Engine Misfire Need Help!

ShadowJ · March 8, 2008

Ok, this is going to be a long story.

I have a 99 Silverado (New Body) with 180,000 miles on it. It's got the 4.3v6. It is my service vehicle and gets all highway mileage. Around mid November I was crusing down the highway, cruise set at 70 and all of a sudden I felt a quick drop in power, then it was fine. I thought "that was weird". As soon as I got home I checked my maintenance records and noticed I haven't done a tune up in over 100,000 miles.

So a tuning I went.... I put in new acdelco plugs, new distributer cap and rotor.

Still had the problem, only now it is much worse. Engine is surging very bad. Sometimes when I leave home it will surge bad for the first 2 miles, then stop. Sometimes it won't do it for the first 2 miles then it will do it at highway speeds. It never does it during acceleration, only when I raise my foot off the pedal to keep a constant speed. One day I drove 500miles and it ran perfectly all day.

Put in a new set of wires.

Still had the problem.

Put in a new Mass Air Sensor.

Still had the problem.

Put in new "Multi Port Fuel Injection" system.

Still had problem.

Put in new fuel pump and filter.

Still had problem.

Put in new Coil and Map Sensor.

Still had problem but now it is intermittent. I'm thinking "Bad ECM"

I finally deceided to take it to the Dealer. After the first hour they come out and tell me they can't get it to do it. I said welcome to my nightmare... I said shut it off and restart it. Bingo! now its doing it. Over the next three hours they try several different things. They change the Distributer drive gear. (It only had 70,000 miles on it. I changed the last one at 109,000 and it was throwing codes). Changing that didn't fix it. They wanted to change the Crank Sensor but they didn't have one in stock. I told them I had one at home. They let me have the truck and I went home and changed it with an old one I had. It didn't fix it. They said buy a new one. I did. It didn't fix it. I bought a new Cam Sensor and 4 new 02 Sensors to install tomorrow. If that doesn't fix it, I don't know what to do..... It is doing it regularly now, so I have to remember to keep speeding up and slowing down so it will run smooth. Funny thing is, its not throwing any codes. Oh, and when it does it bad enough, the transmission will drop out of overdrive until it senses its not doing it anymore.

Arghhhh. Is it time for a new truck? I really like this truck and want to keep it. But at this point I have spent about 2,500 dollars trying to nail this down. I am the original owner. If i'm overlooking something please let me know.

Thanks guys!

X-man · March 8, 2008

Ok, this is going to be a long story.

I have a 99 Silverado (New Body) with 180,000 miles on it. It's got the 4.3v6. It is my service vehicle and gets all highway mileage. Around mid November I was crusing down the highway, cruise set at 70 and all of a sudden I felt a quick drop in power, then it was fine. I thought "that was weird". As soon as I got home I checked my maintenance records and noticed I haven't done a tune up in over 100,000 miles.

So a tuning I went.... I put in new acdelco plugs, new distributer cap and rotor.

Still had the problem, only now it is much worse. Engine is surging very bad. Sometimes when I leave home it will surge bad for the first 2 miles, then stop. Sometimes it won't do it for the first 2 miles then it will do it at highway speeds. It never does it during acceleration, only when I raise my foot off the pedal to keep a constant speed. One day I drove 500miles and it ran perfectly all day.

Put in a new set of wires.

Still had the problem.

Put in a new Mass Air Sensor.

Still had the problem.

Put in new "Multi Port Fuel Injection" system.

Still had problem.

Put in new fuel pump and filter.

Still had problem.

Put in new Coil and Map Sensor.

Still had problem but now it is intermittent. I'm thinking "Bad ECM"

I finally deceided to take it to the Dealer. After the first hour they come out and tell me they can't get it to do it. I said welcome to my nightmare... I said shut it off and restart it. Bingo! now its doing it. Over the next three hours they try several different things. They change the Distributer drive gear. (It only had 70,000 miles on it. I changed the last one at 109,000 and it was throwing codes). Changing that didn't fix it. They wanted to change the Crank Sensor but they didn't have one in stock. I told them I had one at home. They let me have the truck and I went home and changed it with an old one I had. It didn't fix it. They said buy a new one. I did. It didn't fix it. I bought a new Cam Sensor and 4 new 02 Sensors to install tomorrow. If that doesn't fix it, I don't know what to do..... It is doing it regularly now, so I have to remember to keep speeding up and slowing down so it will run smooth. Funny thing is, its not throwing any codes. Oh, and when it does it bad enough, the transmission will drop out of overdrive until it senses its not doing it anymore.

Arghhhh. Is it time for a new truck? I really like this truck and want to keep it. But at this point I have spent about 2,500 dollars trying to nail this down. I am the original owner. If i'm overlooking something please let me know.

Thanks guys!

It could a fuel system issue. A couple of thoughts; did you replace the fuel pump connector? they are known to go bad. Perhaps you could hook up a fuel pressure gauge and route it out near the windshield where it's visible from thedrivers seat. then go for a drive and monitor the pressure when a surge occurs to see if it drops momentarily.

hgl800 · March 8, 2008

I can't help you out, but i have a 99 4.3 5sp and it has been doing the EXACT same thing! So i am also wondering what is causing this. Seems to be worse in the colder temps i find. I was thinking maybe o2 sensor cause i just had one go on my 05.

ShadowJ · March 8, 2008

I replaced the plug on the fuel pump about 6 months ago when I replaced the Gauge Sending Unit. The new pump came with a new plug but since I just changed it I didn't think it was necessary to do it again.

Ok, this is going to be a long story.

I have a 99 Silverado (New Body) with 180,000 miles on it. It's got the 4.3v6. It is my service vehicle and gets all highway mileage. Around mid November I was crusing down the highway, cruise set at 70 and all of a sudden I felt a quick drop in power, then it was fine. I thought "that was weird". As soon as I got home I checked my maintenance records and noticed I haven't done a tune up in over 100,000 miles.

So a tuning I went.... I put in new acdelco plugs, new distributer cap and rotor.

Still had the problem, only now it is much worse. Engine is surging very bad. Sometimes when I leave home it will surge bad for the first 2 miles, then stop. Sometimes it won't do it for the first 2 miles then it will do it at highway speeds. It never does it during acceleration, only when I raise my foot off the pedal to keep a constant speed. One day I drove 500miles and it ran perfectly all day.

Put in a new set of wires.

Still had the problem.

Put in a new Mass Air Sensor.

Still had the problem.

Put in new "Multi Port Fuel Injection" system.

Still had problem.

Put in new fuel pump and filter.

Still had problem.

Put in new Coil and Map Sensor.

Still had problem but now it is intermittent. I'm thinking "Bad ECM"

I finally deceided to take it to the Dealer. After the first hour they come out and tell me they can't get it to do it. I said welcome to my nightmare... I said shut it off and restart it. Bingo! now its doing it. Over the next three hours they try several different things. They change the Distributer drive gear. (It only had 70,000 miles on it. I changed the last one at 109,000 and it was throwing codes). Changing that didn't fix it. They wanted to change the Crank Sensor but they didn't have one in stock. I told them I had one at home. They let me have the truck and I went home and changed it with an old one I had. It didn't fix it. They said buy a new one. I did. It didn't fix it. I bought a new Cam Sensor and 4 new 02 Sensors to install tomorrow. If that doesn't fix it, I don't know what to do..... It is doing it regularly now, so I have to remember to keep speeding up and slowing down so it will run smooth. Funny thing is, its not throwing any codes. Oh, and when it does it bad enough, the transmission will drop out of overdrive until it senses its not doing it anymore.

Arghhhh. Is it time for a new truck? I really like this truck and want to keep it. But at this point I have spent about 2,500 dollars trying to nail this down. I am the original owner. If i'm overlooking something please let me know.

Thanks guys!

It could a fuel system issue. A couple of thoughts; did you replace the fuel pump connector? they are known to go bad. Perhaps you could hook up a fuel pressure gauge and route it out near the windshield where it's visible from thedrivers seat. then go for a drive and monitor the pressure when a surge occurs to see if it drops momentarily.

ShadowJ · March 8, 2008

I had an o2 sensor go bad at 60,000 miles and I replaced all of them then. But at that time a code was thrown telling me the sensor went bad.

I can't help you out, but i have a 99 4.3 5sp and it has been doing the EXACT same thing! So i am also wondering what is causing this. Seems to be worse in the colder temps i find. I was thinking maybe o2 sensor cause i just had one go on my 05.

rjirvine · March 8, 2008

What part number plugs did you use, and at what gap? Does the engine bog down like it could be an accessories bearings freezing up intermittently? Are there any codes thrown when this happens? How's the throttle position sensor look?

ShadowJ · March 9, 2008

The plugs I pulled out were 41-932 and the plugs I was givin at AutoZone were 41-993. The gap is .060. The engine never bogs down. I forgot to mention I did replace the Throttle Position Sensor also. And no Codes are being thrown.

What part number plugs did you use, and at what gap? Does the engine bog down like it could be an accessories bearings freezing up intermittently? Are there any codes thrown when this happens? How's the throttle position sensor look?