I titled it that because the truck seems to be having some issues that are related to the spider going bad. Hard starting being a big one. When I checked the fuel pressure with the engine off it would shoot up and spike in one spot. I can't remember the reading but it would hit one spot and stop which to me means the FPR is stopping the pressure from going any farther. So if the fuel pressure is where the FPR stops it from climbing any higher (how GM engineers apparently designed it) how can I have a fuel pressure problem? Did GM's engineers not know what ethey were doing? Something is not right here... I'm going to double check the pressure with the engine off and time how long it holds pressure later today.

 

Where was the vacuum leak? What did you do to fix it?

 

Vaccum leak was under the intake tubing on the driver side of the motor. It went from a nipple on the intake to the PCV valve. It looked fine from the front but it was missing a big chunk on the back side. I replaced the rubber elbow with a short piece of hose and the idle smoothed right out.

 

the way to check pressure is cycle the key a few times on & off, especially when you first install the gauge...because the pressure will drop a lot more than usual. After the first couple times, it's back up to normal and shouldn't have to cycle the key so much.
The regulator works to keep fuel from reaching the return line and also to regulate while running. The fact that the initial prime is no higher than mid 50's makes me think not enough psi from pump.

Glad to see you fixed at least one problem.

 

First prime gets fuel pressure to around 57-58, after the 2nd prime it hits like 61. Then it takes about 5 mins to drop below 50.

 

There's the problem. You'll need to check maximum pump output pressure and leakdown at the fuel filter outlet as described in post #9.

Regulated fuel pressure must be tested with the pump activated and the engine off because that's when the pressure is the highest. When operating at WOT or cranking, manifold vacuum is near zero, (same as engine off) and the demand for fuel pressure is high. When operating at idle or cruising speed, manifold vacuum is high, and the demand for fuel pressure is low. If the KOEO, (key on engine off) pressure is low, the volume will be low. This will cause long cranking times, and hard or no starts. Idle & cruising speed fuel pressure and volume will also be low which can cause a hesitation, rough idle, induction on acceleration, poor mileage, stalling, etc. Engine running fuel pressure is meaningless, that's why they don't publish it. The injectors/poppet valves require a minimum of ~43psi before they will squirt fuel. However, anything below ~50psi, the engine probably won't start & run on its own. With that in mind, engine running fuel pressure is somewhere between ~50psi and regulated pressure, which really doesn't tell you anything. Basically, it is what it is and don't be concerned with it.

 

Listen to the captain

 

Yea but by those numbers my Blazer should start fine. If you say anything under 50 probably won't run. I'm a little under 60 after the first prime. I bought a new fuel filter to see if that will help at all. Just need to find a little time to put it on.

 

Checking fuel pressure and leakdown at the service port provides an overall view of the fuel delivery system. Kinda like taking your blood pressure. If it passes both tests, it's good. If it fails one or both tests, it means that a problem exists, it does NOT tell us what or where the problem is.

When the pump is activated, fuel pressure must achieve regulated pressure in under 2 seconds. At this point, we don't know for certain what your regulated fuel pressure is. Sure, the pressure comes up to 61psi, but if that's all the pump can build, and your regulator is set above that, it's not reaching regulated pressure and the regulator isn't regulating the pressure, (the engine is consuming everything the pump puts out). This is why maximum output pressure and leakdown need to be checked at the fuel filter. The results will tell us if the pump is able to supply sufficient pressure, and hold it above 55psi for at least 10 minutes after the pump shuts off.

If regulated fuel pressure drops below 60psi, there will be problems, guaranteed. A poorly tuned engine might not even start without a shot of carb cleaner in the intake. Even a perfectly tuned engine will exhibit performace issues.

1998 through 2005 S&T vehicles have a vacant terminal in the underhood fuse panel, right next to the fuel pump relay. The circuit goes directly to the fuel pump, and is referred to as the "pump prime" circuit. Connect the fuel pressure tester. Connect one end of a fused jumper wire to the pump prime terminal. Connect the other end of the jumper wire to battery positive. When the fuel pressure stabilizes on the tester, mark it down. Disconnect the jumper wire. Wait 10 minutes and mark down the pressure reading again. Do this at the service port, and at the fuel filter outlet, and post the results.




This link gives numbers for the necessary parts to make the adapter at the fuel filter:
http://i561.photobucket.com/albums/s...ps5c876ad4.jpg

 

Well I did not realize the line side coming from the pump is threaded so I replaced the fuel filter and hooked the gauge to the outlet side of the fuel filter and I ran the fuel pump from the prime circuit until it stabilized. Got to 61 lbs and would not build anymore pressure. It leaked down to around 52-53lbs. after 10 minutes.