jahajazz

I'm getting intermittent slow starts (takes roughly 2-3 seconds). Only has trouble after sitting for roughtly an hour after driving. Cold starts are fine, and I get absolutely no stumble or hesitation during driving. Replaced the fuel pump, filter, and regulator previously to fix other starting problems. I get plenty of fuel smell after some city driving, so I figure the vapor canister is shot, could a bad one cause slow starts?

Thanks for the help

MikeGyver

A slew of engine specs would help...

jahajazz

140k miles, everything is stock besides some reported porting to the heads when the previous owner rebuilt them. The previous owner also said he did the opti at 90k.

jahajazz

I just checked the fuel pressure: 42psi with the key on, and 35psi with the engine on. After the pump stops priming / the engine is turned off, the fuel pressure quickly bleeds down to zero. The vacuum line to the pressure regulator has no fuel smell, so I'm thinking the regulator is fine. What could be causing the pressure to bleed down so fast? The check valve in the fuel pump?

MarcR94v6

pump may be bad or leaky injector or injectors. How long ago did you replace them pump and did you use the trap door method (hole in trunk)?

MikeGyver

It's a factory regulator right? I would imagine pressure is leaking back through the pump or possibly at the regulator.

jahajazz

I replaced the pump less than 10k miles ago (AC Delco part). I replaced the regulator at the same time I did the pump. I did not use the trap door method. I'm fairly sure the pump itself is okay because other than the starting, it runs fine. No misses or hesitation. How do I determine if its leaky injector(s), a bad regulator, or something wrong with the pump assembly?

Injuneer

Pull the fuel rails up with the injectors intact. Pressure the fuel system. Look for drips.

If its a problem with injectors leaking and flooding it, it should start quicker with the accel pedal on the floor when you crank it. That puts the PCM in "clear flood" mode.

jahajazz

I'm thinking it's the regulator from the pressure readings I get when I turn the key to on. It reads 42psi while the pump primes the lines, then drops immediately to 35psi, then linearly bleeds down. If I wanted to replace the regulator to check if its the problem, do I have to remove the fuel rail? Judging from my last replacement of the regulator, I don't see why I need to pull the rail just to replace the regulator?

Injuneer

There are at least 4 different things that can cause the rapid pressure drop, as have been mentioned already - faulty fuel pressure regulator, faulty check valve in the fuel pump, leaking injector(s), and leaks in the lines, including leaks in the line inside the tank. If you feel that replacing parts is the best way to diagnose it rather than making some basic checks, the FPR would be the easiest thing to replace. But its a 1 in 4 shot that you picked the right part.

You can replace the FPR without removing the rails. You have to release the clamp that holds the 2 hard lines to the bracket on the intake manifold bolt, and remove a single bolt (T-27?) that holds the FPR to the end of the rail. Working blind, but easy to do.

jahajazz

I had the old regulator from when I changed out the pump and regulator last summer and figured that was less work than removing the whole rail. The old regulator has initital pressure of 54 at key on, then dropped quickly to 44 and slowly slid to 0 in a way very similar to the other unit. It did not solve the pressure drop after priming. Next I will probably remove the whole rail and check for leaks, but it hard to believe the car would run so well if an injector or injectors leaked down that quickly. How would you verify a bad check valve in the pump? Also there are not exterior line leaks, how would you verify internal line leakage?

Thanks

bw_hunter

You can believe a car with a leaking injector can run well. That's why it was suggested..it's a valid diagnostic method. The best way to determine if the internal check valve is leaking in to diagnose everything else...process of elimination....