97' 850 LPT Running Rich

[cemonderoglu]

Hello, i own a 97 Volvo 850 2.5T (LPT), engine code B5254T, chassis number is YV1LW5666V2319656. My problems are these

1. Running rich
2. Poor acceleration (especially when its warmed up)
3. Late cranking
4. IAT shows -40 (i dont know sensor location, in front bumper driver side i think?? i have two temp sensor here black socket is AAT but i dont know the other blue socket)

I replaced litteraly everything about fuel delivery and ignition. Here is the list;

Spark plugs and wires, cap, rotor, ignition coil and wire, all filters, fuel pump and relay, fuel pressure damper (i have it w/o vacuum line)

Also replaced MAF, barometric pressure sensor, crankshaft position sensor, PCV, ECT, coolant fan temperature switch... and my o2 sensors tested, working properly

The car still runs rich, OBD scanner only shows EFI-433 rear knock sensor but i think its because of running rich problem. I m getting hopeless about the problem. I cant solve these since last summer. Anyone have any idea about where should i look next ??

[Chuck W]

The blue-plugged sensor should be your IAT. How does that connector look?

Have you checked the FP regulator? Should be down low behind the engine.

[cemonderoglu]

Connector was damaged, replaced with new connector but nothing changed. If the blue connector is my IAT than i think something gone wrong with wiring or worse ECM. As i know FPR mounted to fuel rail between fourth and fifth injectors (i assume driver side injector is first). Unlike T-5's my FPR does not work with vacuum line, i replaced that part (part number 1275658) but nothing changed.

If the blue plug is my IAT, i dont understand how it estimates my intake air temperature and why it shares same place with AAT but two seperate sensors?

Thank you so much for your reply.

[Chuck W]

The piece on the fuel rail is the damper, not the pressure regulator. The pressure regulator is down low behind the engine, like I mentioned.



There is no temp sensor in the air inlet. One of those sensors is for the ECC (Climate controls) and the other the ECU (Engine management). Separate wiring for separate systems.

[cemonderoglu]

Thanks for information about regulator-damper difference. I will check this part.

If we come to the gray and blue socket temp sensors, as i understand, the gray one is AAT and its for ECC and dashboard temp, the blue socket is IAT and its for ECU and it has some role in air-fuel mixture. Please correct me if i am wrong. I am sorry for asking again but im confused with these two sensors.

Obviously i have some issue with IAT but i dont have any error codes in OBD for this. Is it normal ?

Last question, is there a special way to check FP regulator's health ?

[Chuck W]

The IAT is referred to as the "Outer Air Temperature Sensor" for the ECU, and yes you have the general understanding correct of the function of those sensors.

That sensor may not throw a code, but if it's registering -40* there is most likely a problem with it. If you unplug it and test it, what do you get? What if you jumper the plug?

[erikv11]

... Last question, is there a special way to check FP regulator's health ?

One thing you can look at is the vacuum line that connects to the FPR. If the vacuum line smells very strongly of fuel, then the FPR is damaged internally and leaking fuel into the vacuum system. This is not a complete test of the FPR but it is one easy thing to check for. If the vacuum line contains fuel that can affect the fuel trims.

Another thing to do is test fuel pressure directly at the fuel rail with the car running.

[cemonderoglu]

Here is the updates,

We decided to replace knock sensor. hardly found one and replaced it. Engine power is increased after the replacement and EFI-433 rear knock sensor code is gone. Also checked FPR's health it is in great condition.

So, our misfire-like little shakes, poor fuel economy and late cranking problems (especially when its hot, for example, after 1 hour drive i turned off the car and it waited like 10 minutes,in this scenario cranking takes like 3-5 seconds, by the way it is so much better at cold starts) are still on the table. Also serious shaking in steering wheel between 100-150 km/h.

I havent done anything about IAT, it still shows -40. To be honest, i dont sure about what should i see, as Chuck says it is "Outer Air Temperature" for ECM, maybe it works and only dont show the ambient temperature as IAT?? Should i see the ambient temperature as my IAT???

I will replace crank sensor next week and i will share an update about it. Thanks a lot for the all your helps.

Edit: Crank sensor replaced, nothing changed...