I just finished rebuild of 2001 blazer and was checking ac pressures after a couple days and 100 miles of driving on short trips 15 miles or less. I thought I was on my way to being done with the projects when the blazer stumbled and died in my driveway with the manifold gauges on it.

 

I lost fuel pressure. Was about 30 when i checked it at one cycle of the key. One time I was able to cycle the key many times to build the pressure up to 50 and I was able to start again for a short time when it stumbled and died 30 secs later. Sometimes the most fuel pressure I can get with multiple cycling of the key is 30 - 35 psi. No starting here. In the morning when its cooler, was 50 degrees when I tried it this morning and it fired right up for 10 min with out symptoms. unfortunately I didn't have the gauge on it at the time due to a thunderstorm and I was outside. Pressure doesn't leak down when the key is off. I wouldn,t think the pressure regulator would sometime work and sometimes fail and still prevent leak down or a filter would intermittently plug.

My questions are: Has anyone heard of this? Where is a good place to pinch off the return line so I could eliminate the regulator being faulty? I would like some more insight before I pull the trigger on an expensive pump. I wouldn't think voltage should be varying but haven't confirmed it isn't.

Any help appreciated.

 

Anyone pinched off the return line to on one of these blazers to check pump pressure? Where? Lines appear to be metal or plastic no soft rubber to pinch.

 

Got it to start again and this time I had the gauge on it. This time fuel pressure gauge needle was rapidly vibrating from 50 to 54 psi. The gauge was actually making a rattling sound from the needle vibrating so much. What could cause such a pulseing in the fuel pressure? Needle was moving so fast it looked like it was a quarter inch wide.

 

The gauge was actually very rapidly fluctuating between 50 and 60 the next time I double checked. I don't believe the pump is capable of fluctuating pressure rapid enough to actually make the needle look fat. Has anyone seen a regulator open and close repeatedly and rapidliy enough to cause this. I'm curious if my pump flow volume is just on the edge of supplying enough to keep the valve open. Garage is full and its too cold for me to want to get my hands on it for more tests outside right now. I really need to test the volume of flow. If that checks out I'll go swap out the regulator. If that doesn't stop the intermittent low pressure I should probably do a voltage drop test but I may just drop in a pump. Anyone have experience with voltage drop actually being the problem over the pump? In my experience its been the pump.

 

A corroded ground connection or a partially damaged wire, connection, etc could cause intermittent pump operation and the fuel pressure regulator trying its best to do its job.

Think you have a good idea to monitor the voltage at the pump and if good, time to isolate the pump and check its operation. Do a search and you will find how to adapt a fuel pressure gauge at the fuel filter for this.

Probably is the fuel pump, but best to make that determination first instead of just replacing it due to the PITA it is to drop the tank, especially when its cold outside.

Good luck and keep us informed as to what you find out.

 

You'll need to modify the fuel pressure tester so you can check maximum fuel pump output pressure and leakdown. This is easily done at the fuel filter outlet. All pressure and flow must end at the tester, (none allowed to the engine). While the pump is running, pressure must be 73psi to 108psi, and it must remain above 55psi for at least 10 minutes after the pump shuts off. Post your results.

Here is a link for the parts you need to modify the tester:
1997andNewerAdapterforcheckingFuelPump_zps5c876ad4 .jpg Photo by cwhook | Photobucket

 

[QUOTE=Captain Hook;624709]You'll need to modify the fuel pressure tester so you can check maximum fuel pump output pressure and leakdown. This is easily done at the fuel filter outlet. All pressure and flow must end at the tester, (none allowed to the engine). While the pump is running, pressure must be 73psi to 108psi, and it must remain above 55psi for at least 10 minutes after the pump shuts off. Post your results.

Here is a link for the parts you need to modify the tester:
1997andNewerAdapterforcheckingFuelPump_zps5c876ad4 .jpg Photo by cwhook | Photobucket[/QUOTE

When I get around to getting at it I'll post back. It seems cooler weather helps it. Thanks for the link.

 

Well fuel line fitting to filter is now rounded and I'm not going to damage the rusted line by trying more. Last rusted line on a blazer I did ended up needing replacing. 2 days in pb blaster and with flare nut wrenches and it wouldn't break free. I'm assuming the filter is good. When using the prime connection to run pump to empty the tank the pressure varried greatly and the pump stopped a couple of times. I was able to get it going again with a few raps to the tank with a hammer. While doing a voltage drop test I rapped on the tank several times to watch for changes. One time the pump started running full bore, sounded much better. Pressure went up to 62 at the service port and the blazer would run even while pumping gas out into a gas can and still maintain decent pressure. I was losing about .5 volts from battery voltage tested at battery with pump running at the back probed pump connection. I soldered the pump harness connections before these tests as this pump is aftermarket and had the 4 wires just crimped with crap connectors. I'm guessing there is a voltage drop between the top of the pump and the motor itself. At this point I have to pull the pump and have a look.

 

The electrical connection on the top of the pump also has a plug on its underside which goes to the pump and sender. The pump and sender are not hard wired to the top most or outer connection on the assembly. I believe the female end of the spade connector on the ground wire was the problem. It was very loose within the plastic plug and easily slide back and forth. I removed all four wires from the plastic plug and soldered them to the bottom pins of the connector. There is no longer any plastic seperating the spades or locking them all in place. The solder is all it has. I'm having second thoughts putting the pump back in. Thinking what would happen if one of those solder joints would break free and short in the tank. I was thinking of filling the cube shaped female connector with epoxy to encase and keep seperation of the soldered joints. But I don't know how up epoxy will hold up to gasoline.

Any thoughts?