Ok, I have changed the following bits on my 96 850 turbo:

plugs
plug wires
timing belt
air filter
distributor cap and rotor
lots of vacuum hoses and elbows

My vacuum with the A/C on is about -16, with A/C off is about -19, idle is around 900.

I have not done the PCV yet, I'm 100% sure I need to.

I just did a Seafoam treatment the other day as well.

There are NO codes at all.

If I mash the gas on the highway the car hauls ***. Off the line it is a total dog with smelly exhaust and I get horrible mileage. The computer says I average about 18-19 mpg with mixed (mostly highway) driving.

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What could this be? I'm sort of leaning towards the MAF but I don't want to drop that kind of money on a "maybe" part. I don't think I have any vacuum leaks.

Any help is appreciated!

 

Have you ever replaced your cat?
It could be a clogged cat. The smell and loss of power can be a sign of this.

But to be sure
Make sure the fuel you using doesnt contain Methanol, It will give off a rotten egg smell.

Just to make sure I said Methanol not Ethanol..

 

O2 sensor perhaps too

 

+1 on what shelby said: just because you arent throwing a code for your o2 sensor (yet) it doesnt mean that its functioning 100% as it should. Your vacuum sounds as if it's about where it should be. I'd also look at the cat, as was mentioned. A cat could be causing the issues you're mentioning....but it's odd that it runs well under WOT, because thats normally where you have issues if the cat is bad. Keep us posted!

 

I forgot to add that I did replace the (front) o2 sensor with the correct Bosch unit.

If the cat was bad wouldn't I get excessive backpressure and that would throw off the vacuum readings?

If I had a leak in the intake hose after the MAF, that would throw off the mix and the car would attempt to fix the lean condition by dumping in more fuel - but wouldn't it throw a code?

When I unplug the MAF connector the car should run extremely poorly, right? When I unplug it it throws a code (of course) and then keeps on idling with almost no changes. There is a little hiccup after I pull the plug and then it's almost the same idle.

I will say that every time I have changed out a piece mentioned in my list, the car has improved just a little bit. Whatever I'm doing is helping but it isn't addressing the massive gas consumption.

I have one of those ELM chipset OBD2 scanners, is there some magic software that can peek inside and give me a more accurate idea of what is going on? I also has VOL-FCR but it doesn't do engine codes with my version of Motronic.

 

im having the same problem and im looking to change my thermostat to fix it.

If the car is not at ideal running temp it will run rich.
If its not the thermostat it could be the ?ECT sensor iirc its called.

 

I replaced the thermostat as well. the obd system also says the temp is correct. I don't know if there is another sensor that reports to the ecu but according to my scanner I am at the right temperature.

But you're totally correct, if the engine temp is reported wrong the car will run rich.

 

did you change the sensor right under the thermostat? like i said, i think its the ECT, could be off calibration.

 

haven't changed it yet but the computer thinks the coolant is at the right temperature so I'm not sure I need to.

 

I would take some vacuum readings like this How to Use and Interpret a Vacuum Gauge.

What specific numbers do you have on timing advance, coolant temp and 02 voltage swings?

 

Im no Volvo expert but things that affect fuel trim in any modern car; Mass Air Flow sensor, Engine Coolant Temp Sensor, Throttle position sensor and o2 Sensor. To me it sounds like the car is not entering closed loop. Meaning it is staying in warm up mode and dumping excess fuel.

If you have access to a higher end OBD I would hook it up and check to see if the engine is in fact entering closed loop.

 

Describe the smell your talking about...
Does it smell like fuel of rotten eggs?

 

Ok, here is some more detail: The exhaust smells like unburnt fuel, not the rotten egg smell of a bad cat.

I used my scan tool with Torque on my phone and this is what I got at idle:

Engine Coolant: 83c
RPM: 840
MAF: 5.7g/s
Timing: 6 degrees
Throttle position: 10.6 degrees
Fuel trim: Fluctuates between about -2.3 and +1.8

Idle o2 status is "Closed loop using o2 sensor (feedback fault)
If I rev the engine a bit, "Closed loop using o2 sensor for fuel mix"
and WOT is "Open loop"

The "feedback fault" message seems to imply something is wrong at idle but I'm not sure what it could be. I will try to get updated vacuum measurements tomorrow.

Is it possible that I also need to replace the rear o2 sensor? I know that it primarily verifies the cat's efficiency but I don't know if it does anything with fuel mixture.

 

ding ding ding ding

 

Of course he goes on open loop. Based on the symptoms, that's a given. A million things cause a rich condition.

 

Are you in Canada?

Regardless, your numbers seem fine, which lead me to another point. In addition to the vacuum check I gave you a link for, I would also run fuel pressure checks.

There are threads here lately on how to check 3 things: fuel pump, fuel pressure regulator and Fuel pump relay. You can go to k-jet.org, download the Engine / Basic Tests chapter which describes these fuel tests.

I gotta give you props for answering most of the people's questions. 02 voltage swing reading might tell you more on the feedback issue.

Rear 02 sensor: don't worry about it now. Most DIY can't read that sensor. When it fails, it will definitely let you know. That does not cause a rich condition. My bet is on the fuel pump or relay.