After much trouble over the last few weeks, I've managed to determine I have a bad head gasket. It has a bad radiator leak and the previous owner just ran water through it instead of coolant. Over the last few weeks It started running rough and would just die, It had gotten to where it wouldn't start and when it did it would let off a lot of while smoke from the exhaust. So I'm 99% sure its the head gasket. That said how hard would it be to replace on my own? Or am I better off just having a mechanic doing it?

 

Could also be the intake manifold gasket - that's common with these engines.

 

How would I diagnose which one it is?

 

Depends on the area of the leak but its just easier to pop off the intake and look

 

Main goal is to get back to a safe place to work on it, ASAP. Don't let it overheat to much for too long. Aluminum intake manifold may warp.

Typical coolant leaks on 1999 5.7li Vin R engines occur around 80K to 90K miles, right at the life limit of DexCool. It may leak outside, inside, through combustion chamber or any of combination these three. Outside leaks are easy to find because they throw a plume of white smoke from under the hood or out back as driving. Internal leaks (in side the crank case) can be detected on oil dip stick or inside oil filler cap. Leaking into combustion chamber results it white "smoke" out the tail pipe and missfires.

How many and what error codes is the computer throwing? Typical P030x?

As mentioned above and as I have experienced it sounds like lower intake manifold gaskets which is a very common issue. Original factory intake gaskets can't handle old acidic DexCool. They turn to spaghetti then fail and loose their seal. I use Fel Pro gaskets which seem to be the best out there. Repaired mine in Nov 2012. TAKE LOTS OF PHOTOS and MARK ALL CONNECTORS. Take photos as you are working as it makes it easier to reassemble.

As far as cost I would try looking into the intake gaskets first as they are around $50 or so. There are places on the net that show you step by step how to do it.
Note: Be very careful to mark the distributor, shaft, rotor and a reference to block as this step is not forgiving. While you have the intake manifold off you should look at the spider injector as you have torn it down that far. Pay attention to torque specs of intake manifold bolts.

A shop quoted me between 1500 and 2000 to replace intake gasket.

A cylinder head is probably a little pricey and not as easy to swap out. Would be a longer term $ project.

 

wow you got ripped of if that is what you are quoted for an intake gasket.... that should be the cost of a headgasket /rebuild ....

find a different shop