Today I was driving down the interstate going roughly 70mph. Everything was fine and was riding as smooth as butter, until I heard a very loud backfire. I couldn't accelerate, and if I did it would backfire on me again. I pulled over and let it sit for a few seconds, started the motor and tried to accelerate again. As long as I didn't press on the gas everything ran fine, but as soon as I accelerated, it backfired and would almost die on me. I also noticed a very strong smell of burnt gas. I decided to wait a few more minutes and started the truck again, this time it ran fine. I got nearly 10 miles down the road and decided to give it a little extra gas to see what it would do. As soon as I hit 60mph it backfired and nearly died yet again. I pulled over and waited a few more minutes, started it up and drove it the rest of the way home around 40mph.

Prior to this, I bought 20 in gas at a gas station that apparently sells bad gas (didn't find out until later). I checked the air filter and spark plugs, which were good. I was told it could be flat lining, a timing issue, cat converter, or some other fuel related problem (fuel pump, filter, etc.). It is a 1995 4 door 4.3l with 269,000 miles. I've had no problems with the vehicle since I bought it at around 195,000, other than the alternator. Though, there was a similar problem before when I made a 500 mile trip. It didn't backfire, but sputtered a lot when idling. It seemed to magically go away after getting it home and letting it rest a night.

I'm kinda broke right now, and this is my first real car trouble I've had. Don't wanna deal with a crappy mechanic that guesses at everything either, so any help is greatly appreciated.

 

Start with a fuel filter replacement.. check the cap and rotor for burn marks from the backfiring.. then check spark plugs, #3 plug is a hootie to get out and back in unless ya have patience.....all the other plugs go thru the wheelwell to get them replaced..good luck.

 

Thanks for the reply. I did all the things you suggested above. I pulled the fuel filter out and blew through it. With very little resistance, some gas came out, so I figured it was okay and put it back in. The spark plugs were all good, and everything inside the dist. cap seemed okay to.

I was told today, that it could be the cat. converter. Before all of this, I wasn't able to run the A/C without the engine bogging down after driving a little while with it on (no acceleration, etc.). Do you think it could be related? Never had it backfire on me till yesterday. Always ran it without the A/C, cause I figured it was something else.

 

I did`nt see you mention anything about a check engine light, did that come on at all while this was/is happening? heres a little test for ya, get back out on the hwy or whatever its called out by you , and drive normal speed for about 15 to 20 minutes, do it at night, then pull over and look to see if the catalytic conv is glowing red/orange!! Normally if a conv is clogged that bad it will glow from overheating... Also have someone sit in it while someone else stands at the back of the truck have the person in the truck bring the idle up see if any black smoke comes out, also carefully put your hand near the exhaust pipe to feel the temp of the exhaust, dont touch the pipe just try to get the feel of the exhaust.. also b4 ya even go for the drive to test it, knock on the conv, b4 starting it to see if you hear rattling inside of it.. if you do -change the conv automatically that does mean it failing and breaking apart ( honeycomb ) inside..Good luck,.

 

I gave your suggestion a shot and took it for a stroll a few minutes ago. I drove roughly 10 mins with the A/C on max and right around the speed limit. (40-45 curvy, hilly, back road highway) When I pulled in, I immediately checked the converter and exhaust. I did not see the converter glowing, but as soon as I stuck my face under the car I felt heat coming from its direction. The exhaust was also pretty hot, all of this and my temp on the gauge hadn't yet reached 200.

No rattling when I bang on it and no black smoke on idle, but there was some greyish smoke. I have seen some black smoke before when accelerating.

I'm almost 100% definitely-indecisively convinced it is the converter. If I were to say, cut it off, and weld a pipe in its place what would happen? Is there an o2 sensor inside of it, behind it, or in front of it that would go crazy? If I can't do that, would this be a good alternative - 1987-1995 Chevrolet Blazer Catalytic Converter - Magnaflow 94006 - 94000, Universal product

Again, thank you for all your help. Sorry about all the questions.