Shaking in Drive at Idle

[cham]

I’ve been dealing with this for a long time; I understand the basic reasons this might be happening but I’m hoping in providing more specific details I can narrow the scope, also hoping somebody has dealt with this exact issue.
 
With the vehicle warmed up, when in Drive or reverse while stopped and idling the whole vehicle shakes. It doesn’t really start until a few seconds after coming to a complete stop and the RPMs fall and settle slightly below 750rpms (around 650rpm). When idling in park or neutral the RPMs are dead at 750, no vibration or shaking.
 
Certain things like using the window regulators or turning the steering wheel while stationary will additionally make the whole vehicle shake and the rpms drop slightly. Now the shaking is pretty aggressive, turns my seat into a massage chair and it’s been doing it seemingly for years. I’ve always thought it was the transmission but it’s lasted tens of thousands of miles like this and shifts beautifully now.
 
I’m starting to think it might be the alternator (never been changed) not supplying enough output to my battery (new) but I would think that should effect the vehicle at idle in park and neutral as well. I think another likely candidate is the IACV crapping out and not reacting correctly when coming back down to idle with a load placed on the engine (in Drive).
 
I’m sure it can be my torque converter going as well but what I’ve noticed is when the car starts to shake and vibrate at a stoplight for example (in Drive), if I turn on the Air-conditioning or heat, the rpms bump up briefly to between 700-750 and the vibration immediately goes away. Then as the ECU gets used to the additional load it settles the rpms back around 650 and the shaking/vibration comes back.
 
Seems to me like maybe the load on the engine at idle in Drive is too much somehow causing the engine to bog, or should 650rpms not cause my car to shake? Whether it be a failing alternator or not enough air getting in through the IACV, the revs drop because the load is slightly too much. In every other case there is no vibration once the revs are at or above about 700rpm. What do you guys think?
 
 
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[CamperDan]

57 minutes ago, cham said:

I’ve been dealing with this for a long time; I understand the basic reasons this might be happening but I’m hoping in providing more specific details I can narrow the scope, also hoping somebody has dealt with this exact issue.
 
With the vehicle warmed up, when in Drive or reverse while stopped and idling the whole vehicle shakes. It doesn’t really start until a few seconds after coming to a complete stop and the RPMs fall and settle slightly below 750rpms (around 650rpm). When idling in park or neutral the RPMs are dead at 750, no vibration or shaking.
 
Certain things like using the window regulators or turning the steering wheel while stationary will additionally make the whole vehicle shake and the rpms drop slightly. Now the shaking is pretty aggressive, turns my seat into a massage chair and it’s been doing it seemingly for years. I’ve always thought it was the transmission but it’s lasted tens of thousands of miles like this and shifts beautifully now.
 
I’m starting to think it might be the alternator (never been changed) not supplying enough output to my battery (new) but I would think that should effect the vehicle at idle in park and neutral as well. I think another likely candidate is the IACV crapping out and not reacting correctly when coming back down to idle with a load placed on the engine (in Drive).
 
I’m sure it can be my torque converter going as well but what I’ve noticed is when the car starts to shake and vibrate at a stoplight for example (in Drive), if I turn on the Air-conditioning or heat, the rpms bump up briefly to between 700-750 and the vibration immediately goes away. Then as the ECU gets used to the additional load it settles the rpms back around 650 and the shaking/vibration comes back.
 
Seems to me like maybe the load on the engine at idle in Drive is too much somehow causing the engine to bog, or should 650rpms not cause my car to shake? Whether it be a failing alternator or not enough air getting in through the IACV, the revs drop because the load is slightly too much. In every other case there is no vibration once the revs are at or above about 700rpm. What do you guys think?
 
 
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My 2001 R50 Pathfinder 4X4 Manual, recently started doing the same thing. It's almost like it's about to stall when I'm stopped at a red light in neutral, it does this about 3-5 seconds after coming to a stop but it seems a bit intermittent in my case, anyway.

 

Chris.

Edited January 26 by CamperDan

[Mrelcocko]

Maybe clean your MAF sensor.

[CamperDan]

2 hours ago, Mrelcocko said:

Maybe clean your MAF sensor.

I cleaned mine a few times in the past before this started happening. I'll try cleaning it again over the weekend to see if it changes anything.

 

Chris.

[Slartibartfast]

The '02 manual does not spec an idle speed in gear, but in park or neutral, it wants to see 750 +/- 50 if the aircon's off, 825+ if it's on. Sounds like yours is working. Every auto I've driven idles a little lower in gear, so while I don't have a spec for that, I'm inclined to call it normal. Turning on electrical loads or working the steering loads the engine, so it makes sense it's dipping a little more under those conditions. The vibration/stumbling under load, while it's still pretty close to its target RPM, makes me suspect a mixture issue.

 

MrElCocko may be on the right track with the MAF sensor. Yours sounds a bit like how my '93 behaved when the MAF sensor connector was worn out. Sometimes it would idle low at lights, sometimes it would surge, sometimes it would stall completely unless I shifted to neutral or drove with both feet. Wiggling the connector would clear it up for a while. Finally I got around to replacing the connector, and haven't had a problem since. I don't know if the R50 suffers from the same issue, but I would check that the plug feels tight and the sensor is clean. If that checks out, check for cracks in the boot between the MAF and the throttle body, and check for vacuum leaks. Might be worth throwing some fuel system cleaner in the tank in case one or more injectors are a little gunked up. One or two cylinders firing poorly or not at all could explain why it's vibrating so much, though I wouldn't expect that to only act up at low RPM, and I would expect it to throw misfire codes if it was that bad.

 

Probably wouldn't hurt to clean the idle controls, maybe check for signs of the coolant leak those get, but again, it sounds like that system is doing its job. If your throttle body isn't the fussy electric one, maybe give that a clean, on the off chance.

[cham]

Thanks guys, based on research something like this does sound like it can be anything from a bad coil to the IACV. What I should mention is like I’ve said this has been going on seemingly since I owned the car. It has gotten slightly worse over the years but was always there in some capacity.

I’ve cleaned the MAF sensor close to 5-10 times over the years. I’ve taken apart my IACV to replace the gaskets as a preventative maintenance for that dreaded coolant leak issue. I guess the IACV itself could still be bad. When I replaced my PCV valve and spark plugs I cleaned my throttle body and reset the Idle relearn procedure after assembly (drive by cable). Now I do believe there is a potential vacuum leak somewhere possible from my assembly of the plenums but this didn’t affect the vibration post assembly. Vibration remained in the same capacity before and after that job.

I should say since I did that job of replacing the spark plugs etc i started to get P0420 and P0430 codes and have yet to address. My assumption was since they started right after I did the work they are likely being triggered because of a vacuum leak or a bad ignition coil etc something I moved around while I was in there. Takes about a month for the code to come back usually. No misfire codes or O2 sensor codes. I have noted stumbling though when at idle right after a hard drive on the highway if I gun it pretty hard. I definitely think I used too much dielectric grease when installing the spark plugs but I see no misfire codes.

Ever since those codes started showing up my gas milage has been terrible. I’m going to get a smoke test done soon on the intake and exhaust just to rule those things out as there’s more than likely a few leaks here and there regardless of what I have touched.

Should I stay away from those Firestone places for something as simple as a smoke test haha? There’s one near me that has been pretty good with the manager being a classic JDM guy who’s owned them all. Not sure what the mechanics are like though I’ve only had an alignment done by them.


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[hawairish]

Not sure my recent woes align with this, but I had multiple air leaks at the o-rings on my fuel injectors due to them being slightly undersized (seemingly my mistake).  The excess air would eventually cause the engine to stumble every 30s, regardless of gear selection.  RPMs would drop to 600 and engine would run rough.

 

I've also been throwing a P0430, but it's been deemed unrelated to my issues.  I threw P0507 and P0171 codes previously, which are what suggested a leak.  Dropped $80 on a smoke machine from Amazon and it exploited the issue.  The economy is in crisis when baby oil is $10.

 

I also initially thought my issues were alternator related.  The original one crapped out back in June and I slapped a cheap replacement in.  I had never noticed an issue before the new alternator (I had serviced the injectors a year before), but I have one of those voltmeter pods and it indicated things were healthy (around 14.3V engine running).  It sometimes see the voltage drop when the engine stumbled, so had concerns of what was causing what...was bad alternator causing the engine to stumble, or was the engine stumbling causing the voltage to drop?  In the end, alternator was not the problem.

 

Other things I had done:

Cleaned/moved around plugs, coil packs.

Swapped/cleaned MAF (they have aerosol cleaners at parts stores)

Checked compression

Idle relearn

Throttle position relearn

PCV check

Throttle body clean

 

Obviously none of the above solved anything, but looks like you've done most of those.  May be time to check for leaks.

[cham]

Thanks hawairish; seems like your issue pretty much aligns with mine. Something new to note I was in the mountains today for a trip. I pulled up on a pretty steep incline, parked and turned the car off on the forest road I was on. After 20 minutes I went to start the car and back down the incline; immediately after sticking it in reverse the RPMs dropped to 500 and for the first time it felt like the car was about to stall. Never had it happen before until then. It did not stall but came close.

I’m definitely scheduling an appointment for a smoke test but I have a sneaking suspicion my IACV might be having hiccups. When I disassembled it to clean it and replace the gaskets I noticed evidence of coolant seeping into the housing. I thought it was functioning fine still as I never had any rpm surges etc. guess it’s not always necessarily just working or not working. Might be working only in a certain capacity but not in another.

Any chance if I do in fact have a clogged/bad catalytic converter from those P0420/430 codes that could be causing the shake? I wouldn’t think they are directly related as the vibration has been there even before catalytic converter codes but maybe it exacerbates the vibration.


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[Slartibartfast]

A screwed-up mixture might've damaged the cats, or it might just be confusing the sensors, but if the cats were clogged, I don't think a low idle would be your only symptom. I would focus on figuring out the low idle/misfire issue and see if the cat codes go away once the engine is running properly again.

[cham]

Sounds like my best course of action is to get a smoke test done on the intake and exhaust. I need to tear into my intake plenums again anyways to replace my valve covers, I can address whatever leaks they find if any then. I’ll clean the plugs and coils of any dielectric grease I used last time as it really is a scam. Anyway to know if a coil is going bad even without misfire codes? This is a coil on plug setup.

In the meantime I think I’ll also look into engine and transmission mounts as well because I know for a fact my Transfer-case has movement, found out when I pushed up on my rear driveshaft yoke where it connects to the t-case; proceeded to see the entire T-case move up and down very slightly. Looks like a little movement is normal from what I can find online for that T-case bushing.

If none of that fixes my issues I’ll move onto probably replacing the IACV to rule that out and take a look at getting my cats replaced if they are still throwing codes and my mpg is still bad. Got 15.5mpg the other day purely highway driving on a long trip at 70 mph most of the way.

I should note I have a BlueDriver OBD2 scanner that can read some parameters and what I found is the long term and short term fuel trims for both banks is not that bad. Always less than 10% but there has been times where it gets pretty close. Holding at 2500 rpms gets you closer to 0% but at idle it’s usually a little bit higher but still under 10%


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[hawairish]

The things I'd do to get 15.5 mpg on my truck...

 

...

 

It's a little curious that both cats are throwing codes, but as Slart mentioned they could've eventually been damaged.  I know on mine I had the cats off back in 2022 to confirm they weren't clogged, but no real means to test for efficiency of course.  Still, but codes is odd...even with my woes, I only ever got the bank 2 code.

 

From what I understood when doing my investigating, if the STFT is staying under +/-10% and can closely meter around 0% at idle or cruising, then that seems healthy.  When I was diagnosing mine, my truck would just creep from 0 to 25 over 30s intervals and then just "reset" back to 0%, which is when the engine would stumble.  What I had realized is that each bank would do that on separate intervals...the hard stumbles were when both banks were in sync.  But, it became clear that each bank could meter fuel independently, which was a new concept for me (engines aren't my thing).

 

Before dropping coin on cats, I'd do a leak test.  How are the O2 sensors?

[cham]

Yeah I’m used to 19 highway lol. I used to get 15mpg city but now it’s closer to like 10-12mpg city.

The weird thing is P0430 comes back more frequently than P0420 too. I definitely had some of the O2 sensors replaced by a shop probably around 4-5 years ago. Don’t remember which ones. I’m not getting any other codes, no O2 sensor related codes or misfire codes, just the low catalyst efficiency codes. What I’ve been told is when that happens 90% of the time it is a bad cat.

I’ll definitely try replacing the O2 sensors and check for any exhaust leaks before getting new cats. Based on what the manual says; it sounds like the upstream sensor is the only sensor that will change the air fuel ratio based on its reading. In the FSM it says under normal operating conditions sensor 2 (downstream) does not affect the air fuel mixture. But there is one phrase that confuses me. I’ll attach below. How hard is it to get to the cat bolts and remove them?

I still feel like the car is exhibiting a lean condition based on its behavior. Also the stumbling after a hard drive feels like a miss but I can’t be sure. It’s like the car is bouncing rhythmically at idle. Not the same shaking/vibration that is normally exhibited when in gear at idle.

Maybe my MAF is going. I’ve always cleaned it with MAF sensor cleaner like you’re supposed to but I’ve also heard they can be so temperamental. I’d always let it dry for an hour or more before energizing it again.




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[hawairish]

1 hour ago, cham said:

Based on what the manual says; it sounds like the upstream sensor is the only sensor that will change the air fuel ratio based on its reading. In the FSM it says under normal operating conditions sensor 2 (downstream) does not affect the air fuel mixture. But there is one phrase that confuses me. I’ll attach below. How hard is it to get to the cat bolts and remove them?

 

That's been my understanding, too.  Upper sensors control A/F, lower sensors determine upper cat efficiency...at least that's what I believe.  System doesn't care about the lower cats (or resonators if Fed-emissions equiped; mine has lower cats).  But to that extent, that's why I've always attributed P0420/P0430 to possibly faulty sensors.  If the upper and/or lower sensors are buggy, I'd think the delta would be askew.  Of course, I could be totally wrong since there are separate codes to assess the sensors themselves.

 

The cat bolts aren't too difficult...it's getting the stupid heat shields off that really sucks, especially on passenger side.  A couple 10mm are hidden, tend to be rusted in, and only accessible with small wrenches.  After that, just need some sockets and extensions to avoid busting knuckles.  I think I only sheared off two or three bolts on the driver's side, lol.  In general, exhaust work sucks.  In the case of our trucks, you basically need to remove the entire system to pull the cats...at least in my case, there was not enough slack in the hangers to push everything rearward to clear the studs on the components.

[cham]

I’m think you’re exactly right. Going through the rest of that section makes it clear the system is constantly monitoring the health of the sensors as well. Seems more intelligent than I initially thought for an older Lambda system. It has different conditions and thresholds for both the sensors monitoring and the sensor condition itself. It monitors the health of the sensor in more than a couple ways too. I doubt it covers every failure possibility though so there’s always a possible anomaly where it’s bad without triggering a CEL. That section of the FSM is also constantly mentioning the O2 sensor heater. I’m guessing it’s built into the O2 sensor itself as I believe one of the O2 sensor wires is the heater wire.

One thing that dawned on me is the possibility of a clogged EGR system. But to my knowledge most VQ35s didn’t use EGR? I don’t think the 2002 ever had one. There is a vapor canister vent solenoid on top of the engine that I think gets confused a lot for an EGR solenoid.

One final thing I’ll note since I forgot to mention earlier; not sure if this will help diagnosing but when the engine is cold and warming up there is no vibration in gear at idle. Not sure if that’s because the RPMs are up as the engine warms or something else I’m missing. I know bad ECT sensors do weird things for most vehicles. After starting the vehicle with a cold engine and putting it in gear after a minute or so, the RPMs only drop to about 800-850 instead of the 650 when warmed up. Obviously thats because the engine is conditioned to increase rpms when warming but something to note, zero shaking.


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[hawairish]

Logic makes sense.

 

Yeah, no EGR on the VQ that I can recall.  I had the driver's manifold off to extract busted studs, and there was nothing extraneous about the removal.  Unlike my 98 Frontier where the EGR tube nut was so locked into the manifold that I had to make relief cuts in it to remove it!

 

For the last part, the only thing I can think of is just the fuel system condition.  When warming up, it's in an open loop and is ignoring all the sensors.  When it's met conditions, it'll go closed loop and rely on them.  In my case, mine was going to an open loop fault state where it basically wasn't trusting the sensors.  

 

BTW, this is where Nissan Data Scan II came in handy for me.  I could see each bank's STFT and fuel system state, and correlate it to engine stumbles.  What kind of opened my eyes is seeing the banks do them independently, when I just assumed it was the entire engine.  Sometimes they were in sync, sometimes they weren't.  It also allowed me to see the pattern of occurrence...it was happening every 30s, on the nuts.  Have you tried using a stop watch to see if there's some sort of frequency vs. missing erratically?

[Slartibartfast]

Looks like some of the VQs use the variable valve timing to do EGR without the external valve. Neat trick.

 

How have you been cleaning your MAF? It looks like the R50 MAF is shrouded in a way that could make it difficult to clean properly. I remember wiping the last of the gunk off of mine with a Q tip or the corner of a rag when the spray didn't get it all, and the filaments on the WD21 MAF aren't shrouded like that. Yours should be spotless given how many times you've been in there, but if that shrouding gets in the way as much as it looks like it would, there could still be something hiding in there. (I wonder if an ultrasonic cleaner would work on a MAF?)

 

The heater is part of the oxygen sensor. Gets it working faster after start-up. You should get a separate code if the heater circuit fails. The primaries are for the air/fuel mix, the secondaries monitor the cats. I have heard of some later-model stuff possibly using the secondaries for more than that, but it doesn't sound like that's the case here. And yeah, it's got an oxygen sensor on either side, so it controls fuel trims for each bank separately. Allows for slightly tighter mixture control, I guess.

 

Wouldn't hurt to check live data from the temp sensor against the actual temperature.

 

Mine behaved similarly. It ran fine at cold (high) idle, but once it warmed up and dropped, it just couldn't hold the lower speed.

 

There are a bunch of DIY smoke machine designs out there if you want to save a few bucks. One I saw recently used a gas station cigar and a cheap hand pump, and it seemed to work pretty well.

[cham]

15 hours ago, Slartibartfast said:

Looks like some of the VQs use the variable valve timing to do EGR without the external valve. Neat trick.

I read that too somewhere, cool stuff!  Totally explains why my intake was beautiful when I took it off despite some oily walls from the PCV system.  Next to no carbon buildup on the runners at 220k miles unlike modern EGR equipped direct injected motors.  

 

20 hours ago, hawairish said:

For the last part, the only thing I can think of is just the fuel system condition.  When warming up, it's in an open loop and is ignoring all the sensors.  When it's met conditions, it'll go closed loop and rely on them.  In my case, mine was going to an open loop fault state where it basically wasn't trusting the sensors.  

You're absolutely right! Don't know why I didn't think about this.  Since it's in Open Loop to start out with its not reading from sensors but from predetermined parameters set by Nissan.  Only trick is to figure out if the vibration is gone because its in Open Loop or because the RPMs are up.

 

As far as Nissan Data Scan II those guys know what they're doing.  I looked into it a little while ago to see if I can read the Trans Temp sensor live data but Nissan really screwed us on that one.  From what I could find in the FSM and communicating with them our system uses a combination of OBD2 and OBD1 or DDL2 and DDL1.  The TCM primarily uses DDL1 communication while the ECU uses DDL2.  The problem comes when you need a scanner that can communicate using both.  NDS1 doesn't communicate with transmissions apparently because you need to simultaneously be able to communicate through DDL2 too.  "ConZult" also told me their platform won't work either so instead I found in the manual how to read my A/T Temp sensor using a multimeter and extrapolated their provided (simplistic) plot in google sheets.  Now I just plug in the voltage I read with my DMM into the plot and it spits out the corresponding temp (very crude but usable).  Had to use like a 6th order polynomial to try and match the slope of the provided plot.  

 

And yes I also looked into adding an aftermarket temp sensor but I had already dropped my pan a while ago and was not looking to go through that again.  Drain plug sensor worries me for the possibility of a branch getting ahold of the sensor wire offroad and ripping out causing a leak without me even knowing.  An aftermarket sensor in the pan also might read slightly different than the factory sensor on the valve-body.  Thought about making an individual post about this but was unsure if at this point anyone really would be interested.  I'm sure by now everyone has figured out their own way on checking trans level and read temps.  

 

My Bluedriver can read Short term and long term fuel trims as well for both banks its just deciphering it being the task. I'll try to time it like you suggested @hawairish.  

 

15 hours ago, Slartibartfast said:

How have you been cleaning your MAF? It looks like the R50 MAF is shrouded in a way that could make it difficult to clean properly. I remember wiping the last of the gunk off of mine with a Q tip or the corner of a rag when the spray didn't get it all, and the filaments on the WD21 MAF aren't shrouded like that. Yours should be spotless given how many times you've been in there, but if that shrouding gets in the way as much as it looks like it would, there could still be something hiding in there. (I wonder if an ultrasonic cleaner would work on a MAF?)

 

You're absolutely right.  I have found that the actual MAF body is like plastic welded into that intake shroud even with removing the securing bolts.  So instead I remove the entire shroud off the intake box and clean it that way.  I have only ever sprayed MAF sensor cleaner and have only wiped the flat backside (spine) of the MAF body where there was accumulation of gunk but I have never gone near the wire with anything.  I'm unsure what you mean by where you are cleaning with a q tip as the metal wire is all that matters and you wouldn't want to touch that with a q tip right? 

 

15 hours ago, Slartibartfast said:

 

There are a bunch of DIY smoke machine designs out there if you want to save a few bucks. One I saw recently used a gas station cigar and a cheap hand pump, and it seemed to work pretty well.

 

I actually got a little $100 smoke machine maybe 4 years ago from Amazon to test for leaks in my exhaust as I would always hear a faint high pitched whistling at start up.  The damn thing works for maybe a few minutes then starts spewing glycerin (baby oil) through the nozzle so I stopped using it.  I assumed they just all were temperamental unless you were to spring for a shop level unit.  Maybe I'll get in contact with the brand and try for some trouble shooting with that.  Its just the thought of shooting baby oil into my intake or exhaust doesn't fill me with joy haha.  

Edited January 30 by cham

[Slartibartfast]

I played it dangerous and wiped the actual elements. They're delicate, but they're not made of cotton candy, and they're pretty easy to get to on mine. I think you're supposed to just blast them with MAF cleaner, but either I didn't have the right stuff handy or the gunk wasn't budging, so I very gently wiped off the rest. Anything that insulates them will cause the sensor to under-report. Given the limited access on yours, I'd be tempted to see what the ultrasonic cleaner would do about it.

 

Too bad about the smoke machine. Maybe try a lower oil level? I used a proper shop one once, and was not a fan of the smell, but it did work pretty well. Does seem a bit odd to be fogging the engine with glycerine, but I haven't heard of it causing problems.

[hawairish]

20 hours ago, cham said:

As far as Nissan Data Scan II those guys know what they're doing.  I looked into it a little while ago to see if I can read the Trans Temp sensor live data but Nissan really screwed us on that one.  From what I could find in the FSM and communicating with them our system uses a combination of OBD2 and OBD1 or DDL2 and DDL1.  The TCM primarily uses DDL1 communication while the ECU uses DDL2.  The problem comes when you need a scanner that can communicate using both.  NDS1 doesn't communicate with transmissions apparently because you need to simultaneously be able to communicate through DDL2 too.  "ConZult" also told me their platform won't work either so instead I found in the manual how to read my A/T Temp sensor using a multimeter and extrapolated their provided (simplistic) plot in google sheets.  Now I just plug in the voltage I read with my DMM into the plot and it spits out the corresponding temp (very crude but usable).  Had to use like a 6th order polynomial to try and match the slope of the provided plot.  

 

Exactly right.  I can confirm NDSII does not comm with the AT and a few other modules.  But, the ECM comm is key; far more data points than over the OBD protocol.  I tried using NDSII with my 98 Frontier and it can only do OBD, which is unfortunate.  Could've used it the other day troubleshooting some misfires on it.

 

11 hours ago, Slartibartfast said:

I used a proper shop one once, and was not a fan of the smell, but it did work pretty well.

 

I can get past the smell, but the fact that it lingers for so long is what really nagged me.  The little machine I got worked too well at times that I'd have to turn it off and rely on residual smoke to trace the leak.  But, no way I'd have found my problem without it.

[cham]

Thanks guys for the help I'm making some headway.  So I've discovered some things that can help me understand what's going on.  Firstly I tried smoking the exhaust and intake again last night to no avail.  The machine like it always does starts spitting mineral oil again so I stopped after a few minutes.  I definitely was getting a good amount of smoke into the intake and saw no leaks.  I'm now in contact with the company and I believe they will be sending me a new one.  The problem is we have that butterfly valve within the plenum which is closed with the engine off; can I manually prop it open by using that linkage on the vacuum actuator so the smoke can get to that lower plenum intake?

 

When starting my engine in the cold I said what the hell and got under to the vehicle to find condensation pooling at the lower 3rd bolt/nut on the exhaust that mounts to the back of the pre-cats.  Saw condensation vapor coming through it too.  Almost looked like when the exhaust warmed up the seam closed up and no more condensation vapor.  I'm going to get someone to accelerate the engine in park while I'm under there to see if I can see a visible stream.  The leak would be just before the downstream O2 sensor and right after the pre-cat, and its exactly the same on both banks.  I'm assuming this would definitely contribute to my P0430/P0420 codes.  But I would think it would not hurt my gas milage.  

 

Now this isn't a definite answer as I'm now curious if there are any more leaks I can't see not to mention its quite interesting both banks are leaking in the exact same place.  Could my cats be clogging up and the buildup of pressure forced an opening in the same place on either bank?  Fixing the leak could then cause the pressure buildup to get worse.  Is the only real way to check if you have a clogged cat by removing them and looking inside?

 

Lastly I recently discovered from another thread on here that through Mode 6 we should be able to read misfire count on a particular cylinder which will definitely help.  Bluedriver has a Mode 6 reader so hopefully I'll be able to get some data on whether I am actually misfiring or not.  Read online its rare but sometimes misfiring with no CEL codes are possible if its intermittent.  Since I have new spark plugs I would imagine if I find any misfires its either a failing coil, dielectric grease causing issue, clogged injector or harness related.  

[cham]

Here is the linkage for the vacuum actuator of the butterfly valves. The red circle shows where you can move that link to open the valves I believe.




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[cham]

Hey [mention=36148]hawairish[/mention] can you read “misfire count” through mode 6 for individual cylinders in NDS II. Also what year is your Pathy?

Looks like Bluedriver’s mode 6 is pretty limited. Need to figure out what the TID codes mean but it only lists pass or fail.


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[hawairish]

No need to prop the butterfly valves open. If you’re blowing smoke into any of the small vacuum ports, the smoke will just travel around through the runners on the upper and lower plenums. There’s a lower set of butterflies on the intake manifold, but those are normally open if I recall…and they have reliefs on the butterflies. Beyond that, only thing stopping the smoke from going further are the intake/exhaust valves. 
 

As for the misfire counts, I don’t recall being able to see anything cylinder specific, except the ability to shut down each cylinder independently. I’d connect up to double check, but my truck (04) is offline for a while (battery out, engine parts out) and NDS doesn’t allow browsing through menus unless it’s actually comm’ing with the ECU. 

 

[cham]

Gotcha, fleurys in another thread titled "Random Misfire Help!" mentioned being able to read misfire count with an OBD2 scanner but did not mention the one he uses.  I'll ask the guys at Nisscan if its possible, regardless I'd imagine NDS II will come in handy for other things. 

 

I might have misspoke.  When I said butterfly valves I meant those lower intake power valves that famously eject screws.  Is there a another set below them or just the one set?

 

 

[hawairish]

1 hour ago, cham said:

I might have misspoke.  When I said butterfly valves I meant those lower intake power valves that famously eject screws.  Is there a another set below them or just the one set?

 

There are two sets.  The power valves are the ones located on the lower intake plenum ("lower intake manifold collector" per FSM).  These were the ones prone to loosening.  The actual intake manifold, which the fuel injectors fit into, has swirl valves; these didn't have the loosening problem.  With the upper and lower plenums off, you'll see another actuator like the one for the power valves.