Car bucks and stalls when going uphill when the gas tank is at half a tank

MAMABEAR0917

MEMBER
2000 FORD CONTOUR

I have the car listed above 5 Speed with approximately 113,000 miles. It has been in and out of the mechanics and I have spent close to $800.00. My car bucks/hesitates whether going up hill or one a straight road. I replaced the fuel filter and the fuel pump. After that the check engine light came on. I took it back and he said the plug/sensor was corroded and not properly plugged in, he cleaned it and plugged it in properly. Once he cleaned the plug/sensor the check engine light went off, the next day it came back on. I was getting great gas mileage and figured it was a false reading. Today, the car is worse, it seems worse when it's a hot day, I can't use the A/C or the panel because when I do, the bucking/hesitation gets worse. Any suggestions? Thank you

5 Replies

INDYUKE

MECHANIC
416 POSTS

You may have a vacuum leak. The heater doors are controlled by a vacuum switch behind the panel. It is often extremely difficult to diagnose a vacuum leak. A smoke machine seems to work the best, and any good shop should have one.

When the codes were pulled from the car's ECM, did the mechanic say what codes they were? That will give you a hint as to what direction you'd need to go to diagnose. Let us know.

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Sunday, July 15th, 2007 AT 8:28 PM

MAMABEAR0917

MEMBER
3 POSTS

Thank you for replying to my question. I have been to see my mechanic every other week since I posted the original question. So far he has replaced, fuel pump and filter, 1 Oxygen sensor and the IMRC Unit. The check engine light is still on and the code keeps telling them its an O2 sensor. The car bucks and stalls when going uphill when the car has less than 1/2 a tank of gas. The radiator light also comes on now (looks like a little jar with an X through it with a lid) when the car starts bucking and stalling. Could that be because of the vacuum? Ford Contour, 117890, 2.5 liter DOHR, V6.

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Monday, July 16th, 2007 AT 5:22 PM

MAMABEAR0917

MEMBER
3 POSTS

I had the car inspected and have spent over $900.00 in repairs. My mechanic has not told me the code number that my check engine light is giving but he has told me it's a bad o2 sensor. He replaced one of them and said I may need to replace the other, but I believe the gentleman that replied to my first question may have had something with the vacuum leak, my car buck and stalls with less than 1/2 a tank and gets worse as the tank gets emptier. And now I have noticed as its bucking up the hill, the radiator light comes on, but it was flushed in April and there is plenty of fluid in the reservoir. Again, the fuel pump and filter where replaced as well as all fluids replaced, air filter, IMRC unit and 1 o2 sensor.

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Wednesday, July 18th, 2007 AT 5:30 PM

INDYUKE

MECHANIC
416 POSTS

Ask your mechanic exactly what code is being stored. There are multiple codes that have to do with an oxygen sensor. There is a code that says the oxygen sensor reads a lean condition, in which case the oxygen sensor is not bad, merely being a messenger of another problem. There is an oxygen sensor code reading "too rich". Others for "out of range too low" or "too high" and anything in between. They all point to different problems and if we can know the exact code that would give us trail to follow. About the only codes that indicate that the sensor may be bad are ones that say it is responding too slowly and isn't even showing up on the profile.

If it is a vacuum leak, then the code that would most likely show up is a code from the oxygen sensor saying you have a lean fuel mixture condition. That is because a vacuum leak is unmetered air being drawn into the intake that the computer doesn't know about. Causes bad drive-ability problems.

You are saying that the car bucks most often going up a hill with a low tank of gas is a tough one. The only two things I can think of is that the tank has some water or sludge in it and when the tank gets low the pump will pick that stuff up. Other thing, the tank is vacuum sealed. Your gas cap should hiss when you remove it to fuel up. If it doesn't, then the cap might be bad.

I hope this helps. Again, let us know.

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Thursday, July 19th, 2007 AT 10:22 PM

KASEKENNY

MECHANIC
18,907 POSTS

Great advice. Unfortunately this post was almost 15 years old so I doubt it helped them but I am sure this info will help others when they view this post just like you did. Thanks for helping to make the site better. Come back if there is anything we can help you with.