P0303 Misfire Help!

I experienced a misfire on the freeway last week that shook my 2004 Tacoma V6 (185K miles) pretty good and managed into the parking garage at work thankfully. The truck started after work but was idling very rough and would bog down when put into gear. I grabbed a rental car as couldn’t miss work rest of week.

After buying a scanner, I pulled code P0303 and stared to diagnose from there. Plugs were fine. The ignition coil seemed to be the issue as the primary resistance test showed 1.5 ohms compared to max 1.05 ohms per spec. I ordered a replacement coil and ignition wires thinking this would be it.

The next day I cleared the code and swapped the coil to cylinder 1 to see if the code moved after reading a post here. To my surprise the engine fired right up as normal, ran for about 10 seconds, and then died. After dying, it sounded like pressure being released but figured due to air intake being off. The dashlights went crazy too – all lights came on, then ABS started flashing then went away, and finally just showed battery/oil/check engine light. This happened again when trying to restart. I then tested the other coils which read the same 1.5 ohms; therefore, think this is just due to age as all three going out would be a wild coincidence. I tried to pull codes again up nothing shows up.

I tried restarting again yesterday – engine will start to turn but just won’t catch. I tried to jump with another vehicle. I checked fuses and grounds as well. I am basically working solo in the work garage which seems to be limiting. Thought about checking the crank and camshaft sensors and possibly compression testing the engine. I may replace the fuel filter but don’t think that would cause a misfire. My concern is that the new coil and wires arriving today won’t resolve the issue; therefore, would greatly appreciate any thoughts on next steps.

TDLDR: Cylinder 3 misfire and initial assessment of coil might be wrong. Please help with next steps!

 

You’ve done everything else might as well change plugs. They might look fine but I bet everything else did as well. Also might try a fresh battery. My wife’s 4Runner started throwing tons of codes on a low battery.

 

The plugs looked normal as you say but may replace anyway when wires arrive. Battery ruled out as tested fine and attempting to jump had no impact.

 

Compression check and verify TB still in tack.

 

Auto zone will rent you a banjo bolt adapter and fuel pressure gauge. Fuel pump could be dying. Fuel pump and injectors seem to start having problems around 200k.

 

Replaced all spark plugs, ignition wires and put in new coil but still won’t start. Old plugs smelled like gas so believe fuel is getting in.

 

Fuel filter and compression don't seem to be the next step to me. If it was running fine before the misfire and subsequent no-start condition, neither of those seem to be immediate kind of failures. Of course, never a bad idea to replace a fuel filter if is got age on it, but doubt that's your issue.

Sounds like an electrical component failure, as was apparently your first instinct as well. I just had a crank sensor failure on my 3.0l Camry. Was running fine. Turned the ignition to off, and as it was shutting down, it kind of backfired out the intake. Crank but no start after that. Gauges went crazy with tach and speedometer jumping to full, indicator lights flashing, etc. Would try to fire every fourth or fifth revolution, but no start.

When I pulled the crank sensor it had a rusty, crust buildup all the way around, presumably where the magnetic pickup is inside it. I wish I had taken a pic. I assume it was pulling metal flakes from the oil and they gradually crusted enough to block the signal.

My idle speed was down to nothing after I got it running again. I had to go through the idle re-calibration cycle after getting it running, but I am not sure if these 3.4l ECUs have that function.

 

Have you confirmed plugs are firing?

 

Just throwing ideas around, if you know someone that can clear your codes that might help. Maybe even if the problem has been resolved the code that it threw needs resetting. Not an expert or mechanic but that would be my next step.

 

Sounds like no or low fire

 

You are going to have to go back to basics. I would do a compression test first as mentioned above. This will tell you a couple of things... low compression, 70,80,90 psi isnt a death sentance, the cam belt could have let go. If the compression is 150-ish, then you go in another direction. Take a plug wire off of a d/s cylinder and put a spark plug in it, ground the plug and crank her over and check for spark.

 

Okay so found this when searching for the camshaft position sensor and appears this might be the problem. Surprised a code didn’t pop up. I put an ohm meter on the connection and reading bounced all over the place!



Any advice on how to replace? I’ve managed to loosen the timing belt cover but had to stop given no method to catch radiator fluid when removing hose. How much fluid will come out from the block when removing the hose? Thinking a funnel and 5 gallon bucket might do the trick to stock fluid from going’s everywhere in the garage.

 

Are you saying your cam position sensor wasn't even connected? in your original post, you admitted to running the engine with the air intake off. Did you remember to plug your MAF sensor electrical connector back in?

If your coolant is newer, drain some of the radiator coolant into a clean container so you can reuse it. Compress the upper radiator hose constant tension clamp on the engine side of the hose and move it back around 6 inches. Take out all the bolts that hold the timing cover on (the bottom left is the hardest to get to), and then you should be able to move the cover back far enough along the upper radiator hose for you to access the cam position sensor to replace it. I've never tried replacing a cam position sensor like this but I imagine it will work. If this doesn't give you enough room, you could remove the upper radiator hose and get the cover completely out of the way.

 

I unplugged it before taking photo. Hard to see but one sensor wire is spliced and connector to timing belt cover is broken. Most likely fired up as the wire was still hanging by a couple threads.

MAF sensor connected each time. Hoping to check spark based other responses but couldn’t crank engine and see it at same time. Given camshaft sensor controls ignition firing timing hope this is fix.

Correct in that not much room to work. Trying to avoid a mess with radiator fluid in the garage.