How important is knock sensor torque?

[gmac78]

Evening all,

As a lot of you are aware i have recently converted my 3B to RS2 spec with ABY ECU, TFSI coils etc, there have been many trials and tribulations along the way but one that is annoying me is the lack of full boost on both VStream and TS chips. Both are rated for 1.9 bar but i only seem to get 1.7 bar.

I'm starting to to run out of ideas for why i'm not quite getting full boost as i have no obvious leaks up to 2bar, F96 Altitude sensor has been tweaked to read correctly, timing is spot on, running 97ron which is the best i can get on the island, certainly never had any issues with it on the previous homefry. MAF and N75 are relatively new with very little miles on them, MFTS has ben unplugged which made no difference. G62 coolant sensor new, IAT sensor working ok.

About the only sensors which i haven't replaced are the knock sensor but have never got a code for them.

I have in the past had them off to inspect them and noticed the plastic outer casing to be cracked but since they never gave me any other i just fitted them back to the block.

However, i don't remember tightening them to a specific torque, rather just a good nip for the size of the bolt.

What effect would an under or over torque bolt have on boost? If in fact any? Perhaps clutching at straws with this one but got to rule them. I read somewhere that the timing is pulled but no sure about boost?

Not sure what my loss of 0.2 bar equates to in power but i'm sure i would notice the difference.

Any ideas?

Cheers

[LHD_Kid]

As far as I know faults with knock sensors won't throw codes - didn't on mine anyway... any damage, replace...

Torque is critical - Edit 20Nm - thanks Error404...

[gmac78]

So how did you know they were faulty? What was the symptoms?

[LHD_Kid]

So how did you know they were faulty? What was the symptoms?

I didn't have a boost gauge at the time - it just felt a little flat... was almost a last resort, removed one, it looked fine, removed the other and the shielding was breaking down, close to the sensor end.

I replaced both and it's mojo returned...

[gmac78]

Now that is interesting, I really am struggling now to figure out what is causing this reduction in boost. Most annoying!! Hopefully others who have had boost gauges and knock sensor issues can shed a bit of light as to whether boost is in fact reduced. Not so easy to get at them on a 3B but hopefully i can get a torque wrench on them to correctly tighten.

[Error404]

20nm and yes it is important. For the cost I would just replace them both, they are 20+ years old now.
I had an issue with one last year, the wire core was broken down inside, invisible from the outside. Would cause intermittent open circuit and Motronic would cut boost control. New Bosch replacements at about £40 each
If the sensor is falsely reporting knock then there will be no codes, I would guess the ECU will pull boost and timing and add fuel.

[UrS4boy]

G61 and G66 Knock Sensor info

As far as I know faults with knock sensors won't throw codes - didn't on mine anyway... any damage, replace...

Well they should throw a code.

This is what the Bentley says about the AAN knock sensors (electrically the same as ABY and ADU):

From the C4 UrS Robert Bentley manual, pg. J28-27:

"The knock sensors cannot be checked electrically. Check DTC memory => Repair Group 01. For satisfactory function of the knock sensors, exact compliance with the tightening torque of 20 Nm (15 lb ft) is important. Check the harness connection from knock sensor to wiring harness for corrosion".

If there are knock sensor problems, you might get at check engine light (CEL) (aka DTC light) with these codes:

*2141 (Blink Fault Code), 00535 VAG1551/2 Fault Code Number
Knock regulator #1
Excessive knock, timing is being retarded by maximum amount,
Symptom: Low boost on 20V, Fuel octane too low, Excessive Compression, excessive boost

*2142 (Blink Fault Code), 00524 VAG1551/2 Fault Code Number
Knock sensor #1 (G61)
Open or short circuit, Defective sensor Check sensor and wiring
Symptom: Timing retarded, High fuel consumption, power loss, Boost pressure not attained

*2143 (Blink Fault Code),00536 VAG1551/2 Fault Code Number
Knock sensor #2, (Cylinders 3, 4, 5)
Excessive knock, timing is being retarded by maximum amount.
Symptom: Fuel octane too low, Excessive Compression, excessive boost

*2144 (Blink Fault Code), 00540 VAG1551/2 Fault Code Number
Knock Sensor #2, (G66) (Cylinders 3, 4, 5)
Open or short circuit, Defective sensor or wiring
Symptom: Timing retarded, High fuel consumption, power loss, Boost pressure not attained

REFERENCE: Knock Sensors (click on the label in this live diagram

http://members.shaw.ca/ajmills/UrS%20Engine%20Bay%20Device%20Map.html

[gmac78]

New sensors ordered so i'll see how i get on with them. Sometimes when giving it WOT the boost climbs straight up to 1.7bar and kind of flickers around that level until it naturally starts tapering off, however sometimes the boost climbs in an erratic manner where it will climb up to around 1.5 bar, pause, drop back 0.1 bar then up to 1.7bar. Something is going on behind the scenes to be causing this. It's strange because when i had refitted the original DV the wrong way round and eventually tore the diaphragm, i was seeing 1.7 bar then too. I really thought with a new DV fitted in the correct orientation that i would see the 1.9 bar i should be getting. However, there are still gremlins in the system somewhere!!!

[macspring]

Also interested to see your results with the new knock sensors, and their current cost.

Notwithstanding the current issue, and the hassle and cost of doing the upgrade, I presume the car is much better as RS2+ than it was a S2+ ? Would welcome your thoughts.

Thanks.

[gmac78]

I ordered the Bosch Knock sensors from this company for £72 delivered

http://www.bestpartstore.co.uk

There has been several issues along the way since venturing out on the RS2 conversion but i have no regrets to be fair, the power it has now is far more than previous and in all honesty the RS2 turbo is not as "laggy or slow to spool" which ever term you prefer to use, as i had thought it would be. Perhaps a little less snappy than the normal homefry low down but there is not much in it.

Don't hesitate if your thinking about upgrading, get it done!!!

I read somewhere on the forum that a loss of 0.1 bar boost equates to roughly 20bhp, if there is any truth in that i am 40bhp or so down. Yet i am still smiling with the upgrade!!!