Lincoln Town Car surges

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rikdee

New member
Sep 20, 2022
4
1
3
My Lincoln
1989 Town Car Signature Series
1989 Lincoln Town Car surges when warmed up. IAC was replaced last September. Egr valve, sensor and vac. sol. valve replaced last month.
 

Action

Junior Member
Aug 12, 2005
1,703
839
113
Phoenix, AZ 85008-1418
How many miles?
At what speeds does the surge occur?
Does it surge when in park?
Is the check engine light on? If yes post codes.
When were the air and fuel filter last replaced?
Do you have a vacuum gauge?

Action
 

rikdee

New member
Sep 20, 2022
4
1
3
My Lincoln
1989 Town Car Signature Series
How many miles?
At what speeds does the surge occur?
Does it surge when in park?
Is the check engine light on? If yes post codes.
When were the air and fuel filter last replaced?
Do you have a vacuum gauge?

Action
Mileage is 111,194
Surges after pulling out of a parking spot, not in Park . No engine light,
Air filter replaced 9/21, fuel lines and filter replaced 5/14, mileage was 109,385, no vacuum gauge.
Previous code was 34. (EGR)
 

Action

Junior Member
Aug 12, 2005
1,703
839
113
Phoenix, AZ 85008-1418
OK this is an EEC IV system
Surging on any system is typically because teh air/fuel ratio is off (usually lean) and the system is correcting. After the correction the RPM goes up so the system goes lean. That brings the RPM down however it is too lean again and repeats the cycle.

The other issue could be O2 sensors. These sensor give feedback to the processor as to how lean or rich the mixture based on the exhaust. The problem with those with 100,000 of service is they slow down. The signal back to the processor is no longer real time it is a second or so delayed. Which means the processor is making air/fuel ratio adjustments based on old data.

You my ask why don;t I get an O2 code. This is because the code is generated only when the O2 sensor does not return a signal. (It ain't working no more!) If the signal is slow, the warning system does not know the signal is slow. It just gets a signal and it is good to go.

I would recommend replacing the O2 sensors. You can get them on ebay for under $25 each. It is like getting a turn up because the processor will be making adjustments in real time.

The EGR work you did can generate a surge as well IF the valve does not close all the way. The EGR valve should be closed in ALL cold engine operations and slow speed conditions. You can check to see if the EGR is functioning correctly on a hot engine, running in park. Force the valve open and the engine should stall. If EGR does not open during warm running engine and at speed, you should be able to hear spark knock or detonation.

The other things that can cause surge -
Vacuum leak or unmetered air after the throttle body. This is air that is getting into the engine that the processor does not know about. The processor is being told how much air is coming into the engine with a sensor up front. (MAF) If air is getting into the engine that the processor does not get signaled about, the processor is now guessing on how much fuel to squirt. The processor will never get that one right with a vacuum leak.

The other area would be a bad MAF sensor or the connections to the air cleaner, throttle body are not well connected. Easy to check the air intake connections. Usually a failed MAF will have more severe issues than you are reporting.

Hope this helps

Action
______________________________
 

rikdee

New member
Sep 20, 2022
4
1
3
My Lincoln
1989 Town Car Signature Series
OK this is an EEC IV system
Surging on any system is typically because teh air/fuel ratio is off (usually lean) and the system is correcting. After the correction the RPM goes up so the system goes lean. That brings the RPM down however it is too lean again and repeats the cycle.

The other issue could be O2 sensors. These sensor give feedback to the processor as to how lean or rich the mixture based on the exhaust. The problem with those with 100,000 of service is they slow down. The signal back to the processor is no longer real time it is a second or so delayed. Which means the processor is making air/fuel ratio adjustments based on old data.

You my ask why don;t I get an O2 code. This is because the code is generated only when the O2 sensor does not return a signal. (It ain't working no more!) If the signal is slow, the warning system does not know the signal is slow. It just gets a signal and it is good to go.

I would recommend replacing the O2 sensors. You can get them on ebay for under $25 each. It is like getting a turn up because the processor will be making adjustments in real time.

The EGR work you did can generate a surge as well IF the valve does not close all the way. The EGR valve should be closed in ALL cold engine operations and slow speed conditions. You can check to see if the EGR is functioning correctly on a hot engine, running in park. Force the valve open and the engine should stall. If EGR does not open during warm running engine and at speed, you should be able to hear spark knock or detonation.

The other things that can cause surge -
Vacuum leak or unmetered air after the throttle body. This is air that is getting into the engine that the processor does not know about. The processor is being told how much air is coming into the engine with a sensor up front. (MAF) If air is getting into the engine that the processor does not get signaled about, the processor is now guessing on how much fuel to squirt. The processor will never get that one right with a vacuum leak.

The other area would be a bad MAF sensor or the connections to the air cleaner, throttle body are not well connected. Easy to check the air intake connections. Usually a failed MAF will have more severe issues than you are reporting.

Hope this helps

Action
Thanks for the info!
 

rikdee

New member
Sep 20, 2022
4
1
3
My Lincoln
1989 Town Car Signature Series
Acti
OK this is an EEC IV system
Surging on any system is typically because teh air/fuel ratio is off (usually lean) and the system is correcting. After the correction the RPM goes up so the system goes lean. That brings the RPM down however it is too lean again and repeats the cycle.

The other issue could be O2 sensors. These sensor give feedback to the processor as to how lean or rich the mixture based on the exhaust. The problem with those with 100,000 of service is they slow down. The signal back to the processor is no longer real time it is a second or so delayed. Which means the processor is making air/fuel ratio adjustments based on old data.

You my ask why don;t I get an O2 code. This is because the code is generated only when the O2 sensor does not return a signal. (It ain't working no more!) If the signal is slow, the warning system does not know the signal is slow. It just gets a signal and it is good to go.

I would recommend replacing the O2 sensors. You can get them on ebay for under $25 each. It is like getting a turn up because the processor will be making adjustments in real time.

The EGR work you did can generate a surge as well IF the valve does not close all the way. The EGR valve should be closed in ALL cold engine operations and slow speed conditions. You can check to see if the EGR is functioning correctly on a hot engine, running in park. Force the valve open and the engine should stall. If EGR does not open during warm running engine and at speed, you should be able to hear spark knock or detonation.

The other things that can cause surge -
Vacuum leak or unmetered air after the throttle body. This is air that is getting into the engine that the processor does not know about. The processor is being told how much air is coming into the engine with a sensor up front. (MAF) If air is getting into the engine that the processor does not get signaled about, the processor is now guessing on how much fuel to squirt. The processor will never get that one right with a vacuum leak.

The other area would be a bad MAF sensor or the connections to the air cleaner, throttle body are not well connected. Easy to check the air intake connections. Usually a failed MAF will have more severe issues than you are reporting.

Hope this helps

Action
Thanks for the info!
It looks like this model vehicle doesn't have a MAF. It's certainly not on the air intake tube or the filter housing. Have you ever replaced an oxygen sensor on a Lincoln Town Car? It appears that they have to be accessed from underneath. I think I'll take the car to my local Midas service facility.
 
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