Friend's 89 Formula 350 and has 77000 original miles.
About a year ago, the car began hard cold staring and surging while cruising. Had a local garage look into the problems, and they replaced the injectors first and then they replaced a (MAF relay?). I'm not exactly sure about the second one. None the less, the garage made improvements, but could never eliminate the hard cold start.
Since then my friend has replaced the fuel pump, IAC, MAF sensor, H2o Temp and oil pressure Sending unit for the ECM, and finally the fuel pump relay. Some of which improved the idle and staring, but starting had no change. He expects it to start like new.
Currently when the key is turned on, the fuel pump relay runs the fuel pump for approximately for 2 seconds then shuts off. Fuel pressure at the rail is intermittent. For example if he turns the key on 3 separate times with 10 second intervals in off position, the first time he may get 10-12PSIG, the second time he may get 20-30PSIG and the third time he may 30-45. Attempting this scenario multiple times, he has proved that the car will start better if he waits to turn the car over on the third attempt when fuel pressure is where he'd expect it should be.
He thinks that fuel rail pressure should be at or around 40PSIG each time the key is turned on. He installed an adjustable Hilborne fuel pressure restrictor on the return side of the line. This increased the pressure overall, but he still has the same results.
In 89 Pontiac removed the cold start valve from the Firebird, and he is wanting to know where/when the ECM is sending the logic to the injector to open. After the two seconds that the fuel pump builds up pressure, the fuel rail quickly looses it's pressure. He is wondering if the injectors are even opening in this time frame? He not certain if he has an actual fuel problem or if the ECM is failing to do it's part?
Any input would be appreciated.

Thanks,
Rob

 

if the fuel pressure drops rapidly after prime, the check valve in the pump is bad, needs a fuel pump

 

Thanks Dave.

I would say it drops a bit slower than it build up pressure, but not much.

Rob

 

I would agree with the fuel pump check valve being bad if the pump had not been replaced a year ago. It is possible that the pressure is bleeding off elsewhere, such as the fuel pressure regulator, which I do not believe you mentioned as being replaced. I do not know how likely this is to be the case, however.

 

to eliminate the regulator as the problem, plug the return line and recheck pressure, if it holds, it is the regulator

 

He did replace the fuel filter. When he plugs the return, he did get higher pressure from the get go, but he is not sure how long the pressure remained. He will check this again. How long should the pressure remain?

Is it possible the the VATS (vehicle anti theft sys) module is not sending a consistant signal to fire the injectors? On that note, where is the VATS module?

Thank again,
Rob

 

The VATS system is in the computer I believe. My friend had his deleted on his PROM because it wasn't working right. The fuel pressure should remain high for quite some time, several hours I would say. If it changes at all after a few minutes, it is bleeding off somewhere. The only possibilities to cause a loss of fuel pressure are the fuel pump check valve, fuel pressure regulator, leaking fuel injectors, or a leak in the line somewhere. A leak in the line would be obvious(You would smell it).

 

On a side note here,how is the battery? I just had a no start condition on my Astro because of low fuel pressure(wouldn't come-up to the 55+psi),found the battery had a intermittent short. Your fuel pressure should be right around 48#,if you block the return and the pressure comes up then it is probably your FPR.