Okay, so here's the problem. The issue seems to occur mostly in the 60-70MPH range. Basically it feels like the engine loses a little power and then there's like a jolt...one time it seemed like it jolted 2-3 times consecutively; also sometimes the car seem sorta shaky...not like "violently" shaky, but noticeably shaky. I don't know if maybe it's a compression issue or maybe a misfire...I don't have any engine codes except for a P0420 (catalytic converter). I know a misfiring engine can eventually fry a catalytic converter...so I'm thinking maybe misfiring engine. Any ideas? And if it is a misfiring engine, what do you do to fix it...clean/replace the fuel injectors? Any help is appreciated...let me know if you need any other details.

 

You give no Engine or year or even mileage

Your sure the PO420 is the only code ??

When this happens do you notice anything in the gauges the Tach

Hard to tell it could be ignition or fuel related I am thinking more ignition but that should trip the MIL

Battery terminals clean and tight the grounds clean and tight the one for the ecm on the intake is critical

Loose connection that vibrates when you hit the sweet spot causing problems.

Fuel filter unable to keep up with the demand at those speeds

One just needs to work through one thing at a time

 

Please delete this reply.

 

1999 V6. Yeah, P0420 is the only code. It happens so quick, it's hard to say if anything happens on the gauges, but I have looked at the RPM's and didn't see any change. The fuel filter is new, and I noticed the issue before I replaced it. I will check the various cable connections tomorrow. The spark plugs are new...but maybe it could be a spark plug wire or coil? Something stupid I did when I first got the 4 runner: I replaced all the spark plugs but when I pulled out the first coil pack I pulled on the spring inside with needle-nose pliers because I was going to clean it. I pulled pretty hard...it didn't want to come out so I just left it in there. Any possibility pulling on it could've damaged something which is causing a periodic misfire?

 

Well that could be your problem !!

That spring is what keeps the electrical connection to the plug tight by keeping pressure against the plug .

If that tension is off or the spring at times does not do it job like at the certain rpm it just might be easier to notice at that speed .

I would look for arc marks or the boot being burned .

If I had a bad coil pack I would not mind cutting one apart to see just how that does work.

 

Yeah I feel like a moron about that spring-tugging situation...didn't realize it was actually affixed to something until it wouldn't come out. I'll check it out thoroughly today and go from there. If I end up replacing it I'll post an update; thanks for your help so far.

 

Okay, so I compared the potentially offending coil to the one next to it and I couldn't see any obvious difference, but when I looked at the springs inside, the spring on the one in question did look a little tweaked from when I pulled on it a couple weeks ago. I compared the spark plugs from those two cylinders; the one on the top is from the potentially misfiring cylinder...it is noticeably darker than the other...do you think this could be an indication of misfiring?

 

Really hard to tell from the picture .

Did this misfire start after the spring yanking exercise??

 

I honestly don't know. Here's the timeline: bought the car like a month ago. Knew it needed some stuff done so I started doing stuff. I think I swapped the spark plugs within a couple of days of purchasing the vehicle. It's possible it had the issue all along, but the day I bought it I drove it plenty fast and I don't remember noticing an issue. Seems like it wasn't until a week or two later that I noticed it. For me to replace the ignition coil, o2 sensor and spark plug would be cheaper than paying for diagnostics so I may just do that and hope it's one of those three.

 

It would not be the first time New Vehicle Lust caused someone to miss something like this .

Just remember your PO420 code can be anything in that circuit .

Even a exhaust leak

So replacing the sensor might not cure the problem.

At 200,000 miles I am on my second set of catalytic converters

 

No way Wyoming. I just hit cat #2 this week...at 191k now. That was a challenge to take off.

Way I would hit the troubleshooting - real-time scanner...if you intend to rule out faulty components, not just know what codes. Change the sensors if they're due. Look for exhaust leaks - lot of ways to find em, but a pain to find. Assuming everything else upstairs of sensor #1 is tuned up, the cat is the most expensive and therefore the last thing to rule out. Best of luck!