1999 Blazer, Engine misfire

[Mike0313]

I have a 1999 blazer. 4.3 V6, 235,000 km (146,000 miles) The engine has s serious misfire. It starts up and idles good. During acceleration just before the transmission upshifts is when the misfire happens. A guy at Mr. Transmission said it was the transmission and would cost me $600.00 to repair. I thanked him for his time. He's full of crap, the misfire happens in park also, around 1200 RPM. I have replaced the plugs, wires, cap, rotor. Cleaned the MAF sensor, and throttle body. I feel like I'm fighting a loosing battle. Anybody have any Ideas??

[MT-2500]

Originally Posted by Mike0313

I have a 1999 blazer. 4.3 V6, 235,000 km (146,000 miles) The engine has s serious misfire. It starts up and idles good. During acceleration just before the transmission upshifts is when the misfire happens. A guy at Mr. Transmission said it was the transmission and would cost me $600.00 to repair. I thanked him for his time. He's full of crap, the misfire happens in park also, around 1200 RPM. I have replaced the plugs, wires, cap, rotor. Cleaned the MAF sensor, and throttle body. I feel like I'm fighting a loosing battle. Anybody have any Ideas??

What engine code and transmission?
We need more onfo and
You need to do some proper testing.
Missfire codes can be caused by several things.
Low fuel pressure.
Secandary ign problems.
Camshaft retard setting off.
What are codes no?
What cylinders are missfiring?
How many missfires per cylinder?

[TCGrove]

I also have a 1999 Chevy Blazer with 155,000. I began having that problem about a year ago. Generally in warmer weather. Always when starting the engine. I just got the P0300 code along with P0152 O2 Sensor Circuit High Voltage Bank 2 Sensor 1. I'm thinking these misfire are related to that. I'm going to pull the O2 Sensor and check it. I'll let you know the results. I've done the same things you have. New plugs, wires, rotor and cap, cleaned MAF sensor, gas filter, air filter, and new fuel pump a year ago.

[TCGrove]

OK. I pulled both sensors tonight. You can do this with a 7/8" wrench and soak the threads with some penetrating oil. They're easy to reach. I pulled the front right wheel to make it even a little easier. I got the error code on the sensor after the cat. converter so I pulled it first. It really didn't look too bad. The resistance across the heating wires (two brown) was 6.7 ohms and the new Bosch sensor was 3.4 ohms. I'm not sure if that's good or bad. I then hooked up the signal wire and grounded the other to the shell of the sensor. I took a propane torch to heat it up and watched for the 0.1 to 0.9 volt swing. It was very sporatic. Even when I left it in the flame it jumped around, but it did make it to the 0.9 volts. I pulled the front sensor next. It has a lot of white discoloration to it. I didn't bother to test it. I just replaced it. I drove the car about 6-7 miles and it seems to run smoother and have a little more zip to the acceleration. I'll have to drive it for awhile and see if it fixed the intermittent lack of power it suffered from in the past year.

[blazes9395]

Originally Posted by Mike0313

I have a 1999 blazer. 4.3 V6, 235,000 km (146,000 miles) The engine has s serious misfire. It starts up and idles good. During acceleration just before the transmission upshifts is when the misfire happens. A guy at Mr. Transmission said it was the transmission and would cost me $600.00 to repair. I thanked him for his time. He's full of crap, the misfire happens in park also, around 1200 RPM. I have replaced the plugs, wires, cap, rotor. Cleaned the MAF sensor, and throttle body. I feel like I'm fighting a loosing battle. Anybody have any Ideas??

Have the injectors ever been serviced? has the fuel filter ever been replaced? These trucks have had issues with the injectors and/or poppet nozzles getting stuck/dirty/worn out. Seeing what you have replaced, a partially clogged injector(s) or weak fuel system can allow the engine to idle alright, but as soon as it needs more fual (under load) it could be missing at that point.