Good day,chevy optra 1.6 16v , misfire on cyl no. 2.i have had the complete engine overall done,but I am still loosing compression on no. 2

SOURCE: 04 Sedona 3.5 cyl #2 misfire replaced coil,back again 5 mos later

How many miles on the plugs and wires? Misfire can be caused by either plugs or wires, after that check the injector for that cylinder. Let me know what u find. Curt

SOURCE: 2000 CHevy Silverado misfire code

try also the knock sensor..computer cant adjust timing

Harvey N Tawatao

• 3854 Answers
• Posted on Feb 03, 2010

SOURCE: i own a 96 chevy k1500 5.7 l vortec and have a no 5 cyl misfire

It could be a faulty fuel injector, try running a fuel injector cleaner through your fuel system. At worst the poppet nozzle has gone bad and will need to be replaced, you can buy the poppet nozzle it self individually at Auto Zone or buy upgrade MFI system which is much better and less pron to fuel leaking room a cracked poppet line or nozzle which will cause what you have described.

Testimonial: "very helpfull, allthese year i thought i had throttle body as it turns out i have muti port. thanks for the fix."

SOURCE: 2000 gmc jimmy 4.3L misfire on cyl 4 and cyl 5 at

Clean the egr valve which would cause rough ideling and misfire........Hope this helps u out.

ZJ Limited

• 17989 Answers
• Posted on Jul 13, 2011

SOURCE: 2005 Hyundai Tucson 2.0L During start-up

A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.

For example, a P0302 code means that the the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #2; same condition in P0301 - cyl #1, P0303 - cyl #3 and P0304 - cyl #4.

A code P0300 (or 301, 302, 303 or 304) may mean that one or more of the following has happened:
Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer

About your possible solutions, if there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.



So, your code P0170 is one that surfaces with certain makes of automobiles more than others. In writing this article I've added Mercedes-Benz-specific info since it seems that M-B (and VW) are most prone to having this P0170 surface along with misfire codes or other fuel trim codes. P0170 means there was a malfunction in the computer's control of the air:fuel ratio.

It also indicates that the fuel trims reached their limit of adding fuel while trying to compensate for a actual or perceived rich condition. When the fuel trims reach their rich correction limit, the PCM (Powertrain Control Module) sets a P0170, indicating a problem or malfunction in the fuel trims. It may also have a P0173 referring to the same malfunction but on bank two.

Potential causes include a vacuum leak, unmetered air leaks Fuel saturated engine oil Leak in turbo air charge hoses (if equipped) Possibly bad O2 sensor (If Mercedes, may require adaptation with M-Benz compatible scan tool.) Oil contamination in MAF connector or O2 sensor connectors. Also check ignition coils, cam and crank sensors, and oil sensor for leakage contributing to oil intrusion in wiring harness. Defective MAF (Mass Air Flow) sensor (especially on Mercedez-Benz and other European autos. There are a lot of problems with aftermarket MAF sensors).

If you have this code and access to a scan tool, observe the MAF sensor reading in grams/sec. The reading will be different for different automobiles, so get a good spec. I'm going to stick with what would be normal for a Mercedes (1.8L), since they have the bulk of the trouble. Expect to see at idle 3.5-5 g/s (ideally). At 2500 RPMs with no load it should be between 9 and 12 g/s. On road test, at WOT (wide open throttle) it should be 90 g/s or well above. If it's not in specs, replace it. Be careful of Ebay MAFs. Often they don't work according to OE specifications. If the MAF checks out and there is no oil intrusion at the connector, check fuel pressure and ensure that there are no leaks at the regulator internally or externally. Check all vacuum hoses and confirm none are cracked, disconnected or missing. Make sure there are no vacuum leaks at the intake manifold gaskets or tears in the air supply hose. If the engine is turbo charged, be sure the hoses are in good condition and have no leaks. Leaking turbo pressure hoses could cause a rich condition. Inspect the condition of crankcase vent hose under intake manifold and operation of check valve in the hose. (In the "What are the causes?" section) If there doesn't appear to be any problems with the fuel pressure, MAF or vacuum hoses, then inspect the O2 sensor connectors for oil intrusion. A bad O2 sensor could cause a P0170, or P0173. Repair cause of oil leak and replace oil-fouled O2 sensor.

This is location diagram...



Bank 1 is always the side of the engine with cylinder #1.
Bank 2 is always the side of the engine with cylinder #2.

Bank 1 is the bank of cylinders on the firewall side.
Bank 2 is the bank of cylinders on the radiator side.

Sensor 1 is the O2 sensor before the cat.
Sensor 2 is the O2 sensor after the cat.

So the one you want is the sensor AFTER the cat on the FIREWALL side of the engine.

Hope this helps.