I have a 2001 Lexus rx 300 with a check engine light on with code P0301 cylinder 1 misfire. The spark plugs and ignition coils were already replaced. I swapped fuel injectors with known good cylinder and still have same code. Compression check was done and found cylinder 1 to be a bit low. Had the cylinder head sent to machine shop and came back tested fine. Tested electrical signals to fuel injector and got good pulsewidth signal. Checked for spark and got good spark. Don't know what else to do... Help!!

There is no p3100 code!!

I think you copied this wrong. the code is p0301, which is a common one.

The P0301 code means that the cylinder 1 is misfiring or is randomly misfiring. Start by checking for intake leaks an if no leaks are found the next step is to replace the spark plugs on cylinder 1. If the problem persist more tests needs to be done to diagnose problem.

Possible causes
- Faulty spark plug 1
- Clogged or faulty fuel injector 1
- Faulty ignition coil 1
- Fuel injector 1 harness is open or shorted
- Fuel injector 1 circuit poor electrical connection
- Ignition coil 1 harness is open or shorted
- Ignition coil 1 circuit poor electrical connection
- Insufficient cylinder 1 compression
- Incorrect fuel pressure
- Intake air leak

Most likely cause:
Faulty spark plug 1 or Faulty ignition coil 1 (Ignitor coil)

Either are easy fixes. Start with a new spark plug. If the problem continues replace the coil. Pic below. new about $30-$40.

Code 301 means cylinder one is not producing power.
Problem could be ignition, fuel, or mechanical.
If compression is good on all cylinders, check the fuel injector.

check engine light on, code P0300 P0301 P0302 P0303 P0304 THIS ARE ALL MISFIRES, 300 is random, 301 cylinder one 302 cylinder 2 and so on, the evaluation is once apart check the spark plugs condition, if they look ok, replace coils and plugs. if the light is not on, verify it works by turning the ignition to pos 2, if not replace light, if yes, and this here are not the codes, read the codes and re send it, posible bad cylinders, or poor injector.

A coil for most cars are normally not a very expensive part . Take a look on eBay for your type of vehicle for anidea if costings.
A coil is normally positioned in a placedwhichbis usually quite easy for a DIYer to fix themselves.
A Haynes manual or similar vehicle fixing manual may be worth while alternatively YouTube fixing it.

P1354VVT System Malfunction (Bank 2)

• P0300 Random/Multiple Cylinder Misfire Detected
• P0301 Cylinder 1 Misfire Detected
• P0302 Cylinder 2 Misfire Detected
• P0303 Cylinder 3 Misfire Detected
• P0304 Cylinder 4 Misfire Detected
• P0305 Cylinder 5 Misfire Detected
• P0306 Cylinder 6 Misfire Detected
• P0307 Cylinder 7 Misfire Detected
• P0308 Cylinder 8 Misfire Detected

Probably bad plug wires. Start there and then disconnect the battery for 5 minutes reconnect and start engine to see which codes have cleared.

P0301 - Cylinder 1 Misfire Detected.

Causes:
- Improper spark plug at cylinder #1
- Insufficient compression at cylinder #1
- Incorrect fuel pressure
- The injector circuit is open or shorted at cylinder #1
- Fuel injector #1 may be faulty
- Intake air leak

Solutions:
- Perform Injector Service
- Replaced Spark Plug #1
- Replaced Injector #1
- Replaced Ignition Coil #1

P0303 - Cylinder 3 Misfire Detected.
Follow info from P0301.

P0316 - Misfire Occurred In The First 1,000 Engine Revolutions.

Causes:
- Damaged CKP sensor.
- Ignition System.
- Fuel Injectors
- Running out of fuel
- Fuel Quality
- Base engine
- Damaged Powertrain Control Module

Solutions:
Usually the P0316 is combine with a P03XX codes. The P03XX code indicates in which cylinder the misfire occurred.

P0300 - Random / Multiple Cylinder Misfire Detected

Possible Causes:
- Improper spark plug
- Insufficient compression
- Incorrect fuel pressure
- The injector circuit is open or shorted
- Fuel injectors may be faulty
- Intake air leak

Possible Solutions:
- Perform Injector Service
- Replaced Spark Plugs
- Replaced Injectors
- Replaced Ignition Coils

P0301- Cylinder Number 1 Misfire Detected

Possible Causes:
- Improper spark plug at cylinder #1
- Insufficient compression at cylinder #1
- Incorrect fuel pressure
- The injector circuit is open or shorted at cylinder #1
- Fuel injector #1 may be faulty
- Intake air leak at cylinder

Possible Solutions:
- Perform Injector Service
- Replaced Spark Plug #1
- Replaced Injector #1
- Replaced Ignition Coil #1

Most likely your issue is with cylinder number 1. Follow the info I have provided and you should be able to solve this issue.

HELLO: This code means misfire on cylinder #1, Check spark plug, Coil, ignition module and injector. Maybe this will help.

P0300 Random Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0303 Cylinder 3 Misfire Detected
according to this fault codes first mark ignition coils
3 ---------------- 6
2 ---------------- 5
1 ---------------- 4
RB-------------LB
this right banks and left bank, please remove Ignition coils with lids and spark plugs from right bank and swap with left bank, if fault code change as
P 0304 Cylinder 4 Misfire Detected
P 0305 Cylinder 5 Misfire Detected
P 0306 Cylinder 6 Misfire Detected
You can Identify it's a faulty ignition system then next swap ignition lids from ignition coils be careful each coils have two lids one short and other long bit deference and when you remove and fix it to the car keep in mind correct order because each coil two different fire for two spark plugs don't mix up, if you mix it can create the fault code.if you detect any fault ignition coils or spark plugs or lids replace that and also whether god or bad recommend to replace spark plugs, find the right that's most important thing, if this way couldn't found the any ignition fault next step is check fuel presser, when the engine running fuel presser must be around 4.5 bar without engine running must be 4 to 6 bar if the fuel presser too low need to check two different things one is fuel pump other is fuel injectors, in this case you can swap injectors from right bank to left bank and find is the injectors leaking, if not leaking faulty fuel pump.is this information helped you? if yes please leave a comment,

You could have a bad coil pack or a bad fuel injector. swap out the coil packs from the misfiring cylinders and put them in the cylinders that are known to be firing correctly to narrow it down to determine if it is the coil pack first. When is the last time you changed the spark plugs? Pull them out of the misfiring cylinders to check the condition of the plugs.