2016 MDX base, issue stumping mechanics... Help!
08-07-2020, 02:31 PM
#1
Intermediate
Thread Starter
2016 MDX base, issue stumping mechanics... Help!
I have a 2016 Acura MDX Base (Sh-AWD), with just over 100K miles on it.
About a month ago, I had my local mechanic (not acura mechanic but probably the best mechanic in the city of 2 million that I live in!) complete the Acura recommended 100K service interval. This included belt change out, Water pump replacement, valve adjustment, replacement of valve cover gaskets, oil change, tranmission fluid change, basically everything Acura recommend to the Acura specs.
Post 100K work, the car seems to be driving fine for the first 2 weeks, more responsive, and generally everything seems to be good. The first clue something was amiss, was the gas mileage seemed to have dropped by ~5mpg. (from 27mpg to 22mpg) (Covid kept us from driving much, so this took a bit to be evident). Then, out of the blue, the MDX throws up an Emissions system error. (P0171 code, generic code: engine running lean).
Take the car back to my mechanic and his initial thought is Mass Air Flow sensor has gone bad.
Replaced MAF sensor no dice. Starts looking for vacuum leaks, finds none. Has done this several times, and has injected 'smoke' into the system to find out if there is a pinhole leak somewhere. Nothing. Another mechanic friend (who works at Audi), suggests that the valve cover gasket may be wrinkled or folded over, and this may be causing the lean condition. Again, mechanic looks at this, no dice.
At this point car is sitting with mechanic, who's had it for 3 weeks, with no definitive cause for the lean condition. The mechanic is continuing to run diagnostics on the car to see if there are any additional issues causing this behavior. The car previously had Zero issues. (I've driven it daily for the last 50K miles) and have serviced it religiously according to all the prescribed service intervals.
Does anyone have any thoughts what might be triggering this behavior (Lean condition)?
About a month ago, I had my local mechanic (not acura mechanic but probably the best mechanic in the city of 2 million that I live in!) complete the Acura recommended 100K service interval. This included belt change out, Water pump replacement, valve adjustment, replacement of valve cover gaskets, oil change, tranmission fluid change, basically everything Acura recommend to the Acura specs.
Post 100K work, the car seems to be driving fine for the first 2 weeks, more responsive, and generally everything seems to be good. The first clue something was amiss, was the gas mileage seemed to have dropped by ~5mpg. (from 27mpg to 22mpg) (Covid kept us from driving much, so this took a bit to be evident). Then, out of the blue, the MDX throws up an Emissions system error. (P0171 code, generic code: engine running lean).
Take the car back to my mechanic and his initial thought is Mass Air Flow sensor has gone bad.
Replaced MAF sensor no dice. Starts looking for vacuum leaks, finds none. Has done this several times, and has injected 'smoke' into the system to find out if there is a pinhole leak somewhere. Nothing. Another mechanic friend (who works at Audi), suggests that the valve cover gasket may be wrinkled or folded over, and this may be causing the lean condition. Again, mechanic looks at this, no dice.
At this point car is sitting with mechanic, who's had it for 3 weeks, with no definitive cause for the lean condition. The mechanic is continuing to run diagnostics on the car to see if there are any additional issues causing this behavior. The car previously had Zero issues. (I've driven it daily for the last 50K miles) and have serviced it religiously according to all the prescribed service intervals.
Does anyone have any thoughts what might be triggering this behavior (Lean condition)?
08-07-2020, 04:17 PM
#4
Senior Moderator
someone tell Acura then because theyre selling o2 sensors for nothing...
08-07-2020, 04:32 PM
#7
as stated, o2 sensors can get lazy over time, resulting in poor fuel economy.
the o2 sensors sit downstream of the exhaust and read the fumes. then it talks to the ECU and adjusts fuel. (air/fuel terminology)
there's not really a life span, as some can last the lifetime of the vehicle...and some can crap out or get lazy while still presenting good.
the o2 sensors sit downstream of the exhaust and read the fumes. then it talks to the ECU and adjusts fuel. (air/fuel terminology)
there's not really a life span, as some can last the lifetime of the vehicle...and some can crap out or get lazy while still presenting good.
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08-07-2020, 04:41 PM
#8
doing some research; I came across this website
https://www.knowyourparts.com/techni...lve%20guides).
the article seems to indicate that a containment has entered the exhaust stream, either coolant or oil and has damaged the sensor.
https://www.knowyourparts.com/techni...lve%20guides).
Oxygen Sensors
Oxygen sensors are one of the most often replaced sensors. Inputs from the O2 sensors are used by the engine management system to adjust the fuel mixture. This is critical for maintaining low emissions and good fuel economy. If an O2 sensor gets “lazy” because of old age or contamination, the computer may not be able to adjust the fuel mixture quickly enough as the engine’s operating conditions change. O2 sensors that are failing tend to read lean, which causes the fuel system to run overly rich to compensate. The result is increased emissions and fuel consumption.
The responsiveness of the O2 sensors can be tested using various procedures (making the fuel mixture rich or lean and watching the sensor’s response on a scan tool with graphing capability). If an O2 sensor is sluggish or unresponsive, it needs to be replaced. The same goes for any O2 sensor that has a bad internal heater circuit.
O2 sensor failures can be caused by various contaminants that enter the exhaust. These include silicates from internal engine coolant leaks (due to a leaky head gasket or a crack in a cylinder wall or combustion chamber) and phosphorus from excessive oil consumption (due to worn rings or valve guides). Replacing a fouled O2 sensor may temporarily solve the problem, but sooner or later the new sensor also will fail if the underlying problem that is allowing the contamination to occur is not corrected.
Oxygen sensors are one of the most often replaced sensors. Inputs from the O2 sensors are used by the engine management system to adjust the fuel mixture. This is critical for maintaining low emissions and good fuel economy. If an O2 sensor gets “lazy” because of old age or contamination, the computer may not be able to adjust the fuel mixture quickly enough as the engine’s operating conditions change. O2 sensors that are failing tend to read lean, which causes the fuel system to run overly rich to compensate. The result is increased emissions and fuel consumption.
The responsiveness of the O2 sensors can be tested using various procedures (making the fuel mixture rich or lean and watching the sensor’s response on a scan tool with graphing capability). If an O2 sensor is sluggish or unresponsive, it needs to be replaced. The same goes for any O2 sensor that has a bad internal heater circuit.
O2 sensor failures can be caused by various contaminants that enter the exhaust. These include silicates from internal engine coolant leaks (due to a leaky head gasket or a crack in a cylinder wall or combustion chamber) and phosphorus from excessive oil consumption (due to worn rings or valve guides). Replacing a fouled O2 sensor may temporarily solve the problem, but sooner or later the new sensor also will fail if the underlying problem that is allowing the contamination to occur is not corrected.
08-07-2020, 04:50 PM
#9
Hope that mechanic will eat any cost incurred, as this was totally not your fault. totally mechanic at fault.
at this point; you should only pay for the 02 replacement+labor. nothing else. perhaps, he should eat the labor as he had the car for 3 weeks!!!
If I lived near you, I'd swap it out for free!!!
at this point; you should only pay for the 02 replacement+labor. nothing else. perhaps, he should eat the labor as he had the car for 3 weeks!!!
If I lived near you, I'd swap it out for free!!!
Last edited by justnspace; 08-07-2020 at 04:53 PM.
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bmoua15 (08-07-2020)
08-07-2020, 08:34 PM
#10
Hope that mechanic will eat any cost incurred, as this was totally not your fault. totally mechanic at fault.
at this point; you should only pay for the 02 replacement+labor. nothing else. perhaps, he should eat the labor as he had the car for 3 weeks!!!
If I lived near you, I'd swap it out for free!!!
at this point; you should only pay for the 02 replacement+labor. nothing else. perhaps, he should eat the labor as he had the car for 3 weeks!!!
If I lived near you, I'd swap it out for free!!!
OP, please post a update when you can. Thx
08-08-2020, 11:38 PM
#11
Intermediate
Thread Starter
I should hopefully hear something on Monday. I will relay the different things I've heard from you all and a reddit thread with a similar description of the issue.
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justnspace (08-10-2020)
08-11-2020, 11:35 PM
#14
Intermediate
Thread Starter
Update
The mechanic and I spoke this evening.
They have looked all the different things you have mentioned over the past week, and tested them all. They have a Honda/Acura tool and they did the throttle body reset after cleaning. None of them have come back as the fault. O2 sensors are both good. They tested those and they are operating within normal parameters.
They feel that the likely culprit now is the valve adjustment being out of spec. They will be redoing the valve adjustments on the vehicle as both banks are reporting the lean conditions. Both the master tech and the shop owner are working on it together to check each others work, to make sure nothing is missed.
Can someone tell me what the valve adjustment specs should be? 2016 MDX Base, SH-AWD.
TIA
They have looked all the different things you have mentioned over the past week, and tested them all. They have a Honda/Acura tool and they did the throttle body reset after cleaning. None of them have come back as the fault. O2 sensors are both good. They tested those and they are operating within normal parameters.
They feel that the likely culprit now is the valve adjustment being out of spec. They will be redoing the valve adjustments on the vehicle as both banks are reporting the lean conditions. Both the master tech and the shop owner are working on it together to check each others work, to make sure nothing is missed.
Can someone tell me what the valve adjustment specs should be? 2016 MDX Base, SH-AWD.
TIA
08-12-2020, 06:52 AM
#15
The mechanic and I spoke this evening.
They have looked all the different things you have mentioned over the past week, and tested them all. They have a Honda/Acura tool and they did the throttle body reset after cleaning. None of them have come back as the fault. O2 sensors are both good. They tested those and they are operating within normal parameters.
They feel that the likely culprit now is the valve adjustment being out of spec. They will be redoing the valve adjustments on the vehicle as both banks are reporting the lean conditions. Both the master tech and the shop owner are working on it together to check each others work, to make sure nothing is missed.
Can someone tell me what the valve adjustment specs should be? 2016 MDX Base, SH-AWD.
TIA
They have looked all the different things you have mentioned over the past week, and tested them all. They have a Honda/Acura tool and they did the throttle body reset after cleaning. None of them have come back as the fault. O2 sensors are both good. They tested those and they are operating within normal parameters.
They feel that the likely culprit now is the valve adjustment being out of spec. They will be redoing the valve adjustments on the vehicle as both banks are reporting the lean conditions. Both the master tech and the shop owner are working on it together to check each others work, to make sure nothing is missed.
Can someone tell me what the valve adjustment specs should be? 2016 MDX Base, SH-AWD.
TIA
The valve clearance specs are:
Intake- 0.20-0.24mm (0.008-0.009in)
Exhaust- 0.28-0.32mm (0.011-0.012in)
They should also make sure the engine is fully cooled off before the valves are adjusted as a warm/hot engine will throw off the adjustment due to expansion.
08-12-2020, 09:13 AM
#18
Intermediate
Thread Starter
Already paid for the 100K service + oil change + tranmission + diff fluid. Won't be paying that again.
They checked the timing on the belt too. Dead accurate. Curious what they find during the valve adjustment. Will update as I hear more. Will recommend the plugs being pulled.
They checked the timing on the belt too. Dead accurate. Curious what they find during the valve adjustment. Will update as I hear more. Will recommend the plugs being pulled.
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justnspace (08-14-2020)
08-14-2020, 10:02 AM
#20
sounding more and more like timing belt is off a tooth.
if the replacement 02 sensors dont fix it, the mechanic needs to look back at his work and go over the timing belt.
I doubt its the MAF. but we have gone full circle as he's going to be replacing both 02 and MAF...Fingers crossed that it's the 02 sensor
also, I knew the valve adjustment would be spot on, they really dont go out of spec too much
if the replacement 02 sensors dont fix it, the mechanic needs to look back at his work and go over the timing belt.
I doubt its the MAF. but we have gone full circle as he's going to be replacing both 02 and MAF...Fingers crossed that it's the 02 sensor
also, I knew the valve adjustment would be spot on, they really dont go out of spec too much
08-14-2020, 01:27 PM
#22
Burning Brakes
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P0171 indicates a lean bank 1. That is the head towards the firewall. I am leaning towards a valve adjustment issue. A dealer could drill down a look at fuel trim values which would give you a more accurate picture of what is going on. I do not like that the mechanic is not using data to diagnose the car. He is basically guessing.
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justnspace (08-14-2020)
08-14-2020, 02:29 PM
#23
Intermediate
Thread Starter
My mechanic does actually have the Honda/Acura diagnostic tools. They are not using generic all in one scanners. They have indicated that the lean fuel reading is actually coming from both banks.
08-15-2020, 09:30 AM
#24
Lean on both banks should mean there is an air leak from between the maf sensor and the manifold before the air splits into the individual runners for each bank. One bank lean would indicate more of a valve or timing issue(which i only saw the p0171 code you posted) When the timing belt is off it usually throws a lean on one bank and a rich code on the other due to the valves opening at the wrong time. I’m sure the mechanic has already checked for obvious vacuum leaks(accordion boot and vacuum lines to manifold) I would suggest having the mechanic hook up the scan tool and watch the short term fuel trim values while spraying brake cleaner or something like that at certain points around the egr/intake manifold area to see if the st fuel trim values drop closer to 1.00v which is normal range.
Could be leaking air past the throttle body gasket, the intake manifold cover gasket, the egr valve or the evap purge valve. Those are really the only things between the maf sensor and the manifold that could feed air into both banks at the same time that I can think of. Hope it’s gets fixed for you soon though....
Could be leaking air past the throttle body gasket, the intake manifold cover gasket, the egr valve or the evap purge valve. Those are really the only things between the maf sensor and the manifold that could feed air into both banks at the same time that I can think of. Hope it’s gets fixed for you soon though....
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justnspace (08-18-2020)
08-18-2020, 04:07 PM
#25
Intermediate
Thread Starter
Still no dice. Tested all the things listed above and then some. Sounds like he is going to go on Identifix and get further suggestions and is spending some time on IATN to see if he can find anything else.
this is an early 2016. Any firmware/updates to the computer controlling everything that would address this?
this is an early 2016. Any firmware/updates to the computer controlling everything that would address this?
Last edited by fusionrx; 08-18-2020 at 04:13 PM.
08-18-2020, 07:01 PM
#26
Burning Brakes
Sounds like you might have to bite the bullet and hit an certified Acura shop with the condition that if they find something your current mechanic screwed up they pay for it, if it is something else, you are on the hook. Not sure your current mechanic will buy that. But you need to do something.This seems to be going on for too long. At least it would be too long for me!
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justnspace (08-18-2020)
08-18-2020, 08:23 PM
#28
Drifting
Sounds like you might have to bite the bullet and hit an certified Acura shop with the condition that if they find something your current mechanic screwed up they pay for it, if it is something else, you are on the hook. Not sure your current mechanic will buy that. But you need to do something.This seems to be going on for too long. At least it would be too long for me!
08-19-2020, 11:40 AM
#29
Intermediate
Thread Starter
The mechanic checked the evap canister and purge valve. He's working with a Honda/Acura specialist and is comparing the data from my 16 with known good data from a 17 mdx to see if he see where there are difference.
Possible culprit, injectors, which he says would be super odd.
Possible culprit, injectors, which he says would be super odd.
09-02-2020, 09:46 AM
#30
Intermediate
Thread Starter
Update:
Mechanic has gone over all data points from all sensors from a known good vehicle and compared to mine and has been working with 2 Acura specialists via Identifix (mechanics internet database). With a couple very minor differences (off by a negligible amount) my car is identical to the good vehicle. They have literally tested everything, including pressure in the fuel rail (its exactly where it should be). At this point, the thought is that the injectors are the units at fault causing the lean condition. The system reports that the car is running 40% lean on both banks. (idle is sitting around 550rpm, runs fine at speed). The mechanic will be replacing the injectors (these cost $1400!) and reporting back by the end of the week.
Also to address the question that came up regarding the 'cost of repairs', this mechanic is covering all of it. I pay $0. To paraphrase: "You brought us the car in working condition, and now it isn't working correctly after the 100k service. This is on us to take care of."
Mechanic has gone over all data points from all sensors from a known good vehicle and compared to mine and has been working with 2 Acura specialists via Identifix (mechanics internet database). With a couple very minor differences (off by a negligible amount) my car is identical to the good vehicle. They have literally tested everything, including pressure in the fuel rail (its exactly where it should be). At this point, the thought is that the injectors are the units at fault causing the lean condition. The system reports that the car is running 40% lean on both banks. (idle is sitting around 550rpm, runs fine at speed). The mechanic will be replacing the injectors (these cost $1400!) and reporting back by the end of the week.
Also to address the question that came up regarding the 'cost of repairs', this mechanic is covering all of it. I pay $0. To paraphrase: "You brought us the car in working condition, and now it isn't working correctly after the 100k service. This is on us to take care of."
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justnspace (09-02-2020)
09-02-2020, 02:29 PM
#31
Gosh that really sucks your X has been out of service so long. I hope it gets sorted out soon.
I'm glad the shop is being respectful toward you and doing their best to resolve the issue. Good luck!
I'm glad the shop is being respectful toward you and doing their best to resolve the issue. Good luck!
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fusionrx (09-04-2020)
09-05-2020, 10:08 AM
#36
It can still be top tier premium fuel and test bad. Sometimes the gas station has a contamination of water into their fuel tanks or the supplier could have had a bad batch of fuel. Make sure to get it tested with an ethanol tester. They should have one at most shops as this can happen more often than you may think possible. It’s a quick test and it can at least eliminate bad fuel as a possibility.
09-11-2020, 12:39 PM
#37
Intermediate
Thread Starter
FWIW, I got a call from the mechanic today and the new injectors resolved the issue. I'm going to pick it up later this afternoon and drive it home. pheww... 8 weeks in the shop to track this down.
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justnspace (09-11-2020)
09-11-2020, 03:02 PM
#38
Intermediate
Thread Starter
Got the car home, drives like a brand new vehicle. Working like a charm. Gas mileage up where expected, idling as expected. Will be doing a longer ~60 mile drive with it tonite.
Mechanic thinks injectors were affected by part of the cleaning procedure they do when doing the 100K service. They did all the required work per the acura spec. They did mention Honda has has some injector issues on similar vehicles, but nothing that they could definitively point at.
Just glad to have it back and working like expected.
Mechanic thinks injectors were affected by part of the cleaning procedure they do when doing the 100K service. They did all the required work per the acura spec. They did mention Honda has has some injector issues on similar vehicles, but nothing that they could definitively point at.
Just glad to have it back and working like expected.
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justnspace (09-11-2020)
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fusionrx (09-11-2020)
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fusionrx (09-11-2020)