IAT Sensor Problem

cemonderoglu · Post by **cemonderoglu** » 24 Dec 2021, 14:13

Hello, i have some problems with my 1997 light pressure turbo 850. Engine code B5254T. The car starts rough either hot or cold and running permanently rich. I m seeing -40 on my IAT sensor value with two different obd scanners. I checked sensor and socket. I have voltage on socket and my sensor is working. IAT and AAT sensors have same part number, when i plug it for AAT socket i can see the outside temperature on my display. Where should i look? Thanks from now on!!

I recently changed all ignition and fuel delivery parts including ignition coil, also ECT. Nothing changed with my problems, than i checked live data and see -40 for IAT. I think thats the problem, wrong air-fuel mixture.

Post by **misha** » 24 Dec 2021, 15:41

Did you checked FPR...it's vacuum line for fuel in it.There shouldn't be any.
Is it on fuel rail like on t5 models?

Iat shouldn't affect air-fuel mixture that much...but MAF & o2 sensor would.

Also...a bad vacuum leak would do that.

cemonderoglu · Post by **cemonderoglu** » 25 Dec 2021, 10:57

I dont understand what FPR means, i looked up live data on the road, one of the o2 sensor has weird voltages like one second 0.1 and one second 0.6 - 0.7 pulses, i think front o2 sensor is not working properly. I have only one purple vacuum line that comes to vacuum selonoid and goes vacuum tree form there. All the other vacuum tree slots have cap.

Post by **Sveedy** » 25 Dec 2021, 11:18

Misha is saying for you to check you Fuel Pressure Regulator. It has a vacuum hose attached to it. If you pull that hose off, there should not be any fuel in it. I believe the o2 pulses like that when it's working correctly, but someone else can verify that.

Post by **misha** » 25 Dec 2021, 12:49

Sveedy wrote: ↑25 Dec 2021, 11:18 ... I believe the o2 pulses like that when it's working correctly, but someone else can verify that.

Yes...front o2 sensor jumping voltage (up & down)is showing that it's working properly.

cemonderoglu · Post by **cemonderoglu** » 25 Dec 2021, 15:00

Okay, so, o2 sensor is working properly, all the ignition and fuel delivery parts and ECT brand new original parts.

When it comes to MAF, i have the bosch MAF sensor but if i use that MAF, car randomly stalls on the road and not working for 3-5 minutes. So i ordered brand new MAF from FCP Euro (Genuine Volvo as they say). Sensor itself is doesnt look like an original one but it works fine i guess. Random stalls are compeletly gone. So i think MAF is ok.

I suspected IAT because engine starts more normally in the cold weather. Performs more normally until it warms up. Today mechs OBD2 scanner throw 433 rear knock sensor. I have the knock sensors that one socket split to the two sensors.

So, late cranking, running rich, a little shaking i guess(most sensible area is like 1250 rpms when in park) Could all these problems caused by 433 and -40 IAT is normal? Or what should i do or check next?