Hello and thank you in advance for any help offered. My sister has a nice TL with 120k. A couple months ago it was ran with a misfire and cel and the coil pack melted itself and the spark plug broke in half on cylinder 5. I didnt have time to do it for her so she had somebody replace the head. The guy finally finished but its still not right, but I told her I would fix for her since he doesnt answer her call anymore. Scanned codes got a misfire for every cylinder and a p0300. Replaced battery, checked plugs, replaced with NGK iridium. A little better but still off, started pulling coil connectors and found 4 and 5 produced no change in rpm. One coil pack is brand new I guess he put it in, its not oem so I put that one on 5 and it still didnt affect the engine. New codes are for every cylinder except for one. Obviously I dont wanna throw parts at it if it doesnt need it. Assuming the head work is ok and the timing is correct which it seems it is, where should I go next? Car shifts fine, probably has about 30-40% power. Ive read one coil could make em all misfire but honestly most of em look brown and or white at the plug boot. But they responded in the independent test. Please help and thanks again.

 

Got a spark tester today and they all tested good, spark looked strong. As stated before all plugs are new. Checked power and ground at each pack connector and they all had 12v and all grounds were good. Car runs alot smoother but still has a misfire.now getting mis on 2,4, and 5 whereas it was all before. Please help

 

check the A/C drain to make sure its dripping and not letting water onto the ECM. The ECM is behind the center console on the passenger side.

If the head was replaced, verify timing marks and make sure they are good. If the head was repaired, check and see if the helicoil or timesert didn't cause damage.

 

Yes, one coil can give false positives misfires on other cylinders.

Have you checked compression since the head was replaced?


Maybe you can try these troubleshooting methods:

 

So i sent it off to a mechanic to diagnose. Compression on all cylinders were good, coils good, plugs good, they wanted to charge 800 to pull valve covers and plenum to check injectors and valve clearance. Got it back home and need to fix it. I have a feeling its a bad injector. When i was doing balance test by unplugging coils the problem cylinder coil was good but it didnt change rpm. So the wiring,coil, and plug are good so i was thinking the injector isnt spraying correctly or something. Sound right?? How can i test injectors?

 

That mechanic is overcharging at $800 just to check things out. He should have been able to determine the cause of the misfire in his diagnostics. Find someone else.

By the way, I have never seen a valve adjustment fix a misfire.


There are several ways to test injectors but it will depend on what you have available to you.

1. Easiest is to measure the resistance of each injector and hope that the bad injector is way different than the rest.
2. Bi-directional scanner and fuel pressure gauge. You'll be able to prime the fuel system and the see the pressure drop of each injector.
3. Fuel injection pulse tester and fuel pressure gauge. You'll use the pulse tester instead of the scanner, but you'll need to actually plug it directly to the injector.
4. Scope and current probe to see the current ramp waveforms or the voltage waveforms. The bad injector will probably stick out from the rest.

 

Sounds good i will try those as available to me. I watched the vid but i dont access to a scanner with those cababilities. I will post and keep it updated when i come to a conclusion or hit a wall again. Thank you

 

Since you do not have the tools for those tests, then you should try measuring the resistance of each injector. A good injector should be 10-13 Ohms, and you can probably measure at a connector by the firewall or at the PCM.

Hopefully, you get some results that way.

This video shows current ramp test:

 

Good news!! Through the resistance test found the problem cylinder fuel injector to be bad. Swapped it out for a new and voila!!! Misfire gone. Thanks everybody for your input.

 

Thanks for the update. A lot of threads get left without a final fix.

I'm glad it worked out, and you did not have to pay $800 with that mechanic. Ridiculous.

 

Car runs great but now got po430 bad catalyst efficiency. I have a scanner that can read live data but not exactly sure what to look for as far as o2 sensor readings. Any help is appreciated.

 

Have you cleared the code and taken it for a drive to see if comes back?

Downstream O2 should be at steady voltage. A bad cat will have a switching O2 behavior.

Start @ 1:15