2008 4.0 misfire

I have a 2008 Tacoma access cab four-wheel-drive with the 4.0 V-6. 190 k miles.

About a month ago it started randomly misfiring while accelerating. It never happened at idle or without my foot on the gas.

I went ahead and changed out the spark plugs with NGK. No issues until about the last week.

There is no check engine light and my mechanic connected a reader to it and pulled no codes.

My next idea was to replace all six coils, but I’d rather have a better idea of what is going on.

Has anyone ever had this happen before? Maybe the wires from the coils?

 

To check your coils what your truck idol and unplug one coil out of time to see if you hear a difference in the engine

 

See which cylinder is misfiring, swap the coil to a different cylinder and see if the miss follows.

 

I’ll go ahead and unplug one coil at a time this weekend. It happens so in frequently that I don’t know if that will work. For example, I’ve been driving for half an hour and it hasn’t happened so far. It happened this morning but before that hadn’t happened in a couple of days. It really is super random.

 

Is the fuel pump original? It might be going, I had similar symptoms when my original fuel pump was going bad

 

Run a bottle of fuel system cleaner. Berrymen’s B12 is pretty strong. See how that goes. Chevron Techron concentrate, Redline SL1 is pretty good too. I run Amsoil PI every three months.

 

Yeah, fuel pump is original.

 

Have the fuel pressure checked, I don’t recall what the normal range is for our trucks but I do know mine was low. Denso is the oem brand for the pump

 

1. Ordered the OEM denso coils form Rock Auto. Much cheaper than autozone. I’ll keep the truck forever, so decided to go ahead and get them.
2. Will see how much $$ it costs to check the fuel pump.
3. Will go ahead and run a cleaner through the fuel system.

 

word of warning, it is not unusual for any kind of electronic part, for some reason, to not be up to snuff/potentially defective, from Rockauto. I use them all the time myself for certain parts but have learned the hard way not for electronic stuff. I hope it all works out for you. Make sure to install those coils as soon as you get them to make sure if a return is needed so you don't run out of the return window, which I think is 30 days

I bought the Denso fuel pump from them, no issues. Tried getting Denso alternator, after 3 tries or purchase and returns I stopped and went to the dealer. Friends have had similar results too.

 

I replaced the fuel pump with a denso from rockauto 4 years ago during the frame swap. No issues yet.

 

I changed out the plugs and coils, and I am still having the same issue. It randomly misfires; however, it is much less frequent.

thoughts? Took it to the mechanic -they of course couldn’t replicate it when driving.

 

Is it possible it's torque converter shudder instead of a misfire?
Transmission- 5 Speed automatic write up with pics for second gen 4 liter trucks | Tacoma World

 

Maybe. I had the transmission fluid drained and filled about 40 k miles ago.

I think I may have figured it out.

Thinking back to when I changed the spark plugs - one of them had a crack in the porcelain. I replaced the plugs, but didn't replace the coils til 2 weeks later.

Could the bad coil have caused the new spark plug to already go bad (and thus, arc, even though I changed the coil 2 weeks later)? I'm going to check it out tomorrow when I get the truck back.

 

If it was arcing down the side of the plug it could have made a carbon track on the plug and/or in the boot, once a plug or boot is carbon tracked usually both have to be replaced because the spark will continue to follow the same path.

It's usually pretty easy to see carbon tracking, it shows up as a grey to white line on the coil side and a grey to black line on the plug side.
If it's really bad the coil boot usually has a white chalky look inside of it.

 

Did you stick with OEM? I mean copper, maybe iridium, Denso/ NGK plugs? Same with coils, did you stick with OEM? I know the coils can be expensive, however on densoproducts.com they're much cheaper compared to everywhere else

 

Yes, NGK plugs and Denso coils. Ran a can of Seafoam in 1/2 tank of pure gasoline. Has maybe misfired 2 or 3 times since - but way less in strength. Probably the injectors. Gonna run another can in maybe 1/4 tank of pure gasoline.

 

I wonder what the fuel trims are when the miss happens

 

Intermittent problems are a tricky bastard. If it’s been awhile since you cleaned your maf sensor and throttle body, I’d do that. Running in tank cleaner, what I like to do is drive it far to get everything good and warmed up, then find a long hill, drive uphill and do a few hard pulls, in 3rd or 4th so you don’t get too much speed. It seems to help break up any deposits stuck in the combustion chamber. I’ve always noticed a difference after. I prefer jectron.

Other things you can check, air filter isn’t too dirty, battery terminals and posts aren’t boogered up with acid, battery posts aren’t oxidized, no electrolysis issues with the coolant.

 

You said that you had misfires, but no codes.

Did the CEL blink, when you were getting the misfire? That is the ecu recognizing that it misfired. Then it would store a code.

Did that not happen?