Been reading threads on this site for a long time and found the site VERY helpful. But this time I cant figure it out. 2001 put on the SES light several weeks ago. P0300. Idles rough, stutters when you hit the gas from a stop for few seconds then its like someone flips a switch and it goes and doesn't miss a beat. Now the SES is blinking. R and R distributor, cap, rotor, ignition module, coil, wires, plugs, crank sensor, fuel filter, air filter, and coolant sensor. Cleaned EGR, MAP.All parts AC Delco-no junk. Put a new set of intake gaskets in about a year ago. Vacuum is 16 or 17 at idle. Moves correct with throttle. Put a new fuel pump in a year or so ago. Granted it was AIrtex but psi is 55 key on, above 50 while running. Gauge is intermittent but thats another story. Not one thing has mad a bit of difference. Still has original motor and cat. Can a cat give these symptoms with no other codes? ANd run so good at 3000- 5500 rpm? WHere do I go from here?

 

The problem is fuel pressure. Airtex should have been AC Delco. Key ON, engine OFF, fuel pump running: pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off.

 

I thought the motor needed 60 to run properly and stay above 50 for at least 10 minutes after the key is shut off?

[edit] Doh! Ninja'd!

 

Thanks for the reply Captain. I have a follw up question or two. First, it ran fine with the AIrtex for quite a while before the problem surfaced. That means the pump was good for a while right? WOuld it degrade so quickly? Second, when I have the fuel press gauge on it, and turn the key off, the press degrades very quickly. I see alot of discussion regarding that but I don't understand why thats a big deal. If the press is high while engine running why does it matter with key off? Does this leak down so quickly change your mind from the pump to something else? Thanks again.

 

Means your pump was good and went bad quickly like all but the AC Delco ones do.

Could also be a FPR. Best way to diagnose is to check your pressure at your fuel filter so the gas line dead ends into your gauge. If it has good pressure and maintains it, the pump isn't the problem (yet)

But, chances are... it's the pump.

 

Airtex pumps don't cut it with this system, far too many problems with them: Maximum output pressure is too low, the O ring they supply in the box leaks causing EVAP DTC's, fuel tank pressure sensors fail causing EVAP DTC's, Fuel level sensor buffers fail causing fuel gauge to jump all over, check valve leaks causing excessive leakdown, and cheesy bushings make the pump motor extremely noisy. Other than that, they're good pumps

If leakdown is excessive, (drops below 55psi in less than 10 minutes) it will cause extended cranking to start the engine. When you turn the engine off, the pump will run for ~2 seconds before it shuts off. This primes the fuel system for the next start. The fact that pressure degrades quickly doesn't change my mind about the pump, quite the contrary, knowing you have an Airtex pump. Before replacing the pump however, gotta give them the benefit of the doubt and check it. As mentioned above, connect the fuel pressure gauge directly to the pressure line at the fuel filter. Pressure must be 73psi to 108psi and must remain above 55psi for 10 minutes.

 

I will do the fuel checks asap. And your right, the Blazer takes a lot longer to crank up than it used to. Had to put a new starter in it just a few weeks ago after this whole mess had been going on for a month or so. Thanks for the advice.

 

The Airtex pump just cost you a starter, add that to the cost of the pump and it would have been cheaper to install an AC Delco pump to begin with

If you cycle the key on and off a few times before cranking, the pump should pressurize the system and most likely start quicker. Not a permanent fix, just temporary until you repair the leakdown problem.

 

Ok checked the pump with gauge riught at the filter. While pump running shes 77 psi. After pump stops it dropped to 74 psi. From there the readings looked like this. 1 min 30 sec 65psi, 3 min 61psi, 5 min 59psi, and 10 min 52 psi. Sounds good enough right? So with gauge at test port max press was 55 while pump on and after pump off it drops to zero very quickly, like 20 seconds. With engine running the pressure stayed above 50. So, what next? Press regulator sounds like next best thing to me. The spider assy sounds like a bunch of work that I will do if I have to.... One last thing, ever since the SES light came on the milage has been crap. Is that more a spider leak or can the regulator still be the cause. Thanks for the help guys!

 

Either way you are removing the top of the manifold. yank it off, see what is leaking and replace as needed.