95 Blazer fuel issues

Yet another fuel pressure problem post. I searched the forums and couldn't find an issue quite like mine. Here goes nothing.

I purchased this 95 blazer, 4.3 aluminum top vortec the other day. The guy that had it before me said that he could not figure out the problem and wanted rid of it. He said that he replaced the fuel pump (however I neglected to ask him if it was a new unit or used), new fuel filter, tune up, and cut off the converter.

Here are the issues I am having. Will not cold start unless some starting fluid is sprayed into the throttle body. Then it fires up and idles fine. Once in a while after it is warmed up a bit, it will fire a time or two while cranking and then start. If you gently rev the engine, it will do ok. If you stab the throttle, it falls on its face.

When driving, it will not take any more than 1/4 throttle or it just falls right out.

I took some fuel pressure readings and this is what I found

Cold key on, fuel pump running 61
Leave key on, as soon as fuel pump turns off, 0 - Zero
Cranking with a successful start, 57
Running at idle, 57
Revving, between 50 and 60
Turn key off, fuel pump quickly turns off, 0 - Zero
Cranking with no start - 48
Revving to 2500 RPM, 55

I hope someone might be able to shine some light on the situation. I really appreciate all of your help!

Yet another fuel pressure problem post. I searched the forums and couldn't find an issue quite like mine. Here goes nothing.

I purchased this 95 blazer, 4.3 aluminum top vortec the other day. The guy that had it before me said that he could not figure out the problem and wanted rid of it. He said that he replaced the fuel pump (however I neglected to ask him if it was a new unit or used), new fuel filter, tune up, and cut off the converter.

Here are the issues I am having. Will not cold start unless some starting fluid is sprayed into the throttle body. Then it fires up and idles fine. Once in a while after it is warmed up a bit, it will fire a time or two while cranking and then start. If you gently rev the engine, it will do ok. If you stab the throttle, it falls on its face.

When driving, it will not take any more than 1/4 throttle or it just falls right out.

I took some fuel pressure readings and this is what I found

Cold key on, fuel pump running 61
Leave key on, as soon as fuel pump turns off, 0 - Zero
Cranking with a successful start, 57
Running at idle, 57
Revving, between 50 and 60
Turn key off, fuel pump quickly turns off, 0 - Zero
Cranking with no start - 48
Revving to 2500 RPM, 55

I hope someone might be able to shine some light on the situation. I really appreciate all of your help!

Fuel pressure dropping to 0 pump off is not good.

On that one fuel pressure specs is 55/61 lbs of pressure.
You need 59 -60 lbs on cold cranking to squirt injectiror.
You can not leave home without it.:rofl:

Here is some guide line to fuel pump testing.The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Your year and modle should have 55-61 fuel pressure.
Cold start should be 59-60 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 56-60 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

GOOD DIAGNOSTIC WORK - CHECKING FUEL PRESSURE! :thumbsup:

Your static pressure test indicates a leak in the line, or the regulator, or leaking injectors, or a weak spring in the FPR diaphragm (least likely).

You do NOT need to concern yourself with dynamic fuel pressure tests (motor running) at this time - only static tests.

First check, COLD motor = turn the key on. Let it prime the fuel rails, shut off, then turn the key off. Pull the vacuum line that goes to the fuel pressure regulator. If you can, pull it at the manifold, but if not, pulling it at the FPR is OK. Smell the vacuum line for gas.

If it smells like gas, or is wet, then the diaphragm in the FPR is ruptured, and extra gas will get drawn into the intake. (This will make for HARD hot engine re-starts).

If no gas is in the vacuum line, then disconnect the pressure regulator, and cap the line WELL. Connect the fuel pressure gauge. Forget PINCHING fuel lines - you'll damage lines that way. Test again, and have a pencil ready, and watch the gauge drop. NOTE THE PRESSURE BLEED-DOWN TIMES, in 5, or 10, or 15 second increments. Write them down, post that result back.

If it still drops quickly, the injectors are leaking, UNLESS there is a visible leak between the line from the tank to the injectors. You HAVE to check that, before pulling the injectors.

If no leak, pull the injectors, and repeat the test, WITH A MASON JAR UNDER EACH INJECTOR. This will show which injector is bad. Leaking injectors is like a water hose with no sprayer on it - it just runs out. Put on the sprayer, and it sprays fine mist.

If it does NOT drop after 5 minutes or more, the fault is AFTER THE injector rails, and the injectors of course don't leak. The spring in the FPR is bad. There's no place further down the line that matters...

EVERYONE - bookmark this post for reference!

On the 4.3L Vortec CMFI engine you can not access the fuel pressure regulator, the injector, the spider lines or the poppet valves while the engine is running. All of those components are inside the plenum which must be installed for the engine to run. The regulator does not have a vacuum line connected to it. The vacuum port on the regulator is exposed to manifold absolute pressure. Excessive leakdown can also be caused by a faulty check valve in the fuel pump or a leak in the fuel line from the pump to the module. The pump must be isolated, (after it pressurizes the system) from the components in the plenum to determine where the leak is located.