View Full Version : '87 16V - cold o2 sensor?

Rex B
06-18-2002, 12:40 AM
I dropped my ITA project/street car off at the local independent VW shop last weekend. I wanted an expert to look it over and get it into a good stock state of tune so I would have a baseline for improvements. It has the stock cast manifold, dual outlet downpipe into a gutted catalyic convertor shell.
Today they called and said since the cat was gutted, the o2 sensor would not get hot enough to get into the normal range. This car uses the 3-wire sensor, so it's electrically heated. But in the shell of the gutted cat, it is sitting out of the main flow of hot exhaust, so I guess it is running colder than it was designed to.
The tech recommended a new catalytic converter. Since the car passes smog without it, and it's future as a street car was doubtful anyway, I would prefer not to add a cat. So what to do? We are at an impasse - he won't go any farther without a cat, and I won't put a cat on it (other than an occasional black one :).
So how do I get the thing working like it is supposed to? I wasn't really planning on headers at this point, though that would probably give me an opportunity to move the sensor. If I move the sensor into the narrower pipe of the downpipe, it would restrict the flow a bit.
I know some people just cut off the sensor and deal with the mixture in other ways, but I'd prefer to let the CIS do what it is designed to do, and imfluence the mixture as needed with potentiometers or whatever is called for.
So what to do? Suggestions?


06-18-2002, 07:14 AM
Don't spend money on a cat.

The O2 sensor is inoperative 90% of the time in a race car. The WOT switch turns the o2 circuit off.

If that car is still registered for the street, your mechanic has legal issues to deal with and will most likely not tell you what is best for a race car.

Remove the exhaust from the cat flange back and weld a nut (for the o2 sensor) to the new pipe as close to the flange as you can get.

06-18-2002, 10:37 AM
So the O2 sensor is mounted in the cat? It is not in a 55mm pipe before the cat? Usually that is the way they are mounted and it would still operate. Yes, you would have a bit colder exhaust but the cat heats up post O2 sensor. You get some radiant heat but not enought to cause it to work or not work. Did he say what voltage he was reading or what mA he was reading at the fuel distributor? 02's are basically a battery and they need no power supply to work.

But, I agree with the above, on the track it is not used and properly adjusted the cone by the fuel meter is your AF gauge.

Rex B
06-18-2002, 01:14 PM
"... properly adjusted the cone by the fuel meter is your AF gauge."

Not sure I understand this - what cone, what fuel meter? You mean the fuel distributor?
As I understand it, you can't really adjust this unless the O2 sensor is putting out the right numbers.

Where is the WOT switch?
On top of the throttle body casting there is a machined area that looks like a switch goes there. It's a rectangle about 1.5" x 1" with threaded holes at 2 opposite corners. What would go there?

(Bear with me - I'm at work and the Bentley is at home)

I'm going by to pay for the work at lunch, and hope to have a discussion with the tech. I really think he's in tune with what I need, but I did ask for a stock tuneup, and he says he does not have the parameters to get there, strictly speaking. And I do understand the delimna WRT the emissions issues. The tech did recommend I look for a high-flow catalytic convertor. We carry Dynomax, so I'm familiar with that. I'm not totally averse to a cat, especially if the result is a dual-purpose car that is semi-competitive or at least a fun schoolie rental. The CA Spec7 guys seem do do just fine running cat convertors.
As for the O2 sensor location, again I'm going from memory, and I am pretty sure it's in the large part of the cat, right at the front edge of the shell.
But I've been wrong before. Once ;)


06-18-2002, 04:35 PM
The WOT switch is on the throttle body. I don't remember the layout for a 16V (that's what it is, correct 1.8 CIS-E) but it should be mounted there and an idle switch. The cone is under the rubber boot at the air box. Fuel distributor = fuel meter, sorry so used to reading that rule on where you can make adjustments "before the fuel metering device". As that arm goes up it pushes a plunger inside the part where all the fuel lines are connected.

When you hit the switch the ECU will go into open loop control using no feedback from the o2 sensor.

I am not sure what goes where you describe, if I remember corectly the one I had also had those holes (going from bad memory). If you follow the harness that connects to the throttle body you should find the switches.

If he is doing a stock tune up, he should be adjusting based on mA to the small gray box (differencial pressure regulator) mounted to the fuel distributor on the air box. They also talk about adjusting the Idle air stablizer and an exhaust reading that I believe to be taken from the test tube that sticks up by the intake with a blue boot on top (pre cat). They never measure the output of the o2 directly in the Bently (they probally didn't have a meter back when it was written that was fast enought to see the changes)

Again, from memory - 16V idle 5mA full throtte 10-12mA (???) you must be above 2300(?) rpm and press the WOT switch to see it

06-19-2002, 12:09 AM
>>What would go there?

The WOT switch.

Rex B
06-19-2002, 12:44 AM
AHA!! Missing WOT switch = poor performance over 4000!

So, at WOT, with WOT switch present and closed, the only other variable that affects A/F ratio is the fuel meter. And you adjust that by the 3mm allen screw.
What am I missing?

Thanks Bill & tschwenke, that helps a lot.


06-20-2002, 07:03 PM
Actually you want the switch plugged in but you may find that moving it so that the throttle arm does not touch it improves the top end.

>>And you adjust that by the 3mm allen screw.

That's just for idle.

Your not missing anything else really...just have the mechanic get it all back to stock before you worry about making power. Once it's running well then you can start to tweak it.

06-20-2002, 08:42 PM
Funny - I've seen guys put zip ties on their WOT switch to hold it closed...


06-20-2002, 08:58 PM
Sure, and you see items like this some cars: http://www.autotech.com/powermod.htm

To read this you'd think I was nuts....come to think of it ... http://Forums.ImprovedTouring.com/it/eek.gif

It's a trade off. Street performance is very different. Anyone have a manifold vacuum guage? hint hint

06-21-2002, 09:15 AM
HMMM, that's a new one, no WOT switch... The dyno charts we have from our cars it appears to work fine, but maybe that's because we tuned the AF ratio to work with it ON - I guess now that I have said that, it won't matter, on or off just how you tune it. All it does is change the pressure while the switch is on, about 90% of the time on the track. What about that other switch - idle? I think there is a good description of what it does in the bosch fuel injection book (with the blue cover), not the handbook.

It would be nice to have a free couple of days at a real dyno where you could run speed control and do partial throttle settings to check power..

As Bildon says, there are many trades, you just want to end up on the + side.

Rex B
06-21-2002, 10:54 AM
"Actually you want the switch plugged in but you may find that moving it so that the throttle arm does not touch it improves the top end."

That's interesting. I think my current problem is leaning out at the top end. So how do you bring the mixture richer, adjust the pressure?

"Your not missing anything else really...just have the mechanic get it all back to stock before you worry about making power. Once it's running well then you can start to tweak it."

Yep, that was the plan. He still insists on having a cat convertor on it in order to get the O2 sensor hot enough. Doesn't the electric heater do that? Or does it need full exhaust heat on top of that?
One option seems to be to move the o2 sensor, as it is shrouded in the big part of the cat shell and out of the direct exhaust blast. Is there a dual-outlet cast manifold with a O2 sensor port? How about a replacement downpipe with an O2 port, eliminating the cat?

I'm getting further up the learning curve - thanks guys.


06-21-2002, 12:40 PM
The heater gets it going faster but I don't know and have never checked its output during this time. It just means that they don't have to spend as much time in open loop and can pass the federal tests easier.

If yours is out of the main stream it might not ever really work correcty. What you need is a new bung put on in the main pipe and you will be fine. The problem is finding someone to do it. Here in Ohio, they are not as picky as they might be in California and I have used two shops (one a nationally known name) that if I walk in with an exhaust part they will fix it for me. Right then, no waiting and usually free or $10 (free=6 pack).

My guess is that it is because it is out of the stream and not that there is no cat. I go back to the beginning of this thread and think, I would really hate to see you waste money on a cat...

Rex B
06-21-2002, 01:36 PM
Yeah, I'd hate to put a cat on it too. But if this time next year it's still a dual-purpose car, and it doesn't pass inspection, I may consider that.
In the meantime, I do have a welder. I think that thread is 18mm, like the older spark plugs.
But even better, isn't there a cast manifold that has provision for the O2 sensor?
I'm surpised no one has insisted I need headers. I've read so much about problems with headers cracking as the engine moves, that I've moved that down the list quite a ways. I see this car ultimately as a dual-purpose car that will work as a backup for my commuter, or my single-purpose race car, or can be rented to a schoolie (no trailer required).


06-24-2002, 01:54 PM
The 4-2-1 german manifolds found on late Golf/Jettas works VERY well.

These manifolds and downpipes are not tapped for an OXS sensor...that is in the cat.

>> I think my current problem is leaning out at the top end.

You'll need to be at WOT for a while at well over 100 MPH to see the negative rich effect I'm talking about so I wouldn't worry aboout "race tuning" the car until it's on the track.

Rex B
06-24-2002, 02:06 PM
"The 4-2-1 german manifolds found on late Golf/Jettas works VERY well."

Is that different from what I have on my '87 GLI? It's cast 4 into 2, then the downpipe is 2 into 1. Is there a better OE setup?

"These manifolds and downpipes are not tapped for an OXS sensor...that is in the cat."

So if I want to move the O2 sensor to someplace where it will get hot enough, I'll need to weld a bung into the collector area of the downpipe. I was hoping there was a good OE manifold with a provision for the sensor.

Sounds like I need to get the jackstands back out.