I’ve been having problems with my 300 3.5l v6 for some time now (2 or more months). It has about 80k and I’m the second owner (45k when I bought it a year and a half ago). I mostly drive highway miles and drive approx 400+ miles a week. Sometimes when I start the car cold I’ll get a large puff of black smoke, but it doesn’t seem to happen when the car is warmed up. I’ve also have been having periodic multiple misfire codes popping up (can feel it when it happens too). I typically baby my car, slow starts and stops, rarely go over 65, slow turns, almost never come to a quick stop and generally drive like my father did; smooth and steady. But… I normally never do this, but I floored it from a dead stop today (I REALLY had to get by a prius) and a HUUUUUUUGE plume of white smoke came out for maybe a second or two. The car seemed fine before, during and after this happened. In fact about 5 miles down the road I started normally from a stop and there was no noticeable smoke. I had been driving for over an hour at highway speeds when this all occurred.
Did I mention it was a huge puff of smoke? Like “where’d traffic go?” huge.
Thanks for any help!
On the advice of someone I just started the engine (it was cold) and smelled the exhaust, and it smelled burnt, not sweet. I also checked the coolant level and it was above the min mark. I haven’t added any coolant since I’ve owned the car.
First, if the plastic bottle full of coolant is not pressurized it does not indicate that the cooling system is full.
Second, it would be very advantageous to get a really good mechanic to diagnose the apparent rich cold start condition and possible secondary ignition problem.
Third, your post is very informative but seems to indicate that your expertise is in fields other than automobiles. Who informed you of the multiple misfire code? What other information were they able to pull from your cars computer?
Thanks for the quick reply!
You’re right I’m in no way a mechanic. I’m poor and since my first car I have tried to do as much work myself as possible. I use the hayes books and forums as much as I can. I have a obd2 scanner. P0300 is the only code that pops up.
Given that you notice the smoke (1) when starting, and (2) when at wide-open-throttle (WOT), I wonder if the problem isn’t overly rich in open loop. After all, there are two times a car runs in open loop: when starting/warming up, and when at WOT.
Do you notice the missing predominantly at warmup/WOT?
Also, I’d have the plugs pulled and read.
Finally, I’d systematically work to “rule out” other potential causes: like coolant contamination, for example. (It seems you are in the process of doing that.)
hmmm. I thought I had replied…
The misfires aren’t constant, maybe 1 a day, sometimes more, sometimes less. But they do seem to happen in the morning when the car is warming up. Sometimes it surges in the am too, but that’s rare. I live on a long dirt road and drive very slow on it. So slow that I can feel just about everything happening with the car. lol I drive so slow that during tourist season I get at least one guy who honks, yells, or gives me the… high beams on my road. To … with them, I’ve lost too many wheels in my past cars to drive fast down a dirt road.
What’s the best way to check the coolant? I haven’t changed it or added to it since I bought the car. If I had a bad head gasket wouldn’t the coolant level be below the min (when cold) after two months of leaking?
Thanks a lot for your help, you have no idea how much I appreciate it guys!
Hopefully, I’ll be able to scrounge up the money to take the car into the shop.
I’m not sure if it helps, but I just took a turkey baster and pulled out some coolant. It looks and smells fine.
A plume of smoke that you can see from the driver’s seat is pretty substantial, so I’d guess that you have either a leaking head gasket or are burning oil. Don’t put too much faith in the smoke color. One man’s white is another man’s grey is another man’s black. Check both the radiator overflow container, and for the presence of coolant in the radiator. Check the latter when the engine is cold of course, not when it is hot. Also, monitor the oil level on the dipstick.
If I had to bet, I’d suspect oil rather than head gasket because huge clouds of smoke from a head gasket leak generally are the last step before overheating and undrivability. They aren’t likely to go away.
I’m guessing that the misfires are a different problem only because I have some trouble believing that combustion issues are likely to produce a smoke cloud like that you describe.
These engines aren’t known for blowing head gaskets, but of course anything is possible. If you haven’t changed the coolant or gotten a tune up (spark plugs and wires if needed) since you got the car, it’s overdue. If the plugs haven’t been changed in a long time, it may well fix your misfire problem. Depending on the year of the 3.5L engine, you should also consider replacing the timing belt soon if it hasn’t been done. I think yours is an ‘interference’ engine, and if the belt breaks or skips, it can lead to severe engine damage.
Babying the car all the time is overall good for it, but I truly believe that engines need a little exercise once in a while. I’d floor it again and see if the problem returns. It may have been that the engine management system (which somewhat ‘learns’ how to control the engine with the most efficiency based partially on your driving habits) was confused by the sudden wide open throttle, since you rarely do this, and the white cloud you saw was unburnt fuel. Or, if you never floor it, is it possible you were spinning the tires and were seeing smoke from that?
I changed the plugs last summer and from what I remember they didn’t look pretty. I also changed the… I forget what they’re called, but my car doesn’t have wires, but I changed whatever the things that attach to the plugs are called.
I had forgotten this until now, but I was having the misfire problem when I changed the plugs back then and the misfire problems went away. For a while anyway. Then it came back with a vengeance and my local mechanic said it had to do with #6. I pulled and replaced the plug and it looked REALLY bad (I added a few pics of it below). Like a moron I didn’t check the other plugs. Everything was fine until the past few months, then the misfires started coming back and the black smoke at start up started happening.
Sounds like oil getting down the valve stems. You get smoke right at start up from this. As far as the smoke plume this could be a head gasket. You will need to have the cylinder pressures checked. If the oil is getting contaminated by coolant it will turn a mucky brown color. There are coils that fire the plugs and you can compare them with an ohm meter. They should all read close if they are good.
Thank you for the great photos. A photo truely is worth 1000 words.
Looking as best I can at the photos, it looks like you have severe electrode and ceramic damage. This level of damage can only come from extreme heat.
I’ve attached a link that shows various conditions. I recomend a look. I suspect that in your case you have a combination of severe preignition and burning oil, possibly combined with some coolant getting drawn into the chamber and thermal-shocking the plugs. I also see signs that suggest bad carbon deposits.
One other thought just occurred to me…you may be drawing trans fluid past the vacuum modulator and burning that. That can preignite like crazy and do this form of damage.
http://www.gnttype.org/techarea/engine/plugs.html
In short, I think you have serious problems with this engine and I really think the diagnosis can only be done hands-on by a good tech. There’s just too much going on here and it’s too serious.
I’m sorry to have to be the one to tell you this. Sincere best.
I doubt the transmission on this has a vacuum modulator. They have been electronically controlled since the early 90s at least.
Hi all. Thank you all for the help.
Well…
I gave in and brought the car to my mechanic…
They’re still troubleshooting it, but they said I’m getting oil in the air intake manifold and I’m probably going to need a new engine soon.
Since the shop is run and owned by my father inlaw, I trust thier opinion.
$20 says the previous owner was leasing the car and treated it like…
If you truly need a new engine, it is likely someone neglected this one. I have the same engine in mine, albeit some years earlier and am coming up on 260,000 miles. These are pretty good engines overall. Uses about a qt. of oil in 5,000 miles.
If it’s running OK otherwise, I’d just drive it till it dies. No point in replacing/rebuilding it until necessary.
I bet it was neglected and that just burns me up. I switched to mobil synthetic, changed the oil every 3-5k miles (about once every 2 months), only buy shell 89, and changed the plugs to the best I could buy. Other than the occasional occurrence I drive extremely modest.
I used to buy pos every few years, but this time I decided to buy a good car that I could keep for ten years. If I could get my hands on the previous owner…
Man, I wonder what the driver of the Prius thought when you shot past him and laid down that smoke screen!
p.s. I would stick with OEM (original) plugs and change them more often.
Yes, I agree with you, those look like splitfire piugs and the tests I have read suggest that their supposed advantages are mostly marketing hype.
These engines seem to like the cheapest Champion or Autolite plugs you can find for them. I’ve noticed no difference in longevity, performance, or mileage between Splitfire (which I used to use), and el-cheapo Champions. My car actually runs worse if I put Bosch Platinum plugs in it.
I’d also have to say that these engines are the easiest of any I’ve owned to change the plugs on, despite them being recessed deep into the valve covers. (hemi style)