Need help diagnosing...misfire at idle...not sure it is coilpacks...help!
07-11-2005, 09:21 AM
#1
Need help diagnosing...misfire at idle...not sure it is coilpacks...help!
My brother has one of those scanners.
It says that I have a cylinder misfire, but it does not tell in which cylinder.
I don't know what to think of that.
Here is the deal...
My car is not studdering badly at idle....not just at the 3500rpm point. Before, there was just a little hesitation at that point in the rpm powerband, and then it was fine. The other funny thing is that it was not all the time.
Well, now at idle, it sounds really rough....like chug...chug...chug.
I was in the car to see the rpm's while my bro helped me by unplugging coil packs and seeing if there was change in the tone or not.
Here was the consensus:
After we tested them all, we ended up having all three front cylinders(left bank) unplugged, so that they were getting no spark at all. It is going to sound funny, but the car actually ran smoother on three cylinders than it was on 6 with some misfiring.
I put one of the good new coilpacks in one of those front cylinders and it didn't change. That tells me that it is possibly not a spark problem, but maybe a fuel problem? I don't know? Injectors?
I was wondering if, since all three of the fronts are not responding to a new coilpack....maybe it is something bigger than just one injector/all injectors. I don't know....could all of this be caused from a clogged fuel filter and trash getting into the cylinders via trashy fuel? I changed it like 35k miles ago, so I don't know if it would already be dirty? I know what some are thinking....but I use premium fuel, so that is not an issue.
To go about solving it, I would naturally do it this way:
fix the cheapest things and then work my way up to the more expensive stuff until it is fixed. That would put the injectors last.
What should I do?
Help me please.
Should I just buy another fuel filter and put some fuel treatment through it and go from there?
If that is what is recommended.....didn't I hear something about being able to use an older model 300ZX fuel filter because it is bigger or something?
Help on that too would be appreciated.
Here's what I have done:
I changed all the spark plugs with the BKR5E-11 coppers yesterday.
We messed around with the coil packs, and like said above, with all three left bank unplugged, it actually ran smoother......but just on three cylinders.
I was thinking about starting on the fuel system next....what do you think?
Sorry for the long post.
It says that I have a cylinder misfire, but it does not tell in which cylinder.
I don't know what to think of that.
Here is the deal...
My car is not studdering badly at idle....not just at the 3500rpm point. Before, there was just a little hesitation at that point in the rpm powerband, and then it was fine. The other funny thing is that it was not all the time.
Well, now at idle, it sounds really rough....like chug...chug...chug.
I was in the car to see the rpm's while my bro helped me by unplugging coil packs and seeing if there was change in the tone or not.
Here was the consensus:
After we tested them all, we ended up having all three front cylinders(left bank) unplugged, so that they were getting no spark at all. It is going to sound funny, but the car actually ran smoother on three cylinders than it was on 6 with some misfiring.
I put one of the good new coilpacks in one of those front cylinders and it didn't change. That tells me that it is possibly not a spark problem, but maybe a fuel problem? I don't know? Injectors?
I was wondering if, since all three of the fronts are not responding to a new coilpack....maybe it is something bigger than just one injector/all injectors. I don't know....could all of this be caused from a clogged fuel filter and trash getting into the cylinders via trashy fuel? I changed it like 35k miles ago, so I don't know if it would already be dirty? I know what some are thinking....but I use premium fuel, so that is not an issue.
To go about solving it, I would naturally do it this way:
fix the cheapest things and then work my way up to the more expensive stuff until it is fixed. That would put the injectors last.
What should I do?
Help me please.
Should I just buy another fuel filter and put some fuel treatment through it and go from there?
If that is what is recommended.....didn't I hear something about being able to use an older model 300ZX fuel filter because it is bigger or something?
Help on that too would be appreciated.
Here's what I have done:
I changed all the spark plugs with the BKR5E-11 coppers yesterday.
We messed around with the coil packs, and like said above, with all three left bank unplugged, it actually ran smoother......but just on three cylinders.
I was thinking about starting on the fuel system next....what do you think?
Sorry for the long post.
07-11-2005, 09:52 AM
#3
Member who somehow became The President of The SE-L Club
iTrader: (19)
Join Date: Jun 2001
Posts: 16,033
First off I can't believe the car would even run on 3 cylinders are you sure you were unplugging the coil packs? 
Your 99.5 is well known for coil pack failures. Mine have already failed but the issue was misfiring under a load, not at idle.
A fuel injector failure should trip a lean or rich error associated with the misfire.
Check both crank sensors, clean any debri thats collected on the magnetic pickup.
Check the cam shaft angle sensor as well.
Check the pins on the coil packs, they easily bend resulting in a failed electrical connection to the coil pack and a misfire. You can also check the condensor, it's taped to the harness end over by the intake snorkle.
Your 99.5 is well known for coil pack failures. Mine have already failed but the issue was misfiring under a load, not at idle.
A fuel injector failure should trip a lean or rich error associated with the misfire.
Check both crank sensors, clean any debri thats collected on the magnetic pickup.
Check the cam shaft angle sensor as well.
Check the pins on the coil packs, they easily bend resulting in a failed electrical connection to the coil pack and a misfire. You can also check the condensor, it's taped to the harness end over by the intake snorkle.
07-11-2005, 10:12 AM
#4
This is Bruce's brother. I have been helping him with his car.
Yes, we unplugged all 3 coils, even removed them and the car ran the same.
I will help him check a few of the things you listed. Is it possible for the whole front bank of coils to not be getting fire? Maybe one of the wires is messed up?
Yes, we unplugged all 3 coils, even removed them and the car ran the same.
I will help him check a few of the things you listed. Is it possible for the whole front bank of coils to not be getting fire? Maybe one of the wires is messed up?
07-12-2005, 10:20 PM
#5
Well, the problem seemed to keep eluding my brother and me.
We tried all kinds of stuff, and it came down to possibly injectors or something with the fuel line.
Ultimately, we determined that I could very easily pour a few hundred more dollars into the car, trying to fix the studdering problem. We thought this because injectors are like $94 each and anything else would just tack it on to an even higher bill.
Anyway, I decided to just take it in to a mechanic that my brother has had do some stuff, and get a diagnosis. The guy thought, when I explained it to him, that he would be able to find out the problem right away. Sure enough, he found out. It was some kind of intake gasket down under the intake manifold or something. I didn't see, when he had it apart, but he supposedly had to take apart the whole air intake plenum, and intake manifold.....like 3.5 hours of labor. It ended up costing me like $247, but it is running great! The gasket was only like $13, and the labor was the rest. ha ha.
It was not a coil pack problem. I bought a few and put them in, testing it out, and with all the old ones in, the problem is gone. I guess that is one 99.5 that doesn't have bad ones yet. It has like 122k miles on it and it is going on strong. I probably ended up saving myself some money, even though I usually like to do stuff myself on my car.
Anyway, thanks for all your help, guys. I appreciate it.
It was freaking me out there this past weekend, because it would hardly run. It just kept dying and stuff.
Thought you ought to know.
Thanks again.
We tried all kinds of stuff, and it came down to possibly injectors or something with the fuel line.
Ultimately, we determined that I could very easily pour a few hundred more dollars into the car, trying to fix the studdering problem. We thought this because injectors are like $94 each and anything else would just tack it on to an even higher bill.
Anyway, I decided to just take it in to a mechanic that my brother has had do some stuff, and get a diagnosis. The guy thought, when I explained it to him, that he would be able to find out the problem right away. Sure enough, he found out. It was some kind of intake gasket down under the intake manifold or something. I didn't see, when he had it apart, but he supposedly had to take apart the whole air intake plenum, and intake manifold.....like 3.5 hours of labor. It ended up costing me like $247, but it is running great! The gasket was only like $13, and the labor was the rest. ha ha.
It was not a coil pack problem. I bought a few and put them in, testing it out, and with all the old ones in, the problem is gone. I guess that is one 99.5 that doesn't have bad ones yet. It has like 122k miles on it and it is going on strong. I probably ended up saving myself some money, even though I usually like to do stuff myself on my car.
Anyway, thanks for all your help, guys. I appreciate it.
It was freaking me out there this past weekend, because it would hardly run. It just kept dying and stuff.
Thought you ought to know.
Thanks again.
07-13-2005, 03:59 AM
#6
Glad to see you figured it out but i am perplexed why the intake manifold gasket would need to be replaced if it wasn't removed prior to this problem? It is a dense rubber and i don't see it breaking down over time.
Also 124k on my 1999.5 and no coil problems
Also 124k on my 1999.5 and no coil problems
07-13-2005, 12:49 PM
#9
Originally Posted by zack342
Glad to see you figured it out but i am perplexed why the intake manifold gasket would need to be replaced if it wasn't removed prior to this problem? It is a dense rubber and i don't see it breaking down over time.
Also 124k on my 1999.5 and no coil problems
Also 124k on my 1999.5 and no coil problems
They said it was some kind of intake gasket, and they said that they were going to have to take off the intake manifold....so I just that that is what it was. I can't remember exactly what they said. I will try to find out.
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