When does an Engine "Pop"?

Generally, An engine pops when it is improperly tuned. More specifically, in what is often called spitting, backfiring, or coughing, the following would have happened:

1. A spark plug "sparking" when it isn't its turn and the exhaust valve is open. Suppose there is air/fuel mixture that is too rich in the engine cylinder and there is unburned fuel in the exhaust system, cross firing from one spark plug wire to another can occur if they are touching each other. When this happens while the exhaust valve is open, it will ignite the rich / unburned mixture in the exhaust manifold and tail pipes and result in a big bang.
2. Not correct valve timing, esp timing that is too late [etarded] can cause this same thing as above in addition to an engine that is running too rich. When the exhaust valve opens, the mixture isn't done burning so it ignites the unburned fuel in the exhaust system and causes a loud bang.
3. A faulty distributor sends causes a spark to be done by a plug that isn't ready for it yet
4. The air/ fuel mixture is too lean, especially in the morning . Backfiring will happen through the Carb
5. A bad ignition system, for intance, cross firing. The pop will come out with a flame from the exhaust

Car producing a ticking sound upon start up?

There are a number of reasons owing to this:

• 
  

  

  engine piston

  Damaged reciprocating components of the engine such as pushrods, valves and pistons. If these are worn out or damaged in kind of manner and are not replaced the sound may migrate from ticking to whining or clunk, evidently showing more signs of damage.
• 
  

  

  oil pressure light indication on dashboard

  Not enough lubrication on components. If there is a low amount of oil in the system, this may cause a ticking noise from components in the valve train. Low oil is usually accompanied by overheating and damage on the seals and gaskets. If these happen concurrently, then you'll know what to suspect primely.
• Valves not properly set or adjusted. The pushrod which controls the rocker arm from the camshaft needs to be at precise distance from the valve, and if not, it will cause a ticking noise from the rocker assembly
• Warn out bearings. Bearings hold components to a reasonably fixed position. If a bearing warns out and loosens, the corresponding rods will move unnecessarily and thus causing a ticking noise.
• Injectors firing. This you'll need to worry about less because injectors will always need to open and close to allow in and out passage of fuel. Under high pressure and a well functioning pump, a ticking sound will be heard unless if it appears too absurd

My car shows a gear sign on dashboard, it does not show any trouble codes on diagnosis

It may be just a temporary issue. Try this,

Put shifter in park, put the park brake and turn the engine off. Wait a few seconds and restart the engine. If the gear sign still shows, then it's a more serious problem than it looks.

 If such is the case then your transmission is probably slipping.

Drive the vehicle while trying to maintain a constant throttle position as it accelerates upwards thru all the gears. If the transmission is shifting properly, it should be in 4th gear by the time you reach 60 to 80 kph on level ground. Repeat the procedure 3 to 5 times Rescan the PCM for trouble codes, if nothing appears again then the problem could have been a onetime occurrence. If a trouble code appears you take it from there and fix as necessary.

Even if it resultantly appears to be a onetime thing,… that is not an incentive enough for you to trust that your transmission is okay. 

It owes partly to bearing, clutch or hard part failure, and this will come with a grinding, whirring noise but again, not every time.

What are the Effects of a Faulty Speed Sensor on a Modern Car?

"An engine speed sensor retrieves and sends data to your car’s computer system."

Transmission speed sensors are used to calculate the actual gear ratio of the transmission while in use. There are generally 2 of these VSSes that work in conjunction to provide accurate transmission data to the vehicle's powertrain control module.(PCM)

The 1st is the input shaft speed (ISS) sensor. This sensor is used to monitor the speed of the transmission' input shaft. The other is the output shaft speed (OSS) sensor.

If either of these two sensors falls out of alignment or experience electrical issues, it impacts the operation of the entire transmission.

After registering data, the two transmission speed sensors, send data to the PCM,which compares these two inputs and calculates which gear the transmission should engage for efficient driving. The actual gear ratio is then compared to the desired gear ratio.

If the desired gear and the actual gear do not match, then the PCM will set a diagnostic trouble code (DTC) and illuminate the Check Engine Light.

A defective car speed sensor may cause different problems and just below are the most common ::


1. Harsh or improper shifting
When there are symptoms of a bad transmission speed sensor, the powertrain control module cannot control the shifting of gears within the transmission properly.  This may cause transmission revs higher before shifting gear or late transmission overdrive and inability to go into that top gear. Harsh shifting may damage internal components such as valve bodies, hydraulic lines, and even mechanical gears in some cases.

2. Inactive Cruise Control
The transmission speed sensor does not only control the input and output shaft speed. Meanwhile, it also plays a role in monitoring the cruise control. When there are some engine speed sensor problems, an error code will be sent to the car’s Engine Control Unit (ECU). Then the cruise control will be shut down and does not engage when you press the button. The speedometer also may work frantically or sometimes stop working altogether.


3. Check Engine Light comes on
If your car has some engine speed sensor problems, the Powertrain Control Module (PCM) will set a diagnostic trouble code and illuminate the Check Engine Light on the vehicle dashboard. Then the check engine light will come on sporadically and intermittently when accelerating. The overdrive light also may go ‘On’ or ‘Off’ for no apparent reason.