850 Turbo, Auto 106k

I am at my wits end. For the last months, I have been getting these codes 131 and 137 (low o2 sensor volatage front and rear. I clear the codes and they always come back within 50 to 150 miles.

I have recently replaced both sensors with generic four wire sensors.

I used a scan tool that has graphiing capabilities the o2 sensor garph shows a reading of .25 to .90 with good wave forms.odes

All other systems such as the Mass Air Flow Sensor, Throttle Position Sensor are all OK.

I have inspected and replaced most vacume lines and installed a new intake manifold gasket. I have an after market boost gauge which shows reasonable vacume 16-17 at idle (rock solid no flickering)

I replaced the fuel filter, plugs, air filter and dist cap and air filter.

Did at least three Seafoam Treatments through the vacume T.

I tested the fuel pressure regulator (most likely a bad regulator would make the engine run rich anyway.

I have no other codes and no driveabilty issues. Starts easy and no rough idle or any other issue.

I did do a fuel pressure test and have about 30 lbs at idle.

I did install a brand new Bosal Cat which is supposedly high flow but I don't see how that would be because the tight bend in the header pipe.


I have only two thoughts: The generic o2 sensors? but if they were not functioning they would not show such a healthy wave form on the scan tool.

My second thought is perhaps the fuel pressure at 30 lbs is indicative of an aging fuel pump and it may not be delivering enough fuel when the engine is under load thus triggering the lean ( low o2 signal)

Any ideas would be greatly appreciated.

One stumped dunce

 

30 pounds of fuel pressure seems a little light. Most fuel injected cars run between 40 and 50 psi at the rail. Volvo specs for a turbo call for 43.5 psi.

I think (not positive) that the 850 have an additional pressure tap at the input to the fuel filter, might be a fun experiment to see if the pressure is vastly different at the filter compared to the rail.

Low pressure may not be your only problem, but it might be a problem.

 

Hmm...
DTC 131: Code 1-3-1 (RPM Sensor Signal Absent)
and can't find DTC 1-3-7??
or are these abbreviated P codes?

My initial thoughts were same as yours:

1. If you search this site you will note a lot of folks have had problems with non-OEM generic O2 sensors. Just bite the bullet and buy the Bosch OEM sensors.
2. Yes, fuel pressure is low; see below for further diag from manual.

Fuel Pressure
1) Before disconnecting, cover fuel line connector using shop
towel to absorb any fuel spray. Connect Fuel Pressure Gauge (5011)
between fuel line and fuel rail. Seal free end of hose using Plug
(5266) or use Fuel Drainage Unit (981 2270, 2273 and 2282).
2) Lift cover on central electrical unit located in engine
compartment and remove fuel pump relay. See Fig. 1.
3) Connect a jumper wire between relay terminals No. 1 and 3.
See Fig. 2.
4) Turn ignition on. Fuel pump should start. Fuel filler
cover can be removed to determine whether main pump is operating. Fuel
pressure should be about 43.5 psi (3.06 kg/cm ). If pressure is too
low, pinch return hose by hand and check whether pressure rises. DO
NOT allow pressure to exceed 86 psi (6 kg/cm ).
5) If pressure rises rapidly, pump and lines are okay.
Replace pressure regulator and recheck line pressure. If pressure
rises slowly, fuel filter, fuel pump strainer or fuel lines are
blocked. If pressure does not rise, fuel pump is probably faulty.

 

About 32-35 PSI at idle is normal. Under boost it should be around 50 PSI or so.

I am fighting a WAY to rich issue right now(To high of fuel pressure) 40 PSI at idle and 63 PSI at full boost.

But the 850's actually Volvo's for that matter HATE generic O2 sensors.

 

Have to take Tech's word for it that approx 33 psi at idle is normal; i have not ckd it myself.

Note in the diag from the manual, the engine is NOT running; only the fuel pump is running with everything else static; i.e. the injectors should all be closed. With the engine idling the injectors are opening periodically and you also have engine vacuum activating the fuel pressure regulator; both will drop the fuel pressure in the rail.

Tech; about your too high pressure; sure sounds like pressure regulator, yes?

BTW: Also agree w/tech about O2 sensors; volvos are very finicky when it comes to that!

 

Everything in the fuel system is new!

 

what about bosch universal o2's?

 

Wow; that's weird... what about a restricted fuel return line? Let us know what you find...

 

Nope I think the high pressure might not be much to worry about actually.
I think my intercooler might be leaking under boost.

 

what about Bosch universal o2's?....

 

NO the cars hate them as well.