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2006 bmw z4 with 2 litre n46 engine - no airflow but no fault code?? ***FIXED***

Posted By andyfanshawe Monday, February 10, 2020 2:52:01 PM
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2006 bmw z4 with 2 litre n46 engine - no airflow but no fault code??...

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andyfanshawe
 Posted Monday, February 10, 2020 2:52:01 PM
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Hi all.
Interesting one here......N46 engine beemer z4. Erratic power, sometimes falls flat on its face, other times okay. Happening for about 2 weeks now.
Only 2 fault codes are right rear wheel speed sensor and bank 1 sensor 2 O2 sensor ageing. Waveform from that wheel speed sensor has the same shape as the others but loads of hash and spikes on it. DSC light flashes when accelerating away and car has no power. With DSC switched off power is a lot better but not 100%. Most likely phonic wheel, but...………….

Took for a test drive while watching live data. Noticed engine is going in and out of closed loop regularly. Short and long term fuel trims hovering about 0.

Bank 1 sensor 2 is reading full lean sometimes. At that same time, bank 2 sensor 2 is about 0.7v. Then back to normal.

Then I noticed the MAF was reading 0 g/s! Unplugged it, test drove for about 10 miles and no fault code. Plugged in another scan tool and same reading. Plugged in or not, 0 g/s. Powers and grounds to IAT and MAF good. Customer said EML has never been on. Oh, IAT is built in and works fine.

Why is no fault code being produced? Is the DSC system linked to the engine output?

Ran out of time then and customer had to get car back 100 miles to home.

Just before he left I touched a test light from 12V to the MAF output and no change on live data. Unplugged MAF, and repeated test but still no change in the live data.

Cleared all codes, repeated test above and no change.

Any thoughts before I get the car back-if I do.

Seems obvious to change the MAF, but can't understand why a fault code isn't being produced for 0 g/s.

Andy.
11 hours ago by K And R
McTech
 Posted Monday, February 10, 2020 4:31:39 PM
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Hi Andy,

Freeze frame data from the PCM would have some clues.

The DSC needs sorting first as it will possibly affect engine performance.

I would the focus on the MAF - Ref Voltage supply? Does it have one? What was the value of the IAT you say OK but was it accurate?.

Has the car had codes 'mapped' out to put Mil out? O2 sensors maybe symptoms not cause.

Car sounds like its been messed with... what inputs have to be inside parameters for PCM to go into closed loop?

What scan-tool were you using?

more questions than answers...

Mt


I O, I O, its off to work I go!
andyfanshawe
 Posted Monday, February 10, 2020 5:56:34 PM
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McTech (10/02/2020)
Hi Andy,

Freeze frame data from the PCM would have some clues.

The DSC needs sorting first as it will possibly affect engine performance.

I would the focus on the MAF - Ref Voltage supply? Does it have one? What was the value of the IAT you say OK but was it accurate?.

Has the car had codes 'mapped' out to put Mil out? O2 sensors maybe symptoms not cause.

Car sounds like its been messed with... what inputs have to be inside parameters for PCM to go into closed loop?

What scan-tool were you using?

more questions than answers...

Mt


Hi McTech.
Thank you for your reply.
I used launch diagun 4 and my old faithful quick snap on ethos for back up. Both read the same. I can remember looking at freeze frame but forgot to snapshot it! Oops.

MAF had a 12v supply and a 5v supply. Oh, and an earth. Assume one is for the IAT and the other for the MAF. IAT readings were 21 degrees with a warm engine, sat idling in my workshop with bonnet up. I directed air from a hot air gun into the air filter casing and the temp went up quickly. When the MAF/IAT was disconnected the IAT read -40 degrees. So circuit is okay.

Ironically its my past car that I restored over a few years and sold to this owner. As far as Im aware nothing has been tampered with, but anythings possible.

When the car stood on its face, I was monitoring the fuel trims, o2 sensors, loop status and lamda values. Nothing really changed significantly. Not enough to cause the massive power loss. At one point I had to pull over because it wouldn't accelerate at all.

I find it pretty weird that both scan tools show 0 g/s air flow all the time. When I tapped into the signal wires with my scope from the IAT and the MAF, the IAT one was at about 2.6 v and went down when I put the hot air in (NTC?) but the MAF signal wire stayed at 0v whatever I did with the accelerator..

I wanted to simulate a signal from the MAF back to the ecu by the test light to prove circuit integrity but couldn't. Nothing changed at the data pids when I put a 12v test light signal to it. Perhaps the signal circuit is shorted to earth somewhere in the loom? Could put a test light on it from battery positive and see what happens and then disconnect the ecu. I didn't have time to test that theory because the owner had to go home with the car. BUT.....if it was shorted to ground, why is there not a fault code? I also would have thought there would have been a substituted value, but perhaps not if there isn't a fault code. And if it isn't shorted to earth, why isn't it causing a fault code anyway because of the 0 g/s reading. Lol!

I can't believe both scan tools are incorrect. 0 g/s from the MAF?????? But no code!!

Yes I could change the MAF but I am not 100% sure it is that and they are not cheap. And the sheer fact that there are no codes shown is causing an uneasy feeling. Certainly not going to throw parts at it.

I am even thinking towards a partially blocked CAT, but sometimes the power is good then it falls flat. But even that wouldn't cause a 0 g/s MAF reading.

Hmmm. The way forwards? Thinking time.

Thanks again.
Andy.
andyfanshawe
 Posted Monday, February 10, 2020 6:02:50 PM
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Another thought....fuel pressure. But even that wouldn't cause a 0 g/s MAF!! Flamin eck. What did they say in the terminator film?... Does your head in just thinking about it!
jamesfraser68
 Posted Tuesday, February 11, 2020 2:39:52 AM
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Have a good look at pick up rings on the driveshafts - BMW especially prone for build up of corrosion under the rings which can cause this issue. You will probably see shiny spots on the rings where there are raised if that's the case. Have you checked live data for MAF in EOBD rather than manufacturer specific to see if it's also 0v there?
McTech
 Posted Tuesday, February 11, 2020 4:22:48 AM
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andyfanshawe (2/10/2020)
Another thought....fuel pressure. But even that wouldn't cause a 0 g/s MAF!! Flamin eck. What did they say in the terminator film?... Does your head in just thinking about it!


Measure output of signal wire from MAF at PCM - load test wire - if you get the car backBigGrin

I O, I O, its off to work I go!
K And R
 Posted Tuesday, February 11, 2020 4:35:47 AM
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Andy

"MAF had a 12v supply and a 5v supply. Oh, and an earth. Assume one is for the IAT"


You should have 5 wires going to the MAF and you should have 2 5v (s) worrying you are assuming on a customers car with the car in front of you.


What data system(s) are you using.


Kev

"If you dont KNOW how it works, don,t try to test or fix it"
andyfanshawe
 Posted Tuesday, February 11, 2020 10:32:06 AM
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jamesfraser68 (2/11/2020)
Have a good look at pick up rings on the driveshafts - BMW especially prone for build up of corrosion under the rings which can cause this issue. You will probably see shiny spots on the rings where there are raised if that's the case. Have you checked live data for MAF in EOBD rather than manufacturer specific to see if it's also there?
Hi james.
Yep, checked maf pid in eobd also. Still 0 g/s.

Yes, agree on the rings for the abs/dsc. Been there many times before
Thanks for the reply.
Andy.
andyfanshawe
 Posted Tuesday, February 11, 2020 10:40:27 AM
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McTech (2/11/2020)
andyfanshawe (2/10/2020)
Another thought....fuel pressure. But even that wouldn't cause a 0 g/s MAF!! Flamin eck. What did they say in the terminator film?... Does your head in just thinking about it!


Measure output of signal wire from MAF at PCM - load test wire - if you get the car backBigGrin


Yep. Sounds like a good plan.
I still find it weird though. Ecu is seeing 0v for MAF. At all revs. If the wire was broken the ecu would see no voltage change in the wire. If it was shorted to ground it would still see no voltage change when driving. If the wire was intact its still seeing no voltage change. And thats all possibilities covered. But no fault code. So we either have an ecu related issue (internal or power or ground) or both my scan tools are wrong!


Andy.
andyfanshawe
 Posted Tuesday, February 11, 2020 11:21:56 AM
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K And R (11/02/2020)
Andy

"MAF had a 12v supply and a 5v supply. Oh, and an earth. Assume one is for the IAT"


You should have 5 wires going to the MAF and you should have 2 5v (s) worrying you are assuming on a customers car with the car in front of you.


What data system(s) are you using.


Kev

Hi Kev. Not worrying at all really. Long story but car was in for another issue (suspension/steering) which was solved and he was wanting to get back to Leicester pretty quick. He had been standing about in my workshop for about 3 hours prior and was freezing to death! Spotted the MAF issue on a test drive after the previous repairs. Just had time to get out my scope and start prodding! Certainly didn't intend to get diagrams out. Just wanted to check for powers and grounds before he left. Not being paid for this diagnostics anyway.
Yes 5 wires but there were certainly not 2 5v supplies. One was battery voltage and the other 5v (red/white wire and red wire respectively).


If there are supposed to be 2 5v supplies well we have a problem already!


I use AD but z4's and them don't mix very well at all. Diagrams are either not present or completely wrong. The last 4 I have had in for DSC issues I had to get the diagrams from elsewhere.


Thank you for your input though. Always appreciated.


Customer probably unlikely to pay for anymore work. Car has 170 K miles on it and loads of oil leaks and other issues. Just wanted to try to give him an idea what parts may be needed to solve the issue. This is a personal learning trip. Was hoping to post a solution up via ammo gained - if the car reappears.


Will do my best to diagnose this and post back.


Thank you to everybody for their input though. Experience and knowledge sharing is awesome. So grateful to you all. Will payback when I can.
Andy.


.





Andy.






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