Heater core?

Hey no problem, , its always easier going back in,

jim

No problem, I worked at the dealer for 20 years and the parts always work best, next time, order ahead from gmpartsdirect. Com, almost half of what the dealer charges and it would have cost you about a grand or so depending on what part of the country you live in, im glad I could help guide you
jim

If you know what your doing a repair manual would help you out allot. If not I would suggest having a professional perform the task

The entire dash needs to come out. It is not a fun thing to do. You should have a copy of the manual to do it easily. In short you need to disconnect the battery, unbolt the steering column from the dash. There are a bunch of bolts that hold the dash in. One on each end under the dash, two or so in the middle under the dash, then there are bolts hidden behind the A/C vents behind the speaker grills and behind the defrost vent. Once they are all out the dash can be moved out of the way enough to get to the heater case. Figure about six hours if you have done it once longer if you need to learn as you go.

If it's got a/c you have to have the charge recycled then you have to pull the dash and finally the heater core.

It can only cause a "no start" if the fuel pump feed is shorted out. All you have to do is unplug it to eliminate that possibility.

All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.

Every engine requires spark, fuel and compression to run. That's what we have to look for.

These are the basics that need to be tested and will give us the info required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.

2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.

3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

4) If all of these things check good, then you would need to do a complete compression test.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.

It's neither of those. It's not electrical in nature at all. You have a leakdown problem. This can happen at a leaky injector, pressure regulator or bad check valve in the pump.

What is the fuel pressure at peak?

No, the fuel pressure is an issue but not preventing it from starting. As long as you can keep it up around 60PSI when cranking, it will run. Make sure that pressure that you are losing isn't an internal leak fouling the plugs. The dash lights have nothing to do with that but being on when the engine isn't running isn't unusual.

Yes, the dash has to come out to R&R the heater core. It is NOT a fun job and you really should have a copy of a manual for reference if you have never done it before. There are quite a few bolts and clips that you need to remove and some are in hidden places. The Mitchell online manual covers it real well and isn't expensive.