1995 K1500 TBI 350 Running Rich

[IndexOf0]

Hello. I’m having an issue where my TBI 350 is running rich when cold and if you rev it a little it will spray a ton of fuel out of the injectors accompanied by black smoke. It runs fine when it’s warm. I recently replaced the intake gaskets, cleaned the EGR valve and replaced the CTS. Fuel pressure is 11.5 PSI. What would you check next? I’ve also sprayed brake clean around the intake and throttle body looking for vacuum leaks and found none.

 

[Erik the Awful]

Check your O2 sensor swings. Your O2 voltage should swing back and forth from low to high at least seven times in ten seconds. If it's lazy, replace it.

 

[IndexOf0]

If that’s the case it’s definitely lazy.

 

[Schurkey]

I’m having an issue where my TBI 350 is running rich when cold... ...It runs fine when it’s warm.

WHAT VEHICLE???

Connect a scan tool, find out what the computer wants you to know. Verify ALL sensors, and computer outputs. Look for changes in sensor readings between cold operation and hot operation.

Is the catalytic converter destroyed?

How old are the usual "tune-up" parts and when were the adjustments checked? Cap, rotor, plug wires, plugs, air and fuel filters, PCV system, initial timing, timing advance, knock sensor effectiveness, etc.?

Check your O2 sensor swings. Your O2 voltage should swing back and forth from low to high at least seven times in ten seconds. If it's lazy, replace it.

A cold O2 sensor is not going to respond like a hot O2 sensor. That's why engines run in open-loop until the sensor heats-up.

 

[IndexOf0]

WHAT VEHICLE???

Connect a scan tool, find out what the computer wants you to know. Verify ALL sensors, and computer outputs. Look for changes in sensor readings between cold operation and hot operation.

Is the catalytic converter destroyed?

How old are the usual "tune-up" parts and when were the adjustments checked? Cap, rotor, plug wires, plugs, air and fuel filters, PCV system, initial timing, timing advance, knock sensor effectiveness, etc.?


A cold O2 sensor is not going to respond like a hot O2 sensor. That's why engines run in open-loop until the sensor heats-up.

1995 K1509

I don’t have a scan tool yet.

It doesn’t have a catalytic converter.

All of the spark plug wires and components are a year old and the timing is set per factory spec to 0°btdc with the est wire disconnected.

 

[Erik the Awful]

A cold O2 sensor is not going to respond like a hot O2 sensor. That's why engines run in open-loop until the sensor heats-up.

Yes, but if it's borderline rich, when it's cold it will be pig-rich. I should have said "Check the O2 sensor when it's warmed up."

 

[IndexOf0]

Yes, but if it's borderline rich, when it's cold it will be pig-rich. I should have said "Check the O2 sensor when it's warmed up."

It’s pig rich when it’s cold to the point that if you give it a little gas it will stumble because it’s flooding.

 

[Erik the Awful]

Did you check your O2 swings while it was cold, or warmed up? If it was warmed up, replace your O2 sensor. If it was cold, you should re-test it.

 

[IndexOf0]

Did you check your O2 swings while it was cold, or warmed up? If it was warmed up, replace your O2 sensor. If it was cold, you should re-test it.

I tested it while it was warmed up. Sometimes it’s lazy, other times it isn’t. For example if you start it after its been warmed up and you shut it off the cross counts will be high, but then once you drive it they’ll stay rich for a few second then lean, etc.

 

[pressureangle]

If you have no scan tool, try disconnecting each individually your coolant temperature sensor, your intake air temperature sensor, and your MAP sensor. Disconnecting the sensor forces the PCM to use the base map with no modifiers. Maybe you'll get lucky and simply find a failed sensor. It doesn't seem likely but I can't think of anything else that could improve after warmup; Once conditions are met to use the O2 sensor in closed loop, the PCM corrects fuel as necessary so you need to test while quite cold.