ECT reads high when running ?

So Microsquirt with a PNP kit from Kenny.

Installed a few weeks ago and everything has been working as expected, ECT reads as it should be expected.

All of a sudden I am getting ECT temps around 40-60deg higher than normal, After going over the entire cooling system and validating on another car the stock guage is reading correct and the cooling system is working as it should, it turns out MS is getting the higher temps only when the car is running. If the igntion is off then the ECT / MS reads the correct setting but as soon as the car starts coolant temps jump from 190ish to 250-290ish.


Any idea's on where to start checking for issues with the microsquirt. While it sure sounds like a grounding issue nothng has changed since it has been running for the last few weeks and this issue just popped up out of no where on Friday.

Thank you
Mike

If the igntion is off then the ECT / MS reads the correct setting but as soon as the car starts coolant temps jump from 190ish to 250-290ish.

Click to expand...

I am curious as to how you are reading a temperature via MS with the ignition off. Do you mean ignition on, engine running versus not running? If that is the case, then depending on how you have set up the ground connections I would first be looking for something in the fuel pump circuit or the ignition circuit creating a ground offset. If nothing pans out there I would then check your alternator / charging ground connections.

On my B20E, the D jet coolant sensor has a resistance of around 100 ohms at 100 C. The programmed in R vs T curve is approaching asymptotic at that point which means that small changes in sensor resistance or the voltage measured across the sensor cause big changes in the temperature that MS calculates. A small offset in the sensor ground reference can have a similar big change in the calculated temperature. Ground offsets might always be present; but, because of the highly non linear sensor curve shape, the offset error may be insignificant when the engine is cold, only becoming apparent when the sensor becomes hot.

Are you running an electrically isolated 2 wire temperature sensor? In order to affect the temperature sensor, ground offsets have to appear in the ground path for the temperature sensor. If the sensor has an isolated ground back to the MS terminal connector, ground offsets that raise the complete MS ground plane will not change the temperature reading. With a 2 wire sensor, in order to skew the temperature reading with a ground offset you would have to have an insulation failure on the wiring to the sensor to create that offset. If you are running a one wire sensor with ground return through the engine anything is possible. In addition to checking the sensor wiring, check the terminal plug.

If you have a pre 1988 Volvo and are using the original engine harness wiring for the temperature sensor I would examine the wiring carefully because of the known failure problem with pre 1988 wiring harnesses.

I'm with ^^^^ Mike. If it's something with the engine running vs. not, I'd suspect either a failed ground somewhere or some type of offset. The stock 2.4 sensor has a dual pin sensor, both sides should match pretty close. Maybe see what the resistance does at the ECU, see if that resistance is changing or not, as that could clue you in to something setup in MS vs a sensor/wiring issue.

That is what I meant, ign on but not running vs running.

Sounds like I need to chase down some grounds to figure it out or switch to a GM sensor and run its own ground wire.

1995 945t so newer harness but you never know with these cars. I know I moved a few things around interior wise as I relocated my WB but it is using all of the same wiring it was before.

thelostartof said:

I know I moved a few things around interior wise as I relocated my WB but it is using all of the same wiring it was before.

Click to expand...

Be careful with the WB02 wiring - the better ones have separate +12v/Ground wires for heater power and another set for sensor power. The heater power turns on and off rapidly (PWM) to maintain a fixed temperature. If you wire the heater +12v/Ground into the MS sensors, it will generate a bunch of noise. Does the WB02 turn on with the key or the fuel pump? If it's the key, turn the key on but don't start, and let the WB02 warm up. After warmup, is the CLT still OK?

You may be able to turn off BattV filtering in MS and see some noise in the MS logs. A labscope on +12v at the MS box, or on ECT at the MS box, would show if you have noise problems.

So it looks like I might of solved some of my issue in the dark tonight, relocated a ground for MS from the drivers side fender to the engine block under the old injector grounds (ECU gounds). So now my ECT reads 215 or so when running, I didn't get a chance to double check the key on not running temp but I will do that tomorrow. I was to distraced by the s/c 928 we just got running on MS, now we need to figure out the igniton side of things and this thing is going to really move.

Thanks for all of the tips, Now I have much more of an idea on how I want to clean up some of this wiring and go over it in the future to resolve more of these issues.

I thought my old B230FT had a threaded fitting on the aluminum intake manifold specifically as a ground point with a braided flex connection to the firewall. Perhaps I am imagining things. I know my B20E definitely has a treaded fitting for the D jet grounds on the intake manifold.

Issue resolved, I had grounded one of the sensor ground wires that was left with the LH plug and then I had one of my MS grounds going to my wideband wire that grounded to the frame. I moved this to the body and it got better, so next I ran a new wire for MS and left that at the block and moved the wideband back to the fender. This causes my afrs to be off by 1 point. So I moved the WB ground back to the block on top of the MS ground and now my ECT is reading in the 180-190 range as I would expect and WB gauge matches MS reading.

Thank you.

I suspect that bad grounds have messed up (and continue to mess up) a lot of MS retrofits. You probably have a lot of company.

Consider applying some Gardner Bender Ox-gard between the bolted ground connections. Its available from Home Depot (and other places) for about $4 for a 1 ounce tube. It is a zinc bearing grease which improves the electrical conductivity when pressed between metal surfaces (clamped between the grounding lugs). You can apply it to the outside of the ground connection for corrosion protection; but, that does nothing for improved conductivity. It needs to be applied between metal surfaces under pressure for it to do its magic.