So I started having an issue over the last couple weeks where my boost controller would intermittently toggle on and off during a pull. Ended up finding today that my CLT reading in TS was violently oscillating within a 40*F window at full throttle, sometimes dropping below my 175*F minimum CLT requirement for boost control to enable.

I cleaned the ground on my valve cover and added another ground between the valve cover and firewall and the CLT reading shows no noise or abnormal fluctuation anymore.

Shoutout for bringing this to light. Even before it started affecting my boost control, the CLT fluctuations were probably messing with my fueling. Did you ever end up messing with or adding grounds?

 

Kind of, but not really? I tried adding a ground wire from the IM to some sensors I had grounded to the chassis in the cabin, but that didn't seem to make much of a difference to anything.

I basically changed the filtering value in tuner studio to make the coolant sensor less responsive. IIRC the recommended value is 180 out of 240. I had changed it a few times, but never ran it that high. That caused the values to look a lot more like what I'd expect.

Having said that, I did drain my coolant recently and saw more aggressive temp spikes at autocross today. I thought I bled the system well, but I think I need to give it another pass.

 

Fair ‘nuff. Yeah, ruling out bubbles first is probably the move.

You’ve got me curious about what my CLT filtering looks like now, though. I’ll check my settings next time I take my car out.

 

I should also note that while I had my ducting in place the factory belly pan/undertray was off the car. I removed it when replacing the turbo and bushings and did not get it back on the car before autocross. That was likely a large contributor to the cooling behavior this past weekend as well.

The course was also quite punishing from a cooling perspective. Two sections where I was on limiter for a couple seconds but shifting didn't make sense. Everywhere else was pretty much part throttle at mid/high RPM.

 

Isolating RPM vs CLT shows a pretty strong correlation. This is from last week. The temperature trends upward through the run, which I'm not surprised by, but the spikes that follow RPM are what I'm hoping to eliminate at some point.

 

For what it's worth I found the same thing on my NB1. Added an aftermarket temp gauge because I wanted more of a warning than the stock gauge on track. Starting at about 185F (which I believe is the 3rd reference point on the 3 point calibration) TS and the aftermarket gauge start to deviate. Not quite 20F in my case (still on the factory temp sensor), but the hotter it gets the higher the deviation. Interestingly enough, my factory temp gauge doesn't hit the normal operating point until the aftermarket is reading close to 205-210F. I don't know which one to believe, but the aftermarket stays below 230F on track so I'm just not going to worry about it.

 

Late to the conversation here.
When you turned off the filtering the CLT trace showed really significant digitization noise. The filtering hides that, but does not change it. So your sensor analog output signal is very poorly matched to the A to D converter (ADC) in the ECU. This can cause errors in the quality of calibration, and increased sensitivity to ground noise.
Do you have any way to change the gain on the analog input of the sensor, or to change the input signal to digitization range on the ADC? For example, selecting a 1 V per 1024 bit range instead of a 5 V per 1024 bit range.
It probably does not explain your problem, but better quality digitization, (more bits per analog signal range) could reduce sensitivity to ground noise.

 

@Icedawg I agree, the filtering is just a Band-Aid, but doesn't address the issue.

I personally don't have a way (or know how to) adjust the gain of the input. For the time being I'm just going to crank the filtering and move on to other projects around the car. It's an annoyance but I feel like I understand the behavior well enough to write it off as "accepted behavior" for now. At some point I think I'll move on to a different ECU, and I'll be interested to see if this behavior lingers or disappears.

 

I think thats normal if your turbo is watercooled. Here is my log and it acts just like yours. In boost it goes up and when I let off it goes down

 

@frastydragon Just curious, what ECU are you running?

 

ms2pnp

 

What year harness?

 

Me? Mines a 1992

 

Try disconnecting the factory black/green ground eyelet by the back of the manifold, and take another log. There’s two eyelets, if the car doesn’t start, you disconnected the wrong eyelet.

 

Will that smooth out the coolant temp? and ill do that in a few

 

Curly mentioned it earlier in the thread, but apparently the early NA's had 2 wires (grounds?) on the coolant sensor. Removing one of those grounds results in smoother coolant readings that don't track RPM.

So yes, removing that ground could smooth out your temperature readings.