My '98 Pathfinder is throwing DTC codes P0302 (misfire on #2 cylinder) and P0325 (knock sensor) - short story is rough idle on hot start that only lasts about 2 minutes - I'm starting a different thread just to address that - but in the meantime I want to adjust the ignition timing (I know from a recent smog check that it's at the 17 degree upper limit, so I'm going to bring it back down to 15 in hopes of lessening the misfire issue).
In the Haynes manual it says that the ECU has to be put in Diagnostic Test Mode II before performing an ignition timing (they claim this is to prevent the ECU from messing with the timing procedure). However, in the Nissan manual this is not mentioned - Mode II is described as allowing various parameters to be read from the ECU, such as heated oxygen sensor signals. In fact, the normal diagnostic procedure on page EC-85 has ignition timing as step #3, with no mention of ECU Diagnostic Test Mode II...
To me, it looks like Haynes got it wrong and all I have to do is disconnect the TPS and adjust the timing - does that sound right to you folks?
Thanks!
Ignition timing: does ECU really need to be in Test Mode II?
Re: Ignition timing: does ECU really need to be in Test Mode
Yes, you should be fine adjusting the timing that way.
It will not have any effect on misfire in just one cylinder.
Your knock sensor code has probably been there a long time, and also not causing your #2 misfire.
Look at things like dist cap, plug, wire, injector clog or leak, vacuum leak to that cylinder.
Good luck
It will not have any effect on misfire in just one cylinder.
Your knock sensor code has probably been there a long time, and also not causing your #2 misfire.
Look at things like dist cap, plug, wire, injector clog or leak, vacuum leak to that cylinder.
Good luck
Re: Ignition timing: does ECU really need to be in Test Mode
Thanks ezb,
I haven't gone at length into the actual problem I'm trying to fix, thought I'd start another discussion topic on this, but the symptoms are very consistent and can be replicated very easily:
1. When the car is cold, it starts up, idles, and runs just fine.
2. When the car is warm and I stop the engine, if I start it again right away it will also idle (and run) fine.
3 When the car is warm and I stop the engine to run an errand, say get groceries (15 minutes), when I start the car again it will run rough ONLY FOR ABOUT 90 SECONDS. That's when the Check Engine Light blinks (and then stays on). After 90 seconds (maybe 120, but never more than 2 minutes), all returns to normal - every single time. Note that it is not only rough at idle but also while I'm driving.
For example, tonight I stopped to get some groceries so the car was still warm when I got out of the grocery store... I started the engine, it was running a bit rough, I got out of the parking lot, and 2 blocks away I had to stop at a traffic light. While I'm waiting for the light to turn green (this is about 2 minutes after I left the grocery store), the engine goes from rough to smooth idle, just like that. This happens every single time I warm-start the engine.
Given these symptoms, I don't think this problem can be caused by something like a bad cable, spark plug, bad distributor, etc. because if any of these were faulty then the problem would be consistent - hot or cold, at all RPMs, and most importantly, it certainly wouldn't consistently disappear after 90 seconds every single time.
To me it feels like a temp gauge or sensor (O2 maybe?) is acting up at a certain temperature and sending the wrong information to the ECU, causing it to adjust the ignition according to this bad sensor - then when the engine temperature reaches a point where the sensor doesn't misbehave, all returns to normal.
I know 17 degrees is within spec, but for now I'm just trying to make the rough running a little smoother (less advance at low revs).
Thanks for the advice,
Pierre.
I haven't gone at length into the actual problem I'm trying to fix, thought I'd start another discussion topic on this, but the symptoms are very consistent and can be replicated very easily:
1. When the car is cold, it starts up, idles, and runs just fine.
2. When the car is warm and I stop the engine, if I start it again right away it will also idle (and run) fine.
3 When the car is warm and I stop the engine to run an errand, say get groceries (15 minutes), when I start the car again it will run rough ONLY FOR ABOUT 90 SECONDS. That's when the Check Engine Light blinks (and then stays on). After 90 seconds (maybe 120, but never more than 2 minutes), all returns to normal - every single time. Note that it is not only rough at idle but also while I'm driving.
For example, tonight I stopped to get some groceries so the car was still warm when I got out of the grocery store... I started the engine, it was running a bit rough, I got out of the parking lot, and 2 blocks away I had to stop at a traffic light. While I'm waiting for the light to turn green (this is about 2 minutes after I left the grocery store), the engine goes from rough to smooth idle, just like that. This happens every single time I warm-start the engine.
Given these symptoms, I don't think this problem can be caused by something like a bad cable, spark plug, bad distributor, etc. because if any of these were faulty then the problem would be consistent - hot or cold, at all RPMs, and most importantly, it certainly wouldn't consistently disappear after 90 seconds every single time.
To me it feels like a temp gauge or sensor (O2 maybe?) is acting up at a certain temperature and sending the wrong information to the ECU, causing it to adjust the ignition according to this bad sensor - then when the engine temperature reaches a point where the sensor doesn't misbehave, all returns to normal.
I know 17 degrees is within spec, but for now I'm just trying to make the rough running a little smoother (less advance at low revs).
Thanks for the advice,
Pierre.
Re: Ignition timing: does ECU really need to be in Test Mode
Your P0302 is a big clue, and its telling you there is a misfire in only 1 cylinder.
O2 sensors, air flow meters and such effect ALL cylinders. Keep that in mind.
After reading your description, I would tend to agree it is not an ignition problem.
I would suspect a leaking or sticking injector at this point, of course it could be something else entirely.
Diagnosing cars online is difficult to say the least.
Good luck.
O2 sensors, air flow meters and such effect ALL cylinders. Keep that in mind.
After reading your description, I would tend to agree it is not an ignition problem.
I would suspect a leaking or sticking injector at this point, of course it could be something else entirely.
Diagnosing cars online is difficult to say the least.
Good luck.
Re: Ignition timing: does ECU really need to be in Test Mode II?
Can't believe I'm replying to my own post 4 years later, but I happened to drop by for a different topic and saw that I never posted the conclusion of my rough idle...
So, for whomever lands on this from this day onward... it was the distributor.
Cheers!
So, for whomever lands on this from this day onward... it was the distributor.
Cheers!