88 Suburban - Black Soot (no smoke) From Exhaust

Hey guys, I have an 88 suburban, 5.7 liter TBI, 350, auto TH400 trans, 183k miles. It runs great, however I noticed it is shooting a black soot out of the exahust. It does not smoke at all, it just shoots the soot when I rev it up. It comes out like little semi-wet droplets when rev'd and they dry to the concrete pretty fast. Could this be leaky fuel injectors, burned oil, or am I worrying for nothing? ANY advice at al would be helpful. Thanks

black soot will be excess fuel

check the TPS

clean the IAC and the hole it is threaded into in the intake

check and clean the EGR and orifice out also

02 sensor could very well be dead/faulty

injectors may have dirt in them and be stuck, or just need to be rebuilt due to age and mileage

try fuel injector cleaner fuel additive after cleaning the IAC out

i bet it is severely carboned up by now, it is simple to clean, it is threaded into the TB unit and is round and barrel shaped, one electrical connector with 2 or 3 wires- it is the idle air control valve assembly and has a spring loaded pintle on the end of it inside the TB unit- it controls idle speed mainly


fuel mixture is controlled partially by many different sensors including the TPS, ECM temp sensor, and the 02 sensor(s)

the TPS is also attached to the TB unit and is moved by the throttle shaft of the TB unit

the temp sensor will be in the therm housing or in the front area of the intake by the therm housing, there may be two of them depending on the year make model, oval shaped plug, two wires

make sure all electrical plugs are tight and clean

use electrical cleaner spray

check all wires for any breaks inside them that you cant tell, beneath the insulation, it happens sometimes and causes lots of issues often, also make sure ground wires are not broken at the crimp connectors where they are bolted to the engine or body, if the wrong one is broken then the ECM will be affected, but this is mostly the case on FWD cars and such where they are bolted to a bellhousing bolt and do cause running and idling issue commonly


check cap rotor and wires for arcing or leakage

such ignition problems are VERY common on the TBI gm engines and cause all kinds of oddities often

good luck

The Engine Coolant Temp sensor is also important in fuel delivery. If it is off, the engine can run rich but not set a code.

A good scan while running should help point to the issue.

//2000CAYukon

UPDATE:

I noticed yesterday that there was oil in my throttle body, and it was being sucked in from the left valve cover breather (Not the PCV Valve). I went ahead and replaced the PCV valve anyway, but doesnt this usually mean that I have piston blow-by? Seeing as how I am getting black soot from the exhaust, and now this oil in the TB, wouldn't that be the most logical reason as to why both of these symptoms are present? Thanks:cwm27:

UPDATE #2:

Aside from the oil in the throttle body, there now a cloud of light blue smoke thats shot from the tailpipe upon starting up the burban. It also feels as if its loosing some power. I changed the PCV valve and it did not help the oil in the TB or the smoke screen on start-up, however my small oil leaks seem to be gone....go figure.

Should I suspect blow-by or worn valve stem seals in this case? Either way I am going to have to do a leak down test on the cylinders and heads right?

*Sigh* :frown:

UPDATE #2:

Aside from the oil in the throttle body, there now a cloud of light blue smoke thats shot from the tailpipe upon starting up the burban. It also feels as if its loosing some power. I changed the PCV valve and it did not help the oil in the TB or the smoke screen on start-up, however my small oil leaks seem to be gone....go figure.

Should I suspect blow-by or worn valve stem seals in this case? Either way I am going to have to do a leak down test on the cylinders and heads right?

*Sigh* :frown:

the reason you see blue smoke is because your burning off the blowby gases from crankcase this will cause oil to stop leaking in most cases as your engine should have a slight crankcase vacuum when operating...by way of the PCV operating design..


this black soot when giving it the throttle may well be the cannister control valve diaphram has a hole in it and you are sucking gas from tank vent into the engine...if this is whats happening it will cause the engine oil to get gas in it this can damage engine and create excessive blowby...

this black soot when giving it the throttle may well be the cannister control valve diaphram has a hole in it and you are sucking gas from tank vent into the engine...if this is whats happening it will cause the engine oil to get gas in it this can damage engine and create excessive blowby...


Do you happen to know where this valve is on the Suburban?

Do you happen to know where this valve is on the Suburban?


i don't know for sure but it usually is near the charcoal gas vapor cannister....and has about 3 vacuum lines to it...remove lines if it smells/or gas comes out after just turning off engine this should be replaced...it may also be part of the cannister so it may require cannister to be replaced ..

Yet Another Update:

Im pretty sure now that the smoke coming out is white, and mixing with water from either a bad intake man gasket or head gasket. There is more and more white smoke coming out when I start it up now, and also black water droplets are coming out of the tailpipe when I rev it up whille parked. Also, my valves click and tap pretty loudly for about 3-4 seconds when starting also. Sounds like I just need to rebuilt this thing. :crying:

The truck is running progressivly rough lately, and lacks some power - not to mention all of the new noises coming from the top end, etc. The Suburban is in fair condition at best, But it is my main source of getting to and from work right now, so I need to do something ASAP.

Should I look into a junkyard smallblock with a 30 day warranty, or rebuild it myself / have it rebuilt.

Either way im :banghead:

this black soot when giving it the throttle may well be the cannister control valve diaphram has a hole in it and you are sucking gas from tank vent into the engine...if this is whats happening it will cause the engine oil to get gas in it this can damage engine and create excessive blowby...

Is this valve also called the Canister Purge Valve? (See image below)

Is this it?
http://i23.photobucket.com/albums/b389/timbrendelaz/can.jpg

Is this valve also called the Canister Purge Valve? (See image below)

Is this it?
http://i23.photobucket.com/albums/b389/timbrendelaz/can.jpg

yes thats it....



on your vehicle engine problems i would not spend 5cents to repair that engine or pay to replace engine,,,if this vehicle is used to just commute to/from work find one that is economical....you will save a lot of money...1988 vehicle uses way too much fuel.......