I have a '97 850 (non-turbo)with 75,000 miles on it. I'm having problems with the vehicle in that it is blowing out black smoke on heavy acceleration. Once the black smoke comes out, I can stomp on it a second time and the exhaust is clear. Also, sometimes during idle, there is black smoke coming from the exhaust. I've replaced the plugs (they were real dirty), replaced air filter and flame trap (filthy). But the problem continues. It appears that the car is running "rich" and I don't have a clue as to how to fix that. My gas mileage is poor (12 to 13 miles to the gallon) and all my driving is on open road and highway. The vehicle was purchased by me from an estate sale and prior to me buying it, it sat for about 6-months and was hardly driven.

Can anyone point me in the right direction to troubleshoot this. My GMC Yukon XL gets better mileage than this thing does.


Thanks.

My 850 ran rough right at startup; the engine shook the car, and the mixture was obviously too rich. It went away in a few days. I wrote it down to either dirty gasoline or water that was in the gas. You might have some luck checking the fuel delivery system for dirt or water.

I thought at first it was just that...........bad gas or dirty fuel injectors. I had them serviced and have run about three tank fulls of gas through the car. It still continues.

Could be a leaking fuel pressure regulator. I think you can check it by:

"The easiest way to check the fuel pressure regulator is to get a piece of clear vacuum hose, and a inline vacuum hose adapter. Some regulators leak intermittently. So if you make about a three inch clear vacuum hose adapter, hook it between the pressure regulator and the regulator vacuum hose,
watch for bubbles of fuel to go through it while the car is idling, and while snapping the throttle open and closed. If you see dropslets of fuel, here is the problem."

Courtesy of Sean Cahill, Riviera mailing list.

Probably O2 sensors.Or: temp sensor for ECU,being in closed loop all the time:"cold engine". HTH.
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