Having a hard start on my Iroc with the 350 TPI. Fuel Pressure at KOEO is about 40 psi for a few seconds then goes back to Zero. Cranking it goes to 20 PSI. I have spark as well but it won't start at all. Engine is timing is good (when running). After cranking for a while (10 minutes or so) sometimes it will start to catch, not all the time though. Once it runs I can cut it on and off unless it's in my driveway (on a slant). It's an 89 with TPI 350/Auto. Any help is appreciated, I'm tired of this thing not being mobile.

It sounds like you've already done a good job of finding the problem.

Sounds like fuel pump or regulator. They need 40-47 psi to operate. When you turn koeo, pressure should be MINIUM 40.5 psi (should be 45ish) and hold. There is also a pressure valve in the pump assy thats supposed to pressure. It really shouldnt be dropping down while cranking because pump should be running while cranking. By cranking and cranking and cranking its probably building enough pressure to start which is why its a "hard" start as opposed to a "no" start. Also check the regulator. If that is stuck it'll allow the fuel to come in and go right back out. Remove the vacuum line going to it and see if its wet and smells of fuel. If so replace. Also pinch off reurn line (smaller of the 2 fuel lines to rail) and see if pressure holds. If so regulator shot. Hope this gives you a little insight. GOOD LUCK

Who keeps telling you guys to check the fuel pressure with the key off? You check it with the car running and fuel pressure vacuum hose disconnected from the intake plenum and plugged.

There is more than one test. One is with engine running and one without.
Both tests are for diff things.

Could be leaking FPR diaphragm, leaking injectors (including the 9th injector), leaking pulsator, or weak fuel pump.
For FPR diaphragm (as mentioned above), pull vacuum line for FPR and smell/look for gas in vac line.
For leaking injectors, remove intake elbow in-front of throttle body, then open the throttle blades and smell for gasoline inside the plenum.
Pinch-off the return fuel hose near the front of the engine and watch what the fuel pressure does, if it drops and you have ruled out the FPR diaphragm or injectors then you probably have a problem in the tank...

Hope this helps.

Thanks all for the help. I'm thinking it could be the Check Valve in the tank. I remember the PO saying that he went into the tank for some reason, but I can't remember what it was. I'll try to figure out the issue today.


If I could get the car started I wouldn't need to check pressure. That's why I'm checking it with the Key On Engine Off. And yes, there are two different tests.

Matt

I had the EXACT SAME PROBLEM last summer. Fuel pressure went to 38ish and then would drop to 0 in seconds after the pump stopped priming. Its the check ball in the pump. You can also do the fuel line clamp off trick to confirm its the pump. New walbro pump, and have not had a problem since.

Wanted to avoid having to drop the Tank. But I'm pretty sure it's going to need a new pump... I'll check today. Thanks for the help.

-Matt

Honestly, dropping the tank is not hard at all. I didn't even get the car that high, maybe 2nd notch on the jack stand.

Remove the rear end (ITS SOO MUCH EASIER WHEN YOU DO THIS), make sure the tank is empty (VERY IMPORTANT), remove the gas filler neck liner and have a buddy tell you what way to turn the tank while he watches/guides the filler neck out. After the rear was out, it took me about 5 minutes to get it out and about 20 to replace the pump and re install it. Getting the rear out and back in takes the most time.