I just bought this RV conversion van with a rebiult 5.0 L double throttle body and its putting out black sooty exhaust. It starts fine, runs smoothly and is not burning oil. But its either running way to rich or the choke is stuck on or theres something wrong in the emission system. I bought the Haynes manual but it has very few details on this motor. Everything looks stockin the motor and exhaustsystems.
I changed the plugs, rotor and dist cap but no luck. All the hoses are connected. Any suggestions on what might be the problem.

 

Well, as far as the exhaust goes, I'd check the Catalystic Converters if they are equipped, the choke sounds like it also might be a good place to start, however, if the engine runs well, it's hard to think it may be the choke...I'm fresh out of ideas...maybe someone else may have something to say...

 

A simple test; does the check engine light come when you turn the key to the 'on' postion (without going to the start postion)? If not you may have a bad dash light and computer codes.[:'(]

 

I do not believe that a 1990 van has a choke. It should be EEC IV equipped. Scan for codes or just check your fuel pressure. The most common fault is the FP regulator sticking causing high fuel pressure. The post by catfish is right also. Check to see that the check engine light proves out. If it does and goes out after it is started then you will probably not get any DTC's if you scan it. Start with fuel pressure test. 30-35 at idle. Also pull the vacuum line off the regulator to see if fuel is leaking into the intake through the vacuum line. Seen that before. Fuel pressure will be within specs but will still run rich.

 

Just make sure your face aint close to the fuel pressure reg. When you pull the vac. hose it will shoot a stream up 3 feet easy , You probaly gotta remove the dog house in the van to get to it . An if they didnt replace the thermostat I've seen them run smokie too , (engine allways thinks its cold so it dumps more fuel )

 

OH yeah, I forgot about the old stuck open t-stat. Duh. Monitor your ECT or feel of the upper radiator hose when you first start it up and see if the hose gets warm gradually or all at once. All at once means the stat is working.

 

This is an interesting discussion, could I add if this could be the O2 sensor?