: ECM the problem?

03-11-07, 04:42 PM

Our 81' Deville 4.1 V6 is idling rough and accelerates poorly with signs of fuel starvation at mid-throttle.

CCC return code is 44 which indicates lean 02 sensor.
The Check Engine Light comes on sporadically.
The Oxygen Sensor was replaced last week and initially there was great improvement, followed by the current situation as described above.
The Oxygen Sensor was replaced due to 44/55 return codes shown.
The catalytic convertor checked out fine.

Whether the ECM is totally disconnected or connected makes no difference.
Whether or not the EGR Valve is connected or not also seems to make no difference.

Timing looks OK but seems to fluctuate 2-3 degrees either way of 15 BTDC.
IE: It is never steady.

Is a new ECM required?
Is the ECM known to expire or should I be looking elsewhere?

Any insight will be greatly appreciated.

The Ape Man
03-11-07, 05:29 PM
A spare ECM would be nice to have. Ebay seems to be an excellent source. Good luck. You might try looking for another cause for a lean condition first. Maybe leaky vacuum lines, leaky carbonator base gasket or a broken mixture control solenoid spring inside the carb.

03-11-07, 08:07 PM
Thanks Ape Man.

Although the vacuum pipes look old and a shade dicey I cannot find any apparent problems there.
One of the pipes from the canister leads to nowhere but that has always been the case since I took ownership.

I might just replace all the vacuum hose to make sure.
I will also check out the spring in the carb for sure.
The carb is pretty much a sealed unit so I am reluctant to go in there unless pushed.

03-19-07, 08:08 PM

I am back again.

I have replaced many feet of vacuum hose having found several causes for concern.
If anything the problem is worse, indicating maybe that having closed up "illegal" holes the airflow is now even worse and causing severe choke.

The symptom is bad idling and very bad hesitation on acceleration to the point that the engine almost dies until one lets off in favor of very light pedal pressure.

ECC codes are 12, 13 and 44 which still point at the newly replaced oxygen sensor or lean mixture (opposite to severe choke).

Muffler system is new and the CAT Converter checked out good.

I have also replaced EGR Valve (looked really old), PCV Valve and coil in the distributor cap.
The EGR regulator between the EGR valve and the engine looks very old and in need of replacement but I cannot find anything listed for this part.

I found that the CARB idle adjustment port was open and sucking air which indicates that either someone (PO) was in there or the seal cap dropped off.
I have resealed this port which resulted in better idling and cold start.

Since the Caddie ran very well for two years in our possession up until now I am reluctant to pull the CARB apart for any reason as these rarely fail all of a sudden.

Specific Question: Does the ECM (Computer) just monitor the system or does it actually manage combustion mixture?

I am trying to eliminate the ECM as a possible cause of the idle/acceleration problem.

Any ideas will be greatly appreciated?

The Ape Man
03-19-07, 08:22 PM
The carbonator should have 2 idle mixture screws which were originally capped. If a screw fell out then it needs to be replaced.
The ECM provides a duty cycle modulated pulse signal to the mixture control solenoids in the carbonator. The more on time of the solenoid, the leaner the mixture. Same deal as the very popular CCC 307 powered cars. A broken spring will allow one of the 2 mixrure rods to drop into the full lean position.