2004 misfires on cylider #1 (P0310), #2 (P0302) and random(P0300), sudden onset from starting.

I had a P0301 about 6 months ago due to a cracked exhaust valve. I had the exhaust valves replaced and machined. This restored compression and eliminated the misfire.

Last Tuesday I started the truck and I immediately could tell it was not firing on all cylinders. Prior to this it seemed to be running well. I threw P0301, P0302, and P0300. Lots of vibration and above 80km/h its was pretty rough but smoothed out a bit with acceleration. I was out of town for the weekend and was trying to get home to work so drove it the 100km.
In the past year I have:
-replaced the plugs (Toyota)
-replaced High tension leads ( Toyota)
-Air filters, oil, both engine and differentials
-timing belt, water pump, kit, belts, etc.

in my attempt to diagnose:
- I swapped the #1 and #3 cylinder coils which had no effect on the location of the misfire.
-I checked with a light circuit meter the plug to the cylinder #1 fuel injector and it flashed so appeared to be functioning properly. (An ohms meter test showed the old fuel injectors all at 14.5, the new one I tested measured 15.5.)
At this point I assumed it to be fuel injectors ( relatively new OME plugs and high tension wires, and ruled out the coil) so purchased a set from Motor West performance. I had them shipped to Ogdensburg NY borrowed a friends car and drove over the border to get them so I could install them this weekend.
Finished Installing them today and the misfires continued with no change.
-preformed a reset of the ECU, engine still feels like its running on 4 cylinders. At present only the P0302 is coming up on my reader but the others may just be around the corner as it feels the same.
In addition before this all came to a head, I did get codes P0446 Evap system vent control circuit, P0442 EVAP system small leak detected, and H02S12 circuit malfunction. I assumed these only affected my passing an emission control test and not performance so had basically ignored them....
Just wondering if anyone has any ideas of in what direction I should head next...?

 

I had those same codes a bit ago, so I replaced all the spark plugs, wires, and coils, (157,000 miles) and it fixed the problem.

 

I would go that route also however I replaced the plugs and high-tension leads only within the last year (and I got them from Toyota). The previous lead had lasted nearly 18 years, could these new ones be malfunctioning already....

 

That could be, but I really couldn’t say. I replaced everything with new because they were original to my truck & it was 22 years old. Coils & wires are always my 1st suspects.
Are you using the OEM spec plugs with dual electrodes?

 

sounds like it mite be leaky fuel injectors fouling out plugs. Usually happens after it sits for a brief time and leaks into cylinder causing it to missfire. higher rpms clear it out and it will start firing again. Try some redline fuel injector cleaner in the fuel tank.

 

Yes OEM dual electrode spec plugs from Toyota ! High tension leads also OEM from Toyota.
I moved the coils around and it did not change engine performance or error codes.

 

I thought it was the fuel injectors so just finished replacing them with OEM fuel injectors from Motor West Performance.....It didn't change a thing... that's where I'm at... what to investigate next...

 

Have you tested the coil packs? You say you replaced the high tension leads, not totally sure if that also includes replacing the coil packs and not just the spark plug wires.

 

One coil #5 cylinder was replaced 6 months ago but I don't think it was necessary. What I did do was switch the coil packs between cylinders #1 and #3, this did not change the misfire location nor the performance of the engine.... I'm assuming this rules out the coils ?

 

I think that is right but it still might be worthwhile to check the resistance on them to further confirm they aren't the problem.

 

Right!!!
I checked the resistance with my digital ohmmeter cold and the following the readings I got.
Primary resistance : (range 0.67-1.05) cold
#1- 1.1 ohms
#3- 1.1 ohms
#5- 1.1 ohms
Secondary resistance: (9.3-16.0)cold
#1- 12.82 ohms
#3- 12.68 ohms
#5- 12.20 ohms

seems the primary readings are at the high end of the range....

I then ran the engine up to normal running temperature ( although I don't know how hot the coils were) and I measured the following readings.

#1- 1.3
#3- 1.3
#5- 1.3

any thoughts on these readings ?

 

When the exhaust valve was replaced, no cracks were found in the head?

 

My understanding is that it was solid. no history of over heating, no loss of coolant, no burning of oil, both the machinist who replaced the valves and the mechanic who put the head back on though it looked good.

 

Should be good then. My only experience with burnt valves on these 1st gens was on my friends 2.7l, and on my own 3.4l. Upon inspection, both heads were found to have numerous cracks, some between valve seat and spark plug hole, others between the valves. I can't speak to his, but mine never overheated or used any coolant or oil. Also, the cracks weren't only in proximity to the burnt valve(s).
My understanding is that those type of cracks are very common as miles build up, maybe more so when valve adjustments aren't done regularly. I don't know that small cracks like that will cause a misfire though.