1993 Lincoln Town Car runs too lean


Asked by Aug 21, 2013 at 09:45 AM about the 1993 Lincoln Town Car Executive

Question type: Maintenance & Repair

My Town car was getting 25 mph hwy and 17 mph city.  Now, it gets 12 hwy and 6 city. Symptoms: black smoke on acceleration and huge black soot spot on driveway at start up.  I replaced Fuel filter, MAP, TPS (throttle pressure sensor), PCR valve and EGR (very tough to get to by firewall), I did not change the hoses to the EGR, but I did change a rubber T vacuum below the EGR that had a hole in it.  Unexplainably, after throwing all these parts at it, the town car would, on one day, get the great gas mileage as if nothing was wrong, and on the next day get the very bad gas mileage and falter....  It would sputter to nearly a stop, and then "reset" and start working perfectly out of the clear blue on the next start up!  (I was thinking the computer was forced to renew settings by default.)  But now, the mileage is always very bad, terrible in fact. I was also thinking the catalytic converters were clogged... so I had them removed temporarily and this did not fix the poor mileage, but it did solve the terrible sputtering / jerking problem.

I have changed out the plugs twice. The first time, before I threw all the parts at it, they were black. This second time, after I put all the parts in it, they were white as if too hot. Now, the car does not smoke on acceleration, in fact acceleration is good but the car tends to jerk a little, but it still blows a LOT of tangible black soot on start up in the morning on the driveway.

The only thing I have not done is change the O2 sensors because everyone says "they never go bad" and change out the computer. I am at a total loss. I am thinking of re-changing the EGR or buying a new computer for it.

8 Answers

Black smoke is too rich, not too lean. The black smoke is unburnt hydrocarbons, gasoline. And 02 sensors DO wear out, or a wire could have come off. Whoever told you 02 sensors "never go bad" is mistaken, they last up to and beyond 80,000± but not forever. They play a major role in what the ECU sets the fuel/air trim.Get your OBD codes scanned ....The other possibility is leaking valve guide seals, if oil seeps in to the combustion chambers overnight, there is your black smoke/soot on start up.

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Best Answer Mark helpful

The black smoke is the burning of too much gasoline, like David says- You should stop guessing- that guessin' gets 'spensive- for the money you have already spent, you could have taken it to the dealer, replaced the $5 electronic engine sensor that Ford loves so much, and tipped each of the mechanics $100

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Check to see if you may have knocked a vacuum line off of the fuel pressure regulator or if the regulator has gone bad by checking the fuel pressure. If that check good then you will need to have to codes pulled to go any further with diagnosis. As this vehicle is a 1993 it is an OBD1 system so you will need to locate some place that can check OBD 1 systems.

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Check for codes? You can buy a Chilton's or Motor's manual that will show you how to retrieve codes. Like jaminblues says, stop guessing! With all that you've spent throwing parts and money at a system you don't understand, you could have paid a tech to fix it by now.

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Thank you all for your answers. Of course!... What was I was thinking when I titled the question "...too lean?" I was in fact thinking "too much gas," judging from the black smoke (see pic). That's just common sense... so embarrassing. Wish I could go back and rename the title or wish the webmaster would. Hey, it's not just guessing as I don't know enough about this to even venture a guess. In the beginning, I took it to the dealer and one other mechanic. They both wanted more than I could afford to fix it, so I changed the parts myself to save a LOT on labor. The dealer said it might even be advisable to consider buying another car as mine is worth $2,000. (But I want this car to be fixed, as I know it can run beautifully!) Both mechanics pulled the codes and told me it could be any one of the items I changed (including O2 sensors, but they rationalized that when other stuff goes bad it can give a false alarm on those sensors.) I think I will start with rechecking codes, most likely followed by changing the O2 sensors and rechecking vacuum lines, and on down the line with your suggestions. Fellows, I really appreciate your answers; they are, in fact, the best I have found so far online concerning this same problem with older town cars like mine. For this reason I will not use my option to delete the mistitled question, as I want others to benefit from your answers.

2 people found this helpful.

You CANNOT rely on codes when it comes to O2 sensors. The problem is the sulfur that is in North American gas, although that has improved a LOT in the last few years. The sulfur coats the sensor, and causes a run rich situation. There are no codes thrown because the sensors are working properly, in the electronic meaning, but are seriously misreading the air/fuel mixture. The very first thing I tell anyone to do when there is a problem like yours is to change the O2 sensors and then HOPE they have not clogged the cats. Also, run fuel injection cleaner through the tank with each oil change. It keeps them flowing nicely for a very, very long time. One person I know is at 1.3 million kms, or 850,000 miles, and his car is still passing emissions testing with the original injectors and cats, because he has changed the O2 sensors about 20 times!

2 people found this helpful.

I conducted a search along the vacuum lines and found one that was completely disconnected, hidden behind the battery. That was a good suggestion, tennisshoes. The hose runs up to the small input on the PCV valve down to the water tank and behind the fender. I replaced both the hose and valve. The resulting gas mpg improved immediately, but not up to full par. I'm sure the problem is multi-factorial and I am going to have those O2 sensors replaced as David and Michael suggested. It is a fact that my cats were very clogged due to an ongoing extremely rich mixture. I would have never thought of the sulfur content in the gasoline. That is definitely inside knowledge! I am learning a lot in this process and that is good. Thank you all again. I enjoyed reading Michael's comment about the 850,000 car. I own a 1952 Chevy Pickup and drove it for decades up through medical school. It has gone through several motor and transmission replacements, electrical wiring replacements, a paint job every 10 years, etc. Who knows how many miles it has on it! The point is, when you find a car style that you like, there is no reason it cannot be kept running.


The 1993 Town Car has two O2 sensors above the catalytic converters on the top of the manifold. They are visible from above. They are VERY hard to get to. I had to go from both underneath and above to get them changed. Tools NOT to use are crescent wrenches, and maybe open end wrenches. My sensors were VERY stuck even using overnight WD-40. (They say these sensors are only supposed to be hand-tightened). The crescents, even the vise-clamp kind flexed open with extreme torque and would have stripped the nut. It is a 7/8" nut and requires a special socket to remove O2 sensor with notch cut out of the socket to accommodate the wire. A u-joint and extension were also required. I also used a closed end wrench when necessary. Once the O2 sensors were changed, the mph started to improve throughout the day. I went from 18mpg to 22.7 driving around San Antonio's hwys and streets, and it is still improving. I dare say... PROBLEM SOLVED!

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