Technical Air temp 50 deg C?

[red]

Hi,

Having hooked up to the ECU on a '53 Punto, the main error shown was engine temp sensor, fatal error. I has suspected this before because the cooling fan sometimes came on with the engine cold (ECU thinking the engine is too hot?). Had a clean around the connector and measured the resistance to 3.33k, which is about right for a cold engine, based on the spec. in the Haynes manual. Ran the prog again, started the engine (though this was a struggle, several attempts needed) and watched a graph of engine temperature as it warmed up. Went back round to the engine and realised I had not put the sensor connector back on yet! So how come the ECU was seeing a warming up when the temp sensor was not connected? (some sort of default action?) It is definitely the right connector; green in colour, LHS of inlet manifold, two pins with resistance measured as stated above. Anyway, reconnected it and tried again. Temperature continued to increase and steadied off at around 82 deg C.

Thinking that was OK, I decided to look at some other parameters because the engine still seems to be not right (struggling to start). The one that was glaringly incorrect was air temp, showing as 50 deg C. However, there is no error shown, probably because it's OK to have an air temperature this high if you happen to be in Death Valley, USA. Snag is, I am in th UK in March and I'd say it was cool outside, no more than 10-12 deg C.

Do I have a problem Houston? I removed and inspected the manifold pressure/temp sensor and it looks OK but haven't tested it yet. I suppose two of the four pins go to the thermistor and I could check resistance but I don't have any reference to compare to.

red

 

[DaveMcT]

If the ECU thinks the ambient air temperature is 50C it wont be feeding a rich fuel mixture when you start the car so when cold it will be hard to get it going. Check that sensor and its contact resistance.

 

[red]

I'm going round in circles a bit with this one (other symptoms that don't fit with the diagnosis) but will in due course test the sensor resistance at various temperatures to assess its condition.

red

 

[scoop987]

The ECU will know by the O2 sensor (Lambda Sensor). Thats what controls the fuel injection.

 

[red]

Update.

Have had the air temp / map sensor off and checked resistance (thermistor is connected between pins 1 and 2). It seemed reasonable value. I cleaned the contacts and put it back. Reader still shows a static 46 deg C before starting the engine.

The strange thing is that the coolant temp sensor was showing as 56 deg C when cold (cold as in left overnight). I set up to record data for a whole journey (about 3 miles). The air temp stayed at 45/46 deg C. The coolant flipped between 56 and 41 deg C three or four times, settling at 41 deg C then climbing at a regular but slow rate to 47 deg C. After that it climbed faster up to operating temperature of about 80 deg C. I could see the points at which the thermostat opened and closed, which seemed normal. The ECU recorded an error for coolant sensor.

On my return journey, I recorded data again. Air temp was 46/47 deg C throughout. Coolant temp this time started at 22 deg C and climbed in a normal fashion to about 80 deg C.

My next step may be to put resistors of various value across the socket for the air temp sensor to prove that the ECU is OK in that respect.

I don't know why I'm getting varying results from the coolant sensor. There's no good reason for it to give erroneous output at lower temperatures then to behave when hotter.

For either sensor, if there was a connection issue (high resistance), wouldn't that report as cooler than real, rather than hotter?

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[arc]

dodgy loom earth?

 

[T14086]

software update for 'difficult starting' for your age of punto if not already done.

 

[red]

Arc,

I'm gunning for the earths next.

T14086,

Can you elaborate on the software update, e.g.
Could I do it myself, and if so, where would I get the file and what gear would I need?
Is it something that can be messed up and make things worse? (like doing BIOS on a PC)
Would it account for my strange readings for both temp sensors?

Meanwhile, I'll check the software version next time I'm hooked up to the ECU.

red

 

[T14086]

dealer only (examiner + subscription)