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Discussion Starter #1
I've been having a intermittant SES that seems to be staying lit more consistently. I'm also having a "Engine Failsafe Prog" message intermittantly. The engine seems to be cutting out at very low RPM's or just off idle, sometimes it almost seems as if it sputters on application of the throttle as well as when I remove my foot from the pedal- but never when the RPM's are up. I took it to a shop that insisted there were no codes. I then took it for a second opinion at another reputable shop and they also said there were no codes. They suggested I start with a fuel filter. I installed the new filter and nothing has changed. Any help? I feel like it's almost undrivable.
 

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Difficult to say w/o a code (could be almost anything). Taking a wild guess, however, if it seems to almost be OK when you accelerate VERY slowly (i.e. really, really gradual application of throttle), but when you apply throttle normally it bogs, almost dies, and maybe eventually catches and start to pull, well, it might be the intake Cam position sensor(s).
 

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The first time it was done I think it must have just been a generic tester, the second time it was done by a reputable german autosport shop that seemed to have done a more thorough check with more sophisticated equipment. Does that help? I have not had it in to the dealer. Thanks for your help.
 

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I had a similar issue on a 540i and replacing the MAF seemed to fix it, but that is just a thought and please wait for the wiser folks to chime in with responses.

I bought a peake and it is great. A great suggestion from ard.
 

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We need your mileage luva. :hihi:

An easy MAFs test would be to unplug the electrical connectors to them and go for a drive. It only takes a minute to unplug them. Without input from them the DME reverts back to a more basic fueling program. If they're bad your car should improve instantly.
 

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We need your mileage luva. :hihi:

An easy MAFs test would be to unplug the electrical connectors to them and go for a drive. It only takes a minute to unplug them. Without input from them the DME reverts back to a more basic fueling program. If they're bad your car should improve instantly.
Good advice. Multiple reports where people are unable to maintain an idle, but when the MAFs are unplugged it is fine.

Inability to get to rpm- so the car is fine at idle, but fuel starved up top- would point me to fuel filter/pump.

Give the maf disconnect a try, report back. and buy a peake. :)

A
 

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dont unplug the mafs, mafs usually act up under load or wot not right off idle. if you unplug them the engine is running in default which means its ignoring other signals as well, just because the car runs better with the mafs unplugged dosent mean they are the problem. if the engine is going into failsafe there should be codes stored.
 

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Good advice. Multiple reports where people are unable to maintain an idle, but when the MAFs are unplugged it is fine.

Inability to get to rpm- so the car is fine at idle, but fuel starved up top- would point me to fuel filter/pump.

Give the maf disconnect a try, report back. and buy a peake. :)

A
dont unplug the mafs, mafs usually act up under load or wot not right off idle. if you unplug them the engine is running in default which means its ignoring other signals as well, just because the car runs better with the mafs unplugged dosent mean they are the problem. if the engine is going into failsafe there should be codes stored.
So OP has said there are no codes. You say "do not unplug the mafs"... so what is he to do?

Are you saying one should never unplug the mafs and there is zero diagnostic value to this maneuver?
 

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So OP has said there are no codes. You say "do not unplug the mafs"... so what is he to do?

Are you saying one should never unplug the mafs and there is zero diagnostic value to this maneuver?

There is some diagnostic value to this, but without an airflow reading the car won't dynamically adjust fuel trims. If this makes the car run better then this could indeed be an issue with the MAF (often is especially in the absence of a code) or it could be an issue with the O2 sensors... or a number of other things.

Typically if the car is misbehaving without generating a code then it means that the poor running (which noticeable to the driver) is either not being seen by the computer or is just barely within the threshold of being normal. A failed sensor can lead to this condition where the computer is trying to adjust, but is doing so on faulty data.

Best bet is to pull sensor data from the car while it's running, look at the numbers, and figure out what they mean. This may be beyond the scope of what someone can do at home... in other words, it may take a competent shop with good equipment some time to figure out the problem. An absence of codes means that the tech will need to do some serious thinkin' in order to come to a conclusion.

Having said all of that I do think that the MAFs are a plausible culprit. I prefer to test their output using a lab scope rather than the secret menu test.

If you'd like I may be able to refer you to a good indy in your area that can help you.
 
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luva doesn't seem too concerned...he hasn't been back.

I still say he needs to unplug those MAFs. It won't hurt anything so why not do it just to see if anything changes?
 

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it may take a competent shop with good equipment some time to figure out the problem. An absence of codes means that the tech will need to do some serious thinkin' in order to come to a conclusion.
Very true

I prefer to test their output using a lab scope rather than the secret menu test.
.
Is there really any way to test a MAF without a calibrated airflow bench?!?! You can measure whatever you want- but unless you know the airflow you cannot tell if they are accurate.... I worked on this for a while with no real resolution, so any input would be of interest.

A
 

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im not saying theres no diagnostic merit to unplugging the mafs. just that what he's describing dosent sound like mafs. from what i've seen they usually act up under load or wot, not at idle or just giving a little gas. it may be the mafs, just dosent seem like the way they usually fail.
 

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Very true
Is there really any way to test a MAF without a calibrated airflow bench?!?! You can measure whatever you want- but unless you know the airflow you cannot tell if they are accurate.... I worked on this for a while with no real resolution, so any input would be of interest.
A

There is no way to test the accuracy of a MAF, but in the grand scheme of things that's not necessarily a problem. If you look at it from a comparative standpoint you can gain a lot of insight into what's happening.

I like using a throttle snap test with a scope (snap the throttle from idle while recording the trace on a lab scope). This allows me to see the response time of the MAF and determine it's maximum voltage. There are some general guidelines for maximum voltage as well as references for what a "good" response trace should look like. In most cases as the MAF fails it's trace will degrade significantly when compared to the "ideal."

Coming from a science and engineering background it's really hard for me to fight the urge to quantify everything, but I've found that diagnostics is more of an exercise in comparison rather than an exact science.
 
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There is no way to test the accuracy of a MAF, but in the grand scheme of things that's not necessarily a problem. If you look at it from a comparative standpoint you can gain a lot of insight into what's happening.

I like using a throttle snap test with a scope (snap the throttle from idle while recording the trace on a lab scope). This allows me to see the response time of the MAF and determine it's maximum voltage. There are some general guidelines for maximum voltage as well as references for what a "good" response trace should look like. In most cases as the MAF fails it's trace will degrade significantly when compared to the "ideal."

Coming from a science and engineering background it's really hard for me to fight the urge to quantify everything, but I've found that diagnostics is more of an exercise in comparison rather than an exact science.

Yup.

I was trying to figure out a way (other than the 'fuel flow test') to figure out when a maf was becoming fouled. You can look at fuel trims, etc, but I was trying to quantify just the maf....

Good car mechanics and doctors have much in common.

A
 

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I was trying to figure out a way (other than the 'fuel flow test') to figure out when a maf was becoming fouled. You can look at fuel trims, etc, but I was trying to quantify just the maf....

The snap test works very well for this as the MAF response slows as it's becoming fouled. I've seen some where it won't even develop a good inrush peak on the trace. Under normal conditions it appears fine as it can still measure total air flow eventually, but under instantaneous load it doesn't know what hit it.

Also a good test on a dual MAF car to make sure that both senors are showing similar response times. Although the Bosch/BMW MAFs are pretty good it's not unheard of to get a dud... or in the case of Jaguar it's not unheard of to get a good one occasionally.
 

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Discussion Starter #17
Sorry Gentlemen...

The board had notified me of your first few replies via email, then nothing! I had no idea the beast and I were getting this kind of feedback! Thanks to all.

The car has 97k on the clock, is all stock and has never been on the track or driven real hard. I have had a few issues pop up over the last year or two but so far nothing that broke the bank.

I want to try to explain my symptoms again if you don't mind.

The engines really stumbles and cuts out with super minimal pressure on the throttle, such as when driving through town at 29 mph in 3rd gear. Super light throttle while drifting along. Does that make sense?

***I suspected the pedal position sensor at first because while it has been an intermittant problem at times I have felt like I could almost make it stumble or cut out if I held the slightest little pressure on the go pedal.*** Possible???

Other times it will almost seem as though it stumbles or cuts out as I lift my foot from the pedal.

Does this change any of your opinions? I am sorry for the inattentiveness. Thanks for the help.
 

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Any issues with the drive-by wire trigger the same second the engine failsafe aka limp mode which you see in the instrument cluster...



Edit:Just seen you have fail save,so good chance for an drive-by wire issue!

Anyway,this whole thing is useless and senseless without error codes(BMW specific) to work with.
If the car goes into failsafe,it has errors in the memory!It is not possible it does failsafe without errors(exept the ECU itself acts up)...
 

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I had very similar symptoms when I had my throttle potentiometer go bad and unfortunately it had to be replaced. I'm pretty sure I did have fault codes, though. At the very least I had a few mis-fire codes from the Peake reader. I suggest you get your hands on one ASAP just so you can verify some of what the shops are telling you. It has been invaluable in the past so that you don't go to your shop completely in the dark.
 
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