Strange noise especially at low rpms...

[C-24]

Hi,

I noticed a strange kind of sound/noise when I start in first gear, maybe it's also noticeable in second gear. You can also hear it in neutral.
Its the kind of sound that reminds me of a car that overheats (you know when you drive in town, when traffic is jammed and you engage first gear and put some gas, the car behaves like a big truck, it has a lazy sound, like the rpms take time to rise and fall down again and you hear that noise "WOoooo" ?), but the thing is this happens in cold or hot weather, there is no difference if I just started the car (when it's cold) or when it has warmed up after a while, I always get the same sound.

So this is not the sound of the turbos! Let's say you're in neutral, you press the gas pedal slightly to make rpms rise up to 1'300-1'600rpms and you almost can't hear the engine sound of the V6, only that "Woooooo".

I have the feeling that if, let's say, I'm in second gear and accelerate moderately until 4'000-4'500rpms and put my foot down at that moment, the car doesn't seem to accelerate faster or stronger, it just continues it's way at the same pace until 7k.

Do you have any idea of what may be the issue here ?

Cheers,

Andy

[Blue_Thunder]

Viscous coupling siezed on the fan?

[C-24]

Viscous coupling siezed on the fan?

I have changed the viscous thing (dont really know how you say it in english) recently, and its possible that this sound has been noticeable since then.
.
so should it be seized or not?can it affect performance? thanks for your help maybe that is the issue.

[C-24]

If this is an important detail I can move the fan freely when the car is cold, engine off...

[Blue_Thunder]

If you can move it freely when cold then it should be ok.

If it was seized it would definitely sap power because the engine would have to turn the fan constantly.

[C-24]

thank you blue thunder.

It is possible that I'm getting too hard on that car... it has only a remap but not 400 or 500hp... Everybody says the car is a "monster" ... Where I live fuel has low octane so I got to add octane booster (which I didn't do these days and maybe that's why I think it's going slow)...

Is there some measurements I may take with vag-com that may indicate if the car is really going 100% how it should ? Because I don't feel like testing it's top speed right now.

Thanks again!

[Blue_Thunder]

Measuring the FATS time is a good indication of performance, but you'll need to take it up to at least 90mph.

A change of fuel wouldn't cause a noise at idle though. Can you get a friend to rev the car a little whilst you listen in the engine bay?

[C-24]

I did it today, what kind of sound should I be seeking for ? If you're thinking about the pistons in the cylinders making a "click" noise, I think there isn't any.

Okay I will do a FATS time test as soon as possible, I prefer this than hitting top speed. But even though I changed the MAF and some other things, the car can hardly even hit 7k rpms in 5th IIRC... so I will check it.

[C-24]

I've got some interesting news. Those who read my posts in the past probably know I have had issues with Limp mode, turbo leak, throttle body problem, gas pedal...

Then, I changed everything, even the MAF so I thought everything is perfect right, probably because an experienced mechanic installed the new MAF.

I did some FATS tests, here are the results :

On the MRC website it gave me 8seconds (or even 8.5 it was getting worse each following times I did the FATS, did it 3 times).

1# test
0.3 seconds @ 4'200rpms, MAF 234.47 g/s
8.63 sec @ 6'520rpms, MAF 264.72 g/s
9.37 sec @ 6'680rpms, MAF 265.44 g/s

2# test
0.3 seconds @ 4'080rpms, MAF 165.72 g/s
9.33 sec @ 6'560rpms, MAF 205.58 g/s

3# test
0.91 sec @ 4'080rpms, MAF 154.64 g/s (wow getting pretty strong there :p)
10.28 sec @ 6'520rpms, MAF 204.47 g/s (this is 1.65seconds slowlier than at the first test!)

So, the car is really getting slowlier each time you WOT for a prolonged time (those 3 tests were done with about 2minutes pause between them and I was driving at low rpms to make the car recover before next WOT).

When you start the car, let it warm up, drive a mile and hit the gas pedal it runs like a monster, but after 2 or 3 accelerations it's over, so no need to explain further why I can't go more than 260kph (on a private road), because even if the 0 to 160 is excellent, the car begins to struggle after 180-210kph.

I checked the MAF with a friend of mine and it happens that, indeed it's in great condition, but badly sealed, there is air escaping between the air intake and the MAF (it's fixed with one of those israeli plastic belts, not with OEM parts).

Then we had the idea to unplug the MAF and try again... Yes the car runs GREAT, but same thing, after 2 or 3 hard accelerations power is gone. It's empty.

Should I just seal the MAF correctly then ?

[C-24]

We put the air filter out... it's dirty and seems that air can't go through... so will change it and see what happens.

Do we all have such problems ? I love those cars, the RS4, and the others, almost perfect, but the quality of engineering in the electronical compartiment doesn't seem to be top notch on the B5!

On the other hand, my K03 are perfect... Thanks god!

[Blue_Thunder]

If the airfilter was totally clogged, you wouldn't be getting a MAF reading of 265 on the first run.

Even with a decent MAF reading your FATS times still sound 2-3 seconds off the pace for a remapped car.

It could very well be because the engine is pulling back due to the fuel being used, but the slower subsequent FATS sounds like some other issue. And the fact you say there is a noise at idle suggests something other than just a dodgy sensor.

I guess you've checked for error codes?

[C-24]

Yes, I checked the error codes (not these days) but I didn't drive the car for a while and the problem is there since a long time.

I will do it tomorrow just in case.

But the noise at idle seems to be normal (I will try to record it).

We put a new filter, set the MAF correctly and it still can't get more than 250kph...

I don't thing adding octane would do a miracle, because while driving in switzerland (I had it there since the beginning) where fuel is excellent, it didn't change much. And fuel shouldn't be an issue because before it really could go more than 280kph on the clock with "bad" fuel.

[C-24]

I checked everything, and concerning the engine data, the following faults appeared :

18084 - EPC Warning Lamp (K132) Circuit : Electrical Malfunction
P1676 - 35-00

17965 - Charge Pressure Control : Positive Deviation
P1557- 35-00

17777 - Cylinder 5 Ignition Circuit : Short to Ground
P1369 - 35-10 - Intermittent

16486 - MAF sensor (G70) : Signal too low
P0102 - 35-10 - Intermittent

When I would erase the faults, the EPC 18084 fault remained, the others went away. But after a while they would all come back again. I unplugged the MAF but the same errors appeared.

I also checked the level of duty of the N75 valves, seems to be okay.

How may I fix this ?

[C-24]

Should I check the Coolant temperature sensor, O2 Sensor, wiring of the EPC circuit ? Where is the charge pressure control device ?

Thanks

[Dippy]

My best guess is that you have indeed identified the problem which is an air-leak after the MAF. This could explain the noise, the low MAF reading (air is getting sucked in after the MAF, so less going through it), and possibly the positive charge pressure deviation, if the leak is enough to affect the air recirculation control.

However I don't think it answers the 17777 DTC and you should check that circuit.

I am unsure though, since you don't have a 'running lean' DTC. However if your leak is intermittent, maybe periods of correct mixture explain why it is absent (and also why the occasional run and MAF reading were good).

Just my guess, but you really do need to avoid any air leaks with these engines.