I Figured you guys seem very knowledgeable about these gm throttle bodies so i would run something past you. I have a 2.8 tbi motor it gets 13psi steady when running and when i turn the key to on with the motor off the pump runs and it goes up to 13psi also. But here is where i am confused. As soon as the pump shuts off the pressure drops to zero. Isn't it supposed to hold pressure for when you crank the engine? This makes it so that the motor has to be cranked twice before it will start (because the lack of fuel pressure). What i have done thus far is install pressure gauge before tbi and plugged the line before the tbi, this was to check the line between the tank and the gauge and to make sure the check valve in the pump was not leaking. When i primed the pump it went up to around 13 and held and then slowly dropped instead of going straight to zero. So then i unplugged the line and hooked up the tbi and did the same test. The guage reads 13psi while pump is running then plummets to zero as soon as the pump shuts off. So the next thing i did is plug the return line after the tbi. When i primed the pump it went up to 20psi and held... Is my regulator leaking? How fast is the pressure normally supposed to bleed off after priming the pump. Thank you for your help

 

Stock TBI pumps lack a one way check valve like the TPI/MPFI pumps have. The TBI regulator also has a small hole drilled straight into the return passageway to bleed the pressure off. Because of this, the pressure will drop as soon as the power is removed from the fuel pump.

 

So, then a drop straight from 13psi to 0psi is normal for the tbi then? I always assumed it should drop but slowly instead of instant zero. If that is normal then what could possibly be causing the motor to not start on the first crank but on the second?

 

My old 2.8 used to never start on the first crank. Sometimes it took me 5+ seconds of cranking to get it to start. Perfectly healthy, BTW. It was just how lean the ECM was programmed. When I switched over to the later model TBI PCM and tuned it, started on the first hit of the key.

 

I thought they were supposed to bleed off slowly.
I would think your regulator is bad. But I could be wrong too.
My car has always started on the first try.
Well at least until the fuel pump went out.

 

this is by far one of my biggest gripes about my 92. i hate starting it cold. it it takes a solid 5sec. of cranking before firing. my Blazer is almost instant. i guess that TPI is some good after all.

 

Yea, i thought that it was supposed to bleed off slowly too. But i have not done to much work with these throttle body setups. It does seem that these motors should have started on the first crank at some point. Something must be causing the long cranks. I can't see them selling a brand new vehicle that has to crank that much to start even back in the 80s. I did however take apart the regulator to have a look and there is a hole just like he said that goes into the return line, so that would make sense why it is bleeding off. If that is indeed normal something must be causing the long crank. I know something must not be right cuz it will also run great when it first starts then as soon as it switches from open to closed loop it starts to surge. I have checked my pressure when running i get a steady 13psi and i have checked the voltage output of the map and tps and they both check out. The only thing i can do is to unhook the 02 sensor before i start it which prevents it from entering closed loop and this does make it not surge. I am wondering if this and the hard cranking problem could be linked?