Car Loses Power

The car ran fine until 2 months ago when I started hearing a rattle under the hood when I’m driving at about 20 mph, then accelerate. Once I get to about 30 mph the rattle stops. I don’t know if this has anything to do with my problem, which is, the car is losing power, sometimes.

The car starts and runs fine, but I’ll pull into the gas station (after driving for 60 miles), get gas and leave. For the first half mile everything is fine, then the car will lose power for 2-5 seconds, have power for 2-5 seconds, lost power, etc. until I pull into the driveway (about half a mile). This only happens when I pull into the gas station.

I just took the car in and had the fuel filter replaced, the transmission flushed, transaxle fluid replace and an oil change. The car still stalls after getting gas, but the power loss isn’t as severe.

Thanks for the help

When you took it in, did you tell them the symptoms and let them try to diagnose them? Or did you just have the routine maintenance done that you’ve described?

The two problems may or may not be related. The rattle could be a heat shield coming loose (unrelated) or the EGR valve (related). You could have a crumbling substrate in the cat converter (possibly related).

this one needs a hands-on look.

I am in agreement with mountainbike. This does indeed sound like more than one problem, and they are likely unrelated problems.

The hesitation after fueling the car is very possibly a problem with the Evaporative Emissions System. If you (or a previous owner, or another driver of this car) have been in the habit of continuing to force gasoline into the tank after the pump first clicks off, then you could have damaged the evap system. The problem could involve a solenoid valve in the evap system (relatively cheap to fix) or the carbon canister (obscenely expensive to replace). This needs to be diagnosed, but in general, I would caution you to stop fueling the car when the pump first clicks off. (There is a reason why the gas cap and the Owner’s Manual both caution you about the same thing!)

The other problem is–as mountainbike suggested–very possibly a loose heat shield (very cheap to repair). Or it could be the EGR valve (more expensive), or the catalytic converter (you don’t want to know the cost on this one).

You did not tell us the model year or the odometer mileage of your Legacy, but I would remind you that there is an 8 year warranty on the catalytic converter and other emissions-related parts. That warranty should also include the EGR valve.

Find a competent independent mechanic in your area, and take the car in for an assessment. However, if the car is still under any of its various warranties (Bumper-to-Bumper, Powertrain, Emissions), then it needs to go to a dealership.

I’m hoping it’s just the EGR valve. If that’s loose that could be causing the operating problems as well as the rattle.

Wish I were on-site…

“The car.”

What year is your Legacy, which model is it, and how many miles on the odometer?

Believe it or not, all Subaru Legacys are NOT the same.

Thanks for the tips everyone.

It’s a 2002 Legacy L, 4-door sedan, automatic, with 71,000 miles on it. I bought it used a few years ago with only 12,000 miles on it. I have all the scheduled maintenance done on time, I don’t pump gas in after the pump shuts off, and I took the car in specifically for the power problem. Actually, I had the car towed in (free with my insurance). They had the car for two days and couldn’t recreate the problem and their tests showed nothing. They said the fuel pressure was fine, and even a little high. I had the fuel filter replaced as it was due in about 3,000 miles anyway. I drive about 60 miles each way to work, and travel from an elevation of 3,500 feet to 7,500, then back at the end of the day. I too hope it’s the cheap fix.

On the way home today I wanted to duplicate putting gas in the car, without actually adding gas, to see what happened. I pulled over after 40 miles, removed and replaced the gas cap, let the car sit for about 10 minutes and drove off. It ran fine.

20 miles later, I gassed up as usual, and all the problems appeared. For the first time the car died while taking a slow curve. It loses power more when I take my foot off the gas than when I’m accelerating. But even when accelerating it will lose power.

This is sure starting to sound like a fuel problem. When they tested the fuel line pressure, did they test the regulator too?

You can replace the regulator for about $120, probably cheaper than buying shop time, and it’s a super easy DIY job, but it can also be tested. This is starting to sound like a fuel pressure regulator problem.

Did you find the source of the rattle?

I was going to work on Friday when the car started to run a little rough, and the Check Engine light came on. This happened right in front of the car repair place. They were able to pull some misfire codes, and they replaced the Air-Fuel Ratio Sensor (oxygen sensor). I just picked up the car as I was out of town for a couple of days, and it runs fine, so far. I’ll be buying gas on Friday, so we’ll see what happens.

So, the repair shop found a faulty air/fuel (wide-band) oxygen sensor? That’s great; but, I wonder what diagnostic steps led to that. Codes for misfire, alone?

They said they did a lot of research about what could cause the misfire codes. What that means, who knows. And why they didn’t do “a lot of research” when they first had the car for 3 days, who knows.

I’m wondering about the rattling under the hood during acceleration. This may have been spark knock (ping) which can be caused by a too-lean condition, or by using an gasoline octane that is too low for the engine.
Under certain conditions, octane needs can be higher than, even, those recommended by the car maker. Your octane choice? Higher? Lower?

Thanks for the advice. I do have pinging, which is mainly from the quality of gas in the area. But the rattle is more metallic, like a vibrating piece of metal.

The rattle may be from the catalytic converter heat shield. Sometimes, they rust, or break, and become loose. A mechanic can wrap the heat shield with a wire, or a large band, to tighten it up (of course, a dealer, “Can’t do that”!).

I’ll check it out, thanks.

It looks like the problem is fixed. I also bought a new gas cap. Filled up with gas and no real power loss on the way home. One little hiccup as I pulled into the driveway, so I pulled back out and drove around the block with no problems.

Thanks for all the advice everyone.