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1G EU ecu in a US car, knock sensor problem

whereturbo

Probationary Member
6
1
Nov 5, 2021
Marl, Europe
So last week I noticed that the car I've been working on for almost half a year, has a very distinct problem.
After a huge hustle, trying to get my car to start, because my ecu randomly died and the only viable option being a manual switch to ground the MFI relay to get everything to kind of work again, I checked for CEL codes and see there: code 31 for knock sensors in a US N/T.
After a quick research I learned that my ecu might be from an EU N/T model because apparently they came with a knock sensor. I am from Germany, the car is an import.

My questions are now:
Could this be the reason for high emissions and idle? Two weeks ago, I failed the emissions test and my idle is at around 1500. I read something about a limp mode, but I'm not sure if manual transmission models had it.
Is there a way to trick the ecu into thinking that there is a knock sensor without having to buy one.
 
Solution
Well, I figured it out myself. I found a YouTube video of a fellow member, who tested various frequencies.
I picked a frequency with no knock count, taught myself how to model a square wave and wrote some Arduino code that generated the wave with the wanted frequency. If anyone wants the Arduino code, just let me know.

whereturbo

Probationary Member
6
1
Nov 5, 2021
Marl, Europe
Well, I figured it out myself. I found a YouTube video of a fellow member, who tested various frequencies.
I picked a frequency with no knock count, taught myself how to model a square wave and wrote some Arduino code that generated the wave with the wanted frequency. If anyone wants the Arduino code, just let me know.
 
Solution

1990TSIAWDTALON

Moderator
9,845
5,711
Nov 14, 2013
Independence, Kansas
But will the sensor do what it is meant to do if you coded it to a no knock frequency? It is used to pull timing if you have bad gas or too much boost, etc.
 

We're on Boost

15+ Year Contributor
1,624
446
Aug 25, 2007
Seattle area, Washington
Well, I figured it out myself. I found a YouTube video of a fellow member, who tested various frequencies.
I picked a frequency with no knock count, taught myself how to model a square wave and wrote some Arduino code that generated the wave with the wanted frequency. If anyone wants the Arduino code, just let me know.

That's pretty cool!
It will be interesting to hear if it changes the emissions result or the idle speed or anything else.

If you at some point want to put a proper knock sensor on there, the situation for 1g knock sensors is a little iffy lately.
We've had some threads in here lately about that, with some proposed solutions. One as I remember is a sensor that is correct except for the length of the wires on it (need to be longer).
If you ever got into trying one of the other sensors that are much more available but electrical correctness is questionable, I might be able to help a little. I have logs made with an ecu+ piggyback on an otherwise stock car with a new OEM knock sensor on it. In the logs there are graphs for knock sensor voltage and for "knock sum" at the same time. No frequency info though. But the voltage graph I think is accurate and is sampled 25 times per second.
 
Last edited:

1990TSIAWDTALON

Moderator
9,845
5,711
Nov 14, 2013
Independence, Kansas
GVR4 sensor for a replacement on a 1g. Shorter pigtail is all.
 
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