I have a '96 Buick Riviera that I bought used that now has a little less than 150,000 miles on it now. About a month and a half ago, I was in New Mexico around Santa Fe and my car started losing power as I went up hill. I would put my foot on the floor and I could at least maintain my speed (70 mph). After I got my self out of the hills and onto level land, my car drove fine. I had a mechanic the next day replace my fuel filter for me, it was really dirty anyway. I drove my car home to Kansas and it was running fine until yesterday when it began doing the same thing to me, but mostly on hills and a little bit on level ground going 70 mph. I again had to put my foot on the floor to maintain my speed. Now when I get my car to go above 70, it starts running rough, the faster that I go, the rougher it gets. I have had a mechanic friend tell me that it could be a coil and another person told me to change my spark plugs. I don’t wish to pour unnecessary money into a piece of junk.
One thing to have checked is the fuel pressure. A weak fuel pump will cause the engine to lack power when under a load.
I could almost bet that the pump is original, I talked to the previous owners and they did not have it replaced. From what I can find, my car was first owned by a rental car company and they likely didn’t replace the pump since it was a new car.
Changing spark plugs is “pouring” unnecessary money into a (neglected) car?!! OK. Drive slowly.
To clarify, I was talking about something like an engine rebuild as ‘pouring’. Not saying that spark plugs are out of the question here.
I would definitly put my money on something in the fuel system but before I did teh pum I would check the filter again. I am betting that there is a build up of debris in the gas tank that eventualy restricts the fuel filter as it gets dirty. In my experience the only thing that makes a car run rougher teh faster you go is fuel supply. If the filter looks good then you may have to go for a pump but have a garage check the fuel pressure first.
Your problem could be a weak fuel pump. It could also be a dirty air filter restricting air flow, old plugs and/or poor wires causing misfires under “load” when going up a hill. You seem to have some history info on the car. When was the air filter last changed, plugs changed, new wires, etc.?
If this normal maintenance stuff has been done recently (within the last 6 months or 10K miles) then you may have a more substantial problem with the fuel pump. If not, I’d get some basic stuff done first and see if your problem goes away. At the least you’ll get better gas mileage.