o2 Sensor Ongoing Issues

[christianb5s4]

I'm really struggling with a troublesome issue I've been having with the car and could use some help figuring this out. I've researched around but haven't been able to find anything that is exactly similar to my problems, besides this o2 sensor problem there are no other issues or codes that come up.

Codes:

16514 - Oxygen (Lambda) Sensor B1 S1: Malfunction in Circuit
16534 - Oxygen (Lambda) Sensor B2 S1: Malfunction in Circuit

Things Replaced Already:

1. Two brand new OEM sensors
2. New known working ECU
3. Grounds in engine bay checked
4. For reference, normal idle AFRS are 15 (+/-0.3)

Symptoms:

- Car will be running perfectly fine but once up to temperature, it will intermittently idle rough and AFRs will go rich
- Lambda control will max out at -25% while this is happening
- O2 sensors throwing same codes even after new sensors and ecu installed
- Randomly, the issue will go away without any input from me and lambda control goes back to normal as does idle

Ideas:

- Check fuses
- Check wiring from o2 sensor to ECU


Any help is greatly appreciated, I am thinking it is either a fuse or more likely wiring issue. Let me know your thoughts.

[axnjaksn]

mine ended up being MAF sensor....when it would get hot, all would seem normal in vcds blocks, I even replaced my front o2 sensors with jhm ones. swapped out my MAF sensor(since I have 3 or 4 extras) all good. Im currently using a brand new hitachi oem audi(well refurbished) but purchased brand new from the dealer, no problems ever since I swapped

[christianb5s4]

Interesting, I could check the MAF as I got a brand new Bosch RS4 housing and MAF for the build but converted back from hitachi to Bosch. That wiring job/sensor could be an issue, but how would that cause the o2 sensor codes with intermittent circuit issues?

[NOTORIOUS VR]

Do the O2 sensor codes come up if you run the car w/o the MAF attached for a while?

What Injectors are you running?

[christianb5s4]

Reason I doubt it's the MAF is the MAF readings are completely normal and not erratic. I'm running EV14 72lb injectors. Also of note, if I turn the car off for a few minutes while hot then start it back up, the car then runs lean and a handful of random misfires across all cylinders at idle before the issue just goes away and the car begins running normally again.

[jballou]

What about a coolant temp sensor being bad? ECU sees the car too hot and it tries to protect itself by dumping large amounts of fuel into the car. Could also be a MAF issue. Unplug it and see how the car runs.

[christianb5s4]

The symptoms are definitely inline with a MAF reading poorly, but why would that cause the o2 malfunction in circuits codes? Coolant temp sensor was replaced early 2015 with a new OEM one.

[MetalMan]

You can check reported coolant temps with your XTool. When it's misbehaving, if the values reported look normal, then you can probably rules out the CTS.

[christianb5s4]

I will have to look at the values for that, didn't look at it yet since I was focused on the o2s. Will do the same for MAF readings.

[axnjaksn]

I will have to look at the values for that, didn't look at it yet since I was focused on the o2s. Will do the same for MAF readings.

my MAF readings never looked bad when I would watch it live in VCDS....ever, even when it did the weird running idling, car would drive fine under load or boost and even idle fine for the most part, unless I sat with it running for a few minutes (heatsoaking the MAF) then boom, my o2 sensor values would peg one way or the other. I kept thinking o2's since they were the sensors showing pegged, then I realized the o2s are just reading whats coming out of the engine, so I proceeded to diagnose whats feeding the engine, controlling how or what comes out the exhaust.....lucky shot with swapping the MAF out, but it worked.....just some food for thought.. it may not be, but this is damn close to what I had going on, you could always try driving around with the MAF unplugged, car will drive just fine for testing purposes rather should drive just fine

[NOTORIOUS VR]

Reason I doubt it's the MAF is the MAF readings are completely normal and not erratic. I'm running EV14 72lb injectors. Also of note, if I turn the car off for a few minutes while hot then start it back up, the car then runs lean and a handful of random misfires across all cylinders at idle before the issue just goes away and the car begins running normally again.

It could be the MAF scaling or something like that. Running it with the MAF unplugged will force it to run on base tables. If the ECU is correctly scaled to your injectors it should run perfectly fine... no need to go into boost, but it should start and drive normal and see if the O2 sensor codes come back then.

If not, it could be because something in the fueling is whack or the MAF is not happy, etc, etc. Bad fueling (like having maxed out fuel trims) can cause O2 sensor codes... It's not the O2 sensors, but fueling/tuning.

72# EV14's would be modified units, who did them/where did they come from? Are they some guy in a garage reaming them out or is it a reputable company modifying them? What is the spray pattern like? Have you verified the flow between the injectors? It sounds like your issues are generally in the low pulse width areas which is where bad modifications will show up as you need precise control at these points and DC.

[Timtheguru]

How old is your FPR?

[christianb5s4]

my MAF readings never looked bad when I would watch it live in VCDS....ever, even when it did the weird running idling, car would drive fine under load or boost and even idle fine for the most part, unless I sat with it running for a few minutes (heatsoaking the MAF) then boom, my o2 sensor values would peg one way or the other. I kept thinking o2's since they were the sensors showing pegged, then I realized the o2s are just reading whats coming out of the engine, so I proceeded to diagnose whats feeding the engine, controlling how or what comes out the exhaust.....lucky shot with swapping the MAF out, but it worked.....just some food for thought.. it may not be, but this is damn close to what I had going on, you could always try driving around with the MAF unplugged, car will drive just fine for testing purposes rather should drive just fine

Glad someone else has had a similar issue, I'm definitely learning through the process but I wish I knew more about diagnosing these more complex issues. I will definitely try unplugging the MAF to see what happens, it's good that you also didn't see any erratic readings while watching live even when it's running like shit because that's exactly my problem too.

It could be the MAF scaling or something like that. Running it with the MAF unplugged will force it to run on base tables. If the ECU is correctly scaled to your injectors it should run perfectly fine... no need to go into boost, but it should start and drive normal and see if the O2 sensor codes come back then.

If not, it could be because something in the fueling is whack or the MAF is not happy, etc, etc. Bad fueling (like having maxed out fuel trims) can cause O2 sensor codes... It's not the O2 sensors, but fueling/tuning.

72# EV14's would be modified units, who did them/where did they come from? Are they some guy in a garage reaming them out or is it a reputable company modifying them? What is the spray pattern like? Have you verified the flow between the injectors? It sounds like your issues are generally in the low pulse width areas which is where bad modifications will show up as you need precise control at these points and DC.

The injectors I got from my tuner who gets them from a supplier that works directly with Bosch, so a reputable company. The issue is that while it's in the low pulse width areas, it doesn't happen all the time. Only when the car is up to temperature and even then the issue comes and goes. If it was a mechanical issue such as bad or mismatched flow between injectors, I'd imagine the symptoms would show more consistently?

How old is your FPR?

FPR was replaced a few months ago, right before the build began. Only questionable thing is I am going to replace the vacuum line as it still has that braided OEM line on it and I've had problems with those fraying.

[NOTORIOUS VR]

The injectors I got from my tuner who gets them from a supplier that works directly with Bosch, so a reputable company.

Working with Bosch doesn't mean anything if they're modified after the fact. Just sayin'

The issue is that while it's in the low pulse width areas, it doesn't happen all the time. Only when the car is up to temperature and even then the issue comes and goes. If it was a mechanical issue such as bad or mismatched flow between injectors, I'd imagine the symptoms would show more consistently?

No I don't see why screwed up injectors would have to work exactly the same all the time. There's a lot going on in an injector without all the (external) influences like fuel pressure/pulses, fuel temperatures, coil temps from heat soak, etc. Especially after a modification that might have been done incorrectly.

[christianb5s4]

Definitely understand that, the idle problem occurred very recently i.e. in the past 2 weeks. Those injectors have been installed for over 2 months and everything was running great prior. Is there any way to monitor injectors on vagcom that could show if that problem is occurring?

[NOTORIOUS VR]

Definitely understand that, the idle problem occurred very recently i.e. in the past 2 weeks. Those injectors have been installed for over 2 months and everything was running great prior. Is there any way to monitor injectors on vagcom that could show if that problem is occurring?

Sure you can monitor the inj. PW. and MAF for airflow Although not very accurately or fast enough using VCDS. Best to use ME7Logger for that.

That said, I'm not saying the issue is with the injectors.

And again, I ask do you have these issues with the MAF disconnected? Looking at the video it's odd the cars idle is fluctuating like that + rich condition.

I'd almost lean towards a leak after the MAF... maybe back/failing check valve, spider/PCV system failure, etc. Intake leak (after the throttle body).

[axnjaksn]

Sure you can monitor the inj. PW. and MAF for airflow Although not very accurately or fast enough using VCDS. Best to use ME7Logger for that.

That said, I'm not saying the issue is with the injectors.

And again, I ask do you have these issues with the MAF disconnected? Looking at the video it's odd the cars idle is fluctuating like that + rich condition.

I'd almost lean towards a leak after the MAF... maybe back/failing check valve, spider/PCV system failure, etc. Intake leak (after the throttle body).

I definitely did as NVR stated prior to the MAF, I replaced all green check valves, spider hose, all vacuum and boost hoses related on everything, intake manifold, throttle body, everything....some of them were probably contributing to my many issues.... all new coolant sensors, fan switch sensors, pretty much anything that hadn't been previously replaced sensor wise...I knew I had finally gotten rid of the mechanical failures when the car ran pretty damn good and consistent until I sat idling on a hot day and then it would only be wacky at idle. everything I replaced I used brand new oem stuff too, rule out all possibilities.....jballou even had pointed out "something is getting hot and failing" that's when it kinda made sense to swap an MAF out... just to see, if you have extras, hahaha I do...

[christianb5s4]

I've replaced every check valve, the whole spider hose assembly, PCV vale, intake manifold gaskets, new N249 and lines, new vacuum lines, new 710Ns, pressure tested. Everything has been replaced in the last 100 miles max. Everything brand new OEM. I have a feeling it could have something to do with the MAF wiring as during the build, we converted from Hitachi back to Bosch and used a brand new OEM Bosch RS4 MAF and housing.

I only have a few things left to check, do you guys have a preferred vacuum line you blow smoke into to test the vacuum system for leaks? First thing I will do is unplug the MAF when it starts acting up and see what happens. If you guys have any other ideas, I'm all ears.

[NOTORIOUS VR]

First thing I will do is unplug the MAF when it starts acting up and see what happens. If you guys have any other ideas, I'm all ears.

Just unplug it and see if the car acts normal from that point on.

[christianb5s4]

Well, thank you guys for all the help. Went down to the car after a conference call and started it up, it's 100% the wiring splice for the MAF sensor. I moved the wires around and each time I did, the car started idling poorly. When I pressed on it again, it idled perfectly.

Ugh, always the simple things that get you. Will be properly soldering those wires tonight or tomorrow and put this to rest.

[axnjaksn]

Well, thank you guys for all the help. Went down to the car after a conference call and started it up, it's 100% the wiring splice for the MAF sensor. I moved the wires around and each time I did, the car started idling poorly. When I pressed on it again, it idled perfectly.

Ugh, always the simple things that get you. Will be properly soldering those wires tonight or tomorrow and put this to rest.

Just curious, why go from hitachi to bosch? don't most people convert from bosch to hitachi?? no offense meant, im genuinely curious, my car is a 2001, ive had hitachi the whole time...is there an advantage to bosch??

good luck, remember direct hot solder joints are the only acceptable electrical connection, just my opinion and experience... be careful with brittle stuff too and make sure its all secure, if you get lost id be more than happy to offer help wherever I can.

[Bordom]

Just curious, why go from hitachi to bosch? don't most people convert from bosch to hitachi?? no offense meant, im genuinely curious, my car is a 2001, ive had hitachi the whole time...is there an advantage to bosch??

good luck, remember direct hot solder joints are the only acceptable electrical connection, just my opinion and experience... be careful with brittle stuff too and make sure its all secure, if you get lost id be more than happy to offer help wherever I can.

Because he used the RS4 MAF, which is Bosch only

Everything graciously mispelled by Android

[christianb5s4]

Update is that thanks to MetalMan graciously helping, we properly soldered the wires and heatshrink wrapped each individually. Turns out the splice was not the issue, the connector is old and has play in the pins. I will get a new connector and pins and replace eventually, for now a few zip ties have done the trick and idle issue hasn't come back since.

Just curious, why go from hitachi to bosch? don't most people convert from bosch to hitachi?? no offense meant, im genuinely curious, my car is a 2001, ive had hitachi the whole time...is there an advantage to bosch??

good luck, remember direct hot solder joints are the only acceptable electrical connection, just my opinion and experience... be careful with brittle stuff too and make sure its all secure, if you get lost id be more than happy to offer help wherever I can.

They each have their advantages, but for a normal stage 3 car either are more than good enough for the job. Hitachi has a higher range for readings but the Bosch has higher resolution in reading in certain conditions. All in all, the most important decision is to choose one that your tuner is most comfortable/familiar with.

Because he used the RS4 MAF, which is Bosch only

Everything graciously mispelled by Android

Initially I was running a Hitachi VAST converted RS4 MAF but the car ran terribly, thought it was that MAF but I now know it was a number of vacuum/boost leaks that was causing it. Converted to Bosch through trouble shooting and stuck with it.

[christianb5s4]

For the connector, can anyone confirm that these are the correct pins to use in the new Bosch MAF connector?

https://www.ecstuning.com/Volkswagen...tors/ES470511/