Spartan 3 showing over lean figures

Spartan 3
1

Hi there all.

I had bought a Spartan 3 controller, 4.9 sensor.

Up until today it has been running the Honda Goldwing flat six in my Hillman Imp absolutely fine.

But this morning I started the car up and the gauge read 16.6 for about 5 seconds, then read what I’d usually see as a reading for this time of year (New Zealand summer) on warm up enrichment, say in the 13s. It showed that for about 3 seconds then went straight to 19.9.

At first I thought it might be the ‘Just Race Parts’ gauge playing up. I turned off the engine and started it again. Same scenario.

So I got my laptop out, plugged it in and checked the afr readings on tunerstudio. Exactly the same readings as the gauge.

Engine was warming up fine, off the fuel map as there is no afr correction until 70 degrees or below 1300 rpm.

I have tried several starts. Always the same scenario.

I checked the earths and they are fine. No air leaks. Exhaust is fine. Sensor is mounted in the recommended distance from head, at about 9 oclock angle (edit -not 9 oclock. More like 10.30. No chance of condensation forming on it anyway :grinning_face: )

I disabled afr correction and went for a drive, the car now running soley off the existing fuel map. Its fine in use but the gauge constantly reads randomely. Sometimes it’ll just sit on say 15.2 no matter what I do then change to another figure etc etc.

But whenever I stop the car and re-start it it goes through that same scenario. Reads around 16, then drops to whatever I would expect to see at idle for a about 3 seconds (pretty much idles nicely around lambda) and then ramps up to 19.9 again.

I’m not sure what to do next. Its been so good up until now and I bought this unit due to supposedly robust reliability. Btw - I bought this unit through the approved supplier ‘Just Race Parts’ in Australia because I figured they are closer in both distance and time for any potential issues. I have contacted them first by email but no reply yet. I’ll keep trying.

Annoyingly (sods law…) I’m just over 2 months out of the 2 year warranty I think is offered with these controllers but I’m really hoping that if its a fault within the unit I’ll get looked after.

I have had this setup running absolutely fine for 1.5 years now and clocked up over 5000km.

For those interested this is my engine setup its helping to run..

Hopefully I can get this sorted :slight_smile:

Cheers,

Alex

2

Oh and sensor location is just before the silencer..

3

If you are getting the proper calibration voltages during startup, the problem is likely the sensor.

4

Hey Alan,

A day after I’d posted my questions up on here Aaron from Just race parts replied to my email. I went through the first tests he asked me to do. I’ll paste in the results I’d copied into his email below..

So while the vehicle is off, turn on the Spartan & the gauge, check for 13.3 AFR on the screen, followed by 16.7 AFR and then once you go to live readings you should then see 20 AFR on the screen. If you see any major variations to these let me know, if you see something like 13.2, 16.6 etc this is not a big deal, we are looking for anything more than about 0.2 AFR out and this will be something we need to check.

Please report your results here…

13.3

16.6

15

You should also check the voltages coming out of Terminal 6 on the Spartan 3 which is the wideband analog output, this is the terminal that also runs off to the gauge / ecu, this will require a multi meter and what you are looking for just after you first apply power to the Spartan 3 is 1.666v (13.3AFR), followed by 3.333v (16.7AFR) before going to live readings which with the vehicle off will be 5v (20AFR)

Please report your results here…

1.66v

3.32v

Then for the last one it has random figures each time I try - like 2.49v, 3.4v, 3.2v etc etc. Not even close to 5v.

5

So you can see the first two calibration figures look correct. But that final figure, not even close to 5 volts - does that suggest the sensor has failed or is it a spartan issue?

I had also removed the senor, powered it up and it started to heat up. Took maybe 30 seconds to get quite warm.

I then hung the sensor upside down and run neat gas from a butane torch into the end. It certainly didn’t drop down to 0 as it should according to Aarons email.

Cheers

alex

6

after the 1.66 and 3.33 signal, the output will usually be ~2.35v until the sensor heats up and starts reading free air, 5v. When the sensor is cold it will read stoich, ~2.35v

7

Hey Alan,

OK. With the sensor removed from the exhaust and the spartan powered up how long should it take to heat up fully and give the above figure? I can try the test again. Is there anyway it can be forced to do a recalibration if needed (as per the old free air calibration I was used to doing on the older innovate products* with the 4.2 sensors)

I’m having to power up the spartan with a separate feed to do these tests because it’s normally got it’s power feed from the same relay that the ms3 turns on - so avoiding the chance the sensor could be left turned on and heating up well before actually starting the engine. However from what I’ve read the spartan 3 canbus will only start heating the sensor up when it receives can signals from the ms3 to state the engine is actually running - if this is correct then I shouldn’t ever have any issues with thermal shock caused by moisture in the exhaust. Is this correct?

Cheers

Alex

*mtxl setup that was not very accurate or reliable… Hence I’m here.

8

I downloaded termite onto my laptop. Powered up the spartan and left it to heat up for 5 minutes and it was showing around 15 on the gauge as it heated up - this was while I was still trying to connect the laptop up.

I turned the spartan off, sorted the laptop connection out and turned the spartan back on. This time it stayed on 16.7 the whole time. After 5 minutes I performed a DOCAL - twice because we were not sure if it worked first time round or what we should see. I couldn’t get it to screenshot but fortunately I took a photo of the result..

20260120_133314
20260120_1333141920×1056 276 KB

Can you make anything from the above info? I cant..

I will refit the sensor and try the car again. I’m still not entirely convinced the sensor is the fault due to the randomness of the readings? Or is this just what happens when they fail. The failures I had with the 4.2 sensors on my old innovate mtxl setup was a consistent reading of 20 on the gauge and nothing else.

9

This morning the sensor was reading 13.3, 16.6 and then went to 20 and sat on that for as log as it was on. I thought great, maybe its ok now. That’s what its meant to show. refitted sensor and started the car up. once past the first two calibration figures it just went to 19.9 and sat there. No change.

Boo. Not fixed.

10

Did your problems start to happen after you did a free air calibration?

You should do a “RESETCAL” command. Your free air calibration value is way too high.

11

No the problems began before I tried the free air calibration. I just thought I’d give a FAC a go to see if it might have been the issue.

I’ll do a RESETCAL, cross my fingers and report back with the findings…

12

I performed a RESETCAL…

Screenshot 2026-01-21 185753
Screenshot 2026-01-21 1857531046×689 92.7 KB

Back to the same issues I started with. I have taken a short video..

Not sure what to do next. Just order a sensor and try that I guess. Annoying its only lasted this long though :frowning: I feel I’ve done everything by the book and its been absolutely fine until now.

13

It is most likely a sensor issue.

14

Yeah I’m going with that for now. I’ve already ordered a new sensor. I’ll report back.

Question - how long does it take from being turned on for the sensor to get hot enough to potentially get damaged from thermal shock from the likes of condensation in the exhaust etc? 3 seconds? 5 seconds? 15 seconds? Certainly when it’s in my hands heating it takes a good 30 seconds to feel any exterior warmth.

15

Update. Brand new genuine Bosch 4.9lsu installed and it so far seems to be working fine.

However, as I am still on FW1.04 I cant access the optional GETSLOWHEAT settings only available on FW1.05

As per this thread..

I am having the same issues. The black screen disappears as soon as I enter the port number.

16

Any ideas on how to fix this? Or start a new thread and hope someone sees it…

I’d really like to update the controller but looks like there’s some sort of bug/firmware issue that wont allow it and I have only found out now when trying to boot load.

anyone