My car's get up and go, done gone up and went
March 21, 2007 12:04 AM   Subscribe

What is causing my engine to cut out when I come to a stop?

I have a 2000 Ford Taurus with 109,000 miles on it and it has developed a bizarre problem as of late.

About a week and a half ago the check engine light came on but the car seemed to be running fine. Then about three days ago, when I came to a prolonged stop (more than 30 seconds?) some lights would flash on my dashboard (battery and parking brake) and then my engine cuts out. I can immeadiately restart the car but not without giving myself a fright that this time it won't work and annoying the people behind me. The problem is now happening twice a day.

As it was about time for my oil change, I took my car down to a local jiffy lube and had them change the oil, the filters, the fluid, check the battery and all the usual stuff that they do. They said they didn't see anything out of the ordinary but that I should take the car to the mechanic.

So I did and after performing a diagnostic he said the problem with the car was P0171 System Too Lean (Bank 1) and P0174 System Too Lean (Bank 2). When I asked him what that meant he said that he didn't know exactly and that he'd have to run more tests (keep my car for a day and charge me $140) and then he'd be able to tell me what was wrong and how much it would cost to fix it.

I don't really have the money to afford both the test and the repair so I've been Googling the issue, hoping to give myself an idea of what the issue could be but all the websites tend to be written by car people for car people (my knowledge of cars' inner workings is utterly non-existent).

So my question for all is two-fold, does anyone have any idea what might be causing my problem and how much I should expect it to cost to have it fixed?

Also, for bay area people... know any good mechanics?
posted by jaybeans to Travel & Transportation (16 answers total)
Best answer: generally when an engine is running 'lean' it means that the fuel to air mix is lacking in fuel. the fact that you car stalls after prolonged stops promotes the idea that your fuel injectors could be dirty (or going bad). you can try a jug (12oz) of "STP Complete Fuel System Cleaner". I used it once last year, and then every time i filled up the gas tank i put a thing of Fuel Treatment in before the gas. I have an '89 Jimmy and along with regular maintenance (changed oil every 3-4 months, and used 89 octane gas), fuel additives keep the injectors clean and the acceleration acceptable.
posted by cellojoe at 12:24 AM on March 21, 2007

I guess you have fuel injectors, not a carburetor? When I got my current vehicle, with fuel injectors (no carburetor, I learned, because they perform similar jobs) I was told to put that injector cleaner fluid in the fuel tank, every few tanks. Your manual probably explains about what you should be doing.

Also, whenever I go to the mechanic, I get them to explain to me at a basic level whatever part they are working on and typical problems it can have. Gradually I learn. If the mechanic can't/won't do that, they are not a good mechanic for me. Maybe you should start doing it too. You asked the mechanic what's wrong, and they didn't know (yet), but you didn't ask them the questions I ask, which could be helpful to you.
posted by Listener at 12:50 AM on March 21, 2007

Your mechanic should be able to give you possible diagnoses to you from you describing the symptoms to him. I third the fuel injector cleaner, even if it doesn't solve your problem it is something you should do anyway.
posted by Mijo Bijo at 2:11 AM on March 21, 2007

My mechanic friends recommend Techron for keeping injectors and engine top-end clean.
posted by Kirth Gerson at 4:00 AM on March 21, 2007

If you're dealing with clogged injectors, the problem train is simple. You get a cylinder that misfires. Tons of O2 goes by the Oxygen sensor (since the cylinder didn't burn). This confuses it badly -- it's expecting to see orders of magnitude less O2, and it leans out the fuel delivery. This means less power (less fuel burning, less power.) At idle, the fuel charge drops to the point where the engine stalls.

Costs? Fuel injector cleaner costs dollars. If it fixes it, then that's it. Otherwise, you're probably looking at new injectors, and the cost on that is moderate -- it seems they are about $30-50 per, one per cylinder, but I don't know enough about your car to be sure. Injectors can be rather expensive.

The real question is how hard are they to change. In some cars, they're trivial to change, thus, you'd be looking at an hour of labor (or, if you're moderately handy with a wrench, you do it yourself.) Others, well, if step one is "pull engine up..." then the labor will hurt, badly.

The other option is cleaning the injectors. This typically costs about $20 per, plus labor -- if the injectors are easy to get to, not a big deal, if they aren't, it is. Some shops have the gear to clean the injectors in place, which is much quicker (read, cheaper) but it may not work, in which case, you're buying injectors.

Given that you've got 100K miles on it (and we used to rebuild carburetters every 30K miles) this is annoying, but not completely unexpected, esp. if basic maintenance hasn't been kept up and the fuel filter clogged enough to bypass.
posted by eriko at 4:38 AM on March 21, 2007

Good advice above, but there are many more things that could be wrong.... one that comes to mind is the throttle positioning sensor or "TP Sensor".
I had it go bad once on a Ford, I had the same symptons that you describe.

Other possible choices:
O2 sensor
CPT sensor

Good Luck!

Let us know how you made out....
posted by FLHunter3006 at 5:23 AM on March 21, 2007 [1 favorite]

I had this problem a few years back with my Volkswagen. I had my mechanic change spark plugs and vacuum hoses because we assumed there was a leak. He was about to change my O2 sensors ($$$) when I decided to take it to the dealership to get a second (but of course more costly) opinion. I'm glad I did because it turned out my MAF (mass air flow) sensor was bad. This device monitors the amount of air entering the engine which is used to calculate the amount of fuel added. My engine was receiving a bad air/fuel ratio which was causing the frequent shutdowns.

The entire job including labor was around $450. This was somewhat of a relief to me because my O2 sensors were going to cost around $800 to replace.

Good luck...
posted by markulus at 6:33 AM on March 21, 2007

Tauruses in that timeframe were infamous for having timing chain issues, most specifically after high milage. Not to say this is your particular problem, but to be prepared for some sticker shock when that repair bill comes in.
posted by Spoonman at 6:35 AM on March 21, 2007

Best answer: Your car's engine management system stores a rolling history of operational and diagnostic codes that describe the recent history of operation of your vehicle. The codes your mechanic downloaded P0171 and P0174 tell him that both banks of cylinders in your V6 engine are running with fuel mixtures that are too lean for efficient combustion. This is not a good condition, as it not only robs your car of power, and can cause the engine to die at idle, but because lean mixtures generally burn very hot, which can damage engine parts, or lead to dieseling or severe knock conditions.

There are lots of reasons beyond those already suggested which can cause this condition. First is some kind of vacuum leak to the intake manifold, allowing excess air to enter the combustion process. This could be from something as unrelated to engine operation as the vacuum brake booster, which creates force from engine vacuum to assist operation of your power brakes. Or, very likely, any of a number of rubber hoses that connect engine accessories, or Exhaust Gas Recirculation system components to the intake manifold could be cracked or missing. Less likely would be cracked parts (typically plastic) or bad gaskets in the throttle body assembly. Diagnosing and fixing vacuum leaks is usually an inexpensive process of looking the systems over carefully, perhaps measuring engine vacuum at idle, and replacing/repairing/reconnecting the defective parts. The labor charges for diagnosis and repair are usually less, as the components involved are directly accessible, and require little, if any, real disassembly or reassembly time.

Next thing to check would be the Mass Airflow Sensor (MAS), which will cause the engine management system to lean out the mixture unduly, if it is bad. You could also have a bad Throttle Position Sensor causing a lean condition, and this is usually checked by substitution.

Next, you could have a bad Coolant Temperature Sensor, which will cause the engine management system to lean out the mixture if it is reading incorrectly. It can be checked on a cold engine with a scan tool, and should be reading within 3 or 4 degrees of ambient air temperature when checked.

Next, there are a number of causes to check in the fuel system, that could account for a lean mixture condition to both engine banks, beginning with the fuel filters, which could be plugged, and should be replaced anyway on a vehicle with this kind of mileage. Next, you could have a failing fuel pump, or a bad fuel pressure regulator. These are diagnosed by connecting a fuel pressure guage to the fuel distribution rail, and checking that the pressure is within spec, and that adequate fuel flow is available.

You may have one or more fuel injectors that are bad or dirty, but the symptoms for these would tend to include driveability problems, rough idle, cylinder miss, and poor acceleration, in addition to lean idle and dying. Fuel injectors can sometimes be cleaned, but the cost of removing, cleaning and replacing, or of on-vehicle cleaning methods is going to be a significant fraction of the cost of a new set of injectors ($150 compared to $275 for a replacement set of 6). But new injectors will not fix the problem, if any of the preceding causes is the root defect.

So, I think you can see that a systemic diagnosis of your engine is essential, and would require the car be kept overnight, to check cold engine conditions. It's not a good idea to keep driving a vehicle with this problem, as engine damage can occur, and because driveability problems are likely to increase, possibly resulting in loss of engine power in a driving situation.
posted by paulsc at 6:45 AM on March 21, 2007 [1 favorite]

Seconding bad sensor. Also, find another mechanic.
posted by electroboy at 6:45 AM on March 21, 2007

This could also be a wiring issue - an intermittant MAF, O2 or injector line.
posted by rfs at 7:04 AM on March 21, 2007

Best answer: Ford issued this TSB for the 2000 Taurus. It likely applies.

posted by Tacos Are Pretty Great at 8:05 AM on March 21, 2007

(and FWIW, my second guess would be the MAF sensor.)
posted by Tacos Are Pretty Great at 8:16 AM on March 21, 2007

That TSB looks promising. If you haven't gotten to the bottom of it yet though, ask people who know Tauruses.
posted by Doohickie at 9:46 AM on March 21, 2007

Response by poster: Just in case anyone is curious, I finally took it to another mechanic (I found one near where I work by using Yelp) and he was fantastic, charging me far less and being really supportive in how he explained things.

Basically, it seems like there was a hole in a tube that was messing with the air/fuel ratio. And as a bonus, from me dropping the car off to me picking it up it took just under five hours.

I thank everyone who commented. It really helped me out.
posted by jaybeans at 4:46 PM on March 21, 2007

Glad to hear your story had a happy ending, and that it was a relatively minor issue.
posted by Tacos Are Pretty Great at 2:31 PM on March 22, 2007

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