Yet another car repair question

Factual Questions
1

I have a 1989 Cadillac DeVille that is losing power. It is really only noticeable going up steep hills, but the car’s mileage is also going down (19 mpg, when it’s usually around 22).

This isn’t the first time I’ve had this problem. The last time, all I did was changed the air filter and fuel filter, and everything seemed ok. The air filter didn’t look too bad, but the fuel filter had a lot of crud in it.

This problem started when I stopped at a gas station I don’t usually go to, but it just seems odd to me that a little dirt in the fuel filter can so easily make this car go wonky. I’m going to replace the fuel filter again tomorrow, but I’m wondering if there isn’t some underlying problem I need to be worrying about, like a weak fuel pump or maybe some fancy shmancy sensor that’s gone funny.

Some more info:

Where I live is fairly flat, so I have to drive a bit to get to a hill. Still, it seems to me that the car doesn’t have as much of a problem when it is cold. The problem seems to get worse when the car warms up. I’m not 100 percent sure about this, though, because I have to drive a fair distance to get to a hill where I would really notice the problem.

Also, here’s the exact symptoms I’m seeing. When I’m going up a hill, let’s say the speed limit is 45. The car starts to lose power. I back off of the accelerator a bit, and the car goes 40 up the hill, no problem. If I try to go faster than that, though, the car loses power, and I can feel the engine sputtering. If I press the accelerator more, sometimes the engine will even sputter and backfire. It is definitely related to how hard I am pushing the accelerator, though, not the car’s speed.

Just so you know my skill level, I’m just a back yard hack mechanic. I’m not too bad with older cars. I can change fuel pumps, replace brakes and rotors and that sort of thing, but these modern electronic controls baffle me.

Any advice from the auto gurus?

2

I think fuel pump is a likely solution. Also consider plugs and wires if you haven’t changed those in a while (or ever!)

3

Sounds like a sensor. The computer compensates for all weather conditions and allows gas into the engine at the computer determined flow rate. Gas meets air in the cylinder , piston slams down , combustion occurs

So gas is not getting from the tank to the FI port or it is getting to the port but in not enough quantitys. Your physical pushing of the gas pedal is being ignored by the computer as not to flood the engine.

Start with either bringing it to the autozone and having the computer read for error codes or if like my dads caddy the error messages will appear on the dash.

Declan

4

This makes me think oxygen sensor. Oxygen sensors need to be hot to work, and I believe the car’s computer uses some standard settings until the sensor gets hot.(it’s in the exhause system) Then it starts tuning the mixture based on the sensor’s readings.
Stalling, surging and rough running would be common too.

5

It’s certainly possible that you got some bad gas. Getting rid of that tankful and replacing it with good fuel, or at least diluting what’s in there by filling up with good fuel, may solve the problem.

When you get the old filter off, but before installing the new one, blow through both of them. You can pretty well judge how clogged the old filter is by that comparison.

To really judge the fuel pump, you need to measure the pressure and volume it puts out, and/or do what’s called “current ramping” - view the operating amperage on an oscilloscope. Both of these procedures require equipment that the typical home mechanic does not have. However, replacing the fuel pump is not a quick or cheap thing to do, so testing it first is highly recommended.

Since you’re going to replace the fuel filter anyway, and it’s easy to add fresh gas, my counsel is to not worry about what else might be going on until those are done and the results evaluated.

6

Does the OP have a shade tree mechanic option of disconnecting the fuel pump power feed safety, and then restart, (as in Ford) to relieve pressure on the line before he attempts to replace an inline filter?

Part of his description makes me want to think exhaust restriction, as in plugged cat, collapsed inner wall of dual walled wye pipe, or similar.

7

Update:

It’s fixed. The problem ended up being a bad distributer cap.

Thanks to all who responded, especially control-z since his suggestion about replacing the wires was what led me to the solution. All of the responses were helpful, though. I had a good game plan going into it, and got lucky that the problem was up near the top of the list.

I’m really surprised it wasn’t a fuel problem since the symptoms were so similar to the clogged fuel filter I had the last time around.

Anyway, thanks again to all who responded. I really appreciate the help you all gave.

8

No problem. Remote diagnosis is difficult, and sometimes you just have a suffer a little trial and error to find the problem.

Thanks for updating us, I like to know the outcome of stuff like this.