Ignition timing - does ECU really need to be in Test Mode II?

[pwachon]

Happy Labor Day weekend (for the US-based experts out there...).

 

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!

[fixinto]

All you have to do is turn the engine off, unplug your TPS, start the truck, let it idle for a couple of minutes, snap the throttle a couple of times and let it return to idle. "at operating temp" then loosen the dizzy bolt, adjust your timing, tighten the dizzy bolt back down, turn off the engine, plug in your TPS and there you go, all done. You set base timing and the ECU takes it from there. I wouldnt mess with the dizzy because the ECU advances it as your RPM's go up. Just check the base timing and if it is at 15 degrees your fine, 17 degrees is ok too. I would do a spark test on my plug wires to make sure they are "arching far enough" under load. If it has been a long time since plug change, i would inspect the plugs. Also ohm out your wires to make sure they read correctly. "specs in FSM" Check along the length of the wires for white marks where the spark could be arching through to something metal. May wanna pop the distributor cap and take a look at the leads and button to make sure there isnt any carbon buildup deflecting the spark. be a good time to look for cracks and such as well. I would just tell you to throw several parts at it but im on the poor side most of the time so i have to put in the trouble shooting to save cash.

I didn't realize the ecu had specific cylinder misfire codes. kewl. Oh the short answer is yes, i just read the last part of your post hehe. But 2 degrees of timing wont cause a misfire.

 

Pat

Edited September 4, 2014 by fixinto

[pwachon]

Thanks Pat, that's what I thought (unplug TPS, adjust timing, replug, done).

 

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). As for throwing parts at the problem, sorry to say that is against my "policy" - I really dislike changing a part just to see that the problem is still there...

 

Thanks for the advice Pat,

 

Pierre.

 

[Rebelord]

I know the 3.0 are notorious for this, not sure how much on the 3.3. But, double check your coolant temp sensor.

[fixinto]

yes sir, sounds like either you have fuel pressure bleeding off, or you have a bad sensor. Temp is a good one to start with from what i have heard. It's the 90 second thing that make it interesting. Please let us know if you fix it.

 

 

Pat