1998 Honda Civic 1.6 5 speed - Error codes: po300, po302, p0304. Fuel pump pressure at idle = 35, higher rpm's around 45. Replaced plugs, wires, distributor cap, rotor, and fuel filter. Cleaned the fuel injectors. Idles perfectly after a cold start. Will run fine intermittently. Seems to misfire under load. Reminds me of the way a bad accelerator pump on an engine with a carburetor would act while accelerating. It will maintain a constant speed (had it up to 75) without a misfire until the load increases due to a hill, etc. After several miles, it will no longer idle, wants to stall but will easily restart.

PO300 and P1399 are random cylinder misfire detected.
PO301 cylinder 1 misfire
PO302 cylinder 2 misfire
PO304 cylinder 4 misfire
PO306 cylinder 6 misfire
I would say that you have damage to the ignition wiring harness or you ECM is failing.

Mira 847 cc 1993- Engine Code ED 10
Ignition data

• Ignition system type: El-ecu
• Ignition coil make/type: Dia/-
• Supply voltage: 12 + Volts with ballast resistor
• Primary resistance: 1.35-1.65 Ohms
• Secondary resistance: 22000-30000 Ohms
• Distributor make/type: Den/-
• Contact breaker gap/air: 0.2-0.4 mm
• Dwell angle: Deg\par Ignition Timing - unleaded: 5 2/900 Deg eng/rpm (without vacuum)
• Ignition Timing - leaded: Deg eng/rpm (without vacuum)
• Timing mark location: Flywheel
• No 1 plug location: Pulley
• Firing Order: 1-2-3
• Spark plug make: Bosch
• Spark plug type: WR6DC
• Electrode gap: 0.7-0.8 mm

Fuel System

• Fuel type: U/L
• Fuel pump type/pressure: bar
• Engine idle speed: 900+100/-50 rpm
• Fast idle speed: 2000 rpm
• CO level at idle speed: 1.0
• 0.5 Vol %

Engine Data

• Valve clearance - inlet: 0.25 mm (hot)
• Valve clearance - exhaust: 0.30 (hot)
• Compression pressure: 1.2-1.5 bar
• Oil pressure: 2.5-5.6/3000 bar/eng/rpm
• Radiator pressure cap: 0.6-1.05 bar/type
• Drive belt 1 - size: 9.5x925/KDB 925 mm/type
• Drive belt 2 - size: mm/type

Electrical System

• Alternator output: 10/2500 Amps/eng/rpm
• Regulated output: 14.2-14.8 Volts
• Battery: 12/35 V/Ah
• Starter motor make/type: Den/-

Other data

• Clutch operation type: Cable
• Clutch adjustment: 10-30 mm
• Cambelt failure: Damage
• Cambelt Part Number: 13514-87211
• Tyre pressures: 1.8(26)f 1.8(26)r bar (psi)
• it took me 3 seconds to google this then i realized that this is a older engine then yours

Which code you have po300 or po301.po302 .PO301,PO302 will be coil or module.PO300 could be bad spark plugs,vac. leak,clog fuel filter,bad fuel pump,bad battery.

The number 2 and number 4 cylinders are misfiring.I would do a tune-up on it sparkplugs, plug wires, air filter and fuel filter.

codes p 0300 is random misfires and codes p0301,2,3,4,5,6,7,8 are the cylinders that are misfiring
so un you statement the problem cylinders are 1 and 2
misfires are normally problem injectors and low fuel pressures so have the fuel pressure checked to make sure that the pump is running correctly, the pressure regulator is operating correctly ans the EVAP system is venting the tank correctly
use a couple of injector cleaner in the tank to clean the injectors

ck fuel pressure

spray carb/choke cleaner all around intake gasket mating surface on heads. (while motor is running) If rpms change you have a bad intake gasket.

P0304 Cylinder no. 4-Misfire Detected

This means that a plug, wire to the plug, or a fuel injector is not firing on this cylinder, or the compression is dead on it (not likely).

A P0304 code means that the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #4.

A code P0304 may mean that one or more of the following has happened:

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

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.

i have a 2001 chevy z-71 5.3L. I keep getting a random/multiple misfire code for cylinder 1 . I have replaced plugs, wires, coil pack(only on #1 cylinder)., and fuel pump. I still keep getting the cylinder 1 misfire code. I put truck on a scanner and watched the cylinders. # 1 misfires at idle but quickly stops misfiring at around 1000 rpms. you can here the engine miss at idle but truck runs great on road . anyone else ever had this problem?