ThomasBorchers

1981 Cadillac Fleetwood DFI location of oxygen sensor

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Hello,

 

I am trying to find out, why my 1981 Cadillac 6.0 liter with the nice DFI System runs sooo rich. Lots of black smoke and it needs gas like... don't know...

 

I can't start the diagnostic system so I have to try to find it out the old fashioned way.

 

I would like to start with the oxygen sensor and here is my first problem : I can't find it! Perhaps the cable(s) is off and the computer gets no signal.

 

Can somebody tell me where this sensor is located? And every hint regarding this problem with the rich running engine is welcome.

 

Kind regards

 

Thomas

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Determining when it smokes (cold starts, after it warms up, all the time, etc.) will be helpful information.  For example, black smoke only on cold starts is almost certainly not an O2 sensor issue since that sensor only works after the engine is warmed up.  This would more likely be a different sensor issue.  Get and use a GM factory service manual, as it will have diagnostic flowcharts and other helpful info (including sensor locations.)  

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Hi Jon,

 

thanks for your answer. Well, it smokes all the time. Cold, mid warm, hot...

 

I have the original shop manual but there I can see what to do if trouble code XY is displayed. But as I said, the diagnostic system will not work.

 

So my guess was, to start with the O2 Sensor, since it is to rich all the time. By the way : This is ECM #3 I use... so the computer was already changed 2 times.

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81's had a problem with Coolant Temperature Sensor failures, two wire yellow and black wire. It could be showing that the engine is cold all the time, that could cause a over rich condition. Also, those sensors had a propensity to leak coolant between the metal body and the plastic housing. The coolant actually would be drawn up the wire harness and into the ECM. We had a BUNCH of those under warranty back then with coolant leaking from the ECM onto the floor as a small drip. Might be worth looking into and check the wiring for any traces of corrosion. 

 

Also check the connections, all ECM sensors work on milivolts, the smallest amount of corrosion can casue havoc with the readings.

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To answer the first question, the O2 sensor is on the pipe in front of the catalytic converter and because it points up you can't see it when the car is on the ground. If it helps any, it kind of points towards the right front passengers left foot.

 

I remember the leaking ECM's. I don't remember which years had water drip on them when the seal around the windshield leaked.

 

My favorite location for odd problems on the OBD1 cars is the wire harness. These cars are old enough that the cloth tape wrap can be turning to dust or just plain falling apart. The wires don't have to rub through the insulation to have movement be a problem, they just need to be flopping free next to a wire carrying power. The technical term is hysteresis affect, the simple explanation is your wire bundle becomes a mini alternator and if that micro voltage surge of electricity is tickling a sensor wire carrying a microvolt signal, it can tell the engine controller all sorts of strange things

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Do you have this publication?  If not, it's your starting point in troubleshooting this rich running condition.

 

Cadillac DFI Diagnostic Supplement

 

Since the engine is running rich even when cold, I strongly suspect the TBI (Throttle Body Injection) unit is where the problem lies.

As stated by Writer Jon, the O2 sensor doesn't function until it is heated by exhaust gases.  The ECM uses default fuel mixture and spark timing values while in Open Loop. 

Once the O2 sensor provides a rapidly varying output voltage, the ECM then enters Closed Loop (O2 sensor provides feedback to ECM for A/F mixture).  Even if the O2 sensor is toast, the engine should not run that rich while it's still in Open Loop.

 

The TBI unit might have leaking injectors or the fuel pressure regulator (part of the TBI unit) might be messed up. The spring within the regulator gets weak with age and can cause high fuel pressure.

I believe the pressure should be between 12 & 16 PSI.  GM did not provide a tap in the fuel line to measure the fuel pressure, but it can be measured by a decent shop.

 

The Coolant Temperature Sensor is a thermistor.  It's resistance varies with temperature (high resistance when cold, low resistance when hot).   GM Coolant Temp Sensor Reisitance Values 01.tif

The ECM supplies an exact 5 volts to the sensor and it returns a lower value depending on it's resistance.  I doubt the sensor is the problem because even if it was returning a wacko resistance, the ECM would never command the

super rich mixture your are experiencing.

 

Although I didn't own an early 80's TBI GM vehicle, I did own my '84 Toronado (Olds 5.0L with ECM controlled Rochester Q-Jet) for 28 years.  I became quite familiar with the GM CCC (Computer Command Control) system.  It's very durable and advanced for

it's generation.

 

This June 2012 Hemmings article is very informative and will instruct how to 'flash out' any stored diagnostic codes. All you need is a bent paper clip...!   GM CCC System

Since your Cadillac is a 1981 model, the ALDL connector (Assembly Line Diagnostic Link) is only 5 pins.  It should be located at the bottom of the dash near the steering column.

Please keep in mind that the diagnostic system is primitive by today's standards.  It usually stores codes only for 'fairly hard' circuit or sensor failures. Many driveability problems or intermittent issues will not be identified.

However, these built-in diagnostics were a great step forward as engines began to be controlled by computers.

 

Assembly Line Diagnostic Link (ALDL)   (Image Below)

In order to pull the stored codes do this:

1. With the ignition off, jumper the two far right terminals as shown in the picture. "D" is the diagnostic terminal and "E" is ground.
2. Turn on the ignition but do not start the engine.
3. The SES light will begin to flash a Trouble code 12. One flash, a short pause, and two flashes. There will be a longer pause and the Code 12 will repeat two more times.
4. The stored Trouble Codes will now flash. Each Code will be repeated three times. Write them down.
5. When Code 12 flashes again that indicates that there are no more stored Trouble Codes.
Diagnostic trouble codes may be cleared by disconnecting the battery, or removing the ECM fuse for at least 20 seconds. Reconnect and recheck codes to confirm the repair.

 

************************************************************************************

 

You are fortunate to own a 1981 Cadillac.  Even though the one year V8-6-4 engine had it's problems (not mechanical but CCC related), this 368 cid engine (downsized from the 472 and 425) is a very durable engine.  As you may know, the HT4100 

engine which debuted in 1982 was a major disaster for GM and Cadillac owners.

 

Please keep us posted,

 

Paul

 

 

 

81_ALDL.jpg

Edited by pfloro (see edit history)

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If you can get a OBD 1 scanner that looks like this 

 

  http://www.ebay.com/itm/GM-Tech-1-Diagnostic-Scanner-Scan-Tool-Selling-for-Parts-/361642562445?hash=item543393938d:g:hHEAAOSw7XZXg-ao&item=361642562445&vxp=mtr

 

 to plug into the ALDL connector you should be able to look at the readings and quickly tell what the problem is.  The one above is broken.

 

This one might also work. 

 

http://www.ebay.com/itm/Kent-Moore-Tools-J-34775-MPSI-Mini-Scanner-Model-5247-/180988069849?hash=item2a23bac7d9:m:mHhXYJ6ul8zLeRXsmMGCsHw&item=180988069849&vxp=mtr

Edited by Larry Schramm (see edit history)

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Hello,

 

and thank you for all the answers. A lot to read.

 

At Larry : I own a OBD 1 and 2 scanner but have just the OBD2 plug.

 

At Paul : Very interesting, I have to check all this out. No, I don't have this supplement. I have this big, silver Cadillac shop manual and the wiring diagrams.


OK, I have to read now, and will come back later.

 

Kind regards

 

Thomas 

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Hello again Paul,

 

I have tried it with the ALDL but the "check engine" light will not start to flash. I have here 2 other ECM. Both shall be defective but I have not changed them and would like to check it.

 

Kind regards

 

Thomas

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OK, an update : I changed to the other old ECMs and they work really not. Seems that one produce a to advanced spark ( if they can do it ) and the other one makes a similar trouble with a backfire in the carburetor. But both ECM show me the code "14" and "19". I tried to clear the codes but this was not possible.

 

But : As I started with the good ECM, the mixture seems to be ok. But after a while ( perhaps 3 minutes ), suddenly the engine run worse and again black smoke.

 

That's what I found out in the meanwhille.

 

Thomas

Edited by ThomasBorchers (see edit history)

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Remember that the oxygen sensor is just telling you  what is happening up stream of the sensor and then sends a signal to the ECM to make corrections to the fuel mixture to meet the 14.7:1 air fuel ratio.

 

In order I would look at good grounds, coolant sensor, Injectors, fuel pressure, and wiring problems/connections.

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Today, I started the engine again from cold condition. Outside it was 55 °F, the start was hard, I used finally a bit easy start spray. OK, then the engine run, I had a look at the exhaust. Was light white smoke. Then the smoke were more intensive but still white.

Sometimes it seemed, that the engine will stop but run again. This made the engine several times and then at one time, the smoke was black. Then the engine stopped by itself after a minute. But it was possible to start it again and had now again the black smoke…

Could it be, that if it seems, that the engine will stop, that it has something to do with the 8-6-4 system?

By the way : I wonder why I don’t have this instrument, which shows how many cylinders are working.

Now I will try to check the coolant sensor.

Regards

Thomas

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I have seen now, that in the plug which goes from the coolant sensor to the ECM was / is a jumper wire. I pulled it out and checked the voltage, it is 5.7 volts. I plugged in the plug in the connector to the sensor but there was now change, still black smoke. And it will be darker black smoke, the hotter the engine is.

The sensor hat a resistance about 1.8 kOhms

 

The fuel line in my Cadillac has already a tap so I checked the fuel pressure and it is about 9 psi.

 

I have also found the O2 sensor and pulled the plug but it runs still much to rich.

 

When I have the ignition on, I looked at the injectors if they drip fuel but they don't.

 

In an other forum, I have read, that someone had a problem with a vacuum hose and the MAP sensor. So I had a closer look to my sensor. It is a plastic style set like this one on the right side : 19838020rt.jpg

 

But just the lower one has a vacuum hose, not the upper one. Is this correct?

 

For me it seems as when the injectors deliver always the same amount of gas at idle speed. On the road, the car runs not bad. But at idle... in short time, I have a black cloud on my property.

 

Hmmm....

1981 Cadillac.jpg

Edited by ThomasBorchers (see edit history)

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Hello Thomas,

 

There may be more than one engine issue to sort out (white smoke at startup) but the main issue is the rich running situation (black smoke)...

I am still firmly holding onto my sense that the TBI unit (injectors & fuel pressure regulator) is the source of the rich running condition.  With the

ignition 'ON' and the engine not running, the injectors are not being energized (pulsed) by the ECM.  Even though you don't see any dripping fuel,

this doesn't mean that when they are energized, more fuel than necessary is being injected into the intake manifold.  I would either have the

existing TBI unit rebuilt or purchase a reliably rebuilt unit.

 

The 9 PSI fuel pressure is low as it should be between 12 -15 PSI.  The fuel pump (in the fuel tank) is probably weak.  However, lower fuel pressure would result

in a lean running engine, not a rich condition.  I wouldn't make the fuel pump a priority at this moment.

 

Since the outside temperature was 55 degrees F, the white smoke was probably NOT condensed water vapor.  It might be either coolant being pulled

into the combustion chamber(s) due a head gasket issue or it could be transmission fluid being burned due to a leaky vacuum modulator diaphragm.

Your '81 Cadillac uses the indestructible THM400 transmission which has a vacuum modulator.  At this point, I wouldn't troubleshoot the white smoke.

 

The fact that the engine was hard to start when cold and required a squirt of starter fluid points (IMHO) to trouble with the TBI.

 

I am certain that the V8-6-4 system has nothing to do with the rough idling and conking out while warming up.  If you want to verify this, disconnect both

connectors on the tops of each valve cover.  These connect to the solenoids which (when energized) deactivate either one or two cylinders on each bank. 

Startup and idling of the V8-6-4 always uses all 8 cylinders.  I suspect the conk out while warming up is due to the 'load up' of carbon on the spark plugs and

a mixture that is so rich that combustion just ceases.

 

Regarding your MAP sensor in the picture:  There are two sensors attached to that metal bracket.  The lower sensor is the MAP sensor which should

have a vacuum hose attached to it.  The upper sensor (which looks the same) is the BARO sensor (Barometric Pressure Sensor).  It measures atmospheric

pressure and allows the ECM to adjust fuel and spark as the altitude changes (Pretty Neat...!).  It senses air pressure through it's open port so no hose is connected.

 

Once you get this rich running condition corrected, it would be a good idea to replace the spark plugs.  They are inexpensive and probably full of carbon

due to the excess fuel being fed into the engine.  An oil change would also be in order...

 

Please keep us posted.

 

Paul

 

PS:  Interesting reading regarding the V8-6-4 engine:  1981 Cadillac L62 V8-6-4 Engine

 

 

 

 

 

 

 

 

 

 

Edited by pfloro (see edit history)
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Hi Paul,

 

thank you very much for your words and thoughts. Yesterday I disconnected the battery over night and also the four plugs for the 8-6-4 system. I started today again and I let the engine idle with the higher idle speed, which the engine has after cold start. A long time there were no or a very few black smoke. Then I depressed the acclerator pedal for lower idle. Then it startet again the usual black smoke.

But this time, I had not these dropouts in the idling.

 

Well, I have to see, that I can get the injectors and regulator for a resonable price here. But I have a good source, just 5miles away.

 

Kind regards

 

Thomas

 

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On ‎8‎/‎10‎/‎2016 at 6:11 AM, ThomasBorchers said:

In an other forum, I have read, that someone had a problem with a vacuum hose and the MAP sensor. So I had a closer look to my sensor. It is a plastic style set like this one on the right side : 19838020rt.jpg

 

But just the lower one has a vacuum hose, not the upper one. Is this correct?

 

 

The round sensors are known to have a high level of failure.  If you have the black plastic ones you should be good.  Silver- replace them.

 

One of the sensors should have a vacuum line going to the manifold.  That is the MAP sensor.  (Manifold Absolute Pressure) relative to barometric pressure.

 

The other sensor might have a sponge screen on the port.  That is the Baro Sensor.  (Barometric Pressure Sensor)

Edited by Larry Schramm (see edit history)

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Thank you for this information, Larry.

 

@ Paul : When I read 9 psi on my pressure gauge, then actually the pressure regulator should be ok and it is probaly a problem with the injectors?

 

BTW : The presure drops to zero within a minute.

 

Kind regards

 

Thomas

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3 hours ago, ThomasBorchers said:

Thank you for this information, Larry.

 

@ Paul : When I read 9 psi on my pressure gauge, then actually the pressure regulator should be ok and it is probaly a problem with the injectors?

 

BTW : The presure drops to zero within a minute.

 

Kind regards

 

Thomas

 

Are you saying that the fuel pressure drops to zero within a minute.  Is that with the car running or turned off?

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It should not drop with the ignition off.  If it does, then you have either a leaky injector or the check valve in the pump is bad. 

 

With the black smoke on start up I would look to a bad/leaky injector.

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Hi all,

today I have installed two new injectors with all these o-rings and gaskets. The engine started now by the first two turns ( after standing still for a couple ogf weeks ) but now immediately black smoke, not after a while.

 

Weather : Sunny with 83°F

 

So all my hopes are gone in these two new injectors...

 

Thomas

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Hello Thomas,

 

I my previous post (#15), I suggested that you should have the existing TBI unit either rebuilt or purchase a reliably rebuilt unit.  Rebuilding a GM TBI includes

not only testing or replacing the injectors but also replacing other parts as well.  In particular, the fuel pressure regulator section of the TBI contains a diaphragm

and spring which can deteriorate over time.  The TBI unit also contains the IAC (Idle Air Control).  This is a solenoid/spring/valve assembly mounted on the side

of the TBI unit and controlled by the ECM.  It should also be serviced as part of the TBI unit rebuild.

 

Even though your fuel pressure was low which wouldn't cause a super rich mixture , there may still be problems with the TBI.   To rule out these potential problems,

a complete rebuild of the TBI unit should be performed.  You can certainly use the new injectors which you have already purchased.  This was money well spent...!

 

I'm attaching a few images of the TBI unit for clarification.  In the drawing, item #5 (Body Assembly - Fuel Meter) is the fuel pressure regulator.

 

Please keep us posted.

 

Paul

 

GM TBI Image 01.jpgGM TBI Image 02.jpgGM TBI Image 04.jpg

Edited by pfloro (see edit history)

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Hello Paul,

 

thank you, for your explanation. Well, I thought, since the pressure was not to high, that it is not necessary to chnage the pressure valve. But seems, that I was wrong.

Somewhere else I have read, that the TP Sensor could be the problem, sending the wrong position to the ECM. As  you said, that the problem could be also in the TP Sensor.

 

Well, do I need now a full TBI unit or can I change the TPS and fuel pressure valve by myself?

 

Now it is so, that it seems, that the engine gets more fuel as before I changed the injectors. But with this, it starts great.

 

Kind regards

 

Thomas

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