97 Blazer 4.3 cranks but won't start

[jeff1367]

Well I went and bought myself a fuel pressure gauge and some starting fluid. It fired right up on the starting fluid so that eliminates spark. Fuel pressure jumped right to 62 with the key on and after the fuel pump shut off, it dropped to 54. I left the key on for awhile and the pressure started to slowly drop. After about five minutes it was down to 45. Is this normal or is it leaking pressure somewhere? I'm going to pull off the plenum in the morning and poke around in there.

[manicmechanix]

So it will fire up with starter fluid? I don't think fuel pressure should drop that much but I haven't worked on CPI's much. I don't think this is keeping it from starting. It sounds like your injector isn't cycling. Were you able to get battery voltage over 9Vs? Apply +battery with a test light to the harness side of the injector ground to see if the computer is pulsing the injector during cranking.

[jeff1367]

Originally Posted by manicmechanix

So it will fire up with starter fluid? I don't think fuel pressure should drop that much but I haven't worked on CPI's much. I don't think this is keeping it from starting. It sounds like your injector isn't cycling. Were you able to get battery voltage over 9Vs? Apply +battery with a test light to the harness side of the injector ground to see if the computer is pulsing the injector during cranking.

Yeah, it runs for a few seconds with starting fluid. Battery voltage is fine, what I was talking about earlier was the fuse that was labeled crank. It showed 6-7 volts while cranking. I did stick a test light in the injector harness and it was flashing while the engine was cranking.

[Josh Smith]

Originally Posted by jeff1367

Yeah, it runs for a few seconds with starting fluid. Battery voltage is fine, what I was talking about earlier was the fuse that was labeled crank. It showed 6-7 volts while cranking. I did stick a test light in the injector harness and it was flashing while the engine was cranking.

Take that battery to Autozone and have it tested. A good battery should pull down no more than 11v when cranking.

Have them charge it then ARBST test it.

I've seen a bad battery cause your condition exactly ONCE in 15 years. It is not common, but worth checking.

Having worked at Autozone for a bit in my early 20s, I can tell you that most of their stuff is junk, with the exception of the batteries. IMNSHO, among all the lead-acid automotive batteries out there today, the Duralast Gold is the best. I will only run that, or the Optima gel-cell.

Josh <><

[manicmechanix]

Originally Posted by jeff1367

Yeah, it runs for a few seconds with starting fluid. Battery voltage is fine, what I was talking about earlier was the fuse that was labeled crank. It showed 6-7 volts while cranking. I did stick a test light in the injector harness and it was flashing while the engine was cranking.

Well you shouldn't see 6-7V while cranking, but if you are getting power to the injector and injector pulsing, fuel pressure is good and the engine starts with starting fluid, then you pretty much narrowed it down the injector not delivering fuel. Have you checked the injector's resistance?

[jeff1367]

Originally Posted by manicmechanix

Well you shouldn't see 6-7V while cranking, but if you are getting power to the injector and injector pulsing, fuel pressure is good and the engine starts with starting fluid, then you pretty much narrowed it down the injector not delivering fuel. Have you checked the injector's resistance?

No, what is the resistance I should look for?

[MT-2500]

Originally Posted by jeff1367

Well I went and bought myself a fuel pressure gauge and some starting fluid. It fired right up on the starting fluid so that eliminates spark. Fuel pressure jumped right to 62 with the key on and after the fuel pump shut off, it dropped to 54. I left the key on for awhile and the pressure started to slowly drop. After about five minutes it was down to 45. Is this normal or is it leaking pressure somewhere? I'm going to pull off the plenum in the morning and poke around in there.

Should not have a fast leak down.
But check pump pressure before taking it apart.
You need 65 lbs of pressure with good fuel volumn on a cold start.



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.
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.

[manicmechanix]

Originally Posted by jeff1367

No, what is the resistance I should look for?

I don't know, I think the earlier models should have at least 1.5 ohms and later models which I think yours is should have around 12 ohms.