2003 2dr Blazer vin X 220,000 miles poor drivability and check engines light random multiple misfires. Checked fuel pressure with vehicle running 55 psi, engine off drops to 0 in 30 seconds. Checked fuel pressure at outlet of fuel filter 90 psi held for over 10 minutes. I decided to replace fuel pressure regulator, I know too lazy to connect lines and pressurize with plenum open to verify if regulator was leaking so I just replaced it. I did remove the bolt at back of block that holds metal fuel lines but they were still stiff and hard to move around. After regulator change same deal no change. I then replaced fuel pump assembly with New Delphi FG0286. Fuel pressure at engine test port during prime instantly jumps to 65 psi but still bleeds of to 0 in 30 seconds or less. I guess only thing left is an injector leaking or something is the spider assembly. What else can I test or do ? thank you for all replies

 

Do you have any codes? Any other symptoms? It is preferable to diagnose as best you can before throwing parts at a problem that can only get you so far sometimes.

When I had a fuel leak in a fuel-injection spider I had the front O2 sensor give an error. I thought it was the sensor and replaced it but it was actually failing because of the over-rich mixture coating it with carbon. Looking back I should have known that but it was my first vehicle with an O2 sensor. I also had bad mileage.

 

Maybe its not a fuel pressure issue at all.
Have you tried doing a tune up on it?
And, if your thinking its still something to do with the fuel system have you changed your fuel filter?

 

I'm currently having the exact same problem. So I've narrowed it down to an issue at the plenum, but unsure of the proper tests to pinpoint the problem. Not sure how the ignition system could cause pressure to drop almost instantly either. If anybody can shed some light on this we would be grateful.

 

You may or may not have ignition problems but you do have a fuel pressure problem and this needs to be fixed before you can go any further.

The entire purpose of testing and verification is so that is so that you do not throw parts at the problem which may actually make things worse. Replacing a perfectly good AC Delco component with a new but inferior aftermarket part could actually add to your troubles. Failing the pressure test at the engine schrader and passing the test at the fuel filter output tells you that you have a problem and it is not at the fuel pump. Fuel pump replacement at that point is not the next move. You need to find out why the plenum will not hold pressure. At that point replacing the regulator was not a bad move. Since that didn’t fix the problem then you have 2 choices:

Replace the entire spider assembly which depending on the mileage might be the right move.

Diagnose where the leak is and try to repair just that component. There are various approaches if you want to try this. After the pressure loss you can pull the plugs and look for the wet cylinder. You can remove and pressurize the system and look for leaking tubes or poppets. If your tight for resources and have the time and energy then this could be a fun project but if the spider is leaking, more problems may not be far behind. So it depends on whether you have more time and energy or more money. Lastly, reliability and breakdowns are a consideration in a case like this. Do you need to get to work reliably or is this a weekend truck?

George

 

your truck is an 03 so it should have MPFI injectors, so leaky poppets are out. with the upper intake off put the fuel rails back in, bolt em down, and then turn the key to RUN, not start. and visually observe for fuel leaking, also look under and around the truck.