I seem to have a fuel pressure problen with a 1980 non turbo zx.

The problem is hard starting in the morning, once I start the engine it
will run fine? Yesterday I hooked up an inline fuel pressure gauge to check the system, it came up 30 PSI at idle and 38 PSI momentarily when depressing the throttle. According to the FSM fuel pressure is normal.
I decided to leave the pressure regulator on over night to see if there would be a pressure drop in the morning. Last night about 7pm the pressure at the gauge was still reading 30 PSI however this morning it was at 0 PSI.

This does not sound normal, but i'm not an expert..... I can rule out that there is no fuel odor present or visual leaking of fuel coming from any of the fuel lines at the fuel pump, and in the engine compartment.

Is there a Internal Check Valve in the fuel pump that could be failing that is causing this problem? Any other suggestions?

Thanks,

Phil

 

Your fuel pressure is fine. Check the cold start valve & air regulator.... those are the usual "hard start" culprits.

 

I will check both those items Thanks! The air regulator seams to work okay
once the engine starts it will idle at about 1200 rpm during warm up and then drop down to normal Idle speed about 750-800 rpm does it sound to you like the air regulator is functioning okay? I do have a new Cold Start Valve that I will replace to see if that might be the problem. Also is it normal for the pressure reading on the gauge to drop from 30 PSI down to 0 PSI ?

I guess I was thinking that the fuel pressure going to the fuel rail needed to be maintained at all times?

I appreciate your help.

Phil

 

Ah... the fuel pressure should hold even w/ the car off. Have you tried priming the system (turn to ON till you hear the pump shut off), then start? That will tell you if it's the pressure reg or cold start.

 

Actually I can't here the pump priming at all. I know exactly what your talking about when you refer to priming the pump, I have several other zx's (82 & 83)
that prime just as you have indicated. This vehicle however you can't hear anything at all when trying to prime the pump? It doesn't sound normal to me?
I can always here the pump(s) priming on all of my other vehicles. I will get that cold start valve changed out tonight, and let you know how things go.

Thanks,

Phil

 

I've been really busy at work, and just haven't had time to change out pressure regulator, or Cold Start Valve. I did however squeeze in enough time
to put a guage back in line to see if the pressure would hold overnight. After starting the car pressure was fine 30 PSI at Idle, 38 PSI when depressing throttle. Checked it again (Static) about 9:00 pm last night and pressure was still at 30 PSI. This morning around 5:30 before leaving for work check the gauge again and it was at 0 PSI? Does this symptom maybe narrow down
the problem?

 

Sounds like the fuel pressure reg isn't holding pressure.