I've posted about a stalling/starting issue earlier and I adjusted the idle air control valve and it idles better but still seems to spit out some black smoke on start up which is a completely different issue. But I tested the fuel pressure and it was about 33 psi at idle. Is that too low? My buddy told me it should be 43.5 psi at idle but he has a 350 tpi iroc and I don't know if it should have the same. I searched for the pressure but I got varying answers. Also how much psi should it be at prime after purging the gauge and fuel pressure? And what should idle fuel pressure be? If some live data is needed I got a laptop and an obd1 cable with tuner pro but I'm not sure what do with it all. He also gave me an adjustable fuel pressure regulator to do hopefully that helps. Thanks for any answers!

 

After prime (may take a couple primes) it should be 43.5. At idle with the vacuum line connected it should be regulated pressure (43.5) minus idle vacuum in psi. Which is typically about 10 psi on a stock engine with stock cam. So about 33.5 give or take. Idle vacuum depends on idle speed, timing, cam profile, and overall engine condition (static compression), etc.

Smoke on cold start is probably valve stem seals. If the engine is original, the valve stem seals ARE bad. No question at all on that.

GD

 

thanks a bunch adjusting the iac valve seemed to fix my issue because my fuel pressure is fine. It took about 3 primes to get to 43.5 psi and we didn't know we needed to disconnect the vacuume line. So idle was at 33.5 with the line connected which is right. And I need to do the valve stem seals along with the valve cover gaskets and hopefully that's the last engine trouble I have for at least a while. Thanks!

 

Has anybody used the Walbro (255) pump- do they have a check valve, I have a relatively new pump and after key on/no start fuel line loses pressure.

 

Mine lasted less than a year, and I was replacing it again, along with the sending unit, as I had to modify it for the pump to fit. Went back to stock pump/sending unit, and that was still working fine when I sold the car. Of course, that's been a few years ago..... but, its made me leary of their pumps....

 

Even ACD quality these days makes me question. Walbro been in there for a few years and is very quiet- repalced a Carter. Had a new Denso that a mechanic shorted out and destroyed and replaced with said Walbro. My preference is NOS or Jap.

 

Walbro is fine. Have used hundreds of them. But my preference is DW or AEM. Both are much quieter than the Walbro. None of them, including the Walbro, have check valves - which is not a problem. It makes no difference if the pressure holds or not.

GD

 

Thank you. I thought a residual pressure was desirable overnight and after key on pressure drops dramatically. But if that is normal- that is ok.