Hi everyone I am new to the forum. I have a 98 Toyota 4Runner with the 4.3 L. Just turned 230,000 miles. I bought it with 103k and was informed from the dealer that the timing belt had just been replaced. I am regular on my maintenance and have never had an issue with this truck. As of recently my check engine light came on and while borrowing a code reader the P0300 code was first detected, suggesting random and multiple misfire. I took to the auto parts store and decided to start with plugs and wires. I had replaced plugs in the past but have never done wires so I figured I would start here. After installing an test running I thought for short moment I had fixed the problem. I soon realized I had not. I found a three pack of new coils on eBay for less than $50 total and purchased those. They did read to sound like high-quality replacement coils so I opted to purchase those at a huge savings over OEM. I've installed those and test ran. Truck seemed to have been running well for nearly a full tank of fuel. The issue seem to creep up on me again check engine light came on and I checked the code. This time the P0302 code indicating a misfire on cylinder 2 along with very poor performance--best I can describe is it felt like I was running on 4 cylinders and struggled to limp it home. I dove back in, removing the air intake assembly, double and triple checked my work and reassembly, cleaned the mass airflow sensor, pulled out spark plug number two and number four and did a compression test on each. Each of those cylinders came up about 160-165 lbs so I figured that's good? With some research I'm leaning to think I may have a fuel injector problem specifically for sure with cylinder number two. I hope I've done enough troubleshooting and diagnostic to justify my reasoning because I just purchased six new fuel injectors from RockAuto figuring it would be better to replace all rather than just the 1. I intend to have them installed at the shop this Saturday for a grand total of about $650 for labor and parts and I will update this post after. Thanks for reading and if you have any suggestions to add PLEASE do so.

 

Are you sure it's not a 3.4L?
Timing belt interval is 90,000 miles.

Maybe a mod can move this to the appropriate forum?

 

Yes. 3.4.

 

Well, I mentioned that I would update this thread after the work was completed on my four runner. I installed six new fuel injectors, which I ordered from RockAuto, in the truck and now it is running great. Warm and cold starts are much quicker than ever. The job took about five hours and I had 1 helper. I had never attempted taking on a job of this size before so if you're thinking of doing the same, I'd encourage someone to take it on and save a lot of money on their own. I hope this thread helps someone else. I know I would have enjoyed more feedback on my original posting but I'm glad I figured it out on my own.

 

Error Code: P0300
Description:
Random/Multiple Cylinder(s) - Misfire Detected
Possible Cause:
Air Intake System leaking.
Fuel Supply faulty.
Injector(s) faulty.
Ignition Cable(s) and/or Spark Plug(s) faulty.
Ignition coil(s).Exhaust Gas Recirculation (EGR) Valve stuck/open.
Camshaft Position Sensor faulty.
Low compression.
Wiring.

Possible Solutions:
Check Misfire Recognition.
Check Air Intake System.
Check Fuel Supply.
Check Injector(s) and Injector Sealing.
Check Ignition Cable(s) and Spark Plug(s).
Check Ignition Coil(s).
Check Exhaust Gas Recirculation (EGR) Valve.
Check Camshaft Position Sensor.

Error Code: P0302
Description:
Cylinder 2 - Misfire Detected
Possible Cause:
Spark plugs gaps too wide.
Wrong heat range numbers of the spark plugs.
Wiring.
Ignition system.
Fuel injectors.
Fuel pressure.
Running out of fuel.
EVAP canister purge valve.
Evaporative emission system.
Low compression.
Base engine problems.
Engine control module (ECM).

 

was replacing the injectors a tough job? It's something that I see in my near future. Thanks.

 

Forget the injectors at this time. In order to pin point the problem, I suggest you to do the following jobs, you will not have to pay much for it. If you have the required tools you could do it free of cost. If you don't, then ask any technician to carry out the tests, compare the results yourself and do the needful.

1. First of all clear the codes, adjust the spark plugs gaps to 0.70 mm, drive the car and see if it solves the problem. Do not do any thing else at this stage.
- If this trick solve the issue, inspect the spark plugs electrodes. If they are found to be corroded, fouled or have lost their shapes, replace them.
- If it has spark plug high tension cords, check the resistance of No. 2 cord with Digital Multimeter. Set meter range to 100 K Ohms, read the resistance. It is OK if the resistance is 8 - 30 K Ohms. If it does not show any resistance this is the culprit. Replace it.
If it is Coil On Plug system, replace the No. 2 Igniter and fuel injector No. 2.

3. Check the cylinder compression of No. 2 cylinder at operating temperature. The cylinder compression must be in between 150 psi (10 bar) to 180 psi (12 bar). If less than 100 psi adjust the valve clearance of it may require engine overhauling.

2. Check the valve clearance of cylinder No. 2. at operating temperature.
Valve clearance Inlet = 0.25 mm
Valve clearance Exhaust = 0.30 mm. If no clearance or it is less than 0.15 mm, replace or regrind the valve tappet shim to provide the required clearance.

3. Check fuel pump pressure. Attach any pressure gauge having the capacity to read up to 100 psi to the fuel line at the fuel rail securely. Keep starter engaged for 5 Seconds, read the dial. Switch the ignition OFF. Standard pressure = 38 - 44 psi.
If it is less than the standard pressure, replace the fuel pump and fuel filter.

4. Remove the throttle body. Hold the throttle body straight as it was fitted to the intake manifold and look through the barrel pointing to the sky or any suitable light. Inspect the half moon shaped gap. If the half moon gap is on the top and bottom (perpendicular to the throttle plate shaft) and the sides do not permit light to be seen, it is OK. If the light is seen on both sides. it is gone bad and need to be replaced.

NOTE:
Fist of all perform the step No. 1 only, drive the car. If it does not solve the problem, perform the remaining steps thereafter. Hope that works.

 

Well, your first post was so complete, there was not much left to suggest. You were very thorough. Included all the symptoms, diagnosis, initial attempts, etc. I, for one, appreciate you posting the final solution. I wish all guys would do that. I use RockAuto for parts as well, and its gratifying to know that even their injectors are quality.

 

Thank you for your compliments. We are all like a family members and this is our obligation to help each other.
With best wishes and regards.
Shadab Ahmad Khan Lodhi

 

Hey guys, the injectors were not too bad to replace. I consider myself average to maybe above average when it comes to wrenching and I did have help from my brother In-law who has numerous certifications and credentials beyond my knowledge in autos, but his MS really only allowed to help guide me through the process. I've been driving the truck daily since my post stating when I replaced the injectors and everything has been flawless. I'm not sure if it's just a petty complaint or me expecting more from my 4-runner but it does seem like fuel economy is down just a little bit from what I remember it when the OEM i injectors were all good even during the winter here in Minnesota. Time will tell I guess but so far everything is good. Thanks everybody.

 

I had the same issue on a 99 4Runner 3.4; P0300 & P0301- I did most of your initia.steps, but also changed the fuel filter.
New fuel injector in Cyl#1 fixed the problem! Will soon replace the other 5!