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Black Oil
I HAVE A 350 IN A 1986 S10 AND THE OIL IS A BLACK 500 MILES AFTER AN OIL CHANGE. THE TRUCK IS GEARED FOR 3000 RPM AT 60 MPH. THE MOST I DRIVE IS 16 MILES TO THE GOLF COURSE AND 5 OF THAT IS AT 60 MPH. THE REST IS IN TOWN. GAS MILEAGE IS 8 MPG. THE ENGINE IS RUNNING ABOUT 350 HP. WHERE IS THE CARBON COMING FROM TO DARKEN THE OIL. I CHANGE THE OIL VERY FREQUENTLY.
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Comments
-mike
THE TEMP.IS A LITTLE WARM AT START UP BUT ALWAYS RUNS 180-190 ON TEMP. GUAGE.
K.C.
Did you ever think about changing the ring and pinion to get better fuel mileage? Good luck
thanks for the reply
k.c.
thanks for the reply
k.c.
headers and dual exhaust
thanks for the reply
K.C.
You should check to see if your oil dipstick reads HIGHER after your short trip (wait 15 minutes after you stop).
Excess fuel in your crankcase may be acting like a solvent all throughout your engine (this is not a good thing and must be corrected immediately).
I'd suggest you treat your symptoms of black oil with the utmost seriousness until you track it down.
Oil analysis might tell the story.
WILL CHECK CARB MIXTURE SETTINGS AND TIMING TOMORROW.
K.C.
are you getting any oil thru your pvc system or in the breather it's self
K.C.
Another thing to consider is that the distributor vacuum and centrifugal advance mechanisms must both be working properly, before the carb can be set. And the ignition system must be producing a spark of adequate intensity, while the spark plugs must not be misfiring or carbon fouled.
But, in any case, the choke plate should open fully when the engine is warm, and if you look down into the carb air horn right after shutting off the engine, there should be no fuel spilling into the engine after it is shut off.
If you have changed the compression ratio or the cam, then whatever jets came in the carb may be totally off for what the engine now needs. If your carb was not intended for the type of engine it is on, it may also be too rich for that reason. In those cases, you need to either get an exhaust gas analyzer and keep leaning out the jets and metering rods until the air fuel ratio reaches about 12-1 under heavy throttle, and about 14-1 to 15-1 under easy driving. Or take it to a performance shop that has a dynamometer, and have them blueprint the carb by running the truck on the dyno and monitoring the exhaust gas.
If you are good with carbs and tuning, you can also do this by driving the vehicle, and reading the appearance of the spark plugs. But carbs have many different circuits with overlapping effects; so it is necessary to understand how these circuits work, in order to know which parts to adjust and what to change.
I hope this information gets you on the track to fixing this problem. Let me know, if you have further questions.
k.c.
I also would like to know if any other modifications have been made to the engine. I'm particularly interested in any changes to the intake manifold, camshaft, cylinder heads, valve train, and pistons. You say it makes about 350HP; where did those numbers come from? Has the engine been dyno'd?
Also, since the engine has 20,000 miles on it; has it been turning the oil black for that whole time, or has this just begun recently. If it only started happening recently, can you correlate it with any changes or new parts that have been installed? Has this carb been on the engine the whole time? And has the carb ever been taken apart?
I'd appreciate any details you can provide.
Thanks!
When I woke up this morning, a light bulb lit up in my head: S10s made in 1986 and later all had fuel injection, and used an electric fuel pump which is mounted inside the gas tank. This pump produces over 30psi pressure. So, if it's still in place after your V-8 conversion, that high pressure fuel injection pump is just drowning your poor carb with excess fuel. The carb on your 350 engine is designed to work with 4 to 9psi fuel pressure. The fuel injection pump is putting out so much pressure that it wouldn't be practical to try reducing it with a pressure regulator. Instead, I would suggest simply removing the fuse for the S10's stock electric fuel pump, or disconnecting the power wire that goes to the pump at the gas tank. (Be sure you don't cut the wire for the fuel gauge, and that you insulate and secure the cut power wire, because it will still be electrically live.)
If there is a mechanical fuel pump on the 350 engine, then it should be able to draw the fuel it needs through the disabled electric pump. But if you installed an electric pump anywhere that's higher than the tank, it may have trouble pulling fuel up to the engine. Electric pumps are made to push fuel, but they are not good at pulling fuel from a lower point.
There are now lots of after-market electric pumps out there which produce very high pressure, and are made to be used with fuel injection systems. Those of us who have carburetors on our engines have to be careful not to use that kind of pump, because it will create severe flooding problems.
THANKS TO ALL
KENNY CURRAN
Sounds like we both have been on the same trail, but something still is going on to turn your oil black and suck all that fuel. If the mechanical fuel pump has a leak in the diaphragm, it can pump gasoline into the crankcase. This will make it look like the oil level is not going down, but the oil is gradually being replaced by gasoline. In that kind of situation, I've seen an engine blow the valve covers off when the gas in the oil exploded. If you unbolt the pump from the block, it may be possible to spot a leak; if you can see or smell any gas on the engine side of the mounting flange. Or, you can substitute a low pressure electric fuel pump for the mechanical one, and see if the problem goes away.
One other possibility is that someone left out the check ball, and/or the weight in the accelerator pump discharge nozzle. This would make the pump nozzle act as a siphon, and pour fuel into the engine when it was running. If you take off the air cleaner and look into the carb with the engine speed held steady at about 2500 RPM, there should be no fuel coming from the pump nozzle, unless you speed the engine up.
And, of course, it there is a sound insulating blanket on the underside of the hood, and it is too close to the air cleaner or it is loose; it can be pulled against the air cleaner by the force of the incoming air; which makes it act like a choke that is on all the time.
When I used to live in Kissimmee, I would have been happy to drive down there and go fishing, but since I moved back to California after the hurricanes began, it's now too long a drive.
Joel
Along with the points I raised in the preceding post, there is one other test that's worth doing. With the engine off, take off the covers over the metering rod assemblies, and note the height of the top of the rods. Then start the engine, and see if the rods move to a lower position when the engine idles.
If the metering rod assemblies are always in the up position when the engine is running, then the carb will supply the richest possible mixture at all times; and this will grossly overfeed the engine with fuel.
If the rods did not move down, then they are either stuck, or the rod control pistons are not getting any vacuum. If you can press down on the top of the rods, and they move down easily against their spring, then they are not stuck. In that case, the vacuum passage to the piston well is blocked; either by gasket cement, or by an incorrect or improperly positioned carb mounting flange gasket.
Joel