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Discussion Starter · #1 ·
I have a situation where my 79zx loses fuel rail pressure over night, making for a hard start first thing in the morning. Once the car starts and the fuel rail pressurizes, it will re-start instantly. (don't even have to wait for it to warm up or anything)

I'm wondering what is the culprit here, is it my fuel pressure regulator? or is it my fuel damper? could it be either one? and how can I test which is bad before replacing?


Thanks in advance,
Thunder(79zx)
 

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Thunder,

It is either the FPR or the check valve in the pump (not the damper). If you have a FP gauge installed you could clamp the rubber line from the filter to the steel line going to the injectors. If the gauge still shows pressure in the morning then it is the pump check valve but if it is down then the problem is in the FPR. My bet is on the pump check valve.

Charles
 

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It is not likely the Damper.

Put a Fuel Pressure Gauge between the Fuel Filter and the Fuel Rail. You can build one for less than $20.00 CDN.

A simple test here is to disconnect the small gauge wire from the solenoid and turn the key to Start. The Fuel Pump should run and the pressure should build to 36 PSI almost instantly and stay there. Release the key and the pump should stop.

The Damper can be checked by watching the pressure gauge while the engine is running. If the gauge fluctuates wildly then suspect the Damper. The Damper is between the Fuel Pump and the Fuel Filter. It has nothing to do with maintaining the pressure when the engine is off.

The FPR can be checked by pulling the vacuum hose off the FPR with the engine running, the pressure should climb to 36 PSI.

Put a clamp on the return line near the fuel rail and pressurise the system then clamp the fuel line near the Fuel Filter. If the pressure drops then you have a leaking injector or coldstart valve.

If the pressure does not drop remove the clamp from the return line. If the pressure drops below 26 PSI suspect the FPR.

Lastly, clamp the Fuel Line between the gauge and the Fuel Rail. Pressurise the Fuel system if the pressure drops suspect the check valve in the Fuel Pump.

Note that my 79 always has low pressure in the morning. I consider this to be normal for my car, although it will maintain 32 PSI for about 2 hours before it slowly begins to fall. What is important to me is how fast the pressure builds when the key is in the Start position.



Post Edited (Jan 29, 7:06am)
 

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Dirty Pintles...

If your injectors are REALLY gunked up, the pintle may not seat and can also cause a leakdown problem, overnight.
 

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Wasn't this a song???

Flip side of "Snoopy and The Red Baron" in like 1972?

"Does your fuel rail loose its' pressure while sitting overnight?"
Or was it 'chewing gum' and 'flavor', I forget, I'm senile...
What was the wuestion again?
 
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