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Old 03-08-2012, 06:37 PM   #1
OSDCrusher
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1993 K1500 running rich

I have a 1993 Chevy K1500 1/2 ton with a 350 TBI that is hard to start when the engine is cold and it always seems to be running rich. When the engine is warm, the truck will fire right up every time. I believe there is a related problem with engine temp, the temp sender looks new, but the temp gauge only goes to 1/4, never half way no matter how long the truck has been running. The truck has new plugs, wires, cap, rotor, and TPS. I have also replaced the fuel and air filter, and I cleaned the throttle body with carb cleaner and it still runs rich. I have to press the pedal down about half way and crank it for it to start, and if I don't, it will fire and then shut off. The truck registers no codes and the check engine light has never came on, and that doesn't make sense to me. I'm not positive what the issue is here, so any advice would help.

Thank you
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Old 03-08-2012, 06:56 PM   #2
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Re: 1993 K1500 running rich

Welcome to the board!

The temperature senor for the dash gauge is separate from the temperature sensor that the computer uses to determine how much fuel to inject.

The first thing I would test is the coolant sensor the computer monitors.

Here is a link to specs for testing the coolant sensor the computer monitors. It is from one of the links below.
http://67-72chevytrucks.com/vboard/s...25&postcount=7


Running Rich, or acts like no choke = Coolant sensor testing:
http://67-72chevytrucks.com/vboard/s...d.php?t=322811

http://67-72chevytrucks.com/vboard/s...d.php?t=379142

These links are found at the sticky at the top of this board:
88-98 FAQ's "Is your truck running weird? Check here it could help"
http://67-72chevytrucks.com/vboard/s...d.php?t=445487
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Old 03-08-2012, 07:04 PM   #3
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Re: 1993 K1500 running rich

Thanks for the welcome, I've been lurking around for a while, thought I'd ask for help with this nagging issue. I will replace the CTS this weekend and report back.
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Old 03-10-2012, 08:43 PM   #4
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Re: 1993 K1500 running rich

I replaced the coolant temperature sensor and the truck immediately started right up and ran much better. No hesitation anymore, didn't have to pump the gas to get it started. It also drives and shifts better now. It still seems like it's running a bit rich, but maybe it's just my imagination. The exhaust smells a bit rich, and even on a warm day, like today, there will be grey smoke coming out the exhaust until the truck warms up. Thank you for the advice on the CTS.
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Old 03-11-2012, 08:13 AM   #5
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Re: 1993 K1500 running rich

You're welcome!

When the engine is started, does the engine have a fast idle that slows down as it runs? The IAC (idle air control) is what gives the fast idle speed when started cold.

If the IAC does not open at all the engine will usually “load up” or “flood”.
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Old 03-11-2012, 02:26 PM   #6
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Re: 1993 K1500 running rich

When the truck is started, the idle is about 1500 RPM, and as the truck warms up, the idle lowers to about 1100-1200 RPM. Maybe I have bad fuel injectors? When the truck is shut off, there is a bit of smoke lingering out of the tailpipe, could this mean that the fuel injectors are leaking?

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Old 03-11-2012, 06:35 PM   #7
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Re: 1993 K1500 running rich

If the warmed up idle speed is about 1100-1200 RPM, and the temp gauge only goes ¼ the way up, the thermostat could be bad.

If the engine runs cold, it will run rich.

The truck should have a 195 degree thermostat in it. I suggest using a STANT brand thermostat.

If you have an infrared thermometer you could test the temperature right by the coolant sensor in the intake.

Take a look at the injectors just after the engine is shut off and see if they drip.

Smoke lingering out of the tailpipe could be from coolant getting into the combustion chamber. Head gasket failures are a problem on these engines.
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Old 03-11-2012, 07:05 PM   #8
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Re: 1993 K1500 running rich

I will try replacing the thermostat and seeing what changes after the replacement. I will also check the injectors after I shut off the engine and report back. Thank you for all the great info so far. The head gasket theory is starting to make sense because the coolant is dark green and rust colored and when I caught a bit in my drain pan while changing the CTS, it looked thick, like there was oil in it. I changed the oil less than 500 miles ago and it looks and smells odd. Possibly like gas? Why would my oil smell like gas?
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Old 03-11-2012, 08:56 PM   #9
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Re: 1993 K1500 running rich

An engine running overly rich some gas will find it's way into the crankcase oil.
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Old 03-13-2012, 07:04 PM   #10
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Re: 1993 K1500 running rich

The only logical reason why it is still running rich would be a stuck open thermostat, causing the engine to think that it is always cold, thus dumping in too much fuel.
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Old 03-14-2012, 05:50 AM   #11
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Say what?

Quote:
Originally Posted by OSDCrusher View Post
The only logical reason why it is still running rich would be a stuck open thermostat, causing the engine to think that it is always cold, thus dumping in too much fuel.
How about bad O2's? Making the PCM think it's running lean so it fattens up the mixture?

How about a fouled plug or 2?

How about a FPR that is leaking due to a hole in the diaphragm?

How about an injector that is leaking due to the fact that it has NEVER been cleaned?

Since you have gotten it running better, did you change the plugs?

Did you even look at the plugs since you got it running better?
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Old 03-14-2012, 02:19 PM   #12
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Re: Say what?

Quote:
Originally Posted by speedygonzales View Post
How about bad O2's? Making the PCM think it's running lean so it fattens up the mixture?

How about a fouled plug or 2?

How about a FPR that is leaking due to a hole in the diaphragm?

How about an injector that is leaking due to the fact that it has NEVER been cleaned?

Since you have gotten it running better, did you change the plugs?

Did you even look at the plugs since you got it running better?
The O2 sensor is another logical reason for this situation, but my thermostat is stuck open so that should be replaced regardless.
The plugs were replaced about 120 miles ago with ACDelco Rapidfires, so I don't think those are the problem. The FPR could also be another reason. I just cleaned the injectors so that is out of the equation, but they could be leaking.
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Old 03-15-2012, 09:33 PM   #13
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Re: 1993 K1500 running rich

The computer does not use the oxygen sensor data after the engine is started cold until the sensor gets hot enough to operate and take the system to “closed loop” operation.

Make sure the vacuum line to the MAP sensor is in good condition. If you have a vacuum gauge, test the vacuum at the sensor.

A restriction on the fuel return line that causes high fuel pressure can cause a rich condition. Injectors for a larger engine then the truck has can cause a rich cindition when cold.
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