Hi everyone, been doing a lot of research on blazer forum.First the truck would start up run great then shut off after 20 minutes,cool off then same thing. New delco pump all set.abt 10 k miles starting hard then no start would start on carb cleaner idle but stall abt 45 lbs pressure drop right off,check it before filter not much better.I noticed when I took it apart the o rings on the fuel lines were gone both of them no sign . new delco pump runs great 55 lbs drops off to abt 45 2 days later starts running bad my pressure gage is a blur between 55 and45 thinking regulature next I will check before filter.

 

Welcome to the forum!

Definitely a fuel delivery problem. Key on, engine off, fuel pump running, pressure at the service port by the distributor needs to be 60psi to 66psi. It must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of the test, you'll need to check it at the fuel filter.

All pressure and flow must end at the tester, no fuel allowed to the engine. Key on, engine off, pump running, pressure must be 73psi to 108psi, and it must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of the test, the pump needs replacement. If it passes both parts, the problem is in the plenum. Post your results.

 

this is a 1995 with obd 2,I Thought I read on here the pressure was a little less on these

 

thanks for the quick reply,Captain Hook warming up the garage right now

 

well here we go again 50 lbs drop off to 30 brand new delco pump WTF I think I will check it at the tank before the o rings 1 year warranty on pump I bought it on ebay for $44

 

If you have the OBDII connector under the dash, and it says "Vortec" on the plenum, the system is actually OBD1.5, and not fully compliant with OBDII. Your PCM uses a unique protocol and not all scan tools will communicate with it. To be fully compliant, the PCM must be able to control the injectors on each bank separately. CMFI only has one injector and it's "batch fired".

Sorry, missed that in your "garage". Yes, CMFI regulated pressure is 55psi to 61psi at the service port, and leakdown no less than 50psi after 10 minutes. Max pressure at the pump may be slightly less, but leakdown must not drop below 50psi after 10 minutes. With the pressure readings you have, fuel pressure is the problem. You need to make sure the pump can supply proper pressure, (~80psi) and hold it. It needs to be checked at the filter as described in post #2. Reading pressure at the service port only shows you regulated pressure. If 55psi is all the pump can produce, the regulated pressure at the service port will be 55psi, and that's not enough.

EDIT: 50psi and a drop to 30psi could be either the pump or something in the plenum leaking. Need to check at the filter to determine where the problem is.

 

the readings in post 4 are before the filter,the o ring was chewed up at the filter I am going to replace it maybe get lucky anyway this pump made 55lb when I first put it in but never held pressure above 45 now it seems like it is struggling to get to 50 truck ran great for abt 1/2 hour

 

55psi and a drop to 45psi is a problem. It doesn't matter if those were taken at the service port, or at the fuel pump, new pump or old pump, the pressures both fail. If they were taken at the pump, and no pressure or flow was allowed to the engine, the check valve in the pump is leaking, or the flex line from the pump to the module is leaking. Just because it's new, doesn't mean it's good ...obviously in this case The tank has to come down and the pump removed to find the problem.

 

I replaced the oring in the filter 55lb starts right up drops to 35 key off I think I need a better gauge I am going to road test and see how it runs would it run if it the drop off was 35lbs an if so how bad?

 

55psi at the service port is the lowest allowable regulated pressure, (engine off, pump running). Drop to 35psi is a fail, something is leaking, problem could be in the tank or the plenum.

55psi at the filter, (all fuel flow ends at tester) and a drop to 35psi, both fail. The problem is in the tank.