1997 blazer 4.3 213000 miles.
Help me please before I go crazy. My wife drove our 97 Blazer 4.3 to work the other day and on way home she said it ran hot. I was out of town at the time so she had it towed home. When i got back home i got to looking for the reason it ran hot and discovered freeze plug above starter was leaking so i replaced it and that fixed the water leak. its only been about a week now but I havent noticed it loosing anymore water. Now engine light is on and I had it scaned and it showed random misfire code. It idles rough but as soon as you give it a little throtle it seems to smooth out and at driving speed you cant notice it skipping. I pulled all plugs. They were wore significantly. Drivers side plugs all looked whitesh like ash deposits or something. so i replaced them with AC DELCO PLATNIUM plugs. didnt fix it. took horizontal distributer cap off and all poles on inside of cap looked funny like the spark was jumping to the pole too late like after rotor would pass it then transfer ignition spark. put new cap and rotor button on. didnt fix it. im wondering if it could have a blown head gasket or if my distributer is off. any help? anybody?

 

don't guess you noticed any oil in the coolant huh? thats usually a good way to tell if the hg is blown. otherwise i can't think of how overheating would cause a misfire. hate to say it but, my very well be blown hg.

 

no the oil looks as clean as the day i put it in. and the coolent/water looks clear of oil.

 

I just bought a Bravada that had the same thing happen to it. Here is what I've done so far, feel free to follow in my footsteps. I start by doing and changing everything cheap and easy to rule them out. If you don't know or aren't sure how to do these you can certainly try if you like, or head to the shop..

Change the oil. Your oil probably got roasted. Hopefully it doesn't smell burnt. Remember a new drain plug and washer. I'm surprised it looks ok, if so then hopefully it did it's job, but it's life is now shortened very much. Go ahead and set it free, it took a beating.

Cap, rotor, wires, plugs. All of these looked to be either hot, corroded, or whatnot, so I just changed them all out. I ended up doing the distributor itself, because the screw holes were stripped on it.

I did a vacuum test on it, seemed normal enough, but if not, I would have fixed the vacuum leaks if it had any. I think you can borrow this tool from the parts store, or in a pinch I don't think they are too expensive. Harbor Freight has one cheap I'm sure.

Remove and clean the EGR valve, and all carbon build up in its cavity. Replace the gasket with the screen type if you haven't already.

Next do a compression test. See what kind of readings you are getting on the cylinders. Mine was very erratic. Cylinder 4 was about 100 psi, Cylinder 5 was about 170, and the other 4 varied between 120 and 150. I'm getting my misfire on 4. Again you can probably borrow this tool or buy one, again Harbor Freight probably has a cheapo. If you have similar results, moving on to the next step.

This is where you'll want to do a leak down test. This is where you blow air into the cylinder and try to see where it's leaking from. Perhaps the oil filler tube, perhaps the radiator, the exhaust, or the throttle body. Mine was coming from the throttle body which means it's about 90% certain I've got at least 1 leaking intake valve. Depending on where it's leaking from will help to determine the issue. You'll want to research whatever result you get.

So, I'm taking a chance and I'm going to hope that this is the only issue. So I'll be removing the heads and taking them to a shop to have them checked out and probably rebuilt. I assume this is the issue.

So with rebuilt heads, new gaskets, and new head bolts. I'm pretty sure that I'm going to do the MPFI spider upgrade. I trust that she will be purring like a kitten when I get it back together.

Mind you, this all seems kinda silly for something that started out with a simple coolant leak.

 

ok, i hooked a scan tool to it today and it threw a p0306 cylinder 6 misfire. i pulled the plug and it looked ok. I swaped spark plug wire with a buddys to verify that wasnt the problem and it wasnt. so i cranked it with plug out of motor hooked up to spark plug wire. it was firing fine. so this leads me to thinking now it can only be cylinder 6 injector, or head gasket. Im going to do compression test when i get home

 

Could be a valve too. I'm pretty sure the valves on my Bravada are hurting after overheating. I'll be pulling heads very soon!

 

You could verify the timing using the procedure below:
EDI Engine Timing

If the gear is worn on the bottom of the distributor, it would affect the timing.

 

well i went and bought compression tester today and cyl 6 only had 50 lbs so i pulled heads off and thought i would see a blown head gasket but didnt. i took head and filled the intake ports with water and on two of them you could watch the water run out of the valves. i went and got some valve lapping compound and did that but it still leaks. what to do now

 

Take the heads into a engine shop and see what a rebuild will cost you.

 

Sounds like you have bent a valve or two.