nize

h2o is a byproduct of combustion. if you get bad or incomplete combustion (like, due to mismatched injectors), you could get excessive h2o.

it's also possible that the liquid is not h2o, but unburned gasoline, or other liquid, which can also be caused by mismatched injectors.

facboy

hmm, yes, but h2o is a by-product of normal combustion, so given that it's normally present and you have a cold exhaust, it's not unreasonable to believe that an otherwise healthy car would produce these symptoms.

i'm not an expert, but if you have excess air or fuel don't you just end up with excess air or fuel at the end? the water is produced by the two reacting, so i don't see how it's going to be produced purely by an excess of one or the other.

fwiw, i have a brand new set of flow-matched injectors and my car does this when it's cold out. and i'm pretty sure it's water, it looks like water, smells like water and feels like water. i'm not so confident that i've tried tasting it, but i'm pretty sure .

Oddjob

Facboy,

You are correct. Its water coming out. When the car is cold and the exhaust system cold, the water vapor (in the form of super heated steam) leaving the combustion chamber will condense into water droplets further down in the exhaust system. It picks up soot and other particles and is blown out the tailpipe as spatter. Any car that has an open exhaust will do this. A 944T w/o a cat and the straight thru type muffler is very prone to doing it. Cats and baffled mufflers will trap/stop much of this from blowing out.

nize

i beg to differ. if cats and baffled mufflers trap/stop the water, where does the water go? is there an infinite-space water collector in the cat?

Oddjob

Youre kidding, right?

When the exhaust system heats up, the trapped water evaporates and leaves the tail pipe as vapor.

This is why cars that get started often and used on short trips daily, say less than 15-20 minutes of driving time, are very prone to rusting out their exhaust systems, especially mufflers (if they are not stainless). The exhaust system does not get hot enough to evaporate out all the condensed water, so it causes corrosion. Ask anyone that works at a Midas.

Some cars have drain holes drilled at low points in the exhaust systems to let the water drip out. My Jeep cherokee had a factory drilled hole at the low point of the muffler for this purpose. (Also see Cory's post #30)

Youre from Seattle, it gets cold enough there that you should know about this: "Black ice" at intersections in the winter time - water vapor from exhaust freezing onto the road surface as cars sit at stop lights. Discussion here in MN is that the problem is potentially worse with ethanol additives in gas, since there is an extra -OH chain available during the combustion reaction, you get more H20 per mole of fuel burned.

Geneqco

I think the real issue here is the soot rather than the water vapour... all cars will porduce water vapour which can condence at times but it is the soot mixing with that condensed vapour that causes the "black liquid". Soot indicates poor or incomplete combustion which can be caused by leaky injectors or injectors with poor atomization.

Oddjob

Yep, but fuel injected cars will run rich on cold start, the colder the richer. So again, the black spatter is normal on cold starts. As the car warms up, it leans out the mixture and the exhaust heats up, so no soot or water....

Making the assumption that cold start exhaust spatter indicates a bad injector, and can be eliminated by cleaning/replacing the injectors - is incorrect logic.

Now, black smoke after the car is fully warmed up means an overly rich condition. And can be an indicator of a fuel pressure, injector, tunning or chip mapping, etc (i.e. autothority chips) problem. Can also identify this by looking at the plugs.

Geneqco

I just wouldn't expect it to be so rich on cold start as to cause this issue. My 951 is the only car i have owned (of many) that has ever had this symptom - it had a bad injector at the time. The injectors have been replaced and it no longer has the issue.

If I had this issue, I'd at least want to have the injectors checked for my own peace of mind - if they test fine, I haven't lost anything.

Oddjob

Well, you may not expect it, but they do run that rich on cold start.

So your 951 is cat delete, and has what type of muffler? Are you sure it doesnt do it now, or do you just not notice it?

It has to be from a cold start and be sitting/idling for a few minutes or more before seeing anything out the pipe. So, during typical routine driving, it probably wont spit anything out unil after you hop in, back it down the driveway, and get stopped at the first stop light at the end of the block.

I normally never pay attention to it, or look for it. If the car is sitting on blacktop, youll never see it. Concrete driveway; it will show up after the car has been sitting there running for several minutes. I mostly notice it when Im messing with/running a car while in the garage, especially if blipping the throttle - it leaves a noticeable mess on the garage floor or against the garage door.

Ive owned four 944s, and after removing the cats on all of them, and using a turbo muffler (straight thru - no baffles) section on the 944S - they all did it. My 964 spits significantly less, but it has a baffled muffler. It doesnt leave blast marks on the driveway or garage door like the others, but if I put my hand over the tailpipe, it will spatter **** on it. All my other cars have had cats and standard mufflers, so no issue there - but if I put a straight pipe on a honda, it will do the same thing.

If you want to keep Witchhunter in business, by sending him your injectors when a car spits on cold starts - knock your socks off.

billindenver

+1 on everything oddjob has stated. No cat, this is going to happen unless you are running very lean.

IMHO

Acetylene

+2

shaheed

+3...seen it on all 3 of my 951s only after removing the cats.

nize

oddjob (and everyone else); just curious, have you ever had the injectors flow-matched to see if the problem still exists? reason i ask is because after i had my injectors flow-matched, the problem went away immediately.

Geneqco

Well, like Nize, I had this problem and it went away after I replaced the injectors... actually, it was the presence of carbon that helped me diagnose an injector/s as the cause of another symptom.

To answer Oddjob's question, I have LR 4" exhaust with straight through muffler (Magnaflow). I do have a cat but it is a high flow Metalcat... S/S instead of ceramic and 200 cells per sq inch instead of 400 - they are said to have minimal flow restriction. It obviously doesn't stop the carbon as it was in place when I previously had the problem, in any case, it would not be at operating temperature until soem time after start up.

I do have a concrete driveway and have left the car running from cold startup for many minutes on several occasions.

nize

don't knock it 'till you try it.

so far, five out of five who've experienced these symptoms and had their injectors flow-matched saw these symptoms disappear.