97 Blazer 4.3 low fuel pressure

[samiller]

Perhaps someone can help me out. My trouble is as follows;
Turn the key to run, everything works as advertised, all the correct lights come on, fuel pump kicks on for 2 seconds then kicks off. Turn the key to start, engine turns over and no start. Checked for spark, checks good, tried it with a little ether, it runs until the ether is gone then quits. No codes on the computer, checked fuel pressure, is 10 psi with key on. Changed the filter for grins, no help. Jumped the pump to keep it on, still no pressure rise. Ordered a pressure regulator, thinking it is stuck in full bypass. Could it be the pump? I've also checked voltages etc on all of the sensors, and they wring out by the book. I am hopeful the regulator will fix it, but I'm not exactly confident at this point. Any insight would help me a bunch.

[sparky672]

It's most likely the pulsator which is located in the tank with the pump. This is supposed to hold pressure in the line even after the engine is off.

You are only seeing 10 PSI so it seems that the pump and pulsator are the best place to start.

I was told by a dealer mechanic that pulsator failure on the Blazers is very common. Something about the rubber disintegrating and allowing fuel to bypass back into the tank.

Changing both pump and pulsator as a set is a good option since dropping tank is so labor intensive.

When my '95 failed in '98, I was looking at everything but the fuel. When I finally got a pressure guage hooked up, I saw plenty of pressure but it didn't hold when engine was off.

Good Luck

[samiller]

Thanks, I'll post the fix when I get it going.

[samiller]

I replaced the pressure regulator to no avail. Still 10 psi fuel pressure. Ordered up a pump module (330.00) and installed that today. Not too bad of a job, 4 hours. Hooked up the pressure gauge and turned the key, 10psi. Tried to start it, nothing. Vented the fuel gauge line into the intake for a prime, tried it again and it started with fuel pressure within specs. Drove it around about 50 miles today with no further troubles. Looking at the Haynes manual, there is no mention of a pulsator. The pump module includes everything on this year truck. Pump, sender, the whole works, so perhaps this pulsator is integral to the pump module.

[sparky672]

I'm glad you got it. I heard that there were many many problems with the pulsators in '95 so maybe they quickly changed the design for the better. The pulsator is a small plastic chamber with a metal cap on the side. It pushes onto the tube coming out of the pump and the other end pushes onto the stub just under the tank cover.

If there is nothing between the pump and the tube, then you may be right about a new design. Let me know please.

[samiller]

Originally Posted by sparky672

I'm glad you got it. I heard that there were many many problems with the pulsators in '95 so maybe they quickly changed the design for the better. The pulsator is a small plastic chamber with a metal cap on the side. It pushes onto the tube coming out of the pump and the other end pushes onto the stub just under the tank cover.

If there is nothing between the pump and the tube, then you may be right about a new design. Let me know please.

The module in the 97 is a wholly self contained unit. Looking at the removed unit, there is nothing between the pump outlet and the fuel feed nipple (quick disconnect) except the plastic flex line that connects the two. There are 3 lines on top of the unit, feed, retun (into the tank directly), and the vapor vent line (middle line that carries no fuel). The vapor line has an integral check valve installed just below the nipple. Accoding to the haynes manual, 95 and earlier are user servicable units. Pump can be changed only etc. After 95 the "module" concept must have been adopted. I can see where this would be smart. Damage to the sender is possible if one is not careful on removal and installation. Whatever the reason, I think the design has changed. Possibly there is a check valve built into the pump outlet itself, or the pressure regulator acts as a check valve. I dont have the system schematic or a diagram to verify that though. Pure speculation on my part. Hope this helps!