1994 N/A stalling: My thoughts

[luketrash]

After my little string of shotgun approach to fixing my fuel delivery issue, I wound up putting on a junkyard fuel pump to solve the issue.

Thinking I'd be extra special to my car, I cleaned the throttlebody, the IAC, the MAF, and the 02 sensor.

As some of you may recall, the car ran very bizarre after I cleaned all the soot off of the 02 sensor with electrical parts cleaner. I freaked, since I was driving cross state the next day for Easter visits and bought a generic 4 wire Bosch O2 sensor kit.

Video footage of how poorly my car ran immediately after cleaning my O2 sensor:




Anyway, about a week after using the Bosch sensor, my car started randomly stalling on me. The first time during a long coast to a stoplight I happened to notice the dash lights come on. That was the first time, and I got weirded out.

The second time was while stopped at a light, when I gave it gas on a green light it stalled on the spot.

The third time was on a rainy day, coming around a bend at a constant 35mph with mild throttle applied.

The fourth time was last week when I was making a left turn at a green light. I had to coast across the intersection and almost got hit.

So, no more of that.... Last night I pulled out the Bosch generic sensor and rewired my original Volvo sensor. Amazingly, the car has more power and is running a bit smoother. Definitely smoother power delivery.

Whereas the car was running lean with my bad fuel pump, it was running too rich with this bunk O2 sensor.

I knew that it probably had nothing to do with my throttlebody because it was clean, including the little vacuum port on it.

The main thing I noticed with this new O2 sensor was that when I'd let off the gas, the car almost had an engine braking effect. Almost as if the fuel injectors completely shut off (or perhaps choked out.) Something wasn't as it was before...

Upon replacement of the original O2 sensor, the car didn't do that. Letting off is smoother and you don't feel as if the car is cutting out slightly. Luckily, my car runs just fine with the old O2 sensor. I did NOT ruin it by cleaning it. My original hunch was correct in that the car ran poorly afterwards because the computer had to readapt to the cleaned sensor.


So, long story short, I am pretty certain that the universal Bosch O2 sensor is not a perfect match for the Volvo 850 fuel injection system. I have no idea why, but it just isn't. In fact, my 1991 Volvo 240 acted similarly when I tried to use a Ford Mustang (cheap! 20 dollars) 4 wire O2 sensor in it several years ago.

So, the lesson learned is that you may hate paying for OEM parts, but they're cheaper than being run into when you're ghost riding across traffic in your dead 850.

[tjts1]

Mine runs great with a Bosch sensor. Are you sure you wired it correctly? If you get the heater wires mixed up or the signal wires backwards it will run like crap, but it will run. What error codes did you get the the Check Engine Light came on?

[luketrash]

I never got any DTCs or a check engine light.

I had it hooked up correctly. white, white, gray, and black. It's not too confusing The heater wires are not dependant upon anything.

I noticed a lot of 1994 NA stalling posts in the past and I never found any conclusive single cause of it, but I have my hunch that the Volvo FI system is fickle enough that it didn't like the generic sensor. I mean my car ran, and I was getting 25mpg on the highway, but it also died at random.

[Free2drive!]

Hi Luketrash

There are 2 x 02 sensors availabe to Volvo 850's. One is a generic Bosch and the other is more specific to the engine, and a whole lot more costly and still made by Bosch.

Interesting that your motor runs better with the original 02 sensor. If there is any way you can swap your knew sensor for the more specific one then your car will run better. Not sure if it will cure the stalling.

Matt

[MadeInJapan]

Matt, sorry to say but he did that and it ran like crap, that's why the old one is back in.

[bockreiter]

Can anyone educate me on the O2 sensors? Besides the cable length, what is the difference between the rear and the front O2 sensor? On the generic O2 sensor: Since the ECU compares the values off the front and rear sensors, it would make sense to me if the engine might run poorly if one sensor is OEM, the other generic. Am I way off base? Any education will be appreciated!

[MadeInJapan]

Can anyone educate me on the O2 sensors? Besides the cable length, what is the difference between the rear and the front O2 sensor? On the generic O2 sensor: Since the ECU compares the values off the front and rear sensors, it would make sense to me if the engine might run poorly if one sensor is OEM, the other generic. Am I way off base? Any education will be appreciated!

I'm no expert but you may indeed be correct about 2 different 02 sensors (one OEM, the other not) between the front and the rear. The front gauges oxygen before the CAT and the rear one gauges how well the CAT is performing. On some model year 850's the rear isn't even part of the equation on how the air and gas mixture is adjusted by the ECU....on other years it does make a difference. So, the debate here about running poorly and not is also dependent on year of the car...not sure when the design changed but I've heard after '04, but apparently some late model '94's did have the signal from the rear sensor being fed back into the ECU for adjustments.. Also, I should say that since different parameters/values are read, you can't simply put a rear 02 sensor on the front or vice versa.

[luketrash]

Update:

My car died on me yesterday with the original O2 sensor in place.

The car ran great for like two days and progressively fell back to its normal state of listlessness.

My only thought is that it's the MAF sensor and the FI computer fighting it out.

SO..... Off we go again. I've got a whole shopping list of parts to install on my 'new' 245, so I'm not sure when I'll be able to afford to just toss a new MAF on my 855.

Shucks!