I am trying to troubleshoot a hard start condition. When i turn my ignition on after a 10 sec wait, the fuel pressure on the rails goes up to 42psi, but quickly drops to zero after the relay clicks off.

When I pinch off the lower fuel hose, ( the return i think? ) pressure goes up to 60psi and holds.

The service manual recommended replacing the FPR, I have already replaced the FPR diaphragm, there is no external fuel leaking around the rails or fpr.

Any ideas?

 

Just retested for my own sanity, fuel pressure also holds when I pinch off the top hose ( fuel pressure line? ) does this mean that my fpr is ok and the problem lies in my sender unit/pump?

 

Faulty check valve on the pump maybe?

 

Your fuel injector nozzles are leaking fuel down into the cylinders. Very common problem. The bleed down to zero on pressure right away is the classic sign. You need a new set of injectors.

 

As per post # 2.
If injectors were leaking pressure would not hold

Part of the test ;
if pressure drops with both lines clamped then only place leak can be has to be the injectors

 

 

I replaced the pump and sender unit today, checked for leaks on all fuel line fittings ok, now when i pinch off the return hose I get 90psi, that holds. When i pinch off the pressure hose it drains down??

As it holds 90psi when I pinch off the return am I right in thinking that the injectors are ok, and the only place it could be loosing pressure is through the return of the FPR?

Maybe the fpr valve seat is worn..

The FPR holds 35psi at idle and 42 when the vacuum is disconnected, that leads me to believe its doing its job?

Any ideas greatly appreciated..

 

my pressure drops to 0 within 5 minutes of turning the motor off and will start up in 2~3 crankshaft revolutions, even if it has sat for a week or 2.
as long as the fuel pressure comes up right away to the same pressure as with the vacuum hose off the regulator with the motor running, when you turn the key on it shouldn't cause a hard start.

problems with the cold start valve are pretty common, is the hard start only when cold? or is it all the time?

 

What does it do with both lines clamped?

 

I have a Aeromotive reg on my 383 that holds no pressure whatever and fires ups straight away

 

With both hoses clamped ( the pressure hose after the pump has run ) it holds 90psi. I don't have a cold start valve on my year.

I'm thinking the base of the Pressure regulator where the base of the diaphragm seats is leaking.

Interesting that you guys don't hold any pressure but start right away. It does go straight up to 42psi, may be the problem is elsewhere then..

Plugs, cap rotor, coil, injectors, battery, charging system, timing, fuel pump, sender have all been checked..

The EGR valve looks kinda rusty, but can this cause a hard start when cold?

 

Little test.
Jumper the wires in the FP relay so pump runs full time ( maintaining rail pressure )
and do a start.
If hard start still exists ,then not fuel pressure related.
If instant start then pressure drop is your start problem

 

Thanks vetteoz, that's a great suggestion, I added 12v to the red fuel pump prime wire behind the passenger side strut mount, this spun the fuel pump continuously. Still had a hard time starting, fired on second turn of the key,

So I am thinking it not fuel pressure related.

Possibly an ignition problem?

 

How good are your injectors?

 

They all ohm out to be the same resistance, so I am guessing they are good, I can hear them clicking on and off okay through a steth. They are reconditioned ones, about 2 yrs old.

I spraked carb cleaner around the bases to see if theyre drawing in any air, they appear to be good.

The weather had cooled down alot here in AZ, the car starts first time now, although it does take 2-3 secs to fire up.

MAP sensor?