Curiouser and Couriouser '84QV

Okay, I had an earlier thread about a bit of surging and an intermittant "slow down" light. I learned that a bad O2 sensor can cause surging and even heat up the catalytic converter by applying too rich of a mixture. So, applying occam's razor, I decided to replace the sensor. So I got underneath the car and found the O2 sensor (it's got a single stainless steel lead coming off of it--I guess that's normal?). I followed this lead from the sensor into the engine compartment and there it disappared into a hole on the rear wall of the engine compartment (like its leading into the trunk).

Pulling back the carpet to find where the lead enters the trunk, I got all confused. Nearest the engine is the metal trunk wall (black with a crinkle finish); then there was white styrofoam against it; then there was a yellow plastic wall against the styrofoam apparently riveted to the black trunk wall; next there was a sliver "Tyvek" looking insulation glued/epoxied to the yellow plastic wall; and finally, the black carpet inside the trunk.

Is all this normal on a 308? I mean do I have to drill out the rivets to follow the lead to junction in order to replace the O2 sensor? I thought that this was supposed to be easy?

At any rate, I'm suspicous that there's been some post-Italy work in my trunk. Pulling back the carpet further, I see on the floor the same layers with an additional wooden board crossing the floor of the trunk. Honestly, the board looks like it's off of a coffee table. It this normal too? Next, I unscrewed the wooden board and removed it and there was the yellow plastic wall with tin-looking plates riveted to it near the corners, holding it fast to the trunk bottom. So I think: "Now that I'm in here, where the heck is the Digiplex?" Right side on the bottom, correct?

Do we get any kind of engineering degree after a few years of this?

At any rate, I'd like for one who is more in the know to tell me how to change out the O2 sensor.

Thanks,

Andrew

 

The O2 wire on my 85' 308qv comes out between the air filter housing and the body.(not long enough to stick up though) Use a flashlight and I think you'll be able to see it without removing the air cleaner box.
You will have to remove the air cleaner box to get to the O2 wire for changing it, if I remember.

 

Your Jetronic FI Computer and Lambda relays are in the Right Well. Your DIgiPlexes are in the Left Well. Both pieces of hardware are mounted (or 'should-be') to the underside of a steel plate that is screwed into mounting ears lining the well. The cable would be easier to trace/follow from the passenger wheel well once the wheel-well liner is removed.

 

Okay, I knew that I was a newbie, but I just realized how much by something mentioned in the first reponse to my thread. What I'm seeing is coming out of the catalytic converter and I'll bet that it's NOT the O2 sensor, but the temperature sending unit--am I right? If so, then I've not even laid eyes on the O2 sensor yet. Sorry guys.

Heaven forbid that I have to ever change out the temperature sending unit.

As for the other questions about the trunk interior, I'd still like to know if this is normal stuff or something a prior owner put in. But why?

Andrew

 

Well, I only have a 328 and not a 308. But I can reasonably say that Ferrari never used coffee table wood in a car!
At least this part anyway was added by a previous owner. But if it's serving some function and isn't bothersome, I'm sure
it won't cause any problems. Definitely not 'normal'. I wouldn't be happy with it myself. Good luck sorting it all out...

Jedi

 

"Only" have a 328! Last time I checked, the 328 was an improvement over the 308 QV! Not to p ss anyone off, not too big of an improvement but an improvement none the less!

Andrew. I don't think your 02 sensor is the problem. But, I'd this the plug in is under/beside(needing removal-very easy) the airbox, unplug and replace if needed. It's pretty easy to replace and can't hurt except the cost of it.

Jeff

 

You're kind. Thank you

Jedi

 

Well that's my thought: "It really can't hurt to replace it, and it won't be too much trouble anyways." At a previous service, the mechanic wrote that it was time to change the O2 sensor. In sum, because my slow down light is very intermittant and I do have the surging issue, I thought that I would follow the mechanic's advice. If it doesn't fix those problems, then I guess I know to look at the distributors/rotors (replaced within 8 years) and the flywheel sensors (one of which replaced within three years).

Andrew

 

Hope you figure it out real soon. You could try unplugging the O2 sensor first to see if it changes anything as well. Good luck.

Jeff

 

My 328 ran rich as hell until we replaced the O2 sensor when I did a new cat and Tubi.
BIG difference in the 'smell' in the garage! Seems the old one was making things run
too rich, and it was noticeable.

Jedi

 

THAT'S what I'm hoping for too. I do get the raw gas smell from time to time. Still it might not be the O2 sensor, but since it needs to be replaced anyway. . . .

 

Either the O2 sensor or the Lambda relay will negatively alter your air/fuel mixture lean or rich, depending on what crap signals are reaching your FI computer. I'd check both.

 

you know, I just ran into one other QV with just that, a 'coffe table' board under the carpet in the trunk. very odd, wonder what Ferrari was doing? possible insulation?

 

I have that as well in the trunk of my 84 QV, under the carpet....looks like wood paneling.

 

Okay, replaced the O2 sensor and with about 75 miles on it since, no "slow down" light . . . yet. So perhaps it was the problem. However, I did notice a few things. While, overall the car runs smoother, it doesn't seem to pull as hard as it did with the old sensor. Moreover, I still have the "weak pull to 1/2 throttle, then the strong pull thereafter" issue. Is that just the way 308s run?

At any rate, it needed to be done and if it stops the slow down light, we will have learned a little bit, huh?

Andrew

 

Your CAT should have TWO things sticking out of it... the O2 sensor and the temperature sensor (thermocouple). It's the thermocouple that controls your "SLOW DOWN" lights when it senses that the cat is overheating.

 

Mike, I understand all that. But what I've been reading is that a bad O2 sensor can cause a rich mixture. And, as I've been told on various google searches, the sensor can cause so rich a mixture that it will ignite in the catalytic converter (hence the "slow down" light). Now, many previous posters told me that they doubted that the sensor alone could cause so rich a mixture that it would cause the slow down light to shine, but I responded that the sensor needed replacing anyways (last replaced in '99) and so I wasn't losing anything by replacing it.

So, I'm not as lost as you might think I am. Really, the light will probably come back on and, in such event, I will look at the rotors and flywheel sensors, etc., but again, I wasn't losing anything by trying.

Andrew

Here, take a look: http://www.picotech.com/auto/lambda_sensor.html
"If the lambda sensor continually reads low (lean), it will cause the engine computer to richen the fuel mixture. Injector pulse width will increase causing fuel consumption and carbon monoxide emissions to go up. Constant rich fuel mixture can also cause the catalytic converter to overheat and it may be damaged."