Running rich

[aussiebob]

After remedy for running rich 4 litre?

[89 MJ]

There could be a number of factors causing this. Faulty fuel pressure regulator allowing too much fuel pressure, could be an injector hanging open, or could be a faulty oxygen sensor. 
 

I’d start by making sure that the vacuum line for the regulator is hooked up. 

[Eagle_SX4]

Could also be a failing fuel pump. Sometimes if the computer sees that it is running lean it lets the injectors stay open longer causing a rich mixture even with low fuel pressure.

[gogmorgo]

Running cold makes it run rich. A vacuum leak or obstruction in the line to the map sensor could do it. Sticky or leaky injectors. Exhaust leak before the O2 sensor making it think it’s running lean. Incomplete combustion because of a spark problem would cause similar symptoms. 
 

What makes you think it’s running rich?

[pizzaman09]

Since it is free, it is worth checking to see if the manifold bolts are tight.  

[aussiebob]

gogmorgo....califorina smog check.....thanks for the input.

[gogmorgo]

Excess hydrocarbons in the test result then? Usually that’s an ignition concern, the classic tune-up items, plugs, wires, cap and rotor. If they’re newer it’s still worth pulling a spark plug or two just to see how they’re doing. I’d also make sure your engine is coming all the way up to operating temperature. 
Cruiser’s tips at Cruiser54.com could also be helpful if you can’t find a problem somewhere. 

[aussiebob]

New 02 Sensor wham!.