Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

RPMS up...performance down

I recently purchased a 2004 Mercury Sable with about 112K miles on it. I am having some troubles with my car and I’m not sure where to start first in repairing it. I recently took my car to a mechanic because accelerating on the highway or going up hills made my car sound engine run very hard and loud, my RPMs went up to 3K and my speed dropped to 15 mph (which is a disaster when you’re on the highway and hit a steep grade). My car absolutely cannot do any sort of hill so the mechanic suggested that either he or I replace one of the catalytic converters. He showed me which one he thought was throwing the error code. I replaced that catalytic converter and I thought my problems were solved because I could accelerate without difficulty.

However, a day later I tried to drive it up a hill and got the exact same response as before. RPMS jump up and the speed drops down to 15 mph and I’ve just about got the pedal to the floor.

I have friends who repair cars as a hobby and they disagree with each other where I should go from here. One friend says replace the muffler and resonator (possible blockage that cannot bear any stress under a load…like going up a hill). Another friend says replace the third catalytic converter (one was replaced when we bought the car by the dealership, and I just replaced another one). He says when one catalytic converter goes the others are not far behind.

Any thoughts?

You are loosing a lot of power which a restricted exhaust would do. It’s hard to tell unless you describe what else is happening. At some point, you need to go to a real mechanic…maybe a dealer. You are in the " replace something mode" and " let’s see if it works"

Has anyone bothered to check the level, color, and odor of the transmission fluid?
When was the last time–if ever–that the trans fluid was changed?

While poor performance on a hill could be due to a clogged catalytic converter, or to a weak fuel pump, if either of those scenarios were taking place, the engine would be bogging-down, rather than revving to 3k RPM.

If it turns out to be a transmission problem, then this is a strong indicator that you need a new mechanic.

You mentioned an error code. What was it? (The exact, specific code. It looks like “P1234”)

You have a major problem. It may be an exhaust issue. It may be a fuel issue. It may be a transmission issue…ignition issue…etc. Having people guess about it will do no good. Have the car scanned for error codes and report them if they come up.

Either way, these things have to be TESTED - a vacuum gauge will tell you about exhaust restrictions. A fuel pressure gauge will tell you about fuel pressure. etc.

I’m leaning towards the transmission or clutch (if manual). First step is to have dtc codes read.

If your car is downshifting when climbing a hill because of lack of power then your rpms would go up- that is normal. If it is not downshifting and the rpms go up but the speed goes down, then it is the transmission.
If you can’t tell, have your mechanic drive the car up a hill.

+1 to oldtimer’s post.

Post back with the results. Realize too that the cat converter probably did need changing. But older vehicles often have more than one problem, and it sounds like yours is one that does.

The original code thrown said the downstream O2 sensors needed replaced. I replaced them and that did nothing. So a mechanic friend told me to replace the throttle position sensor. I did and that did nothing.

I took it to a very popular transmission auto shop about a month ago. The mechanic said it definitely was not a transmission issue. He said he was backed up with work for a month and couldn’t get to me in a reasonable amount of time so my dad and I replaced the catalytic converter that the mechanic pointed out as the problem.

That seemed to half way fix the problem. Now I can accelerate without the RPMs going up, but it just won’t do a hill. An example would be, I am driving along on the highway at 55 mph with nothing wrong, and then I run into a hill and the car starts running hard, the RPMs go up and my speed drops down down down until I’m practically flooring the accelerator and only going 20 miles per hour.

So, we can rule out transmission issues because the transmission mechanic said no way that is the problem. He only mentioned one catalytic converter was throwing a code. My dad and I replaced that cat and now I have no codes.

That’s the thing that is stumping me. I have no error codes now and it drives fine until I have a decent sized hill to get up.

And this is an automatic.

As mountainbike stated, an older car like the OP’s can certainly have multiple issues, and I am more sure than ever that this is the case. Additionally, based on the symptoms, I still think that a transmission problem is a strong possibility.

So…I will ask again…
When was the last time–if ever–that the trans fluid was changed?

If the answer is either, “I don’t know”, or “more than 3 years ago”, this important service is overdue. Even if it doesn’t resolve the current problem, it could help to extend the life of a transmission that may have received no maintenance or very little maintenance in the past.

Surely there is more than one transmission shop in the OP’s area.
Just make sure to avoid ALL of the chain transmission shops, and look for an independent trans shop that has been in business for at least a few years.

My transmission fluid was changed this month. The fluid was full and was not dark or burnt.
And it is not making the grinding or high pitched sounds a transmission makes. There are no shiny shavings in the bottom. It is not slipping gears. Nothing is indicating transmission. I’ve been to several mechanics in the last month and they charge $50 to keep checking codes and diagnosing. I am in a bind financially right now and really can’t afford to keep taking it to mechanics. That’s why I was turning to you guys. All the mechanics I’ve been to have been open no less than 30 years, and are all five star rated places. It was not a chain. As of now, I have no codes so I really have no idea what it is. Changing the cat cleared the codes and the check engine light has been off for over a week now. I am driving great on level ground…just can’t do hills.

You need to put a fuel pressure gauge on it and watch what happens when you load up the fuel pump by revving it.

How old are the spark plugs and wires? If in doubt, check them and/or replace. It is annoying to get the bank at the rear of the engine compartment, but doesn’t cost very much. Checking the plugs costs nothing, of course.

Preferably you could also get your hands on a scantool that will do live data. If you don’t have something like that, ask around among people that you know.

Cigroller, I will get a fuel pressure gauge. What are you suspecting is the issue? I’m just curious. :slight_smile:

I replaced the spark plugs and the wires a month ago.

When a car runs ok with mellow driving but then dies when you need to load it up (like climbing a hill), the first two suspects are clogged cat or a fuel pump that can’t keep up. That’s why if you get your hands on a gauge you have to try to simulate load. Often a static pressure check will NOT show you what you need to know

Note that lots of bog-box auto parts stores have loaner tool programs for specialty tools (i.e. wrenches and screwdrivers not included). You buy the tool, use it, and get a full refund when you return it. I’d imagine some have fuel pressure gauges. If you haven’t done the fuel filter I’d go and get a pressure gauge and fuel filter. Check pressure - try to load it to see if it can’t keep up. Then put in the fuel filter and check it again. See where things stand.

You’ll have to find the correct fuel pressure spec for it.

Anybody else thinking may be low compression? Or am I off in left field again?

Then the next step would be to do a fuel pressure test to see if the pump is having a problem. If you can tape the guage to the windshield so you can see it while you drive up a hill, all the better.

It is possible the timing is off, how long since air and gas filter change?

Lack of power can come on slowly over time, and will first show itself on hills. Common problems which cause this are a plugged cat, a dirty air filter, dirty fuel filter, fuel pump on the fritz, ignition system or timing problem, compression problem, and some others, but those others would usually throw a code. Presuming there are no codes – neither active nor pending – then the best thing is to connect the car to the Mercury (or probably Ford) scan tool. Not just any old scan tool, the real time parameter display scan tool specifically designed for this car. And someone with expertise using it and access to the car’s factory service manual to run the full set of applicable diagnostics. But having that all done might be too expensive for your budget, so the next best thing … hmmm … well, probably in this order: a compression test; test back pressure in the other cat, the one you haven’t replaced yet; change the air filter and fuel filter; change the spark plugs; fuel pressure test, incuding a visual check of the fuel pressure regulator vacuum line for any signs of gasoline; check idle rpm and idle ignition timing. Edit: Add to this, verify the EGR is working, and it’s vacuum source meets specs, and the EGR is not sticking open or opening too far on accelerations.

I would have leaned toward an exhaust restriction too. You could always remove the O2 sensor and see if it goes up the hill. That would tell you if there was a restriction. Also, a shop can put a gauge in the O2 sensor hole and measure back pressure. I would have fuel pressure checked. It could be low. This car is not truboed is it?

If you can get a vacuum gauge and the directions to use it it will tell you a lot. It will also diagnose a clogged cat or exhaust.