E4MC 1986 307 Oldsmobile idle issues.
02-25-2019, 03:01 PM
#1
Junior Member
Thread Starter
Join Date: Feb 2019
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
E4MC 1986 307 Oldsmobile idle issues.
I am looking for some assistance with what I think is a carburetor problem
Here is the rundown
1986 307 Olds VIN Y, Rochester CCC E4MC
Engine is completely stock as it came from the factory, 106,000 miles, original owner. Carb had never been rebuilt, still had the factory plugs over the mixture screws.
The car would stumble and sometimes stall at idle, so I rebuilt the carb, cleaned everything thoroughly, and replaced the mixture control solenoid (MCS), throttle position sensor (TPS), fuel filter.
Set the new TPS to 0.41 volts.
After putting the carb back on, the car starts and runs, but I can’t get the mixture control solenoid to reach the 30 degrees on the 6cyl dwell scale. It hangs right about 50 degrees, steady. It moves when I accelerate, or when the engine stalls out.
I have adjusted the following, but the MCS stays at or slightly below 50.
- Idle mixture screws: have been between 2 ½ and 6 turns out, no change. Before rebuild these were 2 ½ turns out.
- MCS: Se this to spec when I reassembled the carb. With the correct tool I have turned this in and out several turns, without the dwell moving (though the RPM changes, as does the engine sound/smoothness).
- Idle Air Bleed Valve: Set this to spec when I rebuilt the carb. Turned this and the RPM will change but the dwell does not move.
I have good vacuum at the carb (21 inches), and have checked and replaced suspect vacuum lines.
I have no stored error codes and didn’t have any when I started.
Questions: (And I have read a lot of forums, but am not sure what to make of some explanations). If any of this is covered in another forum, please let me know and I will read it.
1 - The Dwell is always 49-50 on the 6 cyl scale. If the MCS, Idle Air, and mixture control screws don’t change this, what should I be checking? Could this be caused by a bad O2 sensor, even if the car doesn’t idle smoothly when first started? (I have not found a good explanation of how closed and open modes work and how to see if both are working properly)
2 – Could there be different kind of vacuum issue (i.e. bad canister purge valve) that would cause this?
3 – What actually controls the idle rpm on these engines with an E4MC?
4 – Is there another sensor in open and closed mode that would send the mixture control solenoid to this range and prevent it from being affected by the above adjustments?
Any assistance is very much appreciated.
Here is the rundown
1986 307 Olds VIN Y, Rochester CCC E4MC
Engine is completely stock as it came from the factory, 106,000 miles, original owner. Carb had never been rebuilt, still had the factory plugs over the mixture screws.
The car would stumble and sometimes stall at idle, so I rebuilt the carb, cleaned everything thoroughly, and replaced the mixture control solenoid (MCS), throttle position sensor (TPS), fuel filter.
Set the new TPS to 0.41 volts.
After putting the carb back on, the car starts and runs, but I can’t get the mixture control solenoid to reach the 30 degrees on the 6cyl dwell scale. It hangs right about 50 degrees, steady. It moves when I accelerate, or when the engine stalls out.
I have adjusted the following, but the MCS stays at or slightly below 50.
- Idle mixture screws: have been between 2 ½ and 6 turns out, no change. Before rebuild these were 2 ½ turns out.
- MCS: Se this to spec when I reassembled the carb. With the correct tool I have turned this in and out several turns, without the dwell moving (though the RPM changes, as does the engine sound/smoothness).
- Idle Air Bleed Valve: Set this to spec when I rebuilt the carb. Turned this and the RPM will change but the dwell does not move.
I have good vacuum at the carb (21 inches), and have checked and replaced suspect vacuum lines.
I have no stored error codes and didn’t have any when I started.
Questions: (And I have read a lot of forums, but am not sure what to make of some explanations). If any of this is covered in another forum, please let me know and I will read it.
1 - The Dwell is always 49-50 on the 6 cyl scale. If the MCS, Idle Air, and mixture control screws don’t change this, what should I be checking? Could this be caused by a bad O2 sensor, even if the car doesn’t idle smoothly when first started? (I have not found a good explanation of how closed and open modes work and how to see if both are working properly)
2 – Could there be different kind of vacuum issue (i.e. bad canister purge valve) that would cause this?
3 – What actually controls the idle rpm on these engines with an E4MC?
4 – Is there another sensor in open and closed mode that would send the mixture control solenoid to this range and prevent it from being affected by the above adjustments?
Any assistance is very much appreciated.
Last edited by Eric2003; 02-25-2019 at 03:05 PM.
Thread
Thread Starter
Forum
Replies
Last Post
377Z
Engine/Drivetrain/Suspension Parts for Sale
5
09-26-2008 11:48 AM