ThomasBorchers

1981 Cadillac Fleetwood DFI location of oxygen sensor

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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

 

 

Edited by pfloro (see edit history)

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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.

Edited by Larry Schramm (see edit history)

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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?

Edited by Larry Schramm (see edit history)

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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
 

 

 

 

 

 

Edited by pfloro (see edit history)

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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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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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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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Tom,

 

You need to check the specification for the TPS. 1 volt might be high and it needs to be adjusted.  Find a book and see what it should be.  Start there.

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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

Edited by ThomasBorchers (see edit history)

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Hello again,

 

well, in the meantime I am a bit more familiar with the DFI system.

 

As Larry told me, I have checked the TPS adjustment. The voltage was too high for the idle speed. To adjust, I had to remove the TBI body, drill out this small welding spots which block the “adjustment” screws of the TPS. There I found out, that the cam of the throttle cam has a bit too much clearance in the TBI body. But I have replaced the TBI housing as it was.

Then I tried to adjust the engine at 400rpm but this was not possible. The lowest speed I can set is 600rpm. Under this, the engine shuts off. Perhaps this is the result of the throttle cam play, don’t know.

So I set the voltage of the TPS at 600rpm at 0,6 volts which should not be too much. So actually from this view, the mixture should not be too rich.

I tried to do the adjustment as described in the shop manual with ISC and TPS. But the ISC is not moving. Since I know, that the motor can work, if it has voltage, I think the actuation from the ECM is not working as it should. Probably…

I removed then the plug of the ISC, set the plunger to an idle speed around 800rpm. The idling was ok now, the exhaust was perhaps a bit black but not that much as before. Then I accelerated the engine and the was a “hole” in the acceleration, was not really possible to speed it up. When I went slowly back to idle, it run again rough and with more black smoke as before.

 

At this point I decided to order a new MAP sensor since this part is also responsible for the mixture.

 

Today a have installed the new MAP. Well, actually it is like before but I mean, that it now accelerates better as before. But going slowly back to idle, I have than again a too rich mixture and the engine shuts off. When I then shut of the ignition, wait some seconds, start again, the engine runs again better with good idling and just a little bit black smoke or perhaps it is just blue from oil.

 

At the moment I come to the result, that the ECM could have a malfunction and need to be replaced. ( again… ). What do you think? It shows no codes, the ISC is not working and then the rich idling…

 

I am sorry for my English but it is hard to say all this in a foreign language.

 

Kind regards

 

Thomas

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