Saabscene Saab Forum - Saab Technical Information Resource banner
1 - 20 of 20 Posts

·
Registered
Joined
·
507 Posts
Discussion Starter · #1 ·
My '93 CSE LPT failed it's MOT today due to a too high Lambda reading ( 1.08 when max is 1.03) Does anyone know what causes this and how it can be fixed ? Preferably without expensive therapy.( CO & HC were fine)
Also failed for corrosion on the front , lower suspension bush bracket which is made of alloy. Part costs £6 +vat from Saab which seems too good to be true. Anyone ever tried to remove the bush from this bracket? I suspect it's a bar steward of a job.
It's done 187,000 miles.
 

·
Registered
Joined
·
1,245 Posts
Probable cause of you emissions failure is the Lambda sensor. Anew one from Saab costs around £150 or so but they can be got from the likes of Eurocarparts for less than £50.
As for the bearing supports on the front wishbone bushing, I'll let you know on Monday - I'm replacing all of mine this weekend
The car is not yet 6 years old and they are disintegrating with corrosion. I've had 4 9000 some of them much older and this is the first time I've encountered this although I believe it is a common problem.
The job at least doesn't look difficult.
 

·
Registered
Joined
·
1,908 Posts
Derek,

I know that the Lambda sensor is a sensative component, and easily damaged, but could it be cleaned in order to improve upon Lambda sensor reading? Anyone tried it?

Maybe, as the Lamdba sensor wire is self cleaning, there's nowt that can be done?!
 

·
Registered
Joined
·
1,245 Posts
Lamda Sensors can allegedly be cleaned by heating the tip to white heat with a gas torch. I had one go duff a couple of years ago and tried that but it didn't work
No harm in trying though.
 

·
Registered
Joined
·
763 Posts
the 2 aly parts....bearing supports they are called...replaced mine recently......common failure on 9000's! best is to replace both at the same time...front and behind the bush, remove the 2 nuts from the bracket arm bolts and push them as further back as possible, lever the lower arm out and slide them out, needs some lubricant to work loose. When fitting new ones, reverse of removal but you need to twist the bush metal pivot arm to get the bolt through....about 40 minutes work taking it easy.
 

·
Registered
Joined
·
1,925 Posts
Wulbert, before you buy a new lambda, just check your whole exhaust system for leaks. Even a very small leak can sometimes throw the lambda reading out. I've tested a few cars that have gone down on lambda and have had a small hole in the exhaust.

Neil
 

·
Registered
Joined
·
763 Posts
On the lambda reading issue....check the flange joint of the front downpipe where it connects with the CAT, this is the weakest link in the system and develops minute holes in the weld joint of the flange (lower half). You will hear slight blowing when idling if this is the problem, no need for complete replacement, just remove downpipe and have it re-welded at the flange.
 

·
Registered
Joined
·
507 Posts
Discussion Starter · #9 ·
Thanks for the tips people.
I have wondered if there is a hole in the exhaust, sounds a wee bit blowy, not noisey as such just a slight puffing which sounds like it's coming from under the drivers seat( when you open the door) I'll check it out tommorow when it's daylight and the midges are not so bad ( Scottish insect curse) .
I bought the bearing supports today, they look simpler to fit than I thought ,didn't realise there are two per side , from the Haynes manual it looks like one part with the bush in the middle. Good to know you don't need to touch the bush, Saab dealer told me it's a hell of a job getting them out.I'll trust my local garage to do the job.
 

·
Registered
Joined
·
300 Posts
Try the following info about oxygen sensors, can't remember where I downloaded it from but lots of useful info.

Written by Rick Kirchoff ([email protected])
Edited to html by Jim Wright

--------------------------------------------------------------------------------

What does the O2 sensor do?
Should the O2 sensor be replaced when the sensor light comes on in your car?
How do I know if my O2 sensor may be bad?
What will damage my O2 sensor?
Will testing the O2 sensor hurt it?
How does an O2 sensor work?
How can I test my O2 sensor?
Testing O2 sensors that are installed
Testing O2 sensors on the workbench

--------------------------------------------------------------------------------

Comment:
In response to several requests for more information about Oxygen (O2 sensors, perhaps the following information will help.

These procedures are only for self powered conventional sensors. Some very new cars are using a different style sensor that is powered. *Many* Oxygen sensors are replaced that are good to excellent. *Many* people don't know how to test them. They routinely last 50,000 or more miles, and if the engine is in good shape, can last the life of the car.

What does the O2 sensor do?
It is the primary measurement device for the fuel control computer in your car to know if the engine is too rich or too lean. The O2 sensor is active anytime it is hot enough, but the computer only uses this information in the closed loop mode. Closed loop is the operating mode where all engine control sensors including the Oxygen sensor are used to get best fuel economy, lowest emissions, and good power.

Should the O2 sensor be replaced when the sensor light comes on in your car?
Probably not, but you should test it to make sure it is alive and well. This assumes that the light you see is simply an emissions service reminder light and not a failure light. A reminder light is triggered by a mileage event (20-40,000 miles usually) or something like 2000 key start cycles. EGR dash lights usually fall into the reminder category. Consult your owners manual, auto repair manual, dealer, or repair shop for help on what your light means.

How do I know if my O2 sensor may be bad?
If your car has lost several miles per gallon of fuel economy and the usual tune up steps do not improve it. This *is not* a pointer to O2 failure, it just brings up the possibility. Vacuum leaks and ignition problems are common fuel economy destroyers. As mentioned by others, the on board computer may also set one of several failure "codes". If the computer has issued a code pertaining to the O2 sensor, the sensor and it's wiring should be tested. Usually when the sensor is bad, the engine will show some loss of power, and will not seem to respond quickly.

What will damage my O2 sensor?
Home or professional auto repairs that have used silicone gasket sealer that is not specifically labeled "Oxygen sensor safe", "Sensor safe", or something similar, if used in an area that is connected to the crankcase. This includes valve covers, oil pan, or nearly any other gasket or seal that controls engine oil. Leaded fuel will ruin the O2 sensor in a short time. If a car is running rich over a long period, the sensor may become plugged up or even destroyed. Just shorting out the sensor output wire will not usually hurt the sensor. This simply grounds the output voltage to zero. Once the wiring is repaired, the circuit operates normally. Undercoating, antifreeze or oil on the *outside* surface of the sensor can kill it. See how does an Oxygen sensor work.

Will testing the O2 sensor hurt it?
Almost always, the answer is no. You must be careful to not *apply* voltage to the sensor, but measuring it's output voltage is not harmful. As noted by other posters, a cheap voltmeter will not be accurate, but will cause no damage. This is *not* true if you try to measure the resistance of the sensor. Resistance measurements send voltage into a circuit and check the amount returning.

How does an O2 sensor work?
An Oxygen sensor is a chemical generator. It is constantly making a comparison between the Oxygen inside the exhaust manifold and air outside the engine. If this comparison shows little or no Oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between 0 and 1.1 volts. All spark combustion engines need the proper air fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to one part of fuel. When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gasses leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts.

The sensor does not begin to generate it's full output until it reaches about 600 degrees F. Prior to this time the sensor is not conductive. It is as if the circuit between the sensor and computer is not complete. The mid point is about 0.45 volts. This is neither rich nor lean. A fully warm O2 sensor *will not spend any time at 0.45 volts*. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an "illegal" value, it judges the sensor to not be ready. It remains in open loop operation, and uses all sensors except the O2 to determine fuel delivery. Any time an engine is operated in open loop, it runs somewhat rich and makes more exhaust emissions. This translates into lost power, poor fuel economy and air pollution.

The O2 sensor is constantly in a state of transition between high and low voltage. Manfucturers call this crossing of the 0.45 volt mark O2 cross counts. The higher the number of O2 cross counts, the better the sensor and other parts of the computer control system are working. It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil, sound insulation, undercoating or antifreeze, (among other things), this comparison is not possible.

How can I test my O2 sensor?
They can be tested both in the car and out. If you have a high impedence volt meter, the procedure is fairly simple. It will help you to have some background on the way the sensor does it's job. Read how does an O2 sensor work first.

Testing O2 sensors that are installed
The engine must first be fully warm. If you have a defective thermostat, this test may not be possible due to a minimum temperature required for closed loop operation. Attach the positive lead of a high impedence DC voltmeter to the Oxygen sensor output wire. This wire should remain attached to the computer. You will have to back probe the connection or use a jumper wire to get access. The negative lead should be attached to a good clean ground on the engine block or accessory bracket. Cheap voltmeters will not give accurate results because they load down the circuit and absorb the voltage that they are attempting to measure. A acceptable value is 1,000,000 ohms/volt or more on the DC voltage. Most (if not all) digital voltmeters meet this need. Few (if any) non-powered analog (needle style) voltmeters do. Check the specs for your meter to find out. Set your meter to look for 1 volt DC. Many late model cars use a heated O2 sensor. These have either two or three wires instead of one. Heated sensors will have 12 volts on one lead, ground on the other, and the sensor signal on the third. If you have two or three wires, use a 15 or higher volt scale on the meter until you know which is the sensor output wire.

When you turn the key on, do not start the engine. You should see a change in voltage on the meter in most late model cars. If not, check your connections. Next, check your leads to make sure you won't wrap up any wires in the belts, etc. then start the engine. You should run the engine above 2000 rpm for two minutes to warm the O2 sensor and try to get into closed loop. Closed loop operation is indicated by the sensor showing several cross counts per second. It may help to rev the engine between idle and about 3000 rpm several times. The computer recognizes the sensor as hot and active once there are several cross counts.

You are looking for voltage to go above and below 0.45 volts. If you see less than 0.2 and more than 0.7 volts and the value changes rapidly, you are through, your sensor is good. If not, is it steady high (> 0.45) near 0.45 or steady low (< 0.45). If the voltage is near the middle, you may not be hot yet. Run the engine above 2000 rpm again. If the reading is steady low, add richness by partially closing the choke or adding some propane through the air intake. Be very careful if you work with any extra gasoline, you can easily be burned or have an explosion. If the voltage now rises above 0.7 to 0.9, and you can change it at will by changing the extra fuel, the O2 sensor is usually good.

If the voltage is steady high, create a vacuum leak. Try pulling the PCV valve out of it's hose and letting air enter. You can also use the power brake vacuum supply hose. If this drives the voltage to 0.2 to 0.3 or less and you can control it at will by opening and closing the vacuum leak, the sensor is usually good.

If you are not able to make a change either way, stop the engine, unhook the sensor wire from the computer harness, and reattach your voltmeter to the sensor output wire. Repeat the rich and lean steps. If you can't get the sensor voltage to change, and you have a good sensor and ground connection, try heating it once more. Repeat the rich and lean steps. If still no voltage or fixed voltage, you have a bad sensor.

If you are not getting a voltage and the car has been running rich lately, the sensor may be carbon fouled. It is sometimes possible to clean a sensor in the car. Do this by unplugging the sensor harness, warming up the engine, and creating a lean condition at about 2000 rpm for 1 or 2 minutes. Create a big enough vacuum leak so that the engine begins to slow down. The extra heat will clean it off if possible. If not, it was dead anyway, no loss. In either case, fix the cause of the rich mixture and retest. If you don't, the new sensor will fail.

Testing O2 sensors on the workbench
Use a high impedence DC voltmeter as above. Clamp the sensor in a vice, or use a plier or vice-grip to hold it. Clamp your negative voltmeter lead to the case, and the positive to the output wire. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. If not, most likely cause is open circuit internally or lead fouling. If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not likely silicone fouled. If still OK, heat for two full minutes and watch for drops in voltage. Sometimes, the internal connections will open up under heat. This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good. Bear in mind that good or bad is relative, with port fuel injection needing faster information than carbureted systems.

ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age. When replacing a sensor, don't miss the opportunity to use the test above on the replacement. This will calibrate your evaluation skills and save you money in the future. There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph.

---

Rick Kirchhof Austin, Texas | Experience is what you
Domain: [email protected] | get when you don't
Bang path: ...!cs.utexas.edu!peyote!posms!rick | get what
 

·
Registered
Joined
·
1,908 Posts
Thanks for the Lambda info Saabpilot. Iv'e saved a copy for future reference.

Re: Exhaust leak...
>> (CO & HC were fine)

My assumption is that as CO and HC are within limits, that the fault was probably limited to the Lambda Sensor. Wulbert, we look forward to your final conclusions. If, indeed, the Lamda Sensor is at fault, I too can vouch for Eurocarparts selling 'sensibly' priced replacement units. Happy hunting
 

·
Registered
Joined
·
300 Posts
I think the main point from the oxy sensor info above is that many occurences of lamdda out of limits are not actually caused by a faulty oxy sensor but some other fault.
It provides very useful diagnosis before going out and spending dosh on an oxy sensor.
 

·
Registered
Joined
·
188 Posts
If you exhaust is leaking this WILL effect the lambda reading as for the bearing supports not a bad job any competent tech should be able to replace them within one hour unless they are sized on this could take a bit longer
and now back to the footie
aym
 

·
Registered
Joined
·
507 Posts
Discussion Starter · #15 ·
Hooray! It passed today. I ran it through on LPG this time and the tester said it just passed, once he'd found the LPG setting on his gas analyser. It would have failed on petrol though. He also advised me I have a very small hole in the exhaust where the pipe joins the tail box. Not enough to fail as a hole but likely a small gas leak. So this seems to be the problem. Also my friendly fuel inj. guy got back to me before the mot saying in his experience it would likely be a hole . This is a common cause of emmissions failure. Oxygen gets sucked into the exhaust by pressure pulses upsetting the test probe reading. I'll look at it tomorrow in daylight.
Thanks for all the advice & tech help people.
If you live near Glasgow try Douglas at "Re Tune" car electronics:0141-557-1414.He is that rare thing a man who knows what he's talking about. Not cheap tho'
 

·
Registered
Joined
·
507 Posts
Discussion Starter · #16 ·
Oh yeah almost forgot. They fitted the bearing supports for £ 50 for both sides, ok I suppose but would do it myself next time thanks to info posted here.
They cost £6 +vat each from Westcars Saab
 

·
Registered
Joined
·
507 Posts
Discussion Starter · #18 ·
true but the MOT chappie is stiking his probe into the end of the exhaust ( stop sniggering at the back!). Any oxygen coming out here will, I imagine look like unburnt "fuel".
 

·
Registered
Joined
·
1,925 Posts
Yes the fault here is not the engine running wrong, but merely the gas analyser getting the wrong info due to the hole in the exhaust. If we come across this problem we normally just do a repair with paste and try it again. They've always then passed no problem.

Neil
 
1 - 20 of 20 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top