OK, I'll try to make this as brief as possible...

I had a SEL for cylinder 3 misfire a couple months ago that went away. The engine occasionally stumbles when I hit the gas too hard, and lately has been dying out when I use the A/C. If I start the truck, drive for a minute or two hten turn on the A/C it's fine, but if I turn on the A/C immediately, the truck will sputter and die when I put it in gear.

I bought a fuel pressure tester today and tested it out.

At idle it reads 55 PSI
When I rev the truck the PSI drops to 50.
When I shut the truck off, the PSI jumps to 60 but within 10 minutes is back down to about 20 PSI.

So it seems like this is a fuel problem and I'm leaning toward a leaky cylinder 3 injector, but since I don't know a whole lot about fuel issues, I figured I'd post and maybe you guys have another test I should run or another idea.

 

Sounds like the regulator is shot..but then again u did have a #3 missfire...it could be leaking in. time for a new spider set. if its not a injector,it'll rule out the regulator too.

 

What is the pressure with the key-on/engine-off? From the leak down, you definitely have a leak somewhere.

To be able to determine if it were the regulator or the check valve in the pump, you really need to test at the fuel filter.

 

The regulator is part of the spider too? That's good news, I suppose. Anything else it could be? I don't know when the fuel filter was done last, is it possible it's clogging up at higher speeds?


Key-on/engine-off is 55 before I start the truck, 60 after I shut it off.

Testing at the fuel filter isn't something I'm terribly comfortable doing (terrified of kinking a fuel line) but I imagine it wouldn't be terribly expensive for my mechanic to test that while swapping the filter, right?

 

Provided they would have the proper adapter to isolate the pump, it shouldn't be that expensive.

Yes, the FPR is part of the spider.

 

OK then. Next step is to ask my friend about it tomorrow and have that tested.

So I'm understanding this, the test will tell me if the FPR/spider assembly is bad or if my fuel pump is going bad?

 

if you have 60 psi at the filter and it holds pressure,pump should be good. if its good,look at the spider.

 

Yes. If the pressure drop is still present when testing with the fuel pump dead-headed, then the only possible cause is a problem in the fuel pump assembly (either the check valve in the pump or the tube from the pump to the top of the assembly).

 

Then I suppose I'm rooting for a spider since it's less expensive. Thanks guys! I'll report back once I run the next test.

 

I have issues with my Pressure Regulator and with the pulsator on my fuel pump. When I installed my new pump I just reused the pulsator now it seems to be leaking.

Here is a little test you can do to see which part is the issue...in the tank or on the engine...that is if you do not have the adapter kit to test at the fuel filter.

Connect fuel pressure tester to test port.

If the engine will run, start the engine and allow it to run at normal idle speed. The fuel pressure should be 58-64 psi (400-440 kPa). Once the engine is at normal operating temperature, open the throttle quickly while noting fuel pressure; it should quickly approach 64 psi (440 kPa) if all components are operating properly (there is no need to proceed further). If the pressure was in specification before, but does not approach 64 psi (440 kPa) on acceleration, the pressure regulator in the Spider unit is faulty and the assembly should be replaced.

If the engine does not run, turn the ignition ON , but do not attempt to start the engine. Listen for the fuel pump to run. Within 2 seconds of turning the ignition ON pressure should be 58-64 psi (400-440 kPa) while the pump is running. Once the pump stops, pressure may vary by several pounds, then it should hold steady. If the pressure does not hold steady, wait 10 seconds and repeat this step, but pinch the fuel pressure line flexible hose and watch if the pressure holds. If it still does not hold, the spider unit should be replaced. If the pressure holds with the pressure line pinched, check for a partially disconnected fuel dampener (pulsator) or faulty in-tank fuel pump.