just want to say what a awesome web site. lots of information. bare with me as i am new to the whole 4.3 cpi motors. i am used to lsx/lt cars. i ended up buying a 95 blazer 4door 4wd 2 weeks ago to pull my race car. on the way to work the truck started to sputter and lost power. pulled over on the side of the road and tryed to start with nothing. it would turn over just not run. ended up putting 4 gallons of gas and still nothing. finally get it towed back home. go to work and get home and i deiced to start it and it did. let it run for 5 or 6 mins and then i turned it off. came back out to go to parts store to find out no start. couple days go by with me working i finally get a chance to see if it starts. it did but then shut off since then i havent been able to get the truck started. i checked for fuel at the lines by just cracking them open and i get fuel out of the left line if standing in front of motor. also get fuel out of schrader valve. but deiced to hook up a gauge and test it. with the key on engine off. psi jumps to about 59-60 psi but as soon as pumps shuts off, it drops down to about 27-29 psi over the course of 60 secs. and stays about 20 psi after 10mins or so.

guy i bought it from said he did put in a new fuelpump a little while ago but did not say which one.also did not say if he replaced the sending unit and wires. i tryed to call and see if he put in a aftermarket one. but did not answer me back( go figure). i have been doing alot of reading and have narrowed my issues down to a few. i read that i can test it at the fuelfilter but need to go to the hardware store to make one. which i didnt have time today, but will tomorrow. should i go and test the fuelpump directly or if the fuel psi loss is enuff to rule the pump as the cause?? again bare with me as i am new to these trucks

Fp blazer 60secs - YouTube

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Trevor

 

Pressure is good but leakdown is excessive. The leak could be in the tank or in the plenum. The pump needs to be isolated from the plenum to determine where the leak is. The fuel filter on your 1995 does not have a quick connect fitting, so it will take a bit of "creative plumbing" to adapt the pressure tester to it. It will be cheaper and easier on yours to "dead end" the line from the pump to the tester. Then activate the fuel pump. Pressure must be 73psi to 108psi and must not drop below 50psi for 10 minutes. If it passes those tests, the pump is good and the problem is in the plenum.

 

Can you explain a little on dead end line test? never heard that expression. Thank you for writing back captain

 

The pressure line from the fuel pump is routed directly to the pressure tester and the flow "dead ends", sometimes called "dead head", at the gauge. The pump has a built in relief valve to prevent damaging the pump itself.

The valve tool you mentioned has a shut off valve and the tool installs in the fuel pressure line. After the pump pressurizes the entire system, the valve is shut off to isolate the pump from the plenum. Depending on gauge placement, (before or after the valve) it will determine where the leak is. The results are fool proof, 100 % accurate.

 

!995 4.3 with the aluminum upper plenum and black plastic cover with VORTEC logo in orange ? just remove the handful of 10mm bolts holding it down to the lower manifold and check for leaks or wash down inside the cavity where the injector "spider" is located . IMPORTANT - Do not try to start or run the vehicle with the plenum open ! Just pressurize the fuel line (turn ignition key to on - pump will prime and any leak evident)

 

Don't misunderstand, a good visual inspection is a great idea. Usually that method will detect an external fuel leak from the lines and fuel pressure regulator. It will NOT detect an internal leak in the regulator or fuel injector.

 

IMHO - opening the upper plenum is the EASIEST most logical approach to determine the overall condition of the fuel delivery system including the spider injector health , fuel lines (called the NUT KIT) and the 6 nylon poppet lines .The regulator almost always fails with a ruptured diaphragm and results in an external leak ...
no special tools are required and can be done in your driveway or quickly done in a NAPA parking lot like I've done , over the years on these central port batch fired 4.3 motor equipped Blazers ,Jimmys , Bravadas .


On the '95 removing the upper plenum is a 10-15 minute job at most and is not what I would consider needlessly pulling things apart or erroneously replacing good functioning parts .. it is a quick visual diagnosis that You don't need a sun engine performance analyzer to perform .

 

After you remove the plenum and there are no visible leaks, then what? Put it back together, pull the tank and replace the fuel pump? I hate to disagree, but the ONLY thing removing the plenum will reveal is an external leak from the nut kit, regulator, or a spider line. Granted, those are common problems with the CMFI system however, you can't see if the injector or a poppet is leaking, or if the regulator is bypassing. Isolating the pump from the plenum, after it pressurizes the system, will tell you if the leak is in the tank or the plenum, or both in some cases. If it indicates the leak is in the plenum and you remove it, and there are no visible leaks, that's when you install a second shut off valve, in the return line. That will tell you what is leaking in the plenum. I'd rather diagnose it and know what the problem is, than guess and take things apart, or worse yet, replace parts needlessly, but, that's the difference between a mechanic and a technician