My 4Runner was running pretty good, even with a bad O2 sensor that I was getting a check engine light for. I replaced that O2 and the same day, I cut my muffler off, which is two feet or so past the O2. Now my truck takes forever to start and when I'm driving it'll seem to misfire and buck a few times when I'm not giving much gas. Do these V6s need all that back pressure to run well? Or is it the O2 sensor causing it? I've got a vacuum gauge and it's getting good vacuum, idles at about 16 in-HG.

 

Update: cold start injector is not firing, so hopefully that's the issue.

 

Did you replace the O2 with a factory part? Alot of older toyotas dont like the aftermarket O2's and sometimes they can be garbage right out of the box. I'd go with a factory denso O2 and see how it runs.

 

I don't think it's a factory part. It's from rock auto, I can't find what brand. Ultra-power maybe?

 

Cold start injector was the issue for it being hard to start, so I now have that wired to a switch. I've heard that the cold start injector stays on while the truck is running cold, is that true? If I leave my injector on after I start it up it'll bog out and die out until I turn it off. It's still bucking and stuttering on acceleration. Every now and then as I'm driving a check engine light will come on and it'll go into limp mode for a quick second then turn off and be okay again. I've messed with the distributor timing, could that be causing a misfire?

 

The cold start injector is only on during cranking. And not even all of that, if extended. (That's why there is a cold start injector TIMER switch.)

If your check engine light comes on, a code has been stored. So read it! Your truck is trying to help you help it.

And yes, everything you "mess with" can cause misfires and other awful stuff.

 

I'll read the codes tonight as well as put the exhaust back on and get back to you.

 

Went to read the codes and it just flashed continuously, messed with the timing more, no change, put the old O2 sensor back in and its fixed. The new O2 I put in just a few days ago already turned black. What's strange is the new O2 didn't cause a check engine light, but it made the engine misfire, but the old O2 causes a check engine light after about two minutes of driving, but it runs great. I'll find a factory sensor and put that in and hopefully everything will be fixed then.