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1981 Cadillac Fleetwood DFI location of oxygen sensor


ThomasBorchers

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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

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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

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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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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

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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

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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

 

 

 

 

 

 

 

 

 

 

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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)

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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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  • 2 weeks later...

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

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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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Hello Thomas,

 

You definitely want to service both the pressure regulator (replacing spring & diaphragm, etc.) and the IAC (Idle Air Control).

If you car comfortable with removing the TBI unit from the engine and disassembling / servicing / reassembling it, then go for it...!

 

After the rich running condition has been resolved, the TPS (Throttle Position Sensor) should be replaced.  This sensor

tells the ECM exactly how far the throttle blades are open.  

However, even a faulty TPS wouldn't cause the extremely rich running condition which you are experiencing.  

 

If you purchase the proper rebuild kit for this TBI unit, you can service the the fuel pressure regulator and the IAC yourself. Unfortunately,

I can't be of assistance with selecting the proper rebuild kit as I didn't own a GM TBI engine.  Be sure to get a replacement spring for the

fuel pressure regulator as I don't think the spring is included in most (or all) of the rebuild kits.  This replacement spring should be the GM stock

type and not a stiffer spring designed to raise the fuel pressure.

 

After looking at the diagram in my post (#24), it seems that if the diaphragm in the Fuel Pressure Regulator Assembly is damaged and leaking,

this would result in unregulated full pressure to the injectors.  If my logic is correct, this may be the cause of the extreme rich condition.

 

Keep us posted,

 

Paul

 

EXAMPLE - GM TBI Rebuild Kit

 

GM TBI Rebuild Pictures

 

GM TBI Rebuild Video

 

 

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Did you check for good vacuum at the MAP sensor? Sometimes the vacuum port in the throttle body can get plugged with carbon or the hose can collapse or become plugged. No or low vacuum to the MAP will give a really rich condition and black smoke.  You really need to get a scanner on there so you can see all your sensor readings.

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If you get a scanner, with the engine not running ignition on, the MAP & Baro sensors should read almost the same.  If my memory is correct they will read about 4.5 volts or .5 volts +- depending on elevation of the car ( I do not remember which way on the scale, but I think the 4.5 is correct).  If you start the car the MAP sensor will start changing in value.  If the two sensors are not about the same(+-.02 volts) with engine off / key on, Start by replacing the bad sensor.

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Hi Paul : Thank you again. Well, I am working at old cars since 20 years, So I guess, that I could manage to remove the TBI unit and so on. I am not really familar with these electronic things but changing parts, I can do it.

 

@ misterc9 :

I have checked the vacuum hose at the MAP. Actually I wanted to disconnect the hose at the MAP but this was hart to reach since there are all the cables from the ECM connectors. So I decided to disconnect the plastic line from the hose which goes into the TBI unit. But first I tried to suck a bit the the line which goes to the MAP. I did it very carefully but there was no resistance. I had a closer look to the MAP and have seen : There was no clamp at the hose at the MAP. I put one on it and then there was a resistance, as I sucked at the line. OK, I started the engine but ran very rich. But I ran just on 4 or 5 cylinders now, since all sprak plus must be dirty now. So I had now no chance to check if there is vacuum at the hose from the TBI unit. This will be the next step, but first cleaning the plugs.

I would need an adapter for my OSB scnanner but I am not sure if I can read there something, since the ECM diagnostic system will not work.

@ Larry : Is it possible to check the voltage with out a scanner, just with a voltmeter?

Kind regards

Thomas

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13 hours ago, ThomasBorchers said:

@ Larry : Is it possible to check the voltage with out a scanner, just with a voltmeter?

Kind regards

Thomas

 

Not that I know of.  What do you mean that the ECM diagnostic system will not work?

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Hi Thomas,

 

Don't let the rebuild of your TBI unit scare you...!  It has fewer parts & adjustments than the non-electronic 4 BBL Rochester carburetor which was used on the 1980 Cadillacs (non-California cars).

The injectors are simply fuel valve solenoids which are pulsed by the ECM.  The IAC (Idle Air Control) is also a solenoid which is pulsed by the ECM to control engine speed 

as the the engine load at idle changes.  The TPS (Throttle Position Sensor) is just a variable resister.   You don't need to understand the internal workings of the ECM in order to rebuild the TBI unit.

 

You'll need a digital voltmeter (usually a multimeter which also measures both AC & DC, low current and resistance) to read the voltages in the CCC (Computer Command Control)

system.  They are not expensive.  Here's one on Amazon:  Digital Multimeter     This type of meter is needed so that the ECM circuits are not 'loaded down' while taking measurements.

Carefully open the back side of the connectors to expose the wire side of the terminals.  Then you can 'back probe' the terminals with the meter's probes.  I've done this

many times and it's not difficult.  Be careful as the plastic connectors will be brittle after enduring 35 years of heat and cold.

 

You have mentioned that the ECM diagnostic system doesn't work.   I think what has failed is the interface between the serial data output from the ECM and the

climate control system.  In 1981, Cadillac designed the digital climate control system to interface with the ECM.  This made it possible to troubleshoot the CCC system without

external test equipment.  Even without this interface working, you can still 'flash out' any DTCs (Diagnostic Trouble Codes) by jumping two terminals of the ALDL connector and

watching the amber Check Engine dash light.  Since you have an 'early' CCC system, your ALDL connector should be a five terminal connector located under the dash by the

steering column.  However, I am not sure where it might be located on your car.  

 

Before you attempt to 'flash out' codes, I have a couple of questions:

 

1) Does the amber CHECK ENGINE light come on when you turn the ignition key to ON? (engine not running)

2) Does the Check Engine light go out when the engine is then started?

 

Code '12' (the first flash is the 'tens' value, the next flashes are the 'units' values / 10 + 2 = 12).

Code '12' indicates that the ECM is not seeing a 'reference pulse' from the distributor.  A code '12' will always be present when the engine is not running.  A code '12' does

not indicate a problem.

 

As another example, a code '34' would be indicated by 3 flashes and then 4 flashes in quick succession / 30 + 4 = 34).

Once you actually see how the codes are 'flashed out', it will become very clear. 

 

After seeing what trouble codes (if any) are stored, I would concentrate on rebuilding the TBI unit.  Once that unit is squared away and I hope corrects your

rich running condition, we can then work through the trouble codes which exist.

 

Assembly Line Diagnostic Link (ALDL)  / 5 pin 
 
81_ALDL.jpg.e66fb5a8b9f79de6a47e2ce21eac14a9.jpg
 
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 (Service Engine Soon / Check Engine) 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.
 
***********************************
FYI:  In the 28 years that I owned my 1984 Oldsmobile Toronado (no TBI unit but an ECM controlled Rochester 4 BBL), I troubleshot the CCC system with a digital voltmeter, an analog tach/dwell meter and flashed out
codes from the ECM by using the Check Engine light.
 
Paul
 

 

 

 

 

 

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  • 2 weeks later...

Hello again!

 

I was some day on the roads in Sweden and now back to my Cadillac. Thank you for all the thoughts.

 

Today I have first cleaned up the spark plugs.

 

Then I started again but from the start of course again, heavy smoke. I wanted to check the vacuum from the TBI unit at idle speed, my gauge shows there -400 mBar. I don’t know in what I shall it to convert to US standard.

I have read in the shop manual, how to check the TPS, but for this I had to disconnect one of the injectors, then the engine run nearly ok. A bit black smoke but the engine run. After a while I thought, that the idle shall drop down but it will not work. Was still at the same speed with warming up. At this, the voltmeter shows 2 Volts, connected to the ECM. I have removed the ISC from its bracket to lower the idle speed. So I guess that I had the 375 upm but not really sure since I don’t have a tachometer which works for 8 cyl engines. At this idle speed the voltmeter shows 1 Volt which actually is too much, the book says 0,5 Volt. But is this a reason to run much too rich?  

After this, it seems that the ISC is not working.

 

To all your questions :

 

To Larry : Well, the diagnostic system starts not with 88 as it should, it shows just two dots and then nothing. As I changed to the old broken ECMs then it worked as it should.

 

To Paul : I already have a multimeter since I have often to do with car electrical problems.

Yes, I have seen it, that it is possible to open the connectors at the back. Perhaps just one time, as you said.

On page one you have already written about the possibility to check the codes by “check engine” light. And I tried this already but the light will not start to flash. The ALDL is under the dashboard in the middle.

 

1.) : The check ignition lamp is already on, if I switch on the ignition.

2.): When the engine is running, it will not go out.

 

As I have written on Page one, as I used the both broken ECMs, then trouble codes 14 and 19 were shown. I know the reason for these codes : Someone has put a jumper in the connector of the coolant sensor and the relay of the fuel pump is removed and there is also a jumper wire that the fuel pump pumps all the time. I have connected the coolant sensor again.

 

Well, that’s it for the moment.

 

Kind regards

 

Thomas

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  • 2 weeks later...

Hello Thomas, 

 

Your Cadillac appears to have a couple of different issues.  I would put aside all the electronic & electrical issues and fully rebuild the TBI unit first.

I am feeling more confident the the very rich running condition is due to the fuel pressure regulator within the TBI unit.  Address the TBI

unit before concerning yourself with the electronics. 

 

The present ECM is not fully functional.  Since the 'broken' ECMs allowed you to flash out codes (or allowed the diagnostic system to work), the present ECM

has a problem.  You need to get an ECM with is fully functional and allows any stored codes to be retrieved either via the Check Engine light

or the diagnostic system.

 

Paul

 

 

 

 

 

 

 

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  • 4 weeks later...

Hello again,

 

today I had the chance to rebuild the fuel pressure regulator. I haven't seen something broken old parts, but the old spring is longer as the new one.

 

Now... it seems that the engine runs richer as before... hard starting, heavy black smoke... :(

 

Well, since I put in new parts, the engine runs richer and richer... makes it sense to change now the TPS?

 

Kind regards

 

Thomas

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If you can get a scanner, the Throttle Position Sensor should read about .5 volts or less if my memory is correct.

 

The other thing is what is the engine coolant temperature sensor reading?  Also if there is a break in the wire from the ECM to the engine coolant temperature or a bad connector the ECM will think the engine is freezing cold and give it full fuel as if it is in the middle of the winter.

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Hi Larry,

 

thank you. I will check this out. Ah, but I remember I checked already the TPS, the voltage was 1 Volt.

 

What I have seen today : When I disconnect one of the fuel injectors, it runs of course leaner. But : If just the drivers side is running, the mixture seems to be ok, a bit too rich but hard to see a black smoke. When I use just the passengers side injector, it runs too rich with black smoke. Actually the mixture should be the same? Could this be a a note of the problem?

 

Kind regards

 

Thomas

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Hi Larry,

 

today I tested the wiring of the coolant sensor. Seems that the sensor is ok, the resistances look ok. The wiring from the plug of the sensor to the plug at the ECM is also ok.

 

I cleaned up again the spark plugs and started the engine. Hmm, funny… the first minute it seemed, that everything is working, no black exhaust. But after ca. a minute the idle drops a bit and black smoke came again out of the exhaust system. But it seems, that it is not that rich as it was before. I waited the whole day and tried again with cold engine. Was the same… in the first minute it was ok, than again black smoke as it was in the morning.

 

And it seems that I have a problem with the ISC. Looks not so, that it is working. But I have to check this tomorrow with my shop manual. To adjust the TPS, I have to remove the TB and so on. A thing for tomorrow…

 

By the way : With engine running, the gas tank went empty and as the fuel pressure went down, the idle speed went up since the mixture was leaner and leaner. Of course just to the point, as the gas tank was really empty.

 

Regards

 

Thomas  

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After this day, I must say : The solution is close. With too rich mixture idling, I started to remove the whole ISC. I opened the nuts and then of course the idle went down. And… the mixture went leaner. So I got a good, not too rich idling. Hmm, I checked if the motor of the ISC is working but it seems not. I have tested the motor of the ISC outside the car. It worked but not really smooth. So I opened the ISC and cleaned it up with new lubrication. But I don’t understand this : If fully extended, the gear lose the contact to its spindle and it is not possible to retract because the gear turns now free. I don’t if inside is something missing to stop the motor at the end.

I guess, that something is not working correct between TPS, ISC and mixture… ?

 

 

OK, now, since the engine was idling good, I have problems to accelerate the engine. When I push the gas pedal, the seep rise up but then it seems as the mixture is now too lean to pick up speed. With faster push down the pedal, the engine shuts off.

 

At the moment I am happy that the rich mixture is gone but have to solve the other problem.

 

What I would like to know :  How much volt about should I measure at the ISC connector?

 

Kind regards

 

Thomas

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