Long story short, my '95 blazer has 171,000 miles on it. Put new intake and head gaskets on it this past Fall. From what I could see, none of the valves or the springs looked like they were broke or bent. Started it after all the new gaskets and it had a low "poof" backfire sound out of the exhaust. So, new cap, rotor, plugs, wires, Cat., o2 sensor. Re-set the timing as close as I could get it and it still makes that "poof". I've read some other posts on here and have some thoughts. Could I have a bad timing chain, camshaft, or distributor? Maybe EGR valve? Thanks for any help!

 

Does it 'poof' only on starting or at random times?

 

at random times. when I re did the distributor wrong the first time it did the "poof" then wouldn't start.

 

I would start with having the ignition coil tested.

 

Ok I had the coil tested. It was fine.

 

Alright, I'm beating a dead horse here. I have put new threads up and I have been getting some good tips on what to do. All of which have been helpful but, I keep hitting a dead end. SO, I have a '95 blazer, 171,000.

What I have replaced so far.

• Cap and Rotor
• Fuel Filter
• Plugs and Wires
• Head and Intake gaskets
• Cat. and o2 sensor

What I have Tested.

• Ignition coil=Passed
• ICM=Passed

 

I'm not going to rell you "it could be" but a couple of questions came to mind.
1) What motor are you working on?
2) What do your spark plugs look like? Fiuled? If so, with what?
3) Any smells or odors - gas for instance?
It sounds to me like you had a pretty good vacuum leak after the gasket change. Am I right in you saying you changed the head gasket or are you talking about the valve cover gasket? I've noticed with a lot of guys they will just throw parts at a problem until it's fixed. Call that "shotgun troubleshooting" and it's not the way to go about finding out what's wrong. Do you have a decent manual on this vehicle? Mine is a 94 and not the same. Are you showing any codes on your Service Engine Light. You may or may not need a tool for this year. Depends what the data link port looks like.

 

If you already have threads going please do not start new ones. Double posting is against the forum rules. Please just add to the existing threads.

 

Yes, there are a lot of things that it "could be." But there are ways to check all of these things without spending a penny to do them. Almost any part or problem can be tested before replacing it on a maybe.

First off, have you noticed any odd smells especially gas coming from the engine? Crank it a few times and then open the butterfly valve on the intake and take a sniff. If there is a strong gas odor then there is a good chance of fuel leaking into the intake and down into one of the cylinders. This would account for the engine "jamming up." It is called hydro lock and usually occurs in one of the rear cyl's if it is fuel but can happen to any of them if it is coolant. The offending fluid will eventually leak down into your oil. This is usually caused by a fuel line leak or a bad seal on the pressure regulator.

Speaking of fluids, you did change out the oil and filter after doing these repairs right?
During these repairs coolant often finds it's way into the oil and can cause you no end of problems if you try to run the engine before changing it out.

Next step, Pull out ALL the spark plugs and check them over. Check for fouling, covered in fuel or coolant and generally make sure that they all are looking the same as each other. If one or more aren't showing up the same as the others then it can help point you in the right direction of your problem.

With ALL the plugs out, crank the engine over a few times to allow anything that may have gotten into the cyl's to blow out of the plug holes. Put a piece of paper towel over each plug hole before you crank it to see if anything interesting comes out. If it spits out fuel, coolant, or maybe old pieces of gasket then you can get an idea of potential trouble.

Did you replace all the seals that came with the upper plenum gasket kit?
A bad seal in the upper plenum could be sucking to much unmetered air into the intake and screwing your air fuel mixture. A bad seal on the top of the spider assembly is a good one for this.

Here is one that threw me for quite a while the first time I did an intake manifold gasket. Pull off the cap and rotor and check to make sure that no small bits of metal,small screws ect... have "attached" themselves to the magnetic pickup on the distributer.
Took me 2 days of scratching my head to realize that a tiny piece of metal that looked like one of the retaining washers that keep the screw on the distributer cap was on the pickup magnet and keeping my engine from running properly.

There are obviously other things that you can check but the above is a good place to start and work from what you find there.

Oh yeah, and keep the battery fully charged while you are playing around with testing different things. Trust me, you'd be surprised how often that can make all the difference.

 

Thanks for the feedback guys. For sisk, there reason I double post is because i've only got maybe 4 replys back all together from 2 posts, and the replies that i got back didn't help at all. For gimpy i changed the head gaskets and the valve cover gaskets. It's a 4.3 Vortec. When I try to start it, i do smell gas. When i take the intake tube thing off and smell by the butterfly, the smell of gas is noticeable. I have the Haynes manual for this thing.
For awe341, I know that the injector system in these things suck. When we got it, I took the upper plenum off and found gas on one side. Seeing how they are pricey I got one from the junkyard that didn't have any gas around it. I did change the oil after the gasket change, now it has a black color to it, like any other car would after driving it a few months. This thing only ran about a 1/2 hour in my driveway. I will take the plugs out and check them. Thanks for the reply back.