If your Mercury Monterey won’t accelerate, that is a serious cause for concern.
If your check engine light is on, get a code scanner and see what trouble codes are stored in the PCM (powertrain control module). They can provide valuable insight as to what the problem may be and help you narrow down the problem.
There’s a lot of information here, and it can be overwhelming. We’ve put a quick information table to help you determine why your Monterey won’t accelerate.
Check for Codes
Most problems significant enough to make your Mercury Monterey not accelerate will cause a diagnostic trouble code. If your van’s check engine light is on, there’s valuable info stored in there.
Start with whatever parts of the vehicle the codes indicate are having a problem.
Quick Info Table
| Cause | Will it accelerate at all? | Notes |
|---|---|---|
| Misfire | Yes. | You should hear the misfire when revving the engine when the vehicle is parked. There should be a misfire code. |
| Low Transmission Fluid | At first, then eventually no movement. | There may be a burning or sweet smell coming from under the hood. Usually no noise. |
| Torque Converter | Maybe | Maybe a clunking sound. No Codes |
| Clutch | It should start out slipping, and then eventually no movement | You should smell a rotten smell when the clutch is burning up. Manual only. |
| Broken Axle or Driveshaft | No | You may hear a slapping sound when you put the vehicle in gear. |
| Bad Transmission | Maybe | Usually, the van’s transmission will slip before there’s no acceleration. |
| Clogged Catalytic Converter | Yes. It may feel like it has a hard limit to how much gas you can give it. | There may be a rotten smell coming from the exhaust pipe. P0420 may accompany it. |
| Fuel Pump | Yes. It should stall out when giving it more gas. | It may be making a whining noise coming from the vehicle’s rear. |
| Fuel Filter | Yes. The engine should stall out when trying to accelerate. | Same symptoms as a clogged fuel pump. |
| Timing Chain | Yes. | The engine should run rough. |
| Vacuum Leak | Usually | It should still accelerate. You’ll likely get P0171 with the check engine light. |
| O2 Sensors | Yes | OBD II codes should accompany it. |
| Throttle Position Sensor | May limp, or there’ll be no acceleration at all. | Should be accompanied by trouble codes |
There are so many reasons your Monterey won’t accelerate. We’ve made a table to help you try and narrow them down before reading through all of this.
As you can see above, there are only a few reasons why a vehicle won’t accelerate at all. The check engine light should almost always accompany those.
Mercury Monterey Won’t Accelerate Causes
If your Monterey doesn’t accelerate, but the RPMs go up, it’s usually not an engine-related issue. Somehow, your engine’s power is not making it to the rear wheels. This is typically an issue related to the transmission
Here are the most common cause of acceleration with the RPMs going up:
Misfire
You should be able to hear it, and it’ll likely be paired with a code such as P0300 or P030X (where X is the misfiring cylinder).
A few things can cause an engine to misfire. But, more often than not, it’s going to be the spark plugs or coil packs that are the culprit. A misfire is the most common reason your Mercury Monterey isn’t accelerating.
Here are some common misfire causes.
- Spark Plugs– Even under the best conditions, spark plugs will eventually need to be replaced. Oil on the plugs, the wrong or bad spark plugs can cause a misfire.
- Coil Packs– Your ignition coil, or coil packs, create the spark and send it to the spark plug at just the right time for optimal power and efficiency. When one has gone bad, they’ll usually cause your Monterey to accelerate slowly, idle rough, and will hurt fuel mileage.
- Plug Wires– Spark plug wires are not as common as they used to be, but your particular model of Monterey may have them, so they are on the list. A spark plug wire goes bad when it can no longer transfer the spark from the coil pack or distributor properly.
While the ignition system is the most likely reason a vehicle won’t accelerate as fast as it should. It should still move some though, if it’s the cause.
Low Transmission Fluid
The engine should sound completely normal. Look for a red puddle under where you’ve been parking your van.
If your Monterey is too low on transmission fluid, it will no longer be able to transfer power to the wheels. The power goes to the torque converter, and that’s the end of the line.
You should check the transmission fluid immediately. This is a common cause of not accelerating, but the RPM rises.
Before the transmission ran out of fluid, you should have noticed the RPM going up too fast for the speed you were going, indicating that the transmission fluid was low.
Here’s how to detect low transmission fluid signs.
Torque Converter
There may be a noise that accompanies a bad torque converter. Unfortunately, there’s rarely a code.
The torque converter is responsible for taking the engine’s mechanical power and converting it into hydraulic energy.
If the torque converter has gone bad, it will no longer be able to do this job. No power can get to the transmission.
Bad Torque Converter vs. Bad Transmission
Broken Axle or Driveshaft
Depending on which side of the axle you broke, you may hear a slapping sound when you put the van in gear. A quick visual inspection will confirm it’s broken.
If you’ve broken a drive/axle shaft, your Mercury Monterey’s transmission can no longer turn the wheels.
If this were the case, there would not be any movement whatsoever from the vehicle.
Bad Transmission
Slipping usually starts gradually. P0700 is a common code if it’s an electrical issue related to the transmission.
If something has gone wrong in the transmission, your Monterey may not be able to accelerate anymore, or it’ll. If it can no longer shift, it could be caused by a solenoid/valve body that has gone bad, clutch packs, debris, and much more.
Clutch
If your van has a manual transmission, a clutch failure can keep it from accelerating.
Although the manual transmission is going away, if you have a Monterey equipped with one, a bad clutch can cause it not to accelerate.
The clutch is responsible for directly connecting the engine (via the flywheel) and the transmission (via the input shaft).
When the clutch can’t hold on to the flywheel anymore, it’ll start to slip. Typically, slipping starts at highway speed and under heavy acceleration.
It only gets worse as the clutch disk slips and burns up. It’ll be able to handle less and less torque. Eventually, it’ll only move in first gear or not at all.
Clogged Catalytic Converter
A clogged catalytic converter will likely appear with a code such as P0420 or P0430.
Your Monterey’s exhaust must pass through the catalytic converter to get to the tailpipe. It is possible for the converter to clog. This can happen if a rich air/fuel mixture has run through it for a while. When it is blocked, your Monterey will struggle to accelerate.
You may also notice that it has a “top speed” much lower than you would need to drive on the highway. This happens when the catalytic converter is almost full and the engine is choking on its exhaust.
It’ll “bog” after a certain speed. Maybe it’ll drive 20 miles an hour just fine, but after that, it just doesn’t want to accelerate whatsoever. This can also be a sign that it’s not getting enough fuel.
Fuel Pump
The engine should act starved when more fuel is needed. Codes P0087 or P0230 through P0232 may appear.
A malfunctioning fuel pump can cause a menagerie of strange symptoms. The engine may have trouble starting. Then, once started, it’ll die if you try to give it gas.
- The van may die when you give it gas.
- It may hesitate or stumble when you need more power.
- Your Mercury Monterey may be jerking when accelerating.
Bad Fuel Filter
The symptoms of a bad fuel filter are exactly the same as a faulty fuel pump.
A bad fuel filter will not let enough fuel into the Monterey’s fuel injection system to support operation above a certain demand on the engine. It just can’t provide the fuel pressure.
If this is the case, like the catalytic converter, it’ll feel like everything is fine until you hit a certain speed, and then it will bog down.
The only way to know if a fuel filter is bad VS a bad fuel pump is to test the fuel pressure coming in and out of your van’s fuel filter.
Mercury Monterey: Bad Fuel Filter → Symptoms and Diagnosis
Timing Chain or Belt
If your Monterey’s timing chain has jumped, you’ll likely get code P0300 and might even be able to hear it slapping around under the timing cover.
The timing chain (or belt) keeps the upper valve train synced with the crankshaft. This is vital for spark timing. The timing belt may have skipped if the timing is off a little and the engine still runs. If it has jumped too much, the Monterey may not even fire.
Air Intake Issues
It may appear with code P0171 or P0100-P0104
Vacuum Leak
Your Monterey’s engine creates a vacuum as it runs. Too much vacuum creates a situation where the air is not coming in and being read by the MAF sensor, which causes the vehicle to run wrong and not accelerate.
MAF or MAP Sensor
The MAF sensor also may not be functioning correctly. If this is the case, it’ll almost always throw a trouble code.
You can look at the MAF sensor and see if it’s dirty. Auto parts stores sell dedicated MAF sensor cleaners. Make sure to use it and follow the instructions on the bottle. If you clean it with anything else, it can damage the MAF Sensor.
Mercury Monterey: Bad MAF Sensor → Symptoms and Causes
Exhaust Issues
Your Mercury Monterey’s exhaust system has three functions. It releases exhaust gasses behind the van, scrubs pollutants via the catalytic converter, and helps the engine adjust the air/fuel mixture via O2 sensors.
O2 sensors
The oxygen sensors meter the exhaust as it exits the combustion chamber. If one is faulty, it can change the air-fuel ratio to the point that your Monterey won’t accelerate well.
Exhaust Pipe Crimped
Have you driven your van over something that scraped the bottom hard? Your Monterey’s exhaust pipe may have gotten pinched. When pinched, exhaust gasses can’t escape, and your van won’t accelerate.
Throttle Position Sensor
Likely to appear with P0121 or a similar TPS code.
There are two types of throttle systems. They are drive-by-wire and drive-by cable. Most modern vehicles have drive-by-wire, where the throttle is controlled by a throttle position sensor attached to the gas pedal.
When the throttle position sensor fails, it will either put your Mercury Monterey into limp mode or won’t respond.