850r failing emissions miserably (HC and CO) Topic is solved

[JayPea44]

Well apart from the money, if you don't know how old they are, it is a worthwhile Stage 0 service to replace the O2 sensors, at least the upstream one if not both. Make sure they are genuine Bosch parts and not copies. So careful where you source them from!

If you don't have any junkyards near you where you can pull a MAF, let me know the Bosch or Volvo part number and I can see if I have a used one. They cost me around $60 CDN ($45 US) these days at the junkyard. Maybe there is someone south of the border that has one they can loan for testing or sell you. Shipping is way cheaper south of the border.

Neil.

Thanks. I think I’ll end up replacing almost every consumable part on this car at some point as it’s intended to be a restoration, so all sensors will get replaced. I’m just trying to get it through its inspection to get plates.

I did have a peak at the MAF I couldn’t see for sure but it did look like a 107 number at the end. But I’ll pop it off and make sure. I’ve seen them on IPD and yeah, 200 and something for a genuine Volvo MAF. o2 is a 100 odd.

I’ll let you know if I can’t find one at the pull and pay around here.

[JayPea44]

OK another update - I got a vacuum gauge and tested my vacuum, I was getting 15 inhg vacuum before I replace my TCV vacuum lines and now it's slightly lower, between 14 and 15, after replacing them. I also inspected and swapped out some worn-looking elbows but everything else looks relatively decent. I also did the "spray brake cleaner around all the connections to see if the idle changes" trick and it didn't budge.

So my question is, is that a normal reading? The needle is solid and doesn't move at all at idle, and to me, that seems like a decent reading for an engine this old that is also turbo'd (but I don't know - also bearing in mind I'm a mile above sea level). A little bit of googling tells me anything over 14 is "normal" on these, but not sure if I can trust that. Also, if it is a little low would a leak this small really put my emissions readings so high?

I'm starting to think I'm chasing my tail on this vacuum leak and thinking it's more a sensor, probably the o2 or MAF. (I had an old classic mini that had a bad MAP sensor and it ran rich as a pig which is making me think this is sensor related..)

Any input is greatly appreciated.

On both my 98 T5s, I usually get around 16-17 mmHg at cold start idle, then around 21 mmHg at hot idle. But I'm also much closer to sea level.

Can you read voltage for the O2 sensors? Or MAF data on your scan tool? Would help more with diagnosis if it is indeed a sensor issue.

I definitely could read voltages. The front sensor doesn’t seem too hard to access. And I think my scanner reads MAF data.

Any idea what I should be looking for in both cases? Thanks.

[wizechatmgr]

The one thick power connector with the gray end looked like it was to an aux. air pump for cold starts. That also has a vac purge line I think that hooks under the battery tray if I am remembering correctly. I've got a 98 base NA as one of my cars so, may or may not be the same on the 850. The other possibility is that's to the radiator fan, but I don't think it would go that far down from where it should be without some cutting of the harness. The round one I believe is for the oil pressure sensor, but don't quote me on it. @Abscate may have pictures from when I had my engine out. I'll look though mine.

Oil pressure sensor:

oilpressure.PNG (1.77 MiB) Viewed 344 times

[WhatAmIDoing]

OK another update - I got a vacuum gauge and tested my vacuum, I was getting 15 inhg vacuum before I replace my TCV vacuum lines and now it's slightly lower, between 14 and 15, after replacing them. I also inspected and swapped out some worn-looking elbows but everything else looks relatively decent. I also did the "spray brake cleaner around all the connections to see if the idle changes" trick and it didn't budge.

So my question is, is that a normal reading? The needle is solid and doesn't move at all at idle, and to me, that seems like a decent reading for an engine this old that is also turbo'd (but I don't know - also bearing in mind I'm a mile above sea level). A little bit of googling tells me anything over 14 is "normal" on these, but not sure if I can trust that. Also, if it is a little low would a leak this small really put my emissions readings so high?

I'm starting to think I'm chasing my tail on this vacuum leak and thinking it's more a sensor, probably the o2 or MAF. (I had an old classic mini that had a bad MAP sensor and it ran rich as a pig which is making me think this is sensor related..)

Any input is greatly appreciated.

On both my 98 T5s, I usually get around 16-17 mmHg at cold start idle, then around 21 mmHg at hot idle. But I'm also much closer to sea level.

Can you read voltage for the O2 sensors? Or MAF data on your scan tool? Would help more with diagnosis if it is indeed a sensor issue.

I definitely could read voltages. The front sensor doesn’t seem too hard to access. And I think my scanner reads MAF data.

Any idea what I should be looking for in both cases? Thanks.

I'm not sure what the spec values are for either, but for the O2 sensor voltage should jump around a bit at idle and especially when opening the throttle. What it should not do is just read a constant voltage or jump between a high and low voltage of identical numbers. Especially if it's jumping between 0 and whatever max is. The air flow rate for the MAF should be very constant at hot idle (because the throttle isn't moving obviously). The ECU knows what the voltage should be at the upstream O2 based on what the MAF is reading (I think that's how it works). If there is a big disagreement, then it will run too rich (usually) or too lean trying to compensate.

This is a big untested hypothesis on my part: if you unplug the O2 sensors, it should force the ECU to run off the preprogrammed fuel tables. If it runs better, then that may be the issue. May also have to unplug the MAF. Obviously don't drive it like that for too long. But you seemed to indicate that it doesn't run poorly, so without having them test the exhaust gases I don't know you would gain any useful info.

[JayPea44]

On both my 98 T5s, I usually get around 16-17 mmHg at cold start idle, then around 21 mmHg at hot idle. But I'm also much closer to sea level.

Can you read voltage for the O2 sensors? Or MAF data on your scan tool? Would help more with diagnosis if it is indeed a sensor issue.

I definitely could read voltages. The front sensor doesn’t seem too hard to access. And I think my scanner reads MAF data.

Any idea what I should be looking for in both cases? Thanks.

I'm not sure what the spec values are for either, but for the O2 sensor voltage should jump around a bit at idle and especially when opening the throttle. What it should not do is just read a constant voltage or jump between a high and low voltage of identical numbers. Especially if it's jumping between 0 and whatever max is. The air flow rate for the MAF should be very constant at hot idle (because the throttle isn't moving obviously). The ECU knows what the voltage should be at the upstream O2 based on what the MAF is reading (I think that's how it works). If there is a big disagreement, then it will run too rich (usually) or too lean trying to compensate.

This is a big untested hypothesis on my part: if you unplug the O2 sensors, it should force the ECU to run off the preprogrammed fuel tables. If it runs better, then that may be the issue. May also have to unplug the MAF. Obviously don't drive it like that for too long. But you seemed to indicate that it doesn't run poorly, so without having them test the exhaust gases I don't know you would gain any useful info.

Hmm ok good info. I’ll look into that.

When I unplugged the MAF it did run badly. Bogged down off the line and I got a CEL that went away after plugging it in.

My vacuum doesn’t seem as good as yours but it doesn’t seem so bad that it would cause the car to run incredible rich as it is.

Honestly I think I’m just gonna pay the 100 bucks for a new o2 sensor and get some maf cleaner and see what happens after that.

[scot850]

When you clean the MAF, don't absolutely soak it. I use an old toothbrush for the not-electrical parts and a cloth and cleaner. I do give the electrical sensor a soak and let it sit on it's end to allow it to drain and dry. The MAF sensors can get clogged depending on which type you have. One make has a wire mesh which can get pretty dirty, and the other had a plastic mesh with much wider slots.

I am assuming you checked the air box does not have any critters or nest in it and the filter is new? If it is an old K&N chuck it out and put a paper filter in. Some people claim the K&N filters deposit their oil on the MAF causing rough running. Can't say I have seen it as I have a K&N filter but then my car does not do a big mileage ( 10,000 miles in 10 years!).

Still think an O2 sensor is the way to go, but worth the $10 for the MAF cleaner first and then order the O2 sensor.

Neil.

[JayPea44]

Thanks for the tips on cleaning the MAF. I went ahead and ordered the o2 sensor from FCP (Bosch type), it was much cheaper than IPD.

I changed the air filter during stage 0 for an OEM Volvo type, and gave the box a brush and wipe, but it wasn't too dirty.

[scot850]

I thought you might have done, but worth checking!

Neil.

[JayPea44]

Absolutely - the old one was extremely dirty, poor car was probably struggling to breathe!

[Roger_850T]

Adding in my $0.02 worth here... High HC and CO are the result of incomplete combustion. It's trying to burn, but some fuel molecules don't burn at all (so you get HC), and some only burn part way (to CO, not all the way to CO2). This happens when you are running rich, too much fuel / not enough air. (The exception is when the car is running very very lean - so lean as to have lean misfire, which doesn't match your symptoms.)

CO2 is only an issue when it's too low - you get that when there are holes in the exhaust, and too much of the exhaust gases are leaking out and the probe can't get a good sample.

High NOx occurs when the car runs a little lean. This is where the vacuum leaks come in - if un-metered air is getting into the system that isn't measured by the MAF, then not enough fuel is injected to match it, hence the lean running. Since you seem to be running rich, vacuum leaks wouldn't be my first suspect.

So, what can cause the incomplete combustion?
1. Temperature sensor reading wrong - ECU thinks it's too cold and applies enrichment all the time. It's a negative coefficient sensor, so resistance drops when it gets hot. Looking at your measurements, 4.5k is right for 8°C, and 90°C should be about 200 ohms, so your sensor seems good. Make sure there's no chance of an open circuit between the sensor and the ECU, (or corroded connections,) if it goes open circuit the ECU will see that as very cold and cause problems; otherwise it's good.

2. Fuel pressure too high. There's a Schrader valve on the fuel rail - measure it. The ECU assumes a constant pressure difference across the injectors, if the fuel pressure is too high then it will meter too much fuel. You want to see 300 kPa, or 43.5 psig. Lack of vacuum to the fuel pressure regulator will make it run a little high, especially at idle. You should see the pressure fluctuate around as you rev the engine and release the throttle; that would be the pressure regulator responding to the change in manifold pressure. So yes, if the vacuum elbow on the back of the fuel pressure regular is failed, it can cause it to run rich. Also, if there is a blockage in the return line to the tank, that can cause the pressure to go high. (This is unusual.) Best answer is to measure the pressure.

3. Poor spark. If the spark is not hot enough to consistently light off the mixture, this can also cause high HC. Old spark plugs, weak coil, bad wires can all contribute. Check the condition of the plugs, which are a good indicator.

4. Oxygen sensors. The Oxygen sensors are really a binary signal, either it's rich or it's lean. If it's running rich, there will be no oxygen in the exhaust gases, and the signal will be approximately 0.9V. When it's lean, the exhaust gas contains oxygen, and the signal goes to ~0.0V. During normal operation, you would expect to see the signal flipping between 0.0V and 0.9V as the ECU trims the mixture up and down. There are 4 wires to the sensor: 2 white wires are for the heater (one is +12V continuously, and the other is switched to ground through the ECU - it only runs the heater for the first few minutes until the engine has warmed up a bit,) and the other two (black and grey) are signal and signal-ground.

5. Mass Air Flow Sensor. Has 4 wires, you may be able to back-probe and check for correct signals. Green (pin 3) goes to +12V at the fuel system main relay, while green-red (pin 1) is the power ground. The signal output wire (white, pin 4) varies between 0V and 5V depending upon the air flow. 0V is no airflow, ~0.2V is about idle, and 5V is full speed. Pin 2 is brown-white, signal ground, so test by measuring between pins 2 and 4.

Since you've already validated the temperature sensor, my next guess is the fuel pressure. I hope this helps - good luck!

Roger