Nistune Forums

Hey guys,

Recently installed Z32 ECU into R33 RB25DET S2,

[*]When i connect both knock sensors up to the ecu (via the solder bridge on pins 23 / 24) the car wont idle or run properly as it runs rich as hell.
[*]Disconnect the bridge (pins 23 / 24) and car starts up perfect and runs fine.

Question is has anyone got a "solved" solution for this?

[*]Anyone tried the SR20 Knock sensors on? Do they fit straight on?
[*]Disabling is an option but they are there for a reason?
[*]Could just run the one knock sensor say (cyl 4,5,6,) but what if something happens on the cyl (1,2,3)?

Ive done a search on this but didnt really come across any real answers.

Cheers

When i connect both knock sensors up to the ecu (via the solder bridge on pins 23 / 24) the car wont idle or run properly as it runs rich as hell.

Does the map highlighting for timing go into the knock maps (fuel highlighting not working in 0.10.6 but fixed for 0.10.7 coming out soon)

Disconnect the bridge (pins 23 / 24) and car starts up perfect and runs fine.

So in this case its only using a single knock sensor

Anyone tried the SR20 Knock sensors on? Do they fit straight on?

RB25 knock sensors are a hose type which screw directly into the block. The SR20 ones are doughnut shaped and have a hole in them and a bolt goes through them. If the bolt is the same size as the RB25 screw in then this should fit but I would need to try the SR20 sensor on my RB30 block (uses same sensor as RB25) to confirm the fit

Disabling is an option but they are there for a reason?

Yes to pull back timing and jump to knock maps when ECU thinks there is knock. Even stock setups sometimes false positives cause the ECU to act on false knock events so the effectiveness of Nissan knock control is debateable

Could just run the one knock sensor say (cyl 4,5,6,) but what if something happens on the cyl (1,2,3)?

It most likely wont be close enough to detect knock on those cylinders

Could just run the one knock sensor say (cyl 4,5,6,) but what if something happens on the cyl (1,2,3)?

It most likely wont be close enough to detect knock on those cylinders[/quote]

if you have to, mount the knock sensor towards the rear of the block.
It's often warmer and more susceptible to knock.

Had a few do something similar where the car drops in the knock maps and gets a massive heartbeat type fuel curve (like a egt heart monitor) even when normal, knock and gear maps are the same. its a bit random though and by disabling the knock sensors the car runs aOK.

Out of curiosity what is the odometer reading for this engine?

bachig24u wrote:Out of curiosity what is the odometer reading for this engine?

105,000?

ok, sometimes the bottom end rods or mains can trigger false knock positives.

I would expect more around the 150,000+ though.

also heard but not witnessed, rocker gear causing issues. generally it would be solid rather than hydraulic unless of course low oil pressure is apparent.

fullboost_r33 wrote:Hey guys,

Recently installed Z32 ECU into R33 RB25DET S2,

[*]When i connect both knock sensors up to the ecu (via the solder bridge on pins 23 / 24) the car wont idle or run properly as it runs rich as hell.
[*]Disconnect the bridge (pins 23 / 24) and car starts up perfect and runs fine.

Cheers

Hi!
I can't think of anything what might cause this, especially since it occurs at idle.
(There is no knock checking at idle)

Is the issue still open?

Put a resistor across the knock sensor inputs and be happy. Enjoy the consistency. Believing that Nissan's knock detection will save your engine is going nowhere good anyway. Thousands of PFC users seem to be pretty happy without knock maps!

I've seen engines where the knock detection actually works well but it only looks at knock in the low RPM range anyway. Did an RB25DE+T the other day (with R32 ECU). Very knock prone, so it was a good test. Knock detection worked perfectly but it really only made a difference in the boost transition area. Once full boost was reached and rpm increased it didn't matter if it was knocking or not cos knock flags were inactive. Guess I could set the knock flags in the higher RPM range but I kinda think Mr. Nissan turned it off for a reason at higher RPM anyway - mechanical noise.

I think the whole knock detection system was designed to save people who accidentally fill up with low octane fuel - hence the main/knock maps sometimes being referred to as premium/regular. In this role it works really well cos knock will happen in the lower RPM range. But once you start dealing with boosted engines, often with high mileage I think all bets are off cos the amount of mechanical noise is far in excess of the original figures.

Add mismatched knock sensors between Z32/R33 and I think we're in a bad place and a couple of 5 cent resistors might be a quick and easy cure.

PL

Good point,

Yes .. the whole knock system was cerainly not designed for tuning purposes but
to save the engine from the occasional tank of low octane fuel in mid-range.

Still it's kinda nice to know that the ECU pulls timing when it thinks there is knock.

Would it be an option to change the knock sensors to Z32 ones (same as RB20?)

PL wrote:Would it be an option to change the knock sensors to Z32 ones (same as RB20?)

For sure - but I don't think they'll physically fit. They're a very different sensor.

PL

RB25 has a bolt with hose type connector on the end (two of these) same as RB20, RB30 and CA18

Z32 VG30 is very similar to SR20 in that it uses the doughnut connector and single knock sensor. I think the bolt size may be smaller than with the RB25 bolt. But havent checked them size by side

PL wrote:Put a resistor across the knock sensor inputs and be happy. Enjoy the consistency. Believing that Nissan's knock detection will save your engine is going nowhere good anyway. Thousands of PFC users seem to be pretty happy without knock maps!

I've seen engines where the knock detection actually works well but it only looks at knock in the low RPM range anyway. Did an RB25DE+T the other day (with R32 ECU). Very knock prone, so it was a good test. Knock detection worked perfectly but it really only made a difference in the boost transition area. Once full boost was reached and rpm increased it didn't matter if it was knocking or not cos knock flags were inactive. Guess I could set the knock flags in the higher RPM range but I kinda think Mr. Nissan turned it off for a reason at higher RPM anyway - mechanical noise.

I think the whole knock detection system was designed to save people who accidentally fill up with low octane fuel - hence the main/knock maps sometimes being referred to as premium/regular. In this role it works really well cos knock will happen in the lower RPM range. But once you start dealing with boosted engines, often with high mileage I think all bets are off cos the amount of mechanical noise is far in excess of the original figures.

Add mismatched knock sensors between Z32/R33 and I think we're in a bad place and a couple of 5 cent resistors might be a quick and easy cure.

PL

The same type of resistor that is said to add for the exhaust temp? I am about to perform this install and just want it to be done right he 1st time.

Also, do you have experience adding a resistor to the knock sensors with a positive outcome?

Thank You.

I was doing some work with this just this week. In the bench you want around 470Kohm resistors to fake out knock sensors on RB20 ECU. I'll have to check what the Z32 ECU wants tonight.

The bottom line is this - all the ECU is looking for is the correct DC voltage on the knock sensor signal wire. A knock sensor is simply an accellerometer. These devices require a DC voltage on the signal line to work. So the ECU supplies a weak DC voltage. The knock sensor is a high impedance device. This basically means it doesn't draw much current at all. But it will pull that weak DC voltage from the ECU down a bit. So what Nissan (JECS) have done is set up their diagnostics to look for the pulled down voltage. If it's not pulled down then they conclude that the knock sensor is either bad or missing, or there's a broken wire - and it will raise a fault code. So it's a pretty simple system.

Actual voltage levels vary between ECU's. Voltage supplied by the ECU for RB20 is around the 7V mark. When knock sensor is connected this gets pulled down to around 3.6 to 3.8V. So to fake out a knock sensor we simply fit a resistor between the knock signal wire and ground. The value of the resistor is chosen simply by adjusting the resistor value until we get our 3.6 to 3.8V. In the case of the RB20 ECU this is around the 470Kohm mark.

SR20's use different values. From memory the ECU supplies 5V to the sensor and it gets pulled down to around 3V, which can be achieved by fitting a 1Megohm resistor. Z32 uses similar knock sensor to SR20, so I'm expecting that they'll need a 1 Megohm resistor too.

I've done this to SR20's many times and it works a treat. Local workshops keep a bag of resistors on hand specifically for this purpose. Yes. It works.

PL

PL wrote:I was doing some work with this just this week. In the bench you want around 470Kohm resistors to fake out knock sensors on RB20 ECU. I'll have to check what the Z32 ECU wants tonight.

The bottom line is this - all the ECU is looking for is the correct DC voltage on the knock sensor signal wire. A knock sensor is simply an accellerometer. These devices require a DC voltage on the signal line to work. So the ECU supplies a weak DC voltage. The knock sensor is a high impedance device. This basically means it doesn't draw much current at all. But it will pull that weak DC voltage from the ECU down a bit. So what Nissan (JECS) have done is set up their diagnostics to look for the pulled down voltage. If it's not pulled down then they conclude that the knock sensor is either bad or missing, or there's a broken wire - and it will raise a fault code. So it's a pretty simple system.

Actual voltage levels vary between ECU's. Voltage supplied by the ECU for RB20 is around the 7V mark. When knock sensor is connected this gets pulled down to around 3.6 to 3.8V. So to fake out a knock sensor we simply fit a resistor between the knock signal wire and ground. The value of the resistor is chosen simply by adjusting the resistor value until we get our 3.6 to 3.8V. In the case of the RB20 ECU this is around the 470Kohm mark.

SR20's use different values. From memory the ECU supplies 5V to the sensor and it gets pulled down to around 3V, which can be achieved by fitting a 1Megohm resistor. Z32 uses similar knock sensor to SR20, so I'm expecting that they'll need a 1 Megohm resistor too.

I've done this to SR20's many times and it works a treat. Local workshops keep a bag of resistors on hand specifically for this purpose. Yes. It works.

PL

Legit!
If you can confirm and let me know which type of ohm resistor im going to need for my z32 ECU running an RB25 that would be great!