rpeAMP

For the past few weeks, I have had an issue when I cold-start my 4R. Starts quickly and strongly, then when it starts the exhaust is LOUD and smells like fuel, big-time. I mean, I have a Magnaflow muffler, but this is REALLY loud. On a side note, I would LIKE it to be this loud all the time, haha.

ANYWAY, the exhaust sounds like someone's going "buhbahbuhbahbuhbuhbuh", and it of course does this faster when I accelerate. The engine stumbles/misses if I give it quick gas around 1k-2.5k.

Also accompanying this is a huge power loss in the 1k-2.5k area, but as I'm accelerating, it hits a certain RPM and "surges" to its normal power. As the truck warms up, it doesn't do this anymore. It only has a slight miss when in gear anywhere from 1k-2.5k when warm (maybe related to the stumble above?).

Here's what I've done so far:

-Plugs & Wires
-Distributor cap
-Tested cold start injector (ok unless I did something wrong)
-Changed gas many times
-Air filter changed and intake inspected for leaks

Any ideas? I was going to check the TPS next, but it's fairly involved so I wanted to get ideas here first.

89macrunner

i saw just for the heck of it run some seafoam through it when its warm out...also check out the throttle body butterfly and see if its closing or opening all the way...check the cable.
tly

rpeAMP

I'll do that...also it's doing something else. When under load (i.e. going up a hill in 5th gear), it will do the stutter and miss thing, then I hear a loud POP/BAM coming from where I think is right under the drivers' seat. Backfire?

At this point I'm thinking I may have an exhaust leak or a plugged cat? What do yall think about that noise?

rpeAMP

Anyone with any other ideas?

Yota4runner

Have you checked for leaks in the exhuast? A leak could cause the popping you are hearing and would make it louder until the metal heats up and closes the hole.

okidoc

On the passenger side is a valve that is covered by the bag of worms called vacuum lines. You will have to look really hard to see it. It is directly under the ports going into the manifold. You can disconnect it by following the vacuum line from the actuator to the wheel well, disconnecting and capping everything or fix it. On mine the screws backed out and created the exact same symptoms you had. Although I didn't experience the power loss. I just wouldn't use that low range much and either coasted or whaled on it until the engine warmed up and it stopped. That unconscious desire to minimize the noise may be your power loss

rpeAMP

Interesting...I'll look in to that...

Did it only happen when in 4Lo? Mine happens anytime.

okidoc

Sorry, I meant that throttle range. Nothing to do w/ gearing. If I revved it when I just started it in the driveway it would braaahahhhahahahahahah.

fiveofeen

I had ticking at startup I figured was an exhaust leak.... turned out the sparkplugs were working their way loose. check them before it heli coil time!

rpeAMP

Ok so I figured it out...pulled the injectors and the #6 plug had its plastic electrode sheild cracked. Replaced it and it's like I'm driving on a completely new engine.

What causes this to happen? Defect or maybe oil or coolant leaking on to it? How would I know if I had fluids on it?

90!4Runner

When I start my 90 Runner every morning, I let it run for like 5-10 mins, because if you just start it and then take off, then when you step on the gas, there's almost no power for about 2-3 seconds. Sounds like your problem, and I just may check my #6 plug. BTW, this is when it's cold out in the morning.
Also, I usually never drive up a hill in 5th gear, because it loses speed(sometimes 10-15mph). I also have a pinging like noise, but have had it sinced I've owned it, and figured it to be a toyota trait. If anyone knows how you could post sound on here, let me know. I also started hearing an almost turbo-like sound from my 3.0 a couple weeks ago. Only, this is when I'm in 1st gear, and at 4500-5500RPM, which is really high, but if you drive like that, these 3.0's seem to have decent acc., as long as it's not going up a hill.

rpeAMP

I can't tell you how much of a pain this little spark plug has caused. The symptoms had me thinking I was low on compression on several cylinders, and in need of a rebuilt after so many miles. Anyway, these were the symptoms:

- Started out with a slight miss/hesitation when going highway speeds...this didn't affect my power (noticably at least), but made the truck not fun to drive.
- Eventually, missing got worse, and I began to lose LOTS of power.
- Exhaust had a deep "bubububub" sound when accelerating in the low RPM range.
- If I went full throttle or anywhere close when in 5th gear with lots of load, I would get a loud "POP" from somewhere under the hood.
- Starting began to be rough in the mornings, with shaking and missing and absolutely no power.

When I finally figured it out, I almost couldn't get up hills even in 4th gear on the highway.

I'm beginning to think that last time I had the plugs changed, that one was never pulled. If so, more reason just to keep doing things myself.

The plastic cover around the electrode was cracked from top to bottom. This caused more than just a misfire, in my opinion, because there was wayyy too much power loss for one cylinder not to be firing. I think the spark was actually interfering somehow with the rest of the firing. Can this happen if the spark fires to a ground (i.e. some part of the engine in this case)? Near the end it was almost as if I had a rev limiter engaged.