SSI and higher oil temps on 3.2

[Joeaksa]

Just had a set of the SSI headers installed on my 85 3.2 with a stock 73/74 style steel muffler. The change is excellent, with the sound being the way a 911 should be like! I just start the car in the garage in the morning and listen to it... Torque is improved and the motor rev's lots faster.

Problem is that I felt that the oil temps on the motor should be the same or cooler after removing the cat and heavy stock exhaust system.

I have driven the car for three days now and the oil temps are running 30 degrees warmer than before with the stock exhaust on the motor. Outside air temps are running 4-5 degrees higher than last week, not that much of a change.

Anyone have an idea why this would change or has something happened to make my temp gauge read high? Anyone else doing the switch from stock to SSI exhaust experience the same?

Oil level is same as before and all else the same (that I know of, but the work was done at a Porsche garage in the DFW area who knows what they are doing) with no other changes at this time.

TIA,

Joe

[Bill Verburg]

Usually the temps will drop a bit for 2 reasons

• removing the cat removes a heat source
• the oil supply line no longer runs across the back of the engine next to the muffler but rather is in a relatively cool airflow under the car

. You did change the oil lines rather than trying to relocate them a little?

Is it possible the oil temp sensor wire was disturbed during the install?

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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[Early_S_Man]

Joe,

I am not claiming to have any experience with 3.2s, but what did the shop do with the O2 sensor? Since DME operation is highly dependent on a properly operating O2 sensor, it sounds like the DME has leaned-out the mixture excessively, and this time of the year in Texas is probably not the time to be doing that!

I would suggest talking to the shop to see what they have to say about higher temps after their work ... I don't think you can blame the SSIs, but rather something else that was done or not done properly at installation time regarding the DME.

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Warren Hall
1973 911S Targa

[Joeaksa]

Bill and Warren,

Thanks for the ideas.

The installation did include all new oil lines with the old style lines replacing the 85 model lines. One was leaking and so it was a no brainer to go with the new oil lines.

You may be onto something as the O2 sensor is installed and hooked up but the guy said that it would not work as the cat is not installed and without the restriction in the exhaust, any changes that the sensor commanded would not be accurate.

He went on to say that my car would not pass the state "sniffer" inspection for this same reason, but later said that the emissions were not that much higher and might make it when I pressed him for a reason.

I will go out and take a look at the wiring on the oil temp sensor and see if its been disturbed or not making good contact. The motor had been running at 90-100 c oil temps on the road for the last three years and I could not understand why a simple switch of exhaust could do this. Leaning out the mixture could do this but they told me that the mixture was checked when they did the work and that after the switch they did not need to change it??? I would have thought that putting on a free flow system would lean the motor out.

Am giving it back to them on the 10th for more work and will let them look at it again.

Thx,

Joe

[Bill Verburg]

A correctly operating O2 sensor is pre cat (on older pre obd2 cars) and thus the cat removal does not affect it.

Warren may be on to something with this though. It is very easy to ruin an O2 sensor with silicon or other lubricant/antisieze compounds.

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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[Joeaksa]

Bill,

Just got under the car and the wiring to the oil temp sensor looks fine. Found another interesting thing.

When the SSI's were installed the position of the O2 sensor port in the exhaust pipe was evidently a bit futher aft than where it is placed in the cat with the stock installation. When they installed the O2 sensor they simply plugged the wires into the sensor and put the harness up through the sheetmetal and left it there, unhooked.

The wire to the O2 sensor is not hooked up and cannot be hooked up as the wire loom is not long enough... will go out now and try to splice enough wire onto the thing to get it to the plug and back onto the system, but sure wish that the shop had done it before or at least told me about it!

Would running without the sensor in the system make the mixture run lean? Never run without the sensor and do not know anything about the default settings when the sensor is taken out of the picture.

Thx,

Joe

[89911]

You should be able to pull enough through the grommet to reach, at least there was in mine. Give it a try.

[Joeaksa]

Just finished the "jury rigging" of the extended wiring harness for the O2 sensor. It would not make it without an extension of the wiring, was about 4" short.

Motor seems to idle smoother now and runs fine on my tour around the block. Too late and I am too busy right now to take it to the highway and wring it out. Have to drive to the airport tomorrow morning and it will be my test run.

Would be interested to hear what others have experienced with a DME car both with and without the O2 sensor hooked up while using SSI exhaust, especially with regards to any state inspection that tests the exhaust readings.

Even without the cat I would think that its better to have the sensor in the system but thats just a guess.

Thx,

Joe

[Ned, NYNA11]

Joe,
I am working on an erratic idle in my 87 and found that it idled smoother and at just over 1000 rpm with the oxygen sensor disconnected. Have 54k on the car and since a new sensor is recommended at 60k, a replacement is in the plan. Was able to adjust the idle down to 800 and it is now much smoother.
This is all covered nicely in Bently, using the very same words and pictures as the Factory manuals which I also have.
Excess in a good cause being surely a virtue.
I will post the results of the new sensor when I install it in a few days.
Incidentally my sensor connected easily to the SSI's.
Ned Monaghan

[Bill Verburg]

Having to extend the harness is part of the drill, B&B supplies an extension harness with their headers.
This is right from Bently;
The O2 sensor does not reliably work until the sensor reaches ~300C. Make sure the engine is hot and that the O2 sensor heater circuit is working. Power for the heater comes from terminal 87b of the main/fuelpump relay.

To test the sensor itself connect a multimeter to terminal 24(O2 signal,pin1) and ground. Start engine, wait a max. of 2 min at idle, the O2 output voltage should then fluctuate from 0.1 to 0.9 vdc, loosen oil filler cap to admit unmetered air to simulate a lean condition, O2 voltage should drop, you can also simulate a rich condition where the voltage should rise by putting your hand over the air intake partialy blocking it.

If voltage doesn't fluctate and drop as described above check the wiring, if thats ok then the sensor is faulty.

The pin assignments in the connector are pin 1 in half of connector by itself, pin 2 and 3 are in the other half, pin 1 is the O2 output, pin 2 & 3 are the heater.

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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page


[This message has been edited by Bill Verburg (edited 08-03-2001).]

[Joeaksa]

Bill,

Am I correct in assuming that you feel that the 02 sensor will provide information back to the DME computer and that the fuel system and mixture will be compensated for even without the cat in the system?

I can understand that the system (and its being able to correctly adjust the mixture) is designed for a cat and taking it out eliminates lots of back pressure, thus un-balancing the whole system, but I would think that this sensor is still able to provide some information to the computer and then it would compensate somewhat for an improper mixture.

Ideas?

Thx,

Joe

[Doug Zielke]

Is there some confusion here?
It's common practice to disconnect the o2 sensor on CIS engines so equipped. They don't use it for the same purpose that a DME controlled engine does. I thought it was vital to have the o2 sensor fully functional on DME motors to control the fuel mixture.

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[Early_S_Man]

Doug is just emphasizing a point that should be quite evident to anyone who has read even the most basic description of DME-controlled engines of any mfr! DME is a 'closed-loop system,' and the fundamental measurement of mixture-richness feedback (Lambda) is done by the O2 sensor!

And, BTW, any measurement of the O2-sensor output Voltage should be done with a high-impedance Voltmeter or oscilloscope, as a low-impedance VOM can burn them out by loading too much! By high-impedance, I mean 10 megOhms or higher!

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Warren Hall
1973 911S Targa

[Joeaksa]

Warren,

By your comments on "closed loop" system, I assume that you mean that the oxy sensor should be hooked up and working, even without the cat in the system??!!

The owner at the shop who put the SSI's on the car tells me that it does not matter if its on or not and I do not agree with this. He told me that without the backpressure of the cat in the system that the DME and sensor would not work right and thus left the oxy sensor wiring off.

Pls tell me if my viewpoint on this is correct? I assume that this is why they left the sensor connector off when they gave me the car back. For now will run with the sensor connected...

Thx,

Joe

[Early_S_Man]

Joe,

The owner of that shop is either an IDIOT, or a well-practiced BS artist, maybe BOTH!!!

The Bosch Motronic system was designed to work without a catalytic converter, and for many years the European cars did not have cats ... BUT, they made more hp because of tuning for higher-octane gasoline than available in the USA, NOT BECAUSE OF THE LACK OF A CATALYTIC CONVERTER!!! Many USA customers, to this day, confuse the presence or not of a catalytic converter with the higher horsepower levels and completely ignore or are unaware of the more aggressive DME mapping for better gasoline than we have, or will ever have again!

Your shop owner is also in the ignorant group making such confused thinking ... RULE every bit of BS he puts out on the issue of DME engines, catalytic converters, smog rules, etc.!!!

And, for the record, you are not wrong in thinking the O2 sensor must be hooked up and functioning, otherwise, your engine will be running in 'limp-mode' and the DME will not be trying to control the mixture at all!
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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 08-03-2001).]

[Joeaksa]

Warren,

Thanks much and you reinforced what my thoughts were on the subject but I did not have the background with this fuel injection system and computer to be positive.

He made a good argument that the cat was gone and that the backpressure had changed so the DME system could not handle the changed parameters. The more and more I thought of it, it seemed that the oxy sensor needed to be in the loop and would still make changes to the mixture even with no cat in the system.

I had forgotten that the Euro 3.2 DME systems did not have a cat installed until the later years if at all, which throws his logic out the window. The scary part is that this is one of the major shops in my area and you would think that they would know better. I will talk to him when I take the car back for some other work in a week and ask some new questions, after driving the car with the oxy sensor hooked up!

Thanks again for the help from everyone, will get the VOM out and check the sensor back when I get back home! Hope its not bad...

Joe

[Early_S_Man]

Joe,

Unless that VOM is a digital, rather than an old Simpso, Triplett, or Weston( or worse, a Chinese/Taiwanese generic from Radio Shack) ... DON'T! The typical analog VOM is of the low impedance variety I mentioned above!!! It could load down the sensor and damage it!

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Warren Hall
1973 911S Targa

[Joeaksa]

Warren,

Just drove the car 20 miles on the highway and temps were 30 degrees cooler with the oxy sensor hooked up. Engine runs better and that was the problem...

Now for the talk to the shop... and will get my old Simpson 260 out to check the sensor!

Thanks again for the help...

Joe

[Bill Verburg]

Here's a nice description of O2 sensor operation courtesy of Kris Edwards from over on the Rennlist site;

When you first start your engine (when it's cold) It is in what's called
"open loop mode". This means the air fuel ratio is fixed and the engines
computer is not reading signals from the O2 sensor. In open loop mode the
computer puts the engine into a rich condition in order for it to run
while cold. The O2 sensor will not start working until it has reached
about 600F. Once the O2 sensor is hot, the computer will start using it
(along with many other parameters) to calculate how much fuel to inject.
This is the point where the engine goes into "closed loop mode". It is
constantly checking the O2 sensor and readjusting the air fuel
mixture.

One interesting thing to note: The O2 sensor is only sensitive
right around 14.7:1 air fuel ratio. In other words the computer only
knows if the engine is rich or lean, not how rich or how lean. The way it
gets around this is to check the O2 sensor many times a second. The
result is the engine never really has enough time to get too rich or too
lean.

So the answer to your question is: When you unhooked the O2 sensor the
engine defaulted to the open loop mode. The engine, while warm, will run
just fine in open loop mode. All modern engines do this when a sensor
fails that is not really needed to keep the engine running. This is so
you can get home.

Also, you said you only let the engine run for 1 min. There is a good
chance the engine never got into closed loop mode. If you just let it
idle for one min, there is no load on the engine and it will not heat up
very fast. There is a good chance the engine's computer wasn't even
looking at the O2 sensor at the time you pulled it out.

One test you can do is, go drive the car around for 10 min. to get it
hot. Then let it idle and note the RPMs. Then, while it is idling
unplug the O2 sensor. The idle speed should change. Most likely it will
go up. This is one way to confirm the sensor is working.

Kris Edwards

72 911 T
73.5 911 T (crunched)

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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[stlrj]

With the O2 sensor connected it is no longer running on limp home mode (richer) and is now running leaner and cooler all hooked up?

I thought richer was cooler and leaner ran hotter? What's going on here?

Did anyone else catch that?

Joe