Excessive Black smoke

[akeller]

I have a 1993 GM 4 x 4 6.2l with approx 300,000 km on it. A month ago it started to pour black smoke out a various times. 2 things were replaced before I noticed the smoke. I don't think it is running the way it normally did, A bit under powered

A new throttle position sensor was installed and set (a new one was put in a 1 1/2 year ago when I put in a new IP. A new Oil sending unit was put in because the lift pump was not running. After these to things were done I noticed it starting to smoke.

- does not smoke when idling
- when driving in OD (3 speed auto with od tranny) at 80 km
- going up a hill and engine shifts down smokes lots
- string out from a stop it puffs and then quites.

I have noticed that the charge indicating gauge bounces around a bit. Normally it runs 1/2 way but once in a while it will drop to 1/4 etc.

Could this be an electrical problem ?

air filter is good.

Anyone have any other ideas ? Thanks

[john8662]

You didn't mention when the fuel filter was last serviced, this is also a routine service item.

Is this truck an 1/2 ton model?

Reason being, is most of the light duty versions (c code engine) had the EGR system on them. When this system malfunctions, it smothers the engine with exhaust gasses in the intake which depletes the air necessary to get a clean burn. This will be represented wtih BLACK smoke. The TPS is part of the puzzle with the EGR system, so it's possible that it's still mal-adjusted or a bad switch. The OPS (sender unit) won't have a bearing on excessive smoke like you're seeing, if anything the power situation should have improved.

[akeller]

Just changed the fuel filter...didn't make a difference

It is a half ton extended cab 4x4

mileage is poor, normal highway driving I have always gotten around that 28 mpg, last trip pulling a small trailer (600 lbs) I got around 18 mpg.

Give some information of the egr system if you don't mind. Where do you start or what should be replaced ?

[N9Phil]

You might check all your vacuum lines. A loss of vacuum will cause the EGR system to screw up. Take a piece of mechanics wire and wrap each connection then twist it tight. This makes a nifty clamp for the vacuum conections.

N9Phil