Pinging and Smoke

[Superman]

Sometimes, but not always, when I stomp on the gas and run her up to redline, at about 4500-5000 rpm I get a curious event (I assume it's important to, ahem, clean carbon out of the cylinders from time to time). The engine crackles, sounds like pinging sort of, some power and smoothness is lost, and smoke comes out the back. This engine ordinarily does not ping, though ignition timing is set at 35 degrees full advance. Most of the time this event does not occur when I, ahem, clean some carbon out of the cylinders.

Since it does not happen all the time, and since the smoke phenomenon is part of the event, I am not ready to blame ignition timing. I wonder if carbon is getting loose and getting in there, or perhaps some oil gunk in the breather system is getting sucked in. Anybody have an idea what this is?

[vash]

my SC did the exact thing. my mechanic thinks i got crap gas, but he retarded my timing a bit to be safe. the smoke was a grey mess, and my motor rattled. i feel better on the safer side.

[RickM]

Have you noticed any republicans near your car lately?

[echrisconnor]

Your breather idea is interesting. Have you checked after an event like this to see if there's any oil pooled at the bottom of your airbox? Are there any consistencies for when it does happen? Is the engine always hot, under load going uphill, etc?

Or, it could just be a timing issue, and the smoke is some byproduct of the pre-ignition. You said yoiur timing is set to 35 deg full advance... Are you sure though? A while back I had almost this same problem. I'd been checking my timing solo, and I'd be there revving the car with one hand and holding my light with the other. 6000 revs is loud and scary on my car (headers and a very open exhaust). It turned out I was only revving up to around 5k when doing my timing. The timing on these cars will continue to advance past 6000, so when I was hitting 35 deg at 5k, it was getting well out past that when at 6k. I didin't notice the problem until the car got really hot, I was heading uphill at WOT and started getting pinging and bucking.

I re-checked timing with a friend and retared it back a little, and haven't had any problems since.

[dd74]

Jim - I've had this before as well. It was an exceptionally warm day the time I really noticed. However, it happens only once. Subsequent stomps on the engine have never yielded the same pinging as I imagine you're having.

Tyson initially rectified the problem by setting the advance back to factory specs, and for the most part, all is well. Sometimes I think I hear pinging while driving hard up the rev scale, but who's to say? My car is quite loud and hollow, and L.A. roads notoriously bad - so the sound could be anything.

FWIW - when my engine does ping, I notice no decrease in power, nor do I blow smoke either while accelerating or decelerating.

Hot days seem to be the culprit as well as the initial "stomp." Oddly enough, after repeated stompings at Willow Springs Raceway, and while the engine got up to 270 degrees, there was no pinging at all - and I trust a race track much more for sound feedback than a city street, for obvious reasons.

Simply put, your timing might simply be too advanced, at least it might be while a spate of bad gasoline filters through the engine. I'd check that, if possible. Or try setting it down to factory spec until the weather cools off...

[Superman]

My engine runs very much better at the advanced ignition timing. So I don't want to retard the timing if I don't have to. It's abotu seven degrees more advanced than factory spec.

One of the reasons I think this is not simple pinging due to advanced ignition timing is because it generally does not happen. Not repeatable.

Another reason is the smoke. I don't recall smoke in the cars I've seen that ping.

And also, the power loss. Again, this generally does not happen or is not pronounced where the problem is simple pinging.

I have not conducted exhaustive experiments, but it seems to me that once it has happened, it doesn't happen again for quite a while.

Oh, and Chris, it doesn't seem to happen at 6000 rpm. It seems to happen at five.

[jluetjen]

You'll be surprised how fast you can burn a piston that way if you're spending a lot of time in the 4000-4500 RPM zone. Generally engines won't ping all the time (unless the timing is altogether wrong!), but if they're going to do it, they'll do it around the peak torque engine speed under open throttle conditions (when cylinder pressures are the highest). Increasing temperature will compound the problem. Lots of carbon in the cylinders will also add to the problem.

I'd set the timing back to stock, get good fuel and add a note to the winter to-do list to pull the heads and inspect the pistons. You don't want to wait until there's a hole in the piston since there's a good chance that you'll mess up a cylinder as well.

Ask me how I know...


(Photograph of a piston that I burnt myself in my ITB engine. )

[island911]

Originally posted by jluetjen
. . .
(Photograph of a piston that I burnt myself in my ITB engine. )

Yikes.

. .. but look at the bright side -- almost zero carbon build-up.

[dd74]

Originally posted by jluetjen
...hole in the piston...
(Photograph of a piston that I burnt myself in my ITB engine. )

Which is precipitated by an occasional then increasingly often pronounced loss of power, right John?

[echrisconnor]

Sup,

My pinging was starting around 5K when it happened. The point in my talking about where you're checking total advance was that you need to make sure that the 35 degrees total advance is actually at 6000 revs and not coming on earlier. If it is, then your whole timing is advanced regardless of where you are rev-wise.

I'd thought that it wouldn't really advance much past about 4k since it seemed to taper off a fair amount when I watched things. So, as long as I was getting up to 35 degrees at 4-5k, then I was fine. Well, I was getting the 35 degrees early, so all across the scale I was too far out. Like was said, you'll get the pinging at peak torque, so it wouldn't be surprising if you're too far advanced that the pinging wouldn't start until 4-5k.

After retarding it a few degrees the pinging went away, and I believe I actually got more high-end power. Pull it back a couple degrees and see if it makes a difference.

Here's another idea though. I have a rev-limiter on my BMW. It's the kind which kills spark, but not fuel delivery. So, if I really bonk the limiter and let it hang there, I'll see a huge cloud of smoke from the unburned fuel come out the tailpipe. I wonder if you've got some sort of rev-limiter thing going on. Do you have a rev-limiting cap in your dizzy?

[dd74]

So Chris, when your timing reaches 35 at 4K and you say from then on, you're "too far out," does that mean your timing rose even higher?

BTW: what exactly does advancing the timing do. I seem to have forgotten. Doesn't it add torque?

[island911]

dd, see twinplugging thread for some great explanations.

[jluetjen]

Which is precipitated by an occasional then increasingly often pronounced loss of power, right John?

Yes, I'd say that happened across about 1.5 track sessions of a total of maybe 40 miles.

BTW: what exactly does advancing the timing do. I seem to have forgotten. Doesn't it add torque?

Not necessarily. Only if your engine is reaching peak pressures when the pistons are well past the center of the stroke. In that case initiating the combustion sooner moves the peak pressures closer to range of the stroke where piston gets more leverage -- a good thing. But more of a good thing results in the pressures increasing before the crank gets to the high leverage zone when the piston is traveling the fastest. This results in significantly increased pressures and temperatures which can spiral out of control. The uneven combustion also destroys the boundry layer that protects the piston from combustion temperatures which means that the piston temperatures can exceed safe temperatures for the piston material. These hot spots also initiate more pre-ignition. Once that point is reached, the piston starts to burn or melt and I believe can burn through pretty quickly.

I've kept that piston as a reminder of what playing with the ignition timing can do if you don't know what you're doing. To put it differently, my next race engine will have the timing set on a dyno before it goes on the track. That way I'll know exact what is the correct spark timing rather then too much.

[dd74]

Originally posted by jluetjen

Not necessarily. Only if your engine is reaching peak pressures when the pistons are well past the center of the stroke. In that case initiating the combustion sooner moves the peak pressures closer to range of the stroke where piston gets more leverage -- a good thing. But more of a good thing results in the pressures increasing before the crank gets to the high leverage zone when the piston is traveling the fastest. This results in significantly increased pressures and temperatures which can spiral out of control. The uneven combustion also destroys the boundry layer that protects the piston from combustion temperatures which means that the piston temperatures can exceed safe temperatures for the piston material. These hot spots also initiate more pre-ignition. Once that point is reached, the piston starts to burn or melt and I believe can burn through pretty quickly.

I've kept that piston as a reminder of what playing with the ignition timing can do if you don't know what you're doing. To put it differently, my next race engine will have the timing set on a dyno before it goes on the track. That way I'll know exact what is the correct spark timing rather then too much.

Well, that pretty much takes care of advancing the ignition timing for me. I'm glad I'm at factory spec, though I'll double check it soon.

[vash]

yowza john. thanks. i think i will go and drop off a box of donuts at my mechanics. he still hasnt really charged me to check my mix and timing....yet.

[dimps8]

Gents,

This link; http://www.kb-silvolite.com/feature.php?action=read&F_id=29

will expose some myths and preconceptions about detonation, which we normally call "pinging". not to confused with "Pre-ignition"

[Lorenfb]

Very insighful thread to all and which should be VERY insightful to many
3.2 owners.

See here ( www.systemsc.com/tests.htm ) for info which indicates problematic
possibilities for 3.2s simliar to 3.0s

[Superman]

Okay, perhaps I'll back the timing off a bit and see what happens.

dd, while John and others are correct in that too much ignition advance can destroy pistons, you should also be aware that advancing the timing without detonation has a significant effect on power and performance. In the olden days (before computerized control systems that map fuel and ignition with a chip), gearheads would routinely advance timing until detonation occurs, back timing off until it stops, back it off another degree or two to be safe, and Voila! This works, and it maximizes power and fuel efficiency.

And again, in my experience detonation is not intermittent. With an engine up to temp, under full load, it either detonates or it does not. This is not the way my engine acts, so I question whether it's an ignition timing problem or not. Further research is needed.

but again, the decision to advance is a balance between performance and engine damage, but you can retard timing enough to protect the engine. Some 911 engines don't like being advanced beyond factory spec. Many can safely be advanced several degrees. And you can certainly tell with your butt dyno. The improvement can be similar to SSI's, I would say.

[echrisconnor]

Sup,

Did you consider the rev-limiter thing? If you've got a rev limiting cap, or a faulty electronic limiter, it could be acting up, partially kicking in early, and giving you both the hesitation and smoke. The one on my Bimmer does this occasionally and I get just the symptioms you've described.

We've been focusing on pinging and timing advance, but this may not be it at all.

c

[Superman]

Chris, thanks. I guess I forgot to comment on that. My SC has a fuel shutoff rev limiter. Still, you may be on to something. I know my fuel pump is weak. Indeed, with at least a third of a tank of gas, at AX two months ago, at the end of the 180-plus-degree turnarounds my engine was cutting out. Every time (two of these turnarounds on the course, ran four times....so eight turnarounds). Then, before "fun runs" I gassed up another 5-10 gallons and this went away. So, now I'm wondering if the FP might be having trouble keeping up. Maybe the mixture is going lean, or going rich. I'm actually thinking along those lines more than the simple ignition timing cause.

Thanks.