Random misfire
April 22nd, 2014, 02:07 PM
#1
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Thread Starter
Join Date: Oct 2011
Location: NW of Chicago
Posts: 43
Random misfire
1997 Regency 84,000 miles.
Got a random misfire and O2 sensor code at 80,000 miles. So I replaced the O2 sensor and put in new A/C irriduim plugs and A/C wires.
Now at 84,000 miles i get the random misfire code again. The only thing that comes up on the freeze frame is the engine speed at the time of the event. So now I've had the vacuum lines checked ,the fuel pressure is good at idle and not running, the injectors checked for single fire and multiple fire and the fuel pressure drop is exactly the same across all 6 cylinders, all three coils were replaced at around 65,000 miles. The upper intake was replaced at around 60,000 miles.
I'm in the hospital and all this was done wiith the exception of the coils, was done by my son-in -law who was an ASE certified brake,suspension,snd steering mechanic but gave it up to sell Mack Tools. I personally don't have a lot of faith in his engine skills, but I;m in the hospital and can't do it myself. He said it sounds as if it still has a slight misfire.
My question is what else can I check. I don't want to just throw parts at this cause that can get costly.
Got a random misfire and O2 sensor code at 80,000 miles. So I replaced the O2 sensor and put in new A/C irriduim plugs and A/C wires.
Now at 84,000 miles i get the random misfire code again. The only thing that comes up on the freeze frame is the engine speed at the time of the event. So now I've had the vacuum lines checked ,the fuel pressure is good at idle and not running, the injectors checked for single fire and multiple fire and the fuel pressure drop is exactly the same across all 6 cylinders, all three coils were replaced at around 65,000 miles. The upper intake was replaced at around 60,000 miles.
I'm in the hospital and all this was done wiith the exception of the coils, was done by my son-in -law who was an ASE certified brake,suspension,snd steering mechanic but gave it up to sell Mack Tools. I personally don't have a lot of faith in his engine skills, but I;m in the hospital and can't do it myself. He said it sounds as if it still has a slight misfire.
My question is what else can I check. I don't want to just throw parts at this cause that can get costly.
April 22nd, 2014, 02:37 PM
#2
Just an Olds Guy
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
First, my best wishes for your speedy recovery.
You've done all the right things so far. One thing you might want to check is your EGR valve. Depending on what speed the sensor reading came in at, you might have a binding pintle on the EGR. You can take it off, clean it and reinstall it using the same gasket. Had that problem come up on my wifes 96 Saturn and that's what ended up curing it.
Was it the front or rear O2 sensor that you had to replace?
You've done all the right things so far. One thing you might want to check is your EGR valve. Depending on what speed the sensor reading came in at, you might have a binding pintle on the EGR. You can take it off, clean it and reinstall it using the same gasket. Had that problem come up on my wifes 96 Saturn and that's what ended up curing it.
Was it the front or rear O2 sensor that you had to replace?
April 22nd, 2014, 05:57 PM
#3
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Join Date: Oct 2011
Location: NW of Chicago
Posts: 43
Random Misfire
I was thinking along that line. I didn't know I could use the same gasket. Do I just clean the pintle ,seat ,and shaft with a scotch pad?
The code came in at an idle 725 rpm. That's about right cause my wife was stuck in rush hour traffic.
I had asked my son-in=law to take the egr off and clean it and according to his reaction it went over his head. I also wanted him to take the ignition control module (sits under the coils) in to Advance so they can check it and I just think he didn't want to do it.
Are these my only other options?
It was the rear O2 sensor.
The code came in at an idle 725 rpm. That's about right cause my wife was stuck in rush hour traffic.
I had asked my son-in=law to take the egr off and clean it and according to his reaction it went over his head. I also wanted him to take the ignition control module (sits under the coils) in to Advance so they can check it and I just think he didn't want to do it.
Are these my only other options?
It was the rear O2 sensor.
Last edited by oldsmoguy; April 22nd, 2014 at 06:00 PM.
April 22nd, 2014, 06:27 PM
#4
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 47,259
You mention coils, but what about the ignition module itself? This is the "plate" that the coils sit on. Wires?
What scan tool are you using to look at the telemetry when it starts to misfire? Your car should record misfire counts by individual cylinder. I know my Genisys can read those (I used this feature recently on my 1999 truck to pinpoint the bad plug wire). Other scan tools should be able to also. If the misfire is consistently on one cylinder, it's likely the plug wire, spark plug, or something mechanical related to the cylinder. If the misfires are all over the map, it's likely the ignition module or cam or crank sensor.
The rear O2 sensor is only there to gauge the performance of the catalyst. The front O2 sensor is the one that is used by the EFI software.
What scan tool are you using to look at the telemetry when it starts to misfire? Your car should record misfire counts by individual cylinder. I know my Genisys can read those (I used this feature recently on my 1999 truck to pinpoint the bad plug wire). Other scan tools should be able to also. If the misfire is consistently on one cylinder, it's likely the plug wire, spark plug, or something mechanical related to the cylinder. If the misfires are all over the map, it's likely the ignition module or cam or crank sensor.
The rear O2 sensor is only there to gauge the performance of the catalyst. The front O2 sensor is the one that is used by the EFI software.
April 22nd, 2014, 08:18 PM
#6
Registered User
Thread Starter
Join Date: Oct 2011
Location: NW of Chicago
Posts: 43
You mention coils, but what about the ignition module itself? This is the "plate" that the coils sit on. Wires?
What scan tool are you using to look at the telemetry when it starts to misfire? Your car should record misfire counts by individual cylinder. I know my Genisys can read those (I used this feature recently on my 1999 truck to pinpoint the bad plug wire). Other scan tools should be able to also. If the misfire is consistently on one cylinder, it's likely the plug wire, spark plug, or something mechanical related to the cylinder. If the misfires are all over the map, it's likely the ignition module or cam or crank sensor.
The rear O2 sensor is only there to gauge the performance of the catalyst. The front O2 sensor is the one that is used by the EFI software.
What scan tool are you using to look at the telemetry when it starts to misfire? Your car should record misfire counts by individual cylinder. I know my Genisys can read those (I used this feature recently on my 1999 truck to pinpoint the bad plug wire). Other scan tools should be able to also. If the misfire is consistently on one cylinder, it's likely the plug wire, spark plug, or something mechanical related to the cylinder. If the misfires are all over the map, it's likely the ignition module or cam or crank sensor.
The rear O2 sensor is only there to gauge the performance of the catalyst. The front O2 sensor is the one that is used by the EFI software.
I realize that the post O2 sensor has no effect on a random misfire situation and the only reason I put that in there is because Allen asked which sensor I replaced. As stated in my original post I did have a code for the post O2 sensor.
Now, the cam sensor will cause a random misfire code? Didn't even think of that.
April 22nd, 2014, 08:33 PM
#7
Just an Olds Guy
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
2. To clean the EGR, take it off and use TB spray cleaner (comes with a spray tube extension for things just like this). The area you're working with on this valve is not that big. Spray in the pintle area and bore. There should be tons of carbon coming out. Try pushing the pintle to see if it has free movement - it should. Sometimes the spring on the pintle can get jammed with carbon. Work it and spray it to break that stuff loose. Let the TB cleaner soak in for some time and then respray. Repeat as needed till it's clean. You won't be able to jamb any scotchbrite into that little opening, but a small flatblade or pick tool might help. Dry with a blast of compressed air (or let it dry on a shop towel)
3. The EGR factory gasket is metallic and has 3 tabs on it. Unless you're a real demon taking it off, it should be re-usable. If the EGR on your car was really badly plugged your ECM would have thrown a code for that. You can buy a replacement gasket if you want - they're about 8.00
4. Clean the weather pack connector pins with ELECTRICAL CONTACT CLEANER before you bolt the EGR back in.
I'm with Joe on the codes and misfire. My scan tool will identify which specific cylinder is a misfire. Makes the repair so much easier.
Last thing - if the misfire condition is only periodically about 4k miles apart, it also might be the type of fuel you're using. Are you gas station brand specific or price specific? Some of the lower priced fuels are high in ethanol and this may be a contributing factor. Then again some gas stations just plain and simple sell bad gas.
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