Jump to content

Bit of advice on Megasquirt temp sensor prob's

Recommended Posts

Sorry boys if this is in the wrong section again but I have tried searching but couldn't find if this has already been posted or asked before.

My newly rebuilt 4 litre'ish is running so rich it's unbeliavable it's actually popping on tick-over there's so much fuel up the exhaust,

The triggers wheels bang on, it's a new cam chain etc, so I'm convinced it's down to settings, it was basically crank grind and new rings and a good clean up following a sump full of gritty water so nothings really changed much.

The MAP on tickover's roughly 50Kpa, everything looks bang on, its starting OK but running stoopid rich and I have also loaded a nice easy 3.9 map of Nige to do an event the other weekend, loads of power and response but thirsty and you can smell and see it at the rear end plus its spitting flames at times when its had a good burst of pedal, so whats wrong?

My observations and suspicitions are temp senders/sensors, the cars been stood for a week in the garage (no sunlight blinds are always down, and no heating), so temp is pretty constant, turn on laptop and power up ECU (not started engine or turned over) water is 18*C, air is 8*C, I would of expected them to very similar.

So next move was to change air ATA1010 and now were up to 12*C, so today we go and get a Intermotor water sender ETC8496 and it says 22*C, now bearing in mind these are cold readings but if they are so far out at rest in a cold garage and with my trusty fish tank thermometer indicating that the ATA1010 is not a million miles out what diffence is this going to make to the final map and fuelling, a lot I suspect especially when cold. But if the Megasquirt thinks the engines hotter than it is and the airs colder than it is surely it will fuel to this.

The big problem is this motor is stricktly off road and datalogging is a real pain but a nice mild 3.9 map shouldn't be letting it run so rich.

I also disable the O2 sensor because of it dipping in water a lot at Challenges, and yes its still rich when warm to.

So what do the guru's think, everything to me looks about right on the screen and the only thing that is blatantly obviously wrong is the temps but the water warms up and roughly agrees with a seperate capillery fed water temp gauge and the fuel pressure is also set at 38psi.

Thanks lads

Link to comment
Share on other sites

I wouldn't read too much into temperature sensor readings, they're not laser-accurate so as long as they're ball-park and go up and down with engine/air temp you can probably assume they're working OK.

If it's pig rich then try knocking the REQ_FUEL value down by ~10% at a time until it seems to be closer to running right. If the sensor readings are OK and there's nothing funny with the TPS (EG always triggering ACCEL) or O2 correction there's not much it can be other than the map is set to put too much fuel in.

Link to comment
Share on other sites

To make it run that rich on a known fuel map suspect CTS Sensor.

These do die esp when "Dunked"

Also check lamda is working prop when tuning - if in doubt just e-mail me a log xls file

other than the above suspect would then be jammed injector which would cause havoc,

or PRV overpressuring fuel rail giving injectors too much pressure to close



Link to comment
Share on other sites

Fridge, your dead right there, the reading on megatune and the mechanical temp gauge agree with one another when warming up and running at operating temp, this is also further backed up by the fan temp switch which is again a seperate.

I do like the theory behind the TPS because I have changed that for a "better" one and metered it though to make sure there were no deadspots but do recall reading somewhere that there is a high and low reading that it should be kept between, and last night I couldn't find this info or remember where I'd seen it. I think it was something like 20 - 218 or similaar.

Can I see when stationary if its triggering the ACCEL easy enough, I can't recall from memory.

Nige, I tested the injectors recently for flow, spray and drips and they were fine but will unplug them and do a basic "in situ" test to see if one is stuck open or similar, I do have an adjustable fuel pressure regulator with a gauge on so I can observe that the pressure is constant and more or less where it should be, and I have (just in case a new CTS and ATS).

What I don't have because they don't seem to last 10 minutes for me is a working O2 sensor although I have a brand new 4 wire Bosch one ready if need be that could be connected for datalogging at a playday or something similar, but I have disabled the adjustment %.

Thanks again lads


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy