So is my MAF,NAFF or is it my MATH?

[Corvr6 0]

This post has been edited due to hindsight

I have noticed a missfire since my Head gasket/timing chain tensioners replacement carried out by Stealth,I'm not pointing fingers I just want to fix the problem. 8)

 

My Ignition leads were arcing at the plugs,so these have been replaced.

The coilpack looks ok,and is not arcing under a mist of water.

The thermostat was sticking open,so this has been replaced.

Checked Temperature coolant sensor(steady reduction in resistance as temp rises)

ECU Reset.

Once up to operating temp (+80'C) I can pull the MAF connector and she carries on idling after a tiny increase in revs,but doesn't cut out.

 

Incorrect Method :oops:

Lamda sensor unplugged!

With the MAF connector replaced, the Lamda Sensor reads 600-900 mv when idling,and 900 mv at any other rev range.The supply voltage is 14v.

If allowed to idle again the voltage starts to drop only fractionaly,eg,after 10 seconds of idle voltage would still be +850 mv.

Incorrect Method :oops:

I pulled the plug out of the socket to do this reading,should have measured it with the plug still in :oops:

 

Correct method; 8)

1)Supply voltage present.

2)Connector must stay connected and multimeter probe should be inserted into the top of the connector on the signal terminal(The terminal that is isolated from the others).

Then the reading should cycle from 0-1v on anything but full throttle or high RPM

Full throttle/high RPM reading should be a steady voltage between 700-900mv

Correct method; 8)

 

Following test wasn't relevant after realising my mistake :oops:

If I disconnect the Lamda sensor connector and the MAF, the voltage drops very quickly to less than 100 mv from 900mv in about 15 seconds and the engine is trying to stall,so I reconnect the MAF and the revs come back up at the same speed along with the voltage.

 

So can't really ask this question either

Does this suggest conclusively that the MAF is faulty,I presume that the Lamda sensor is doing what it should? :?:

 

Always do this first

If not then I will find a garage with VAG-COM and get the errors read,and proceed from there. 8)

 

I have just read in the manual before reading the DTC the following should be carried out;

 

Perform a test drive of at least 10 minutes during which:

 

1)Coolant temperature must exceed 80'C(176'F) for 3 minutes minimum.

 

2)The accelerator pedal must be completely floored breifly at a speed in excess of 4600 RPM.

 

3)There must be acceleration at half throttle for approx.4 seconds in 4th gear from a speed of roughly 30 mph.

[stormseeker 0]

It really is MAF month this month so far isn't it :-)

 

I think the conclusive answer is that your MAF might be OK, or it might not!

 

Best to get VAG-COM, clear the DTCs (cos you''ll have thrown some disconnecting MAF/OXS etc.) or just reset the ECU if VAG-COM isn't available, drive the car for a few hours/days and then get the ECU diagnosed and start from there :-)

 

Sorry can't be more helpful ;-)

[Corvr6 0]

It seems to me that just about any one or more major sensor can be faulty giving rise to missfires/flat spots/lumpy idling and the ECU will mask the problem with a slightly less than perfect style of performance. :mad:

Without VAG COM (OR EXPERIENCE) to tell you conclusively which one it is, a trial and error approach to sensor changeouts would be very costly/frustrating and foolish IMO. :wink:

Therefore I am "off to see the wizard" at my local VAG. :)

They have offered me a free quick download,or£40 ish for a detailed printout. 8)

 

I will update this post on the findings.

[dr_mat 0]

I wish my local place would offer me a "free quick download"...

They wanted to book it in (in three days!!) and do the full treatment...

[Corvr6 0]

I was surprised too,as I have not used them yet for service,maybe these are the breadcrumbs of enticement,a new ploy to bring in business,maybe they already know whats wrong with my car.

[Corvr6 0]

To follow up after my visit to my local VAG,"No fault recognised" was what it said on the printout.

Now it was quick and free so I shouldn't grumble,but I have to say I am disapointed if only because I still don't have a definitive answer. :(

 

From what I can gather It does mean I only have few things now that may be the culprit,but its finding the one that is proving difficult without spending mega bucks.

 

I believe my list has been narrowed down to these; :?

 

MAF Sensor(Could still be working but out of calibration/range)

Coilpack(Could have faulty circuitry)

Air intake leaks(How do you test for these?)

Compression leaks(don't really want to go there!yet!)

 

To reiterate my symptoms of the misfire is like this;

 

Idle(cold or warm) misfires

Cruising(any rpm) misfires

Afterrun/deceleration misfires

Accelaration up to about 3000 RPM,usual vr6 reluctance,could be misfiring.

Acceleration after 3500 RPM Normal,no misfires,full power.

 

Anybody?

[dr_mat 0]

Wonder if the timing has been checked? Could be that your timing chains have slipped a tooth?

But then I'd have thought you'd notice a lack of power at high revs too...

Puzzler indeed!

You *are* running it on good petrol we take it, a good couple of tank fulls of optimax/bp ultimate quality?

Misfiring can be down to poor valve seal or holes in the valves, or so I've heard. This is obviously something you don't really wanna mess with until you're sure it's not something else...

[Corvr6 0]

Stealth carried out the following last month

 

Valve guides/seals replaced

Valves reseated/replaced as nescessary,

cam followers replaced,

gasket and reskim I presume.

Timing chains and tensioners replaced.

Clutch replaced

 

I am sure their work is good,because of the reccomendations they've had,and after speaking to Vince he suggests trying to eliminate the MAF and coilpack before worrying about compressions.

I've been told a tooth out on the timing would give terrible driving and its no where near that.

Always optimax :)

 

I did manage to get my hands on a "repaired" coilpack but one of the lugs was glued on at an angle making it hard to put the lead on and another lug was all cracked,really need known workers to be sure.

 

Vince has offered to help, so I suppose that's my next step. 8)

[Kevin Bacon 5]

Can you just confirm you have a proper misfire, i.e. like it's running on 4 or 5 cylinders and stinking of fuel? If it's just a hesitancy/jerkiness, it'll be the MAF, but if it's a proper misfire (i.e no spark) then it'll be the Coilpack.

 

K

[johnxl1s 0]

where is the maf,what does it look like.

[Kevin Bacon 5]

where is the maf,what does it look like.

 

It's bolted to the airbox lid and has an electrical connection on it.

[Corvr6 0]

To reiterate my symptoms of the misfire is like this;

 

Idle(cold or warm) misfires

Cruising(any rpm below about 3000RPM) misfires

Afterrun/deceleration misfires

Accelaration up to about 3000 RPM,usual vr6 reluctance,could be misfiring.

Acceleration after 3500 RPM Normal,no misfires,full power.

 

I should point out it is an ocasional miss not every cycle it seems.No smell of fuel.

 

I have been back to Stealth today and there was an error In the DTC when I got there (as its a 75 mile journey for me),

Lamda sensor, Intermittant signal fault. :shock:

(Hadn't occoured in the 3 X 30 MIN driving sessions I put in after I reset my ECM and before taking it to my local VAG) :mad:

But then after checking the sensor it performed flawlessly,just couldn't fault it. :?

Whilst we were waiting for a replacement part to arrive just to be on the safe side,Vince eliminated the other possible major causes Coilpack,MAF Sensor,spark plugs,compression tests. :)

 

After fitting the Lamda sensor and taking it for a test drive,the missing is still there,although the throttle seems more responsive. :?

 

Other possible causes will be a little more involving and means leaving it with Stealth for a few days to do there magic. :wink:

 

Another test for the MAF sensor is to see if the filament is actually working at all.

You can do this by lifting the top of the air filter cover and looking down the intake tube.

It requires 2 people,someone to switch off the ignition and someone to look down the pipe.

Run the car for a minute or 2,then switch off,the filament in the MAF Sensor should glow orange for a fraction of a second,to burn off crap etc.

This is not a conclusive test as the filament may still light up and be faulty in some other way.

[Corvr6 0]

Well then,this would have had most people stumped i think,as my missfire is now cured. :D

 

Eliminated or replaced the following;

 

Spark plugs(Replaced)

Leads,(Replaced)

Coilpack,

Lamda sensor,(Replaced)

Coolant sensor,

MAF sensor,

Fuel filter,(Replaced)

Air filter(Replaced)

Fuel injectors,

Compression tests passed,

Leak down tests passed,

Camshaft position sensor(Replaced)

Possible twisted Camshaft(Replaced)

 

The cure came after the last 2 items were replaced,the possible twisted camshaft is apparently rare but can occour after removal due to the high Torque setting of the camshaft bolt.

 

What ever the cause was is now history and the VR has never been smoother,all thanks to Vince and the lads at Stealth Racing.They may be a couple of hours drive from me but I would rather take my VR there,knowing its in experienced hands. 8)

 

Oh, and Stealth done a professional job fitting my oil cooler,which is a must if you want your oil doing what its supposed to when chasing cruising along side that 5 series. :roll:

[stormseeker 0]

 

Spark plugs(Replaced)

Leads,(Replaced)

Lamda sensor,(Replaced)

Fuel filter,(Replaced)

Air filter(Replaced)

Camshaft position sensor(Replaced)

Possible twisted Camshaft(Replaced)

 

 

Sounds a touch heavy on the wallet?

 

Glad you've got it sorted! ;-) :-)

[Corvr6 0]

Stealth warranted the camshaft replacement and labour,I just paid for the other parts that were replaced as most had good reason for replacement anyhow. :)

 

I now know what its like to drive a VR that is truly running in its prime,if your VR does not make the hairs on your neck stand up when you floor it,then at least one of the above parts is faulty,fix it,and you will understand what owning a VR should really feel like. :D :D :D :wink:

[Kevin Bacon 5]

How much was the cam and which bank's cam had twisted, or were both alignment marks off? It's more common than Stealth are letting on....

 

Just wondering if one of mine is in the same way as I too have replaced just about everything and the engine still isn't quite right.....might get Vince to give it a leak-down test. If it fails that, the car's going in the Autotrader!

 

K

[Corvr6 0]

Well the miss is back,or it has become noticeable again. :x

It never really went completely at idle anyway,and I think I was trying to convince myself it had gone completely as it was really undetectable when I left Stealth's last Thursday.

The agreement was to run the car untill the problem becomes "gradually worse enough" to start to point to a particular component fault or does the opposite and starts to fade away.

It definatley is less noticeable than before,but is still there.Not noticeable at all when running the car hard,max power is still there,only really at idle and throttling off and a touch when cruising at about 2K rpm.

I think both cams were exchanged,there was no "test" as such done to measure the "twist" as far as I am aware,it was just an exchange to see if the fault cleared up.

Not sure I know what you mean when refering to alignment marks,but there was no mention of timing issues,as I understand the fault would have been far more noticeable if timing was out due to chains/sprockets.

I wander if moisture is playing a part with a connector somewhere,when I get it garaged in a couple of weeks,gonna get a hairdryer on all the connectors..... :wink:

 

How can you think of parting with it,when its running tip top it really is stunningly quick,and the best looking car on the road today imho. 8)

I think a programmable chip might be on the cards to iron out some of the roughness/hesitancy below 3500 rpm,getting the torque at lower rpms is what the VR is crying out for. :evil:

[Bruno 4]

....timing chain tensioners replacement carried out...

 

I think you got it at the beginning of the sentence. Have u checked that the CAM sensors were correctly realigned? Its dead easy to get it wrong.

[Kevin Bacon 5]

How can you think of parting with it,when its running tip top it really is stunningly quick,and the best looking car on the road today imho. 8)

I think a programmable chip might be on the cards to iron out some of the roughness/hesitancy below 3500 rpm,getting the torque at lower rpms is what the VR is crying out for. :evil:

 

A simple thing called "diminishing returns" mate :wink:

 

Mine hunts at 2K aswell, which I'm confident is the MAF, despite being on my 3rd one. I live with it as I'm not at 2K at part throttle for long enough for it to be a real nuiscance.

 

VRs always lump around a bit at idle, they always did, even when new....but it seems to be the 2.9 that suffers the most, and from premature bore wear. The 2.8 always the better engine.....

 

Did you change the throttle position sensor?

 

You can adjust the idle a bit by altering the adaption values with VAG-COM, perhaps speeding it up slightly will smooth it off a bit?

 

Cam wheels - if the shaft twists enough, it will throw out the mechanical AND electrical timing....but you'd feel it, no question. Plenty of bumpstarts, regular redlining and mis-shifts are contributing factors.....

[Corvr6 0]

No, haven't changed the TPS,don't really understand why I would? :?

The more I listen to the engine at idle the more it seems like its just a lumpy idle,with the occasional miss. :?

It's more lumpier at idle when cold than when warm,and the miss is more noticeable when the engine's not at load,and like you said we don't really care at these speeds as long as its fine everywhere else,which it seems to be for me. :)

I've never gotten any real throttle response below 3000rpm,but always get full power above 3500rpm when I floor it,nothing less than "stunning". 8)

[Kevin Bacon 5]

No, haven't changed the TPS,don't really understand why I would? :?

The more I listen to the engine at idle the more it seems like its just a lumpy idle,with the occasional miss. :?

It's more lumpier at idle when cold than when warm,and the miss is more noticeable when the engine's not at load,and like you said we don't really care at these speeds as long as its fine everywhere else,which it seems to be for me. :)

I've never gotten any real throttle response below 3000rpm,but always get full power above 3500rpm when I floor it,nothing less than "stunning". 8)

 

Mate, that's just the way VR6s are......

 

As for the TPS, well it controls your fuelling, that's why you should consider changing it if you're getting weird hunting and flatspots..... They consist of electrical contacts moving around an arc of carbon tracks, which wear with age. The angles and resistance of the TPS control fuelling, idle and over-run shut off, so it's a key component.

 

To be fair, they last for ages but at around 100K, replacement should be considered. They cost £40 from VW.

 

K

[dr_mat 0]

This is the problem. There's so many things that "last about 100k" on these cars that I wish I'd held out and got a low mileage one.

[Kevin Bacon 5]

Bought mine with 73K on it Matt and have been replacing bits left, right and centre ever since! Corrados are Corrados, I don't think mileage, unless it's exceptionally low, excludes it from problems!