Jameswsb

M5 MAF test a tad low

21 posts in this topic

Just done the OBC maf test and I get 125-126 l/h. As far as I am aware the figure to aim for is above 140 l/h so I am looking for the potential reasons why the car is not hitting that. It has recently had the air filters changed (about 3k miles ago), the service history paperwork shows a relatively recent fuel filter swap (about 15k ago) and I put new Bosch maf's on it a few thousand miles ago (proper 033 part number before anyone says it). Any thoughts? I have some pre cat 02 sensors to put on as soon as it stops pissing down but I am open to any other suggestions.

 

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MAF tests using LPH indicators on the OBC are crude at best. Personally i would only be using this as a delta for something wrong if the car was woefully under that rating, like 90-100 LPH.

 

By all means swap out pre cat O2's as preventative maintenance but personally i wouldn't be overly worried at this point, particularly if you're doing the test "just because".

 

Is this something you're carrying out in light of that reason or have you been hitting 140LPH and/or the car seems not right lately?

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To be honest Jamie the car runs really well. The only reason I did the test was as I was curious really and sometimes I get a bit of a jerk when changing between first and second, say if i hit a bump when applying the throttle and the car rocks about a bit. There seems to be a school of thought that this can be due to maf's which are passed their best so I wanted to check their operation given that they are pretty new.

 

Other than that the car feels very strong and is very well maintained so I have no immediate worries, I just want it to be at its very best. 

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If you have the ability to read and reset your fuel trim adaptations, please do so as these numbers (fuel trims) can help investigate any possible issues, or do it after fitting the pre cat o2 sensors and check for leaks around the bungs that hold these.

 

Several factors can influence that reading.  (Post maf intake air leaks, post combustion leaks (like around pre cat o2 sensor bungs), pre cat o2 sensors themselves etc etc)

 

 But as Jamie rightly says, most likely nothing to worry about.

 

 

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I have INPA but, to be honest I am not very computer literate and can just about manage ok with interrogating the car for fault codes so fuel trims maybe a bit beyond me. The car does seem very happy though and records good fuel consumption (for these!) and pulls like a train. Many thanks for the pointers, I'll get the 02 sensors fitted and have a good luck at the exhaust for any damage/leaks and give the car a full inspection 2 and see if that makes any difference and report back.

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Should be looking at this page on INPA  :

 

 

analog2_jun_25_12_39.png

 

 

Resetting Adaptations are quite straightforward.  I used to be able to do it with my eyes closed but haven't used inpa since 2013 so can't walk you through it anymore.  Just have a little look around.  I believe from the main menu it was F7 or F8 and says Adaptations if I remember correctly.

 

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Great stuff, thanks for the pointers. What exactly should I be looking for with regards to the figures? Does this have to be done with the engine running or does the car store the data from the previous journey?

 

Sorry for all the questions.

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Doesn't need to be running really.  No harm if running though.

 

Get a screenshot of yours and we can see where you are at.  

 

I reckon yours should be showing pretty much all ok.

 

Really looking to see if the DME is adding extra fuel, or fuelling less and also if its similar on both banks.  If there is significant fuel trimming occurring then even if you have brand new mafs and pre cat o2 sensors you won't be getting max fuelling (LPH) at WOT.

 

Good to have engine running in any case especially when you do the adaptation reset and you will feel the car stumble for 2/3 seconds and then back to normal.

Edited by M5 London
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That is most helpful, cheers. Ill swap the sensors this weekend and then fire up INPA and let you have a look at the figures. Thanks in advance.

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Update on this - I had an Inspection 2 service completed at Darren Wood Stockport the other day and asked him to give the car a thorough health check. All came well apart from bank 1 failing its vanos test. Apparently its not the end of the world and a lot of cars will fail the test as it is so precise. However, if this is effecting the engine performance significantly then I want it sorted. The car is booked in for a dyno run at Riverside Racing in Liverpool next Saturday so hopefully I will get some answers then.

 

In the meantime I will re run the MAF test and have a look at fuel trims and post the results. 

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See if it passes the vanos test with a slightly raised idle, i.e operator giving some gas to elevate rpms to 1250 or so. If it does i wouldn't worry about it.

 

Do you have the results at all?

 

Although the test stops at the point of failure which is a bit of a pain, often it can point towards the likely cause.

 

How old are your cam sensors?

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2 hours ago, jamiepeers said:

See if it passes the vanos test with a slightly raised idle, i.e operator giving some gas to elevate rpms to 1250 or so. If it does i wouldn't worry about it.

 

Do you have the results at all?

 

Although the test stops at the point of failure which is a bit of a pain, often it can point towards the likely cause.

 

How old are your cam sensors?

Unfortunately I left the car with them so I had no input as to what they did/how they did it. Darren Woods are well regarded to hopefully they know what they are doing, however I didn't get a copy of the test results.

 

Its funny you should mention the cam sensors, it was on my list of things to do as I believe they are original, however on the way back from the Malton breakfast meet on Sunday the car seemed down on power and then I got an engine check light appear. Having read about the symptoms I was pretty sure it would be a cam sensor. I hooked up inpa when I got home and lo and behold I got a fault code on one of the exhaust cam sensors along with the accompanying vanos regulation fault. I have ordered all 4 sensors so hopefully I can get this done prior to the dyno run on Saturday. I have heard that the sensors are a right pita to change!

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Exhaust CPS are easy....intakes are a bit of a fiddle !

 

Well worth changing these critical engine sensors.

 

Also they saw an update during their life and the originals are definitely the older design.

 

What were your INPA fault codes please ?

 

 

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3 hours ago, M5 London said:

Exhaust CPS are easy....intakes are a bit of a fiddle !

 

Well worth changing these critical engine sensors.

 

Also they saw an update during their life and the originals are definitely the older design.

 

What were your INPA fault codes please ?

 

 

Yeah a lot of people say the same, which is why I'm not too bothered that one has gone. Its another job off the list and will hopefully make a useful difference to how the car runs. I have seen a few posts regarding the old ones which appear to have a thinner probe, I am assuming that's what you are referring to?

 

I am getting '8 EVANOS2 - HALL SENSOR' & '113 EVANOS2 REGULATION'. I assume its specifically the exhaust sensor on bank 2? I have never seen either fault before and I tend to read the codes regularly, in fact I did it the day before the check light came on so I'm am pretty confident the two codes relate to each other.

 

I'm also getting '171 SECONDARY AIR VALVE STUCK' which I have had before and from what others say, just basically ignore it and also '143 E-BOX-FAN' again which I have seen once before. That looks like a bit of a sod to fix but I'll look at that in the next few weeks as its very sporadic.

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14 hours ago, Jameswsb said:

Yeah a lot of people say the same, which is why I'm not too bothered that one has gone. Its another job off the list and will hopefully make a useful difference to how the car runs. I have seen a few posts regarding the old ones which appear to have a thinner probe, I am assuming that's what you are referring to?

 

I am getting '8 EVANOS2 - HALL SENSOR' & '113 EVANOS2 REGULATION'. I assume its specifically the exhaust sensor on bank 2? I have never seen either fault before and I tend to read the codes regularly, in fact I did it the day before the check light came on so I'm am pretty confident the two codes relate to each other.

 

I'm also getting '171 SECONDARY AIR VALVE STUCK' which I have had before and from what others say, just basically ignore it and also '143 E-BOX-FAN' again which I have seen once before. That looks like a bit of a sod to fix but I'll look at that in the next few weeks as its very sporadic.

 

I have been off the boil with E39 M5s since about 2012 or so, but from memory those Decimal codes, which translate to Hexadecimal codes of 8 = 08 and 113 = 71, are Intake Camshaft Position Sensor Cyl #5-8  AND Intake Camshaft VANOS position control Cyl #5-8 which suggest to me its more likely a Vanos Solenoid issue rather than a CPS issue.  I think the clue, deep in my memory somewhere, is suggesting if you don't have a code that stated there is a Crankshaft/Camshaft position correlation Cyl #1-4 or #5-8 error, then CPS are ok and look into Vanos Solenoids.

 

Above diagnosis from memory.

 

Having said that if the car is a keeper changing all 4 CPS is a good idea, especially if originals.

 

Vanos solenoids usually need a overhaul, if never touched previously, and are quite easily done.  Solder joints crack and sometimes debris gets stuck in the solenoid oil squirt holes too.

 

Lots of info on all of the above on the famous M5 specialist forum.

 

E Box Fan - Easy replacement part, or have a look at it and service it.  Some people ignore this code.  I wouldn't.

 

Secondary Air Valve Stuck 171 = AB is not as common as Secondary Air system, flow too low code 170 = AA.  I wouldn't worry too much about this for now.

 

 

 

 

 

 

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As above.

 

I would have a vanos test redone after fitting of the CPS as even cars that do not throw codes with old sensors do fall foul of the vanos test. As you say its a very precise test and lazy or old ones will mean the difference between a pass and a fail

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Thanks Guys, helpful as always.

 

I am in a bit of a quandary to be honest as I had a look last night to scope out the CPS job and even after removing the cabin filter boxes and ducts, I have no idea how my spade hands will ever get in there. The guides on M5 board arent that great either as they don't seem to show the wiring that runs just below the back of the plenum. How is this moved out of the way? is it easier just to remove the whole plenum?

 

If it is correct that the solenoids are likely the source of the running fault then I'm tempted to get the vanos units rebuilt for piece of mind. Only issue is that both Phil at CPC and Mr Vanos both reckon that its a good idea to do the chains/tensioners/guides at the same time. Apparently its 'common' for the timing to slip which could be contributing/causing my check light and running fault. In that case i'm looking at a bill of over £2k which I wasnt really budgeting for! 

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Refurbishing the Vanos Solenoids is very straight forward.  

 

No need to remove the VANOS units themselves.  However doing these at some point is wise.  So are the timing guides, tensioner and chain.  So are the rod bearings.

 

I have never heard of VANOS unit self destructing at all so for me there is no urgency with this.  But I have heard of catastrophic damage due to timing guides giving up and also rod bearings being spun....

 

If it was my car I would swap Bank 1 Vanos Solenoid with Bank 2 and see if the codes follow to the next bank. If they do you can follow some online guides to inspect all the solder joints, remove any debris from the failed gauze filters etc and make sure all oil squirters are unblocked.  Then re fit and things should feel a lot better.

 

What's the mileage on the car ?

 

For CPS sensors, the exhaust ones are easier from the top. I did the exhaust CPSs myself and I am no mechanic.  A mini ratchet set is handy as the bolts are quite long from memory and with the limited space you don't want to keep realigning an allen key or similar tool about a 100 times for the required revs....

 

The intakes are easier from underneath, having said that I got Phil to do them for me, and he did the Intakes from the top, but he is a bit of whizz with these cars.

 

 

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Having done this recently, I managed to create a bit more room for doing the intake CPSs from the top by removing a plastic panel right behind the plenum (between the two cabin intake tubes covering the wiper mechanism, sat underneath the middle part of the bonnet seal).  It's held on with a few spring clips.

 

Even with this this out the way though it's a fiddly job.  I can get a picture of what I mean later if needed.

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2 hours ago, M5 London said:

Refurbishing the Vanos Solenoids is very straight forward.  

 

No need to remove the VANOS units themselves.  However doing these at some point is wise.  So are the timing guides, tensioner and chain.  So are the rod bearings.

 

I have never heard of VANOS unit self destructing at all so for me there is no urgency with this.  But I have heard of catastrophic damage due to timing guides giving up and also rod bearings being spun....

 

If it was my car I would swap Bank 1 Vanos Solenoid with Bank 2 and see if the codes follow to the next bank. If they do you can follow some online guides to inspect all the solder joints, remove any debris from the failed gauze filters etc and make sure all oil squirters are unblocked.  Then re fit and things should feel a lot better.

 

What's the mileage on the car ?

 

For CPS sensors, the exhaust ones are easier from the top. I did the exhaust CPSs myself and I am no mechanic.  A mini ratchet set is handy as the bolts are quite long from memory and with the limited space you don't want to keep realigning an allen key or similar tool about a 100 times for the required revs....

 

The intakes are easier from underneath, having said that I got Phil to do them for me, and he did the Intakes from the top, but he is a bit of whizz with these cars.

 

 

I quite fancy the solenoid reseal and clean, looks like a nice job and is within my capabilities. That, along with swapping the CPS's is my preferred course of action simply due to cost and the fact the car has relatively low mileage of 112k. I had scheduled the chains/guides and rod bearings for circa 140k miles as this seems like a safe point for renewal from what I have read. (Jamie's project thread was a good resource on helping me make this decision).

 

However, I am getting paranoid about a noise I get on tick-over when warm which can only be described as a bit of a knock which increases with throttle input for only a few hundred rpm's and then at around 800 totally disappears. My old Alpina B10 V8 also makes this noise and when it was in for a service the tech said he didnt hear anything abnormal so initially I was happy that it was just me being super sensitive and everything was ok. Paranoia has now set in though! Does anyone else get this noise?

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Vanos rattle is very susceptible at low rpms and IMO if its something thats eliminated by about 100rpm i'd say its likely no more than that and nothing to worry about

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