Component Physical Checkup

[mdmellott]

I'm not one to schedule physical checkups with my doctor when nothing's wrong with me, just to be poked and prodded to maybe find something not quite right, but I do this to my Pathfinder once in a awhile to get a jump on components that may be at the limit of their operational goodness, so to speak. I don't ignore hiccups that appear as unknown gremlins so I try to test what I can to figure out if I have a Gizmo or a Mohawk.

I was examining my two Hall effect camshaft position sensors, while trying to find the cause of a minor rpm drop at idle that almost seams like a switch opening or closing that drops my rpm by 100rpm more than normal. A 50rpm drop at idle is normal, while in drive or reverse, and that is what I typically see. In neutral or park, I have a steady, consistent 750rpm at idle. Seeing the rpm drop to 600, as if it was triggered to do so, does not cause me any operational issues and it doesn't happen all the time but it does most of the time.

The service manual indicates a resistance check of these sensors where zero to infinity ohms is acceptable or is that an exception, as the manual states "Except 0 or infinity". This where I'm confused. Since continuity means low or zero ohms and no continuity means very high or infinite ohms, a measurement of zero or infinity cannot both be right. Can they? The measurements I get are from 1.2K ohms to 25M ohms. There is no continuity but it's not infinite. Is this a Gizmo or a Mohawk or is it that a measurement of anything other than zero or infinity is acceptable. That just seems odd to me.

[mdmellott]

Never mind. My Haynes manual indicates any reading other than zero or infinity is satisfactory. Haynes makes be feel good all under.

[mdmellott]

Of course, I still don't know why my rpm sometimes drops like it does at idle while in drive. IACV stuff is all good. My diet and exercise is good. Old age is no excuse. There is bound to be a replacement of some little bit that will make it behave.

[VStar650CL]

The ECM is constantly making small (and usually invisible) changes to the run parameters based on temperature, load, airflow, A/F mixture, etc. Your best bet might be to boot a copy of NDS-III and see what parameters change before and after your little RPM fluctuation. Some things like the MAF should change, others like VVT timing probably shouldn't. If you can sniff out exactly what the ECM is responding to, it will likely lead you to the culprit.

[mdmellott]

You got me thinking smarter, not harder. I appreciate that. A new tool like NDS and the right ODB adapter is a good idea. I like new tools!

[mdmellott]

It turned out to be a self inflicted ailment. Dropping rpm like it did at idle was not as low as I thought, just by looking at the tach, but the occasional burp when it did drop is what I found puzzling. As best I can tell from all my scanning and probing is that the burp was a knock or a ping or whatever you want to called it when using low grade fuel instead of the recommended premium. All components I checked are within spec. I thought I would get away with using 87 octane given the ignition upgrades I made but I was wrong. I dumped a couple bottles of Lucas Oil octane booster into a full tank of regular to get it up to at least the 91 octane premium I had usually fed it until some government failure got the prices jacked up so high. Paying $6.10/gal for regular makes me burp too. $6.50/gal for premium gives me heartburn. The rpm of course still drops at idle while in drive but it no longer burps. What a picky eater this thing is. I was later told that the ignition upgrades I did will demand premium fuel. I'll pay the price for premium for now on.

[VStar650CL]

Most Nissan ECM's these days have a "Target Timing Adjustment" that you can actually use to de-tune if you need to use lower octane. Your '02 probably has it, I think all the VQ's do. You might need to visit the dealer, I'm not sure if NDS-III will do that, but at a $0.40/gal differential, an hour at the dealership would repay itself in 375 gallons (long before a certain senile old man leaves office and prices come down again).

[VStar650CL]

Yep, I just checked and your '02 has it. See page EC-101:
https://www.nicoclub.com/service-manual ... 2%2Fec.pdf

[mdmellott]

Most Nissan ECM's these days have a "Target Timing Adjustment" that you can actually use to de-tune if you need to use lower octane. Your '02 probably has it, I think all the VQ's do. You might need to visit the dealer, I'm not sure if NDS-III will do that, but at a $0.40/gal differential, an hour at the dealership would repay itself in 375 gallons (long before a certain senile old man leaves office and prices come down again).

Thank you! I'll look into this more. I was wondering if there was a tweak or two I could do or have done that would optimize my performance and efficiency. Aftermarket tuners were a thought but most of what I have seen just trick the ECM into behaving one way or another but mask potential issues that could arise from say a faulty MAF, ECT, IAT, or other sensor that's had it's signal spoofed. It was a short thought.

[VStar650CL]

You're most welcome as always. One caveat about the timing tweak (and also the Target Idle Speed Adjustment, if you use that), most Nissan ECM's will not execute an IAVL if either of those numbers are non-zero. So should you need to perform an IAVL, you have to first reset both adjustments to zero, perform the procedure, then return the adjustments to where you want. The ECM won't tell you about it. If you start the IAVL with the tweaks in place, it will sit there forever in "duh" mode and the procedure won't complete.

[mdmellott]

You're most welcome as always. One caveat about the timing tweak (and also the Target Idle Speed Adjustment, if you use that), most Nissan ECM's will not execute an IAVL if either of those numbers are non-zero. So should you need to perform an IAVL, you have to first reset both adjustments to zero, perform the procedure, then return the adjustments to where you want. The ECM won't tell you about it. If you start the IAVL with the tweaks in place, it will sit there forever in "duh" mode and the procedure won't complete.

So I purchased a copy of NDS II and adapter cable so I can tweak my timing a bit. The manufacturer of my high output coils has confirmed to me that it is not uncommon for the high energy output of these coils to cause a natural timing advance in combustion. That is to say the combustion is happening so much faster that I get a knock because it's like having my timing too advanced. Along with an increased ignition voltage booster like I just installed, ignition knock is more frequent even with premium fuel. Octane booster has it under control for now but this weekend I plan to reduce the timing. The spec is 15deg + or - 5deg. I'm currently right at 15deg at idle in park or neutral.

I can adjust to my hearts content but I'd only be guessing without putting this through dyno testing at the same time to see where optimum performance is achieved. That's not going to happen. Do you think it would be best to set the target timing at 10deg to start with and see how it behaves or change it 1deg at a time and see how it behaves at each adjustment? I'm not sure how subjective evaluating this either way will be. Maybe just set it at 12 or 13 and call it good unless it has a fit.

[mdmellott]

So I purchased a copy of NDS II and adapter cable so I can tweak my timing a bit.

That was fun. (talking to myself) The software allowed no more than + or - 2deg of change from the factory set 15deg BTDC timing. That was enough to get this running better after dropping it to 13deg. There is an active test mode where I can temporarily change the timing even further but any further makes it worse so 13deg BTDC is where it needs to be. Before changing the ignition timing I saw more accurately my idle speed bouncing around from 738 to 775rpm. I used NDS to do the IAVL, pushing one button and done, and now it's much more consistent at 750 to 762 compared to what I was able to achieve doing the manual relearn procedure. Seeing all the actively monitored sensors on one screen in real time is a great time saver and takes the guess work out of many laborious diagnostics. New tools are so mush fun.

[VStar650CL]

I thought you might like it.

Like I said, if NDS won't tamper the target timing permanently, you can definitely have the dealer tweak it. The only caveat is that IAVL may not execute again unless it's un-tweaked. That's actually a crapshoot. Some ECM's will refuse IAVL only if the idle speed has been tweaked, others will refuse if the idle or timing have been tweaked. Trying is probably the only way to find out.

[mdmellott]

I thought you might like it.

I appreciate the tips. NDS has permanently set my timing at 13deg. I think that's all it will need. I was a bit concerned at first regarding the IAT reading so high. The way the IAT is positioned under the fender in an odd looking air duct within the space between the fender and wheel well, quite a bit of heat builds as the engine heats up. It was up to 140 while I was parked idling for awhile but then dropped to around 120 when I got back on the highway. It was only 85deg outside. It's a 5yr old OEM IAT. I'll have to pull it and test it to be sure but I think this is typical of these R50 models' fender hot box design flaw.

I am curious though about that odd looking air duct the IAT is mounted in. I've read descriptions calling it a resonator as well. It looks like it has functional pieces to it but I cannot find out anything about what it does. It is more than an air duct but why it has these features is a mystery to me and I can't help wondering, whatever they are, if they can become defective after 20yrs or sucking air. Why does this look so weird. It looks like a cow's udder.

[VStar650CL]

The ECM needs to know the temperature in the tube because that's the air it will be making mixture from, the temp outside the tube doesn't really matter. If you're looking for mileage and not power then you actually want warmer air and not colder, so if that cubby in the fender gets warm, it might be a benefit now that we're all living in -- hm, how do I put this politely> -- $5/gallon senility-world?

Those goofy bumps probably are just a resonance arrangement. Much of the time they're tuned to make specific noises go away. Gen 2 Rogues get a horrendous "burp" at certain RPM's if you ditch the intake resonator. That one is a goofy shape too, although nothing approaching that Pathy pipe-organ.

[mdmellott]

Not a flawed design after all. Good to know. Thank you. Time now to fill it up and see far it gets per gallon.