Please help me with a car problem
May 31, 2010 3:03 PM   Subscribe

Doing 60mph on an incline, I pressed down on the accelerator and nothing happened. What's going on?

I replaced the alternator on my 2000 Chevy Astro minivan yesterday. Today, I had an acceleration problem. Are these two incidents related?

Yesterday morning, I started the car and my battery light was lit. Battery guage began dropping as I drove it to a repair shop. Pulled into a garage to have it checked and it died within moments while idling. They replaced the alternator with its belt, and recharged my battery. After the alternator was replaced, I drove it on a highway at 50mph for about 10 minutes last night and for about 15 minutes on local streets in Queens, NY.

This morning, my family and I got in the van to drive to CT. I was on a steep on-ramp for a bridge about 5-7 minutes later, when I put my foot on the gas to make sure I didn't lose too much speed. The engine raced but the van didn't accelerate. I pumped the gas. Each time, the engine would race as if I were in neutral. My "service engine soon" light began flashing. I put on my hazards and the car's speed dropped to about 40mph, at which point the gas pedal began working again.

The "service engine soon" light stopped flashing and stayed solidly on. Hours later, it's still on.

I stopped at a gas station on the far side of the bridge. Filled my tank. Checked my transmission fluid. Clear, and a good level. Oil is fine.

I drove cautiously to CT and didn't go over 55 at any point in the trip. Just drove home. The problem didn't re-occur.

Some questions:
What the hell happened?
What should I do now?
How do I make sure this doesn't happen again?
Should I try and see if I can recreate the problem?
Is the minivan still safe to drive?
Is it possible that this is in any way related to the alternator being replaced yesterday? If so, did I not run it for long enough on the highway last night to make sure the battery was properly charged?
My manual says that the "service engine soon" light goes on when emissions rise above acceptable levels. How is this related to what happened?

Any advice as to what my next steps should be? I'm planning to take the car to a mechanic next weekend, but I'd like to know what to expect now.
posted by zarq to Travel & Transportation (16 answers total)
If the engine was revving as if in neutral, then it could be a transmission problem. Maybe it has something to do with the spark plugs? I was having a lot of problems with my car not responding to pressing down the accelerator until the spark plugs were changed.
posted by Ryogen at 3:29 PM on May 31, 2010

Check your owner's manual.... sometimes it lists very specifically what causes the "service engine soon" light to come on (on a certain Toyota for example it mainly has to do with a fuel-related or fuel-cap issue).
posted by crapmatic at 3:34 PM on May 31, 2010

A blinking check engine light means there's a gross misfire problem. It is blinking to warn you to stop and turn off the car immediately, because if you don't, the unburnt gas being dumped into your exhaust is going to destroy your catalytic converter(s). This is a big deal because it/they are hugely expensive.

Was it raining or very humid when this happened?

I don't think it's related to the alternator thing, but it is a serious problem and it may have been caused by disturbing things like plug wires while that work was being done.
posted by fritley at 3:38 PM on May 31, 2010

If you want to check this out yourself, you can go to one of the big auto parts stores - they often let you borrow their diagnostic scanner, which when you hook it up to the connector (under your dash) will spit out a trouble code. You can google around to find out what the code means - sometimes they're straightforward, sometimes they're more obscure. It's a good way to get an idea of what's going on, and whether or not it's something you can tackle on your own.
posted by god hates math at 3:44 PM on May 31, 2010

It's true you can have the codes read (I hear Autozone does this for free), and if you have a misfire problem the codes will tell you which cylinder(s) are misfiring (P0301, P0302, etc for cylinders 1, 2, etc) if it's a problem on just some, or it will report a random misfire condition (P0300). This information can help you or your mechanic narrow it down.

If your light blinks again, stop driving the car and have it towed to your mechanic.

(An engine racing and acting like it's in neutral doesn't sound like a misfire. A misfire is roughness and lack of power. Are you sure you heard it racing or did it just FEEL like it was in neutral, i.e. not responding to the pedal?)
posted by fritley at 3:58 PM on May 31, 2010

Thanks for the answers so far.

fritley, It was a clear sunny day. About 75-80 degrees F. I kept driving it afterwards for more than 40 minutes. Afterwards, it ran smoothly. Are there any symptoms I should look for to find out if I damaged the catalytic converters? Thank you very much for the warning about the flashing light by the way. I had no idea.

The engine definitely revved when I hit the gas pedal.
posted by zarq at 4:05 PM on May 31, 2010

Check your owners manual for something like, "Limp Home Mode". I would think if you didn't have anything last night you wouldn't have issues with this today, though.

I had symptoms like this when I blew the hose off my turbocharger (I didn't tighten the hose clamp enough after doing some work). Could there be a vacuum hose or some such that got pulled off its nipple and now something isn't opening or closing enough when you need a lot of power (like climbing a steep on ramp)?
posted by Kid Charlemagne at 4:17 PM on May 31, 2010

It's not a misfire, your catalytic converter is fine. Take it back to the guys that changed the alternator and have them check for connectors or hoses that they either forgot to hook up or might not have tightened completely.
posted by Rhomboid at 4:40 PM on May 31, 2010

What the hell happened?
It sounds like a transmission issue to me - if the engine revved and sounded normal (as in not 'lumpy' or uneven).

What should I do now?
I'd take it in and get it checked - losing drive is pretty serious and could well be dangerous. You can probably drive it to your nearest garage as long as you're cautious.

How do I make sure this doesn't happen again?
You get it professionally assessed. There is no real option. Transmission issues like that can't be ignored. It could be as simple as a gear selector adjustment or a filter issue, but it does need looking at.

Should I try and see if I can recreate the problem?
Not really. No point.

Is the minivan still safe to drive?
I would say to be on the safe side, only as far as a suitable repair shop.*

Is it possible that this is in any way related to the alternator being replaced yesterday? If so, did I not run it for long enough on the highway last night to make sure the battery was properly charged?
Absolutely no. This is completely unrelated.

My manual says that the "service engine soon" light goes on when emissions rise above acceptable levels. How is this related to what happened?
It will also come on when some fault is triggered. Take it to a repair shop.

*I'm often one to say 'drive it and see what happens', but I'd never risk that with a loss of drive - that can have significantly detrimental affects on handling stability.

Other than limp home mode (And Rhomboid's answer, although I very much doubt it is at all related), most of the answers so far are completely guessing.
posted by Brockles at 4:58 PM on May 31, 2010

My manual says that the "service engine soon" light goes on when emissions rise above acceptable levels. How is this related to what happened?

Ugh, I feel like an ass for suggesting to check the owner's manual... somehow I missed reading the entirety of your question. Sorry about that.

posted by crapmatic at 6:08 PM on May 31, 2010

My "service engine soon" light began flashing.

A vehicle's Service Engine or Check Engine light will flash ONLY if the car is experiencing a misfire. There is no other condition that will cause the Check Engine light to flash. That's true for every single OBD-II vehicle in production. Flashing as the result of a misfire is a mandated function that's part of OBD-II.

When the engine misfires, a condition is occurring in one or more cylinders that results in the fuel not being burned. The engine computer detects this through fluctuations in the RPM combined with oxygen sensor readings. When the engine stumbles, the RPM signal fluctuates and unburned fuel in the exhaust will change the oxygen sensor voltage. Unburned fuel in the exhaust constitutes an emissions increase (hydrocarbons -fuel- being excessive emissions). The light will flash when this occurs because the catalytic converter (the exhaust component that chemically cleans the tailpipe emissions) can become extremely damaged as the result of prolonged misfiring. The converter operates best when hot and when unburned fuel enters the exhaust, the hot converter can reignite the fuel and subsequently begin to melt itself. Although this damage typically requires prolonged neglect of the malfunction, I have seen bad misfires cause converters to glow cherry-red-hot after about an hour of idling. It depends on the severity of the misfire.

A number of things can cause a misfire. The engine needs correctly proportioned fuel and air combined with correctly timed spark to make the requisite combustion to motivate the car. Your Astro Van has a Mass Airflow Sensor located between the air filter and the throttle that helps the computer determine the amount of air flowing into the engine. Since I'm sure they removed the air filter housing and ductwork to get to the alternator, check to see if it's hooked up correctly. If the engine computer can't calculate airflow, it will run very poorly. Double check that other sensors, like the throttle position sensor are connected and weren't disturbed by the previous work. Also, check and make sure that all of the spark plug wires are connected tightly.

Aside from double checking the work, you're really going to need to get a scan tool hooked up to the van to determine the source of the misfiring and to clear the Check Engine light. If the repair shop is a reasonable distance from your home, I recommend taking it back there and making it their problem.
posted by Jon-o at 6:41 PM on May 31, 2010 [2 favorites]

Also, late model vehicles will have an electronically controlled transmission. The control unit for the transmission will share inputs with the engine control unit. Calculated load, vehicle speed, throttle position, and intake manifold pressure, for example, are inputs common to both the engine and transmission control units. If the alternator installation disturbed the throttle position sensor or the MAP (manifold pressure) sensor, then a faulty input could be creating the appearance of a mechanical transmission malfunction. I have seen a number of harsh or no-shift concerns turn out to be a throttle position sensor malfunction instead of the feared catastrophic transmission failure.

Whatever the case is, you should probably take this back to the folks who did the alternator install. I have a feeling something is loose or disconnected.
posted by Jon-o at 7:16 PM on May 31, 2010

If you wrecked your cat, the Check Engine light will come back on, even if the car is mechanically OK. The car will drive fine, but you'll be dumping extra emissions into the atmosphere, and won't pass inspection. (Also, be prepared to spend ~$1000 on a new one)

If you have AAA, they'll tow you to a repair shop for free. If you don't have AAA, it's well worth it if you've got an older car.
posted by schmod at 9:40 PM on May 31, 2010

I agree with Jon-o that it may not be just a coincidence that your problems started right after the alternator was replaced. It wouldn't be the first time that a mechanic dislodged or forgot to reconnect a sensor wire. Take it back to the place where you had the alternator replaced and have them read out the codes and check for a loose wire. With any luck they may have you fixed up in 10 minutes. With a little more luck, you will find that your catalytic converter is still okay -- replacing it could be very expensive.
posted by JackFlash at 11:11 PM on May 31, 2010

It's true you can have the codes read (I hear Autozone does this for free),

They do (at least the ones by me do), I found this out shortly after buying an ODB-II code reader, and wondering if I should return it when I found out I could get it done on request. I didn't; Older cars throw codes all the time, and having it around has made it much easier to diagnose when there is a problem.

If you continue to have problems with the "service engine soon" light coming on, it would really be a wise move to have someone throw a reader on it to identify exactly what is failing.

All that said, I think Jon-o has it exactly right; this started after you had the alternator fixed, have them check to make sure they didn't forget to reconnect something.
posted by quin at 2:42 PM on June 2, 2010

I worked on a car today that reminded me of your problem. It was a Ford Mustang that would stall out constantly. The gauges wouldn't work and it ran poorly sometimes. When I would start it back up after stalling, it would crank kind of slow. It turned out that the battery was so shot that when the RPMs dropped when the clutch was let up, the charging system couldn't keep all of the electronics running. A new battery fixed this problem.
Many cars will misfire or have other problems when the system voltage drops. While the alternator is supposed to supply adequate power, if the battery is in too poor a condition to excite the field windings in the alternator, it won't generate the required output. Get your battery rechecked. It could be weak from when the alternator failed previously.
posted by Jon-o at 7:10 PM on June 3, 2010

« Older Dresser drawers wont open. Help!   |   Why are my eyes so itchy? Newer »
This thread is closed to new comments.