a reading of 75 or higher? if the reading goes up does that mean that the fuel regulator is faulty? and if it doesnt go up does that confirm that the fuel pump is the issue?
any information you can give me would be greatly appreciated
ill post back the results after the return line test
thank you

[old_master]

#1 Get rid of the Haynes manual. Half of the procedures are flat out wrong, the other half isn't even in the book, and the other half, the specs are either not there, or totally incorrect.

#2 (Perfect example of #1) Key ON engine OFF fuel pump running: Fuel pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off. Straight out of the GM shop manual for your engine.

#3 (another example of #1) Blocking off the return line is quick and easy way to rupture the diaphragm in the fuel pressure regulator, (not a cheap fix). Blocking the return line is done with 2 special tools for diagnosing certain fuel delivery problems. Unless you have a factory shop manual, and the special tools, don't attempt it.

#4 (yet another example of #1) GM does not publish any engine running fuel pressure specs for this engine. There are far too many variables involved.

60psi is at the bottom of the spec range: Have you checked the fuel filter for restriction? You mentioned while driving, pressure goes up to 60psi then it "starts to break up" do you mean the fuel pressure drops? Under hard acceleration, fuel pressure will read either key on engine off pressure, or maximum pump output pressure, which ever is lower. Check your fuel pressure and leakdown, then post the results.

[maxwedge]

Originally Posted by old_master

#1 Get rid of the Haynes manual. Half of the procedures are flat out wrong, the other half isn't even in the book, and the other half, the specs are either not there, or totally incorrect.

#2 (Perfect example of #1) Key ON engine OFF fuel pump running: Fuel pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off. Straight out of the GM shop manual for your engine.

#3 (another example of #1) Blocking off the return line is quick and easy way to rupture the diaphragm in the fuel pressure regulator, (not a cheap fix). Blocking the return line is done with 2 special tools for diagnosing certain fuel delivery problems. Unless you have a factory shop manual, and the special tools, don't attempt it.

#4 (yet another example of #1) GM does not publish any engine running fuel pressure specs for this engine. There are far too many variables involved.

60psi is at the bottom of the spec range: Have you checked the fuel filter for restriction? You mentioned while driving, pressure goes up to 60psi then it "starts to break up" do you mean the fuel pressure drops? Under hard acceleration, fuel pressure will read either key on engine off pressure, or maximum pump output pressure, which ever is lower. Check your fuel pressure and leakdown, then post the results.

Amen to all points!

[YooperJ]

I had a similar problem and did lots of things to try and fix the problem. Car was at local gm dealer who replaced the fuel pump under warranty. Still had problems with no codes. Changed plugs, cap, rotor ac deco brand, stll had the problem. Long story short, I cleaned the mass air flow sensor with electronic contact cleaner since I did not have maf cleaner. Worked like a charm ever since, about 5 months now. Worth the try. Good luck.