I drive a stick Ford Focus 2002 and when I accelerate, the car hesitates/bogs down. This happens more when it is going up and heavily loaded. It happens more on low RPM but it also happens on high RPM. I can accelerate on idle and it does not have any problem. At the same time, I know when this is happening, or about to happen, because the radio volume rises suddenly together with the speedometer needle that goes crazy (up to 150mph) while the car is going at 30mph. The radio volume and speedometer needle settle down after the spurt.
Does anyone have any idea about what is happening around here?
Check your battery connections and make sure they are clean. The alternator may be going out and have AC ripple on it. Reseat and clean ll grounds too. Reseat connections on alternator.
I would be looking for an arc over of some high voltage circuit. It could be an ignition coil arcing; the wiring to the spark plug; or the spark plug itself. How long has it been since you had spark plugs and wires replaced? Alternately, it could be a high voltage ~300 volt discharge in the igniter. I suspect that the arcing is radiating into the VSS signel line and upsetting the signel to the ECM and thus to the speedometer head.
BTW has the Check Engine Lamp come on. You might have the ECM scanned for codes even if the light has not come “on”. How many miles on this Focus?
The fact that it occurs under heavy load indicates that the voltage breakdown is occuring when the spark has to jump an electrode gap in the presence of high cylinder pressure. So the first thing would be to put in a new, correctly gapped, set of spark plugs. The mechanic might be able to isolate the offending spark gap by using an ignition test gap to stress the high voltage and coil drive system and see if the problem surfaces.
I looked up the wiring diagram for you Focus (I am assuming that the engine is the 2.0 L single overhead cam). The igniter transistors are in the Power Control Module. If one of the power transistors is breakdown, it might be leaking ignition pulses onto the PCM power supply line (or anywhere for that matter). If this problem remains without any other part substitution affecting it, you might try a new PCM which would be a last resort.
I suspect that the reason the radio volume goes up is that the Body Control Module is sending a command to the radio to raise the volume according to the erronous speed input signel.
If and when you find the solution to this problem, please post back to educate the lurkers.
I had a guess that an ignition coil is going bad. Can’t prove it but I just wanted my guess to go in the hat.
Thank you very much for the comments. Here is more information.
The car has 75 000 miles. The Check Engine light is off.
I will let you know when I find the solution.
I’d check grounds. Just because you have a connection between two points that happen to measure near zero ohms with the car off, does not mean a ground connection isn’t missing: designers often have a number of ground connections on one particular part so that higher currents don’t go through grounds meant for sensors on that part. Higher currents going through sensor ground lifts that particular ground potential and wreak havoc with the electronics. Ideally, they have grounds come together in one point but that’s often not possible with cars. Sometimes an extra ground somewhere was put in as a band aid to alleviate a problem that was found after production was started.
Point being: Get a wiring diagram. They often have all ground points indicated. Check them all.
I’d guess that you have a flaky speed sensor, probably at the output of the transmission. The sensor flakes out, generates a lot of pulses, causing the speedo to jump. A lot of newer cars will automatically raise the radio volume for you as you go faster to offset road/wind noise–I suspect this feature is active on yours and that’s why the radio volume goes up. The ECM, confused by the erroneous input, causes a surge when trying to cope with a nonexistent condition–it may be your car is speed limited by the ECM, and when it sees a 150 MPH speed suddenly, it cuts fuel or spark to slow the car down, even though you’re not going that fast, resulting in a surge or lurch.
It could be a bad sensor or wiring, or even misrouted wiring–if the wires for the speed sensor are close enough to ignition wires for example, the high voltage pulse in the ignition wires may be inducing a current in the speed sensor wires, causing the condition.
From what you stated about the problem I tend to think there may be a problem with the voltage regulator for the charging system and is most likely inside the alternator. The DC voltage may be getting excessive when the trouble happens. The head lights would also brighten if that is the case. Checking for excessive AC ripple voltage would be good to do also like @knfenimore mentioned. AC voltage at the battery should be less than .1 volt while running around 1,500 RPM
I got the car to my mechanic and here is the diagnostic.
The alternator went bad. It should maintain the voltage between 13.5 and 14.5 Volts and it was spiking at 18Volts. This was overloading the electrical board and creating the spikes on the speedometer and the radio or the radio was increasing due to the speed associated increase of volume. The alternator had to come from the dealer. They tried a different model and it was not compatible. $332 for a rebuilt alternator + $275 for the labor.
Once the alternator was in place, they were able to diagnosed the engine misfiring. Actually the spark plugs were from origin and the wires were burned up. The car has 80 000 miles (the previous estimation was incorrect) and it is recommended to change them when the car approaches 100 000 miles. Spark plug wires $65. Spark plugs 4x $15 = $60. Labor $125.
Let me know if you have any questions.
Happy to hear you got the trouble solved. The trouble sounded like it was related to the alternator. Having the plugs and wires changed out is good to do also as they don’t last forever. Thanks for the feedback.