A Few Issues With a 4.0L - Are they valid or am I going crazy?

I took off everything up until the intake manifold. Leaky fuel injectors would exhibit traces of evaporated gas, correct? Also, during my last oil change the oil came out smelling nice and oily. The spark plugs also came out perfectly brown and even with not a single smudge of anything. I even felt bad throwing them away.

I watch the coolant levels like a hawk. Growing up my pops and I had to struggle with a few cars that had serious overheating issues and they made me appreciate a good cooling system. In the time I've owned the car I haven't noticed any changes. This has seriously made me appreciate this engine much more. This engine/truck is truly one of the best designs I've ever seen. With respect to functionality and sheer simplicity I have never been happier to own a car.


For good measure I did check the engine bay again to make sure everything looked right and found some oil seeping through on the passenger side valve cover near the dipstick. It was a very small amount that seemed to be there for quite some time since it had already accumulated dirt over it and didn't look wet. In any case, I will disassemble the entire air intake assembly and go through the engine with a mechanic's stethoscope to find any leaks in the vacuums or exhaust. I haven't reset the electronics like some folks have suggested, I'm betting some on this as well.

 

I used MAF and TB cleaners to clear up both. The exhaust issue is only during acceleration. I've tried listening while on the freeway but the wind doesn't help. I'm beginning to think the gapper I used might be out of whack.

Would a significant difference in gap cause the issues i'm describing?

 

gap isn't that critical with the high energy ignition we have

My 99 taco went 100k before I changed the plugs and the gap was doubled and I still had good MPG

I have 193k miles on original plugs. Still get about 420 miles per tank. I will re gap my plugs again at 200k since at 100k there were a bit off but still ran well.

 

I thought so.

I had a 66' Mustang for a few years and I remember gapping the heck out the plugs. When it gave me issues I just threw a bigger coil on there. Quick and easy 30 dollar hp gains.

 

Cool! Just keep an eye on it '05's and early '06's are prone to bad head gasket on cyl. 6.

When mine went out, NO test detected it! I ran my own tests, dealership ran tests, just knew something was off.

Lol! You know who diag it? Buddy who has building with 40+ years experience building every kind of custom engine you can imagine. I picked him up to go eat lunch one day he said how long your head gaskets been bad? I said their not. I ran tests, dealership ran tests. He saod yes they are! Sure enough, few months later got missfire on cyl 6. Ran tests again, dealership ran tests... nothing. I asked him to help, he said change head gaskets. I asked why are you so sure? He said that day you came pick me up, when you started the truck i heard water under the dash. You got a hairline crack in head gasket leaching small amount of exhaust into cooling system. Sure enough, pulled heads, hairline crack in gasket on cyl 6, lol! Moral of the story... never doubt the 'old guy' around the shop, lol!

 

So after various weeks of putting things off I finally got around to looking at every angle you guys have suggested on here.

I found..... nothing. All vacuums were sealed properly, all electronics looked clean and all plug boots were finely seated. I've driven it a couple hundred miles since then and the noise is about 80% of what it once was.

The issue I am having now is a seemingly noticeable drop in throttle response. These potential head gasket issues are starting to come to mind.

 

the old saying dont fix it if it isnt broke i have 303764 on my 4 liter never touched it just oil changes

 

I figured out the cause of my shaking at idle issue and exhaust leak type noise, same symptoms as you were having. After doing several head gasket tests and them not showing anything, I started to swap parts with my brothers truck to see if I could get lucky. After switching over his big plastic intake manifold plenum (or “surge tank” as Toyota calls it) on to mine, my engine all of a sudden ran smooth again. I’m not sure if there’s a pinhole or hairline crack or something in mine, all I know is that it fixed my problem. Maybe this could work for you too before pulling the trigger on a new head gasket?

 

After many attempts to try and ignore the "problems" I spent the latter half of Monday tearing down the upper end to get to the issue.

Before anything, I did a Seafoam treatment Sunday night and it spewed more fumes than any other car I had ever done. I guess 200k miles really do take their toll. In any case, I ran it hard afterwards and it really showed difference. Throttle response was better and the engine felt all around more limber.... nonetheless, the ticking remained.

Monday came and I took apart the intake, vacuum's, spark plugs, throttle body, coil packs etc...

The plugs were kinda fouled up from the Seafoam and had some black residue on the ring. I've seen it before and with time the residue is simply burned away. I cleaned up the throttle body and made sure all the vacuum lines were clean with no cracks or tears. Everything checked out.

When I got to the spark plugs I checked the gaps to make sure everything was fine and realized they were gapped over .045"!!!!
I'm not sure how picky these new engines are with respect to plug gaps but I assume with the VVT and coil plugs being so sophisticated a minor gap could be an issue. I gapped them down to .040" and cleaned up the threads from the anti-seize. I torqued them up 15 ft-lbs and put her back together.

My jeeeebuus, she came roaring back without a tick or flicker. There is still a noticeable and slight exhaust leak but the diesel-esque sound is no longer there.

Moral of the story kids, make sure the gaps are right cause you can't always trust the fellas at NGK. All in all, this was a great experience and I learned alot about the sensitivities of modern ignition systems.

Oh, and, Seafoam is amazazing.

 

Making me wanna pull mine back out and check again... Also, did you just pour the seafoam in through a vacuum hose? or how exactly did you do your treatment? ive done it some on some other vehicles but not the taco. Thanks

 

I used the brake booster vacuum to introduce the Seafoam.

I used about a third of the regular bottle and let it sit for 40 minutes. I did it at night time to avoid the attention.

Like I mentioned before, the smoke show was unlike anything I had seen before. I can't attribute the change in response to the Seafoam alone but I don't doubt it had a large part in bringing things up to par. I'm somewhat shocked at the change. The La Cienega/Manchester on ramp for the Southbound 405 is where I test my cars and the Tacoma was a thing of beauty. It was smooth until 60mph with solid shifts and a beautifully linear throttle. I might've picked up a bit more than triple digits but I won't admit to it.

 

when I read the post I noticed that you didn't have any performance parts on the truck so your Pistons are probably trying to move a little bit too fast for what your intake can provide so you might be having slight stalls causing the shakes I'm not sure if you're using 87 or 91 try changing up the gas to 91 or higher and see if that helps or up the flow of your intake cuz you need to get more air and fuel mixture since you did the tune it's probably adding fuel but you're not getting any more air than what the stock intake and provide.

this is just a opinion of course and it's just one of many many ideas who knows what it truly is but this is just my go at it

 

The torque spec for 2nd gen’s should be 15 ft/lbs, I believe.

 

Is that small hose you are referring too on the drivers side or passenger side? I just had my intake off to replace the knock sensor harness and now that I've got it all put back together the brakes are completely jacked up. I know it has to be some huge vacuum leak but all the obvious hoses are connected like they're supposed to be. I checked the small one on the passenger side that's connected to the air filter box and it's all good. Is there another sneaky small one I may have missed?

 

I've forgotten about one on the driver's side before. Not sure I'd call it small, like the vent tube on the front diff. More like a standard size vacuum line. It was audible and, iirc, more of a ticking than a hissing. Not sure if that helps.