Stutter/misfire, 2007 4.0l 191k

I keep getting an intermittent stutter/misfire at start-up. Only threw a code once for random misfire cylinder 1. I have since changed the plugs/coil packs, cleaned MAF and throttle body, and changed injectors. Any other suggestions? Love my truck, want to fix my girl.

 

Did you use oem injectors, coils and plugs?

 

how many miles sense last plug change?

 

Yes, and yes

 

Changed factory at 120k, so 70k.

 

This pic of most recent.

 

The plugs are supposed to be changed every 30,000 miles. You could try swapping coil packs and see if the misfire follows. Worse case scenario you need a new fuel injector.

 

Changed injectors, plugs and coils.

 

Possible one of those is defective in some way? I don’t really know what else would cause a misfire like that. Hopefully someone else here has some more knowledge to share.

 

Test fuel pressure, Sometimes bad fuel pressure will cause misfires; possibly failing fuel pump_ Or dirty fuel filter(but I think our filters are in-tank?) Anyhow I've ran into these problems on other vehicles before. Replacing fuel injectors are kind of a waste of money, Injectors rarely ever fail and you can clean them up easily by removing them, apply 12volts to the terminals to keep the injector open then spray carb cleaner into the injector and it'll force all the crap out if its dirty.

Fuel pressure may drop below normal operating PSI if the fuel pump is just not putting out like it use to, this can cause random misfires now and then, you've already replaced everything anyone would've replace, now its time to look at fuel pressure and go from there.

 

Dump a bottle of seafoam in the tank to help clean up the fuel system also, it may not help right away but with time it'll keep the system clean. I do a bottle every 15k miles(Not really needed but it helps)

 

I also see you went to an iridium plug? go back to coppers, they perform so much better in these engines.

 

I run sea foam through every 15-20k, plus I’ve ran sea foam through brake booster into intake 3 times now. I guess fuel pressure. Filter is in the tank attached to pump. Unless any other ideas. Crank or cam position sensor? Any other sensor?

 

Yeah go with fuel system I would think. Start with Cheap shit if your gunna shot gun parts like I do. Yes filter is in the tank. Try FPR. And if you can test fuel pressure. Then you'll know if you need a pump

 

There was a thread on something similar to this, turned out to be the crank key was twisted just a bit.

heres the thread...resolved on the second page.
https://www.tacomaworld.com/threads/misfires-hesitation-underpowered-02-3-4l-prerunner.536215/

 

Crank key?
Please tell us more... I'm dumb

 

Problem is that's a completely different engine, not the v6 4.0 which is a timing chain, not belt. That problem won't exist with the 4.0. He needs to test the fuel pressure and go from there, turn the key to the ON position, watch the fuel pressure and see where it sits at; Start the truck and watch the fuel pressure, give it some throttle and watch the pressure. It must remain constant Fuel pressure is around 45-52PSI is consider good, maybe a few PSI higher, I don't know the specs on these trucks but other cars I've worked on anything 45PSI-52PSI was consider good.

 

Just a note, these trucks don’t build fuel pressure until the starter is engaged. Turning the key to the on position doesn’t turn the fuel pump on.

 

OP, swap the coil packs around as mentioned above, and if it still persists, if this were mine, I would want to determine the compression pressures. It is not a whole lot of work on this engine.

 

Check all of your vacuum hoses' ends. For splits and cracks.