thmpr

All,
Want to share some troubleshooting I did to attack the P0301 error code which means " Misfire Cylinder 1". First off, I went to Autozone to rent a OBD2 code reader for $150.00 which is fully refundable before the 30 days lease.
There were 5 main probable causes that can cause this error:
1) Spark Plug
2) Wires
3) Coil
4) Fuel injector
5) Valves

1st/2nd task: Determine if Spark plugs/wires was the culprit.
Since I had the spark plugs and wires for a future maintenance, I went ahead and replaced these items. Cleared the error code and ran the engine for 10 mins. Error came back. Read the Theory of operations on the firing order and found that 2 cyls. share the same coil, thus swapped coils between #1and #5, Cleared the error code and ran the engine for 10 mins. Error came back.

3rd task: Determine if FI#1 was the culprit.
Ran an ohms test on Cyl. #1 FI an found 94 ohms and would change to 63 ohms and would change up and down depependent on the temp. Specs is around 12-16 ohms. Measured other FI that was accessible and found it to be 15 ohms.

Ordered FI from www.fiveomotorsport.com decided to replace all with valve cover, spark plug, and Intake manifold gasket.

Took about 6 hours to complete the tasks and now the engine runs much smoother and run alot stronger.

Hope this helps!

iwilli1169

I need to diagnose an intermittent misfire that I think is the FI. I didn't see what year/type Toyota rig you have. I have the 97 4Runner with a 3.4L. Can I reach the FI connectors without moving anything for the 1,3,5 cylinders on the passenger side bank?

thmpr

Yes you can. They are the only FIs that are accessible without any major removal of any parts except the FI connectors.

I have a 96 SR5 4X4 soon to have the SS 7.2 system this week.