Infobit: inexpensive BOSCH heated O2 sensor

[Munchen]

Quote:

Originally Posted by Tifosi Some folks pull the whole thing out to do the soldering at the bench, which is likely what you saw. If you do decide to go that route, it's not too big a deal. In your case, there will be 3 wires on 2 harness plugs, (single wire on one, 2 wires on the other), all located near the clutch and brake master cylinders. (the single, which is the sensor signal wire, will likely be a green wire with an orange or yellow plug insulator) Disconnect them, then release the wires from the little hold down thingies on the chassis (the metal tabs that are here and there to guide wires) and drop them down through to the shop floor. Once you unscrew the sensor, it'll all come right out to be worked on wherever you are conmfortable.

[Tifosi]

A year later:

It's still working just fine.

Activation after startup while idling during warmup is about 30-40 seconds.

While driving it gives continuous signal, even while sitting at intersections.

I had oppertunity (read as 'had to do it because it was in the way of what I was doing') while doing some exhaust work a couple weeks back and it gives every outward appearance of functioning correctly.

It didn't look like a nasty sooty bit of charcoal, nor did it appear burnt gray or disfigured from overheating. Just a decent appearing condition one would expect from a device hanging in the exhaust flow. (kinda like a slightly rich spark plug actually)

[bayalfagtv6]

Tifosi,
I have a 85 S3 spider and have recently installed Centerline headers on it. I now have a slight hesitation when the car idles for a while like at a stop light, have to give it a little kick to get it going. Since I have a single wire sensor does it make sense putting in the 3 wire? Will this help to performance from idle? Sounds like the problem you had in the first post. Not enough heat and flow thru the exhaust.

Thanks

[Tifosi]

I kinda doubt it would effect that for you. (the problem I was having was related more to how long it took for the sensor to go active once on the move)

When L-jet is at idle, it's running a pre-programed idle map due to the TPS switching and that map totally ignores any O2 sensor output until the TPS tells it otherwise.

What you're likely experiencing is a bit of lag due to '?' (ignition, AFM flap slow, slightly dirty injectors, dirty or slightly malajusted TPS, a small false air leak, low or lacking fuel pressure boost when the manifold pressure drops. Something along that line.)

Once all that stuff has been double and treble checked, you might be able to try dialing it out by using the adjuster bypass screw on the AFM, but go with caution as it'll effect your idle CO2 output, or tweaking the AFM spring by 1-2 ticks looser (realistically that should not be neccisary though and only a last resort). But I'd only suggest options if you're confident in your ability and keep track of everydamnthing so you can revert it back to where it was should the need or desire arise.

[andy303]

Bayalfa:
I dont want to hijack this thread, but if you would, kindly comment on your experience in installing the Centerline header in my post "Damaged Exhaust Stud Removal". I am curious if you had to use more than one than one copper gasket or encountered any problems with the seal of the headers on the exhaust ports. Thanks!

[Elio Comello]

Hi Bay, Just to add to Darren's sage advice....

One possible cause for your lag is the Manifold Pressure sensor.

It is a Silver coloured mushroom shaped device located next to the Enginemanagement/Ignition ECU on the wall under the carpet behing the driver's seat.

This sensor sets the sets the ignition timing. They are a bellows device and the bellows fatigue over time and leak (usually signalled by a whitling noise from the sucked in air).

The sensor connects to the intake plenum, it is easy to find the little connecting hose and give it a suck. If it does not hold vacuum, thast nay be your culprit.

The dizzy has no mechanical advance mechanism.

Another possibility is that your injectors are in need of solvent/ultrasonic cleaning (poor spray pattern or low fuel delivery from one or more injectors) This is less evident at greater flow rates from the injectors.

[bayalfagtv6]

andy 303,
I had my exhaust guy install the centerline headers, they looked good to begin with but he had a hell of a time doing them. Ended up that the lineup was completely off. he had to cut the headers apart and reweld them to get them to fit. To reweld them he had to get a second head and do it off the car, couldn't tack them in place, no room. They turned out nice but it ended up costing quite a bit.

[andy303]

bayalfa: Cut them apart!!! I bought the Centerline ones because they are supposed to be made well enough to avoid those kind of hassles. The Centerline header (PH118) comes in to pieces like the old style manifolds:Outer branches and inner branches. I actually had mine all fitted up, it was a struggle to get the flanges on the studs but with some gentle persuasion and a little banging they went on OK. I am worried about the seal at the head, as I related in a parallel post. I sent an email to Joe at Centerline and he suggested using Walker Acousti-seal.

[bayalfagtv6]

Andy 303,
yeah, had to cut and then reweld at the branch.The muffler guy said he laid a straight edge across the flange and they were'nt even straight. I guess with the work the muffler guy did mine lined up good, no problem with sealing at the head.
Tifosi,
I only started to get the slight hesitation after the headers were installed, I am getting a nice acceleration though, that's why I thought maybe the lambda sensor ( 3 wire) would help. I'll look into the list of things you suggest.
Thanks

[Tifosi]

The 3 wire will certainly be a good upgrade and help ensure that (1) the sensor heats up enough (the header in particular will allow a 1 wire job to run cooler more frequently) and (2) that it goes active, or stays active longer which in turn will improve your fuel economy because it gets you into, then keeps you in, closed loop operation longer.

The side benifit being that the longer duration closed loop operation means you're spewing a bit less emissions also.


Query:

Was the header set a 'long tube' version? (ie: did the collector go on at or beyond the point where the transmission exhaust support would normally go?)

If so, that in itself can potentially help create the off idle pick up issues (in conunction with any problem in the previously mentioned items) as that type can screw with the harmonic scavenging in a big way.

Basically they are for high end power gains, at the almost equal exchange sacrifice of very low end response/performance.

Still, it can be compensated for by ensuring that everything else is in proper tune/adjustment. To the point of not even being able notice it, or outright eliminating it all together.

Query 2:

Do you have a catylist, and if so, has this issue been getting progressively worse as time goes by?

Query 3:

Did you, or did you have to, readjust your idle speed post header install?

[bayalfagtv6]

Tifosi,
I don't think the header was a long set type but will have to check. I do have a catalyst installed , CA emmisions are tight, it is a hi flow round type, the new ones on the market, but I haven't noticed it getting worse, just that little blip when sitting at idle too long. 3-Before installing the headers I had problems, car wouldn't idle, wouldn't start etc. i went thru Greg Gordon's tune up for spiders and ended up replacing 1 flywheel sensor, showed open. Also did all the other procedures, everything seemed fine but I think the cat was partially clogged also causing the hard start, etc. The car does burn oil though, I sort of thought this may have been the root cause of the cat being clogged. Am thinking the valve stem seals are bad, rebuilt the engine 4 years ago but it has sat alot and think the seals have dried up. Any advice.

Thanks