I have a 2002 Chevy Blazer 4.3 liter Vortec V-6 4x4 No modifications.
I bought it in 2020 with something like 180,000 miles.
It has been throwing a left cylinder bank running rich since purchased 2020.
The wire to the coolant temp sensor had a short so replaced that.
Then late 2024 I replaced the coolant temp sensor and coolant thermostat running rich code went away.
It seemed to doing fine for a while and then starting throwing a code left cylinder bank running rich again this past January.
Then it started multiple cylinder misfire after that cylinder 3 being the biggest offender.
So in May 2025 I had the intake manifold gasket, spider fuel injection unit, distributor shaft assembly with gear, cap, rotor, spark plugs and spark plug wires replaced.
It'* not throwing an engine running rich or lean code anymore but still has multiple cylinder misfire code with cylinder 3 being the worst.
The auto shop I had replace all the above parts listed said they couldn't figure out the misfire and gave the Blazer back.
They didn't charge me for the spark plug wires and distributor.
They did a compression test and didn't charge me.
They told me the compression test was all good and that specifically cylinder 3 that has the worst misfire has good compression.
So timing is good and compression is good.
I have heard that the replacement spider fuel injector units that the parts stores sell are known to have issues out the box that was replaced back in May.
Is it possible to have good compression and have a lifter or valve be shot?

Does anybody know how to use a dvom? Call a shop tat does electrical .

How many miles on it now?

Why?

Were any of these diagnosed as bad? . . . or did they just throw parts at it? . . . or some other thing?

What are the compression numbers?

These two things aren't related, so I'll answer separately:

So . . . you're thinking that the original one was bad, and the new one was bad in the exact same way?

Not really, and unlikely on a 4.3.

What is the fuel pressure on this with the key on and engine stopped?

What is the fuel pressure on this with the engine idling in Park?

I believe 220,000 miles

I was told they all those parts were bad.
Well not the spider injector but they suggested replacing while they were in there.
They said the timing was off so they replaced the distributor gear.
The shop said the spark for cylinder 3 was dirty.
The shop said there was a tear in the intake manifold gasket near cylinder 3.

I'm not sure what the compression numbers were.
The first spider injector unit wouldn't even pressure up.
I'm not sure what the fuel pressure is.

That'* a lot of parts to all go bad at the same time.

Can you get us a fuel pressure reading?

This garage sounds like they don't test much. They can guess all they want but without testing it'* a swap meet.

Yuuuup!

I can get you a fuel pressure reading I have a fuel pressure tester kit.
I started it the other day and checked the codes with my little cheap eBay code reader.
It is throwing a code for misfire cylinder 3.
I don't think the fuel pressure would have anything to do with a misfire on one single cylinder would it?
The shop said that when they changed the spark plugs they inspected the old plugs(after changing the intake manifold gasket that had tear near cylinder 3) and cylinder 3 spark plug was dirty.
Would a good quality motor vac clean any carbon that could have built up from a tear in the intake manifold gasket in cylinder 3?

Ummm . . . there'* this that I don't believe I've seen resolved:

. . . but it could also be fuel pressure combined with other issues and cylinder 3 is showing it first because it is the most marginal of the bunch.

I decided to take the Blazer to a different repair shop and they figured it out.
They replaced the spark plug wire and spark plug on cylinder 3 and the misfire is gone.