I ran diagnostics and it said misfire on cylinder 3. I replaced plugs, wires, distributor/rotor cap, coil pack (which was about 2 years ago) and now spider fuel injector. Just got on the freeway and my check engine light still comes on. It only comes on when its very high on RPMS and past 75+ mphr. It blinks for about 20 seconds and when I let off the gas it goes away. If I keep pushing the gas it blinks but then
eventually the check engine light will stay on. However i must admit sometimes it does and other times it does not.

Has anyone else had this issue before? I thought it might be oxygen sensors, but I don't believe that is the issue. I was told by a mechanic who checked it out and ran compression test that it could be the fuel injectors so I spend money and got them replaced now I'm at a loss. The mechanic told me that the rotor was good. I have never encountered this issue before. I have done most of the work on this truck myself except replacing the spider and when my fuel tank when out during grad school.

It's a 2004 base model Silverado v6 4.3. I just hit 190K miles.

Should I test the coil again? Anyway I can test if it is faulty? I did drill it out of the bracket and then replace it.

 

If the Check Engine Light flashes On and Off, that is telling you that there is unburned fuel being dumped into the catalytic converter and if you keep driving like that you can destroy the catalytic converter because it will melt down!

Remember, a P0303 is telling you that there is a misfire condition on cylinder #3. It does not tell you that the spark plug is bad, that the spark plug wire is bad, that the distributor rotor or cap is bad, etc. Hence you need to do some detective work in order to figure out why there is a #3 cylinder misfire condition.

Do you have a Digital Multi-Meter (DMM) that you can use to check the resistance of the spark plug wire? Have you removed the #3 spark plug and swapped it with the #1 spark plug to see if the P0303 changes to a P0301?

If it was the ignition coil, you would see misfires for several cylinders, not just one.

Do you have a code reader/live data scanner that will let you look at individual cylinder misfires, fuel trims, etc.?

Good Luck!

Good Luck!

 

I don't have a DMM or live data scanner. . But the issue is the check engine light does NOT stay on so I can't read the code anyways. For example drove it this morning for 1 hour running errands and the light never came on.

Question:

does it matter which spark plugs I switch? Example: remove #3 with #2 or #6?

 

No, it does not matter which spark plugs you swap the #3 plug with.

If you plan on doing you own maintenance you are going to need a DMM and a decent code reader/live data scanner. By the way, decent does not mean expensive. If you have an Android device, you can get the Torque Pro app and a Veepeak Bluetooth OBDII dongle for under $25.00. $5 for the app and $14 for the Bluetooth dongle ( ).

This set up will allow you to read codes, erase codes, and monitor virtually all of the systems in your truck and save the data for analysis on a PC.

Regarding the check engine light, if it comes on and is flashing/blinking - that is a very bad thing even if it goes away and the light goes out. Driving with a SOLID check engine light is OK. Driving with a FLASHING/BLINKING light is a bad thing. You can destroy the catalytic converter.

 

Issue is in the past when it did blink eventually it would stay on.

I'll try to swap the plus first and see what happens but I've always done all the work on my truck had for 20 years and never needed a DMM wouldn't see a reason to purchase one now

 

Without a DMM, how can you test spark plug wires, sensors, ignition coils, power at connectors, the 5 VDC reference voltage to various sensors, voltage drop in power circuits, etc.? Also, using a test lamp can be deadly for the various control modules and computers in these vehicles.