1993 Lincoln Town Car runs too Rich


Asked by Nov 12, 2014 at 04:41 PM about the 1993 Lincoln Town Car Executive

Question type: Maintenance & Repair

We had already addressed this last year in a SOLVED forum string at: http://www.cargurus.com/Cars/Discussion-t16140_ds556620   (The string was mis-titled "too lean.")  The car had been repaired and the gas mileage increased.

ALL of the emission components had been replaced including the O2 sensors. The catalytic converters were taken off, cleared, and replaced. The only thing I did not do last time was replace the computer (and I did not replace all the vacuum hoses because there is no telling where all they run.)  After replacing all the emission parts, the car was finally fixed when changed the O2 sensors and I found a disconnected vacuum hose up near the battery.  It was back to getting great gas mileage, but now it is broken again dagnabbit.  

The car still runs smooth and luxurious, and does not show any signs of poor mechanical behavior or poor acceleration, except this: it leaves a large sooty black mark of dust on the ground when I start it after a long period of sitting, like in the morning, or after several days of non-starting;  and, emits black smoke out the tailpipe when I accelerate. It does not burn off oil, but it gets horrible gas mileage.   The engine and transmission are still good, I see no reason to trash it.  This car once got 17mph city and 24mph hwy and still should.

The car has old vacuum hoses, hard to get emission components between the firewall and engine (which I doubt are broken). As I said, one of the vacuum hoses ran up by the battery in front then back up to the PCV valve and I discovered it loose back then. I wonder if I can shorten the run to all the places the vacuum hoses go to and simplify it.... even if I lose some of the computer readouts on the dash.

For example, I just removed the pesky buzzer from under the dash because the temp gauge kept (literally) bouncing to high, then low, then high, thus sounding off the loud alarm. I replaced the thermostat and flushed the cooling system. The car was NOT overheating. Now, after disconnecting the buzzer, I have sweet silence, but have lost use of some of the dash features (I can't use the "select" switch to go between the various readouts.)  But I traded that convenience for silence. (Note: the car was running rich and emitting the black smoke BEFORE I did this).  

Also, the ABS breaking system does not work all the time. It stops working in mid run! When that happens, the brake pedal temporarily bottoms out for 1 second (if I happen to be braking when it goes out)  then restores functional brakes just fine without the ABS system. (the ABS light comes on the dash when that happens). I want to disconnect this ABS altogether. Also, 3 years ago, I also removed the air bag suspension due to expensive busted air shocks, and put in an aftermarket spring system. (No change in comfort... maybe even better now), so the suspension light also comes on the dash.... "who cares."

I want to simplify this vehicle closer to basic emissions necessary. Shorten the vacuum hoses to only the necessary places for good engine operation, like straight to the PCV valve and other necessary places. Right now, the hoses go to the PCV valve and beyond to who knows where. I don't want to go to a new manifold and carburetor system and get rid of the emission system and computer... too expensive... too much work... bad for ozone.

Maybe my computer is giving out. But, as I said, the car runs great. Just black soot and bad gas mileage. That is what I want to fix for the sake of my pocketbook.

In sum, I have to commute a 7 hour highway drive frequently between cities. I want to do it at 24 - 25 mpg in this comfy highway car, and not at 9 - 12 mpg.  That is my only goal here.

3 Answers


If you have black smoke, there are 3 main things to look at. #clogged fuel return line, not all cars have these, so you will have to check. #fuel pressure regulator problems, definitely can affect mileage #leaky injectors. you could have one or more of these problems, hope this helps.

1 people found this helpful.

Good suggestions, thanks. I'll check into those things. The leaky injectors may be part of the problem. The black smoke & soot seem worse after it has been sitting a while, if fuel leaks into the cylinders while the car is not running. Not so much after running all day (but still a little). Can the injectors leak when the car is off?


fuel system has pressure yup

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