High Knock Sensor Output on 1 out of 4... 1

[DonRoss]

Hello, I'm not a regular on this forum but have been spectating...and I couldn't think of a better place to post my problem that perhaps you gentlemen can give a little more insight on.

I am VW enthusiast and about 2 weeks ago I had bent a stock rod on cyl 1 by a 30 psi spike in boost and decided re-build the motor using reinforced internals with Pauter Rods and Wiseco pistons keeping the stock 81mm bore.

Here are some pics...

Cyl 1 piston kissed the crank from bending of the rod...

Here I deglazed the cyl walls for the new pistons...

Here is piston 1, no signs of leaning out or detonation...

This is a pic of it all together...

My appologies on the pics just wanted to give you gents a visual that may help in my problem.

Since the rebuild I have been monitoring my knock voltages and cyl 2 tends to max out @ 30 volts throwing an engine code. The motor has 2 knock sensors one monitoring and located between cyl 1 & 2 and the other 3 & 4. The high knock output happens during partial load at about 3000 rpm between -5 in of mecury and 2 PSI and decreases instantly at full throttle under full load @ 12 psi till about 5000 rpm where it increases again. During that time I hear something resembling a mechanical fluttering noise or vibration. During this time Cyl 1, 3 & 4 are well within spec knock voltage outputs. Timing Correction Factors from timing adavance are at 0...and the spark plugs seem to show no signs of detonation.

-Fuel being used is Sunoco 94 Oct.
-Piston to wall clearance was within spec of 0.0030" tolerance.
-Rod Bearings used were VW OEM and rod-end caps torqued to Pauter's specified torq.
-Air Fuel ratios are between 14.7:1 and 11.5:1

The valve train is also a little noisy...but not sure if the knock sensor would pick-up on that.

I appreciate any comments, suggestions and insight on the matter. Thanks in adavance

Don R

 

[Lou Scannon]

I'm assuming this is the stock knock detection system.
A great deal of effort goes into calibrating their sensitivity and "listening" windows, to avoid extraneous engine noises as much as possible when the system is "listening" for knock. Rebuilding the engine introduces many potential variables that can affect this background noise. You've addressed some of those so you understand where I'm coming from. But if you've introduced a mechanical noise that wasn't there before there is an excellent chance it is being picked up as knock. I wouldn't rule out piston slap with the non-stock, forged pistons.
What to do about this - not much that is practical, unless you find the cause of an abnormal mechanical noise that can be fixed. Recalibrating the knock system is not something that is done in your garage with mechanics tools. You could disconnect that knock sensor and tune for a margin from audible knock - risky in itself! Best advice would be to get on a forum that deals with modified VW engines like yours, and find out what solutions they may have found.

 

[DonRoss]

I appreciate the reply...Yes this is correct it's the stock knock detection system.

I am part of the

http://www.vwvortex

1.8T Technical forum and no one has really come across this before.

I guess really there is no solution other than tricking the ECU with the use of diodes to control the max voltage it will see - but that too becomes a risk.

I am going to further explore the valve train and it's effect on backgorund noises. Perhaps, the cams are a little worn causing slap on the hydraulic lifters allowing the knock sensors to pick up on it. I wouldn't be surprised since the sensors are located just beneath the head.

 

[SMOKEY44211]

This is kind of a long shot guess but is there any possibility that the piston is contacting the head? Does it trigger the code at elevated rpms might be a clue. It appears from the pictures that the wrist pin is full floating. Is the pin bushing within spec? Post your findings when you get it sorted out I'd be curious to know what you found.-------Phil

 

[DonRoss]

Smokey, thanks for the input; at first I thought the same, piston may be hitting the head but at idle or full boost knock is well within spec.

The code is triggered when i'm in part throttle at about 3000 rpm with boost pressure around 0 psi (atm)then it will happen again around 5000 rpm...and you are correct the wrist pin is full floating as were the OEM's. I might have overlooked if whether they were in spec...since the Wiseco Pistons came as piston kit. I'm baffled with this whole ordeal.

I will defenitely keep this updated with my findings.

 

[WilliamH]

Looking at your image of the piston top, even though it is a little out of focus, I would say detonation. The coloration and almost total lack of deposits indicate extreme heat.

With a ten power lens look at the edge of the top land for any loss of aluminum.

Thats my two bits worth.

Will

 

[DonRoss]

William, it would seem that way but I tried to clean the piston top as best I can and almost completely removed the carbon deposits. My appologies for the misleading pic.

Here are some datalogs taken 2 days after the build WOT @ 22 psi. You will note that my knock his high but timing retard is @ 0 and Total Timing advance is at full spec.

Since then I've decreased the boost to a mild 12 psi and knock of course has been reduced but...Cyl 2 is still showing high knock above all the rest even at 12 psi.

 

[magnograil]

Don -
Knock sensor interface chips are looking at the frequency of the ringing caused by knock and not the magnitude of the spike. Check out Texas Instruments TPIC8101 knock sensor interface literature on their web site. You should be looking at the output of the sensor with an oscilloscope triggered by the number two cylinder ignition to get an idea of what is going on.
Any possibility that the intake runner of that cylinder is causing a weak mixture with boost?

 

[Azmio]

Don

By any chance, did you change the engine mount rubber or any other component from the engine. The same engine will require ECU fine tuning if it is shared across several vehicles. The engine seems to pick up different signal to noise ratio with different engine mount configurations.

 

[toytech]

A standalone ecm can be programed to ignore piston slap at light or off throttle, it will also give more of a marginof safety so you can run bigger injectors so they are never near saturation. Also does your intake flow evenly accross the cylinders? some engines notably the 3gte toyota mill in my alltrac has notoriously uneven flow, +13% on #3 not an issue stock, but well who wants stock anyway :^).

 

[DonRoss]

The intake pretty much flows evenly no doubt...I'm thinking it's a valve train issue. The sensors are located just below the head by 1" to 1 1/2" so I'm sure they'd pick up a more than normal noisy valve train.

Still in the midst of diagnosing...

I appreciate the input, thanks.

 

[enginead]

There's no doubt the knock sensors will pick up things like valve train noise, piston slap (almost anything high frequency depending on the calibration). On a recent hot trip I had an engine let go at WOT (due to a miss build of the oil pick up) and subsequently looking at the recording there was a dramatic increase in knock activity ~1s before the oil light came on to signal end of play (it was a further 1s or so before there was anything audible from the drivers seat).

What caused the bent rod in the 1st place (you mentioned a 30psi spike (ow!!) but what caused it)? How confident are you in your boost control and wastegate actuation?

Good luck!

enginead

 

[DonRoss]

The 30 psi spike was caused by the OEM Boost Solenoid unable to control the bigger wastegate actuator. I had overlooked it and when I went for a test drive I got a 30 psi spike in 4th gear at 3200 rpm.

I had the car on the hoist and narrowed it down to piston slap or valve train. The knock values increase in 10in of vacuum and over and above 6000 rpm...but at idle and under partial load they are as quiet as they can be. My experience with piston slap is average thus far I've heard piston slap during idle on other setups and once the pistons get hot they expand enough minimizing slap. I have little experience in knowing if it were to happen on my application where it happens only at 10in Vacuum and in the higher rev ranges.

...confused

 

[Micker747]

Hello DonRoss,

thank you for your post.
I installed Pauter rods in my Golf 1,8T AGU 3 weeks ago, and i am expiriencing the exact same thing! I am still using stock pistons, so i don't think piston slap has anything to do with it.
My best guess is the tolerance in the wrist pins. The original rods have an oil channel going from the main bearing to the wrist pin, keeping a constant oil pressure surrounding the wrist pin. This i would think minimises the tolerance, hence creating less noise.
As i only changed the rods, this is the only variabel i can think of.
Did you solve your mistery??

Best regards from Denmark

 

[DonRoss]

Micker,

Since this post I have put about 6200 miles on the motor & have no more major knock sensor issues...Still a litle higher than normal off-boost between 3500-4500 rpm but good overall being a rebuilt motor.

-I have changed my SW from REVO BT to Unitronic BT.
-I now use 5W-40 oil with a quart of Lucas Oil Stablizer.
-Seems to get better and better as I work in the motor.

It just maybe a simple issue of working in the motor properly.

Thanks for posting your findings. Please keep this posted.

Don