CWUSMC

97 blazer 4.3 vortec 150+miles.

for a few months now the car would not start if it sat for more then 6 hours, so i would spray throttle body cleaner in the engine and it would fire right up. once started the car runs fine never stalls or gives me trouble. As of today I went out to start it did my usual with the cleaner and it wont start!

I just changed the fuel filter about a month ago and my fuel pressure start at 50 then once you turn it over it drops to 42 I know thats really low but thats where its been for some time now and it has been running fine. I hear the fuel pump turn on and i wait for it to come up to pressure before trying to crank it. Any help guys.

thanks - chris

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Only owned 3 Mo.

cbec1999

Any loping rpm's at idle when warm?

Do an ohm test of the injectors. Takes 5 minutes if you take your time.

old_master

Your fuel pressure is too low. Key on, engine off, fuel pump running, pressure must be 60 to 66 psi. Must remain above 55psi for 3 to 5 minutes after pump shuts off.

CWUSMC

no the RPMs hold fine, I got it up and moving again by having the girlfriend crank it and I spray starting fluid into the throttle body.

Hopefully I'll have time this weekend to drop the tank and run a full test on the fuel system, in the mean time she's running on a band-aid.

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Only owned 3 Mo.

cbec1999

Do all FP tests first. Static, idle with vacuum off of FPR, idle with vacuum ON FPR, and pedal down (guage taped to windshield / checks for acceleration enrichment for increase vacuum).

Also check leakdown time after shutdown. Could be leaky injectors...

old_master

All fuel pressure and leakdown tests on the 4.3L "W" & "X" engines are performed with the engine off and cold. GM does not publish any "engine running" fuel pressure specifications for these engines. There are too many variables involved. Elevation above sea level, engine load, engine condition, etc, etc, all affect fuel pressure when the engine is running. The engine must be cold so the heat does not increase fuel temperature/pressure in the lines giving a false reading, (especially important when checking leakdown).

cbec1999

Didn't know that.

L98 and LT1 has specs for these tests; figured there was also for newer GM's too.

Who's the mod here with the "gauge taped to the mirror" posts? Why does he have that?

Airjer_

you tape them to the window to find a possible intermittent loss of fuel pressure. Sometimes they have to be driven to get them to act up.

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MT-2500

Guide lines for checking fuel pump and pressure.
Specs on the 97 code w 4.3 is 60/66 lbs of rsrarting and running pressure.
Full direct pressure from fuel pump should be 95 to 105 lbs.

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 and fuel pressure testing guide line.
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.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 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 60-66 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.

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Remember proper testing gives us the answer to many problems.
MT