1996 Blazer hardly starts

[dct73]

Hi everyone. I've spent the last couple days reading threads and I still don't know what to do. My 1996 4.3 blazer with 145,000 miles has gradually gone from running good to will hardly run at all over the last few months. The colder it is the worse it runs. When it's hot out it runs good, but in Wisconsin it's 20F today. It started out with just a miss under light acceleration and giving P0300 code. If I got on the gas hard it went away. I replaced the plug wires with NAPA premium guaranteed for life plug wires. Replaced plugs with Autolite 605 gapped around .050 if I remember right. This new distributor was installed because the old gear was looking pretty worn. Along with it came a new cap, rotor, and sensor. The cap and rotor are actually nice parts with brass contacts, much better than what I took out. These changes didn't make much difference. I tried squirting carb cleaner around various areas but never did find a vacuum leak, but I'm not ruling it out. The fuel pump was replaced maybe 30,000 miles ago with a GM unit. Fuel filter replaced a few months ago. Today I did a fuel pressure test. Key on no start, pressure hits 65 psi and drops to 60 when pump stops. Fifteen minutes later it was still at 52 psi. I don't know what else to do. Can someone please advise me on the next steps? Thank you.

[dct73]

The truck used to start but the problem is so bad now it won't even start without starting fluid or carb cleaner shot in it. I found the "Engine Cranks but won't run" in the Tech Articles and started going down the list.

1. Perform OBD system check - I'm not sure if this is the same but my scan tool went through some tests and returned a P0300 code. I've been getting that code for months.

2. Attempt to start engine - Now will only start with some carb cleaner shot into the air cleaner.

3. Is VTD parameter displayed as active - I don't think I can see the VTD parameter with my scan tool

4. TPS - Registered 0% with throttle closed. Slowly sweeps up to 100% as I open throttle.

5. Is ECT below -22F - No

6. Check for spark at two plug wires - Yes, spark is present

7. Test fuel pressure - 65 psi pump running and engine off, drops to 60 psi when pump shuts off. I missed the ten minute reading but it still read 52psi at 15 minutes.

8. Does injector test lamp flash for each injector circuit? - I don't know. Can I do this test with just a regular test light or DMM?

I'm starting to think I have a big vacuum leak somewhere. Is there supposed to be a gasket on top of the throttle body? Because there isn't one there. As soon as I get the motorcycles out of the garage I'm gonna pull the Blazer in and look for vacuum leaks again. Are there any particular areas I should pay special attention to?

[dct73]

Now it won't even start with carb cleaner sprayed in it.

[dct73]

I finally got a friend to come over with a scanner with live data. The data stream was all messed up. He back probed the ecm connections and said the computer was bad. I just replaced the ecm and it runs great again.

Thanks for all the help