Misfiring Cylinder #3 or Slipping Transmission

Hello,

I drive a 2001 3.4 V6 Auto 4x4 with 240k miles. I noticed last Wednesday that when I would accelerate from stop/near stop the truck would briefly struggle to accelerate until I got to about 5 mph or over 2k rpms. It felt almost like the back tires were spinning on the ground, but obviously they weren't. The truck would be just fine driving normal until I had to start from a stopped position again, or if I hit the gas heavy while coasting slowly. A couple days later I noticed while cruising at around 60 mph some shaking, similar to what it felt like when I accelerated from a stop. It would shake for about a second or two and then go away. Happened about 5 times in a half hour. At first I thought it could be the transmission starting to slip so I checked the ATF and it was a tan color, almost like engine oil, and it was low. I topped it off with fresh stuff and made an appointment with my mechanic to change the ATF and get his opinion. After topping it off on Thursday, I noticed no difference in symptoms. However, this morning while driving to work on the highway I noticed the CEL pop on for about 2 seconds and then go away. I checked my scangauge and it pulled a P030 code, misfire on cylinder 3. I called my mechanic and told him to check on that instead of doing the ATF change because I feel like that's probably my issue (I know the ATF is worn out and needs changed but I want to fix the problem first). I dug around the forums and the internet a bit but couldn't find anything that matches my symptoms exactly, so I guess my question is does this sound like a misfire or a transmission slippage? And if it is the misfire, why isn't the CEL coming on every time the cylinder misfires? Thank you.

 

If the tranny fluid was tan in color, it could be that either the tranny overheated and the fluid was burned, or that you have coolant in the tranny. I would guess that the tranny is on the way out.

As for the CEL code, I would say (from recent personal experience) that the injector for cylinder 3 is on its way out. The symptoms you describe (intermittent CEL, CEL code, and poor performance) indicate a probable injector problem. Your mechanic (if he's any good) could check the injectors more closely to see if they are firing properly and then give you his opinion.

 

Toyota used a semi clear fluid sort of tan at one point. With that kind of mileage changing/flushing the fluid could have you walking in about a week. It takes awhile for a code to "lock in" but an intermittent code is trying to tell you something fix the misfire it can damage the cat.

 

I read about how changing the fluid at such high mileage can cause more problems, so does that mean that nothing can be done in terms of maintaining high mileage transmissions that haven't had regular maintenance? I know it's a Toyota, but everything has a breaking point. Hopefully the 3/4 quart of fresh fluid I topped it off with doesn't mess anything up.

 

The CEL won't come on unless it has a few consecutive misfires. That's why the CEL isn't on all the time. It sounds like it could be a weak spark under certain conditions. Could be a number of things, bad spark plug or wire, or bad injector.

I'd guess the problem is related to the misfire, not the trsnsmission.

People say not to flush high mileage transmission. Drain and refill is fine. The theory is that a flush will dredge up old deposits and clog things up.

And are you checking the ATF level properly? Warmed up, engine still running, just after putting shifter through all gears slowly then back to P?

 

I hope it's the misfire and not the transmission. And yeah I made sure it was warmed up to operating temp, running, and shifted through all of the gears before checking the fluid.

 

I don't recall trans fluid being anything other than red. Brown usually means it's burnt. What does it smell like?

The fact that your trans fluid is brown, and was low, that's very troubling. Hopefully the mechanic doesn't simply ignore the trans because now you have a CEL indicating a misfire. It's so easy to check, just smell the dipstick, lol.

Given how relatively consistent your "slipping" issue is, seems like the CEL would have come on a long time ago.

 

I'll give it a another whiff when I get home, but I don't remember it smelling burnt, maybe slightly. I wish I had more experience with this to be able to tell if it's the trans or a misfire.

 

The red color is just a dye and not necessarily an indicator of the condition of the ATF. If it's not red it could be old but not necessarily terrible. It won't hurt to drain and replace it just to be safe though.

 

Well the truck has 240k on it and I haven't changed it in the 40k I've owned it. I don't have a history report so I don't know if its ever been changed honestly, but I would imagine it had to have been at some point. FYI I drive about 100 miles a day five days a week.

 

Isn't this why you enlisted a mechanic, isn't it?

If you still have some new stuff in a bottle, take a whiff of each and compare them. Even a "slight" burnt smell isn't good.

Here's my thinking: If you give it an either/or approach like your mechanic seemed to be suggesting, which one is WORSE if you ignore it? A misfire is really just loosing power, and won't necessarily grenade your motor, but if you focus on that and don't address the trans fluid color/level issue, that will surely grenade your trans.

As DrZ said, a simple drain and fill of the trans is a good place to start. But of course you want to address the misfire, too. You said your fluid was low, so either the trans fluid was always low, or your trans is eating it somewhere along the way. Neither are good, really.

 

True that. Thanks for the advice. We'll see what he says tomorrow. I get hung up on mechanical issues and want to learn as much as I can and that always leads me down a rabbit hole of "what ifs." I definitely plan on getting the trans fluid looked at, but I want to make sure I'm educated on all possibilities. I understand the can of worms transmission work can be so I was actually thrilled when my CEL came on and I pulled that code lol. We'll see what he says tomorrow, fingers crossed.

 

Oh for sure. The more educated you become, even if you don't do the work, you can at least speak intelligently to the mechanic, and not only better understand the issue, but also make it clear they won't be able to take advantage of you.

Good luck!

 

Changing the fluid won't hurt it, flushing the fluid could. Auto trans flushes aren't recommended at higher mileage if they haven't been done regularly before. But a simple drain and fill with new fluid will be fine.

 

Don't mess with the trans until you fix the misfire that more than likely is your issue. The additives and detergents in new fluid added to a high mileage trans will remove the stuff that builds up on clutch plates it is what keep high mileage transmissions going. They all have a finite life so here is what I have seen many times (I was the shop manager for one of the largest shops in MD) vehicle comes in for a trans service with high mileage the fluid is dark and has a slight burnt smell to it we recommend he should not change it but he insists we do, so 2 weeks later it's towed in for a rebuild. If it smells burnt the damage is already done new fluid will not put material back on a burnt clutch pack but is sure as hell will take off what is left.

 

That is mostly true but still chancy but what good does it do to change 3-4 out of 9-11 quarts of fluid?

 

I don't have an auto so I can't say from experience but some people say it helps. And some do the process a few times over the course of a few hundred miles to get the majority of the old stuff out.

 

3-4 qts of good oil mixed in with questionable oil is better than no good oil... You can repeat the process a few times and slowly replace the old crap.

But having questionable oil in the first place should be addressed first, or at least simultaneously with the misfire. A misfire doesn't cause your tans oil to be low or turn brown.

 

Ok you do the whole thing over again this time you are dumping the same oil you put in about 40% so you do it again eventually you have all new oil after 4 changes and it's amounts to the same problem of dumping it all. If it ain't broke don't fix it drive it until it's time for an overhaul why take a chance it may last until you sell/scrap it. None of this applies to routine changes like someone that tows a camper/trailer but waiting till 250K is only asking for a pretty quick death.

 

I agree that if you've waited until 250k to change your fluid then you're pretty much asking for trouble one way or the other, but I don't think a drain and fill will hurt. The 'turkey baster' method for power steering fluid is essentially the same thing...pull some out, pour some in, turn the wheel back and forth...repeat a dozen or so times and eventually the old dark fluid starts looking clear and new. It works but it's definitely not as efficient as getting it all out via flushing the system.