What cause misfire on cylinder #3 & #4?

what cause misfire on #3 and #4 cylinder I replace #3 coil no change made I check for pulse at 3 and 4 injector with a noid light the light flash and injectors are clicking.engine codes are P0300, P0303, P0304. compression #1, cylinder 195psi, cylinder #2, 190psi cylinder #3, 185psi, cylinder #4, 190psi.

Good job checking the compression, lets remove the spark plugs for inspection. We need to see what color they are so we know in what direction to go in the make the repair. The fuel injectors maybe getting a signal but if the injectors are bad/clogged it wont make a difference. Please unload images of the spark plugs so I can see them. Also here is a guide and video which can help in the meantime.

https://www.youtube.com/watch?v=QTE8k06MzwQ

and

https://www.2carpros.com/articles/engine-misfires-or-runs-rough/

Please go over these guides and get back to us.

You may have a PCM that is bad, lets check the injector pulse and power feed, this guide will show you how.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector/

You should have 12 volts on one of the injector feed wires for each injector . Let us know how it goes

12 volts at the injector feed wire with key on

That is a good sign, did you go over the guide above to check the injector pulse?

yes i went over the guide. i have injectors pulse but sometime on injector #3 my noid start blinking and then stop and start back.

This can be a wiring problem or the PCM is bad. Did you look at the wiring yet? This guide can help.

https://www.2carpros.com/articles/how-to-check-wiring/

Please go over this guide and get back to us.

misfire on #3 and #4 cylinder i replace ignition coils and spark plugs i check compression #3 185psi #4 190psi when i check for pulse at #3 fuel injector the noid light flash stop and flash while engine running what is causing theses problem? the engine codes are p0300, p0303 and p0304.

It sounds like the ECM is bad, I would get another one which should fix the problem.

when i check the trigger ground signal from the PCM i connect the clip end of test light to the positive post battery and the other end to the signal wire on injector while engine running the test light blink stop blink stop and so on. i check the signal wire from injector to PCM i find no break in wire.

So it sounds like the PCM is working, does the other wire of the injector have power when the key is on?

yes the other wire have power when the key is on, why the test light don't constantly blink at all time when doing the test? and why my noid light don't constantly flash at all time when doing the test at #3 injector?

It sounds like the injector driver inside the ECM is bad, I would replace it with another unit.

where are the places i can buy another unit? can i get one online?

Yes, we use this company, they know their stuff

https://www.flashmastersecm.com/

Please let me know what happens.

I did a second Injector pulse test on #3 cylinder with a Noid light while engine running the noid light would blink for about 30 second. and stop for about 30 second and start blinking again it does this all while the engine is idling.

hello, have you checked the resistance of that injector? both cold and hot. It sounds like the ECM is intentionally shutting down that injector due to the misfire code. Toyota does this with other circuits as well. I have seen the ECM shut down an oxygen sensor heater circuit after 10sec each time after I would clear the code.
It might be that an injector's resistance is changing according to hot/cold, (this is common), and at idle the engine would get warmer than when driving. Heat increases resistance. Id check the injector resistance cold and then hot as well. This is a situation where we would use an oscilloscope and look at the current ramp for the injectors, that would clearly show any shorted injector windings.
Check the control wire for a short to ground or short to power as well. Look for any corrosion inside connectors as well, green or whitish crusties.

the resistance on #3 injector cold is 12.8 ohm, why my noid light don't blink constantly is the oxygen sensor bad are the ECM? i check the wires from the injectors to the ECM i find nothing wrong with the wires. hen you say check the control wire are you talking about the signal wire at the injector?

no, that was an example of how Toyota's can operate, shutting down certain circuits if the ECM is seeing a problem, which it is with setting misfire codes. The fuel injectors are controlled on the ground wire, the ECM switches the ground on and off to activate the injector. So if that wire, which is opposite the power wire, has corrosion somewhere in a connector or inside the wiring, it will effect how the injector works. 12.8 ohms is around the correct measurement, but see what the resistance does when the injector gets hot. You may see it change.

can i use a handhelded Oscilloscope to check the injectors pulse?

Yes, but you will need an attenuator to bring the voltage level down, unless you have an automotive scope that is designed for higher voltage levels. The injectors will have an inductive voltage kick of usually 70-80volts, this you will see on the control wire. So using a 20:1 attenuator will protect the scope from these higher voltage levels when testing. I use an automotive Pico scope, which can handle up to 200volts +/-, so I dont need to use an attenuators unless checking ignition coils or I am not 100% sure what I am going to see on a circuit.
If you have a low current clamp, such as a 20Amp clamp, you can also look at the current waveform with a current clamp. This can show you a shorted injector, as well as the changes to the injectors pattern when cold or hot. It can also show you the pintle hump of the injector actually opening. Although I have seen a good pintle hump on bad injectors too, never know what you may see or find in this field. But the current waveform will tell you a lot.Very helpful testing. I will post some shorted injector waveforms for you so you know what youre looking for.

here is an example of an injectors voltage and current waveforms. The Red trace shows a nice current ramp on the first injector firing, and a shorted injector coil on the second. That, along with the pintle hump are what you want to compare to some other cylinders, to get a known good waveform on that vehicle if possible. Just be aware of your scopes limits, they are too valuable to burn out. What brand scope are you using? I have a 2 chan handheld as well, good for quick checks.

Heres a quick video where he shows using an amp clamp and small Pico scope to look at the current ramp. The 2nd video he does a voltage reading using the same scope, I know that scope can only do about 20volts max, so it would require a 20:1 ratio attentuation.


https://www.youtube.com/watch?v=6yaox9b9M5A

https://www.youtube.com/watch?v=F3n9YVbnaeA