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1989 GMC Sierra K1500 4x4 5.7 Liter

This is a discussion on 1989 GMC Sierra K1500 4x4 5.7 Liter within the Technical / Maintenance forums, part of the General Discussion category; I have a 1989 GMC K1500 that is giving me 3 codes 33,34,45.It is idleing very rough and smells very ...

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    Unhappy 1989 GMC Sierra K1500 4x4 5.7 Liter


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    I have a 1989 GMC K1500 that is giving me 3 codes 33,34,45.It is idleing very rough and smells very rich.I checked the map,throttle position,and 02 sensors and they are working correctly.I checked the fuel pump and the psi is 12.It also sounds like the idle goes low then high,low then high over and over.It runs good when driving at high speed,but really bad in park and when at a light.Could someone please give me some helpfull tips on solving the problem.I had a smog tech guy use a diagnostic machine to help me and all sensors seem to be working just fine he said,then he had me give the truck gas while he held his hand near the exaust and he thought their might be a restriction in it somewhere.So I cut the exaust after the motor and in front of the cat so that the cat and muffler were eliminated and it still ran bad and still got the check engine light and the same codes.The very latest work that Idid to the motor before this problem was change a bad water pump,thermostat.

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    How did you check these sensors to determine they're good? Please give more info. The smog guy telling you a vague "they seem to be working" ain't good enough.

    Beyond the codes and onto the rich mixture, although I'd rather see the codes addressed first:

    If you have or can borrow an infrared temp gun, I'd check the temperature right at the thermostat housing with the truck fully warmed up and see if you're getting 195F~200F or so. That new thermostat doesn't necessarily mean it's a good one, or the right one. It's one of those parts that is quickly becoming "often junk right out of the box" anymore, much like master cylinders and rebuilt A/C compressors. If you can find them near you I suggest using a Stant Superstat, and the correct one is a 195F.

    If the engine is running at proper temp, verified with a temp gun not the dash gauge or what the ECM thinks the temp is, then next most likely suspect is the coolant temperature sensor (CTS) - you can test it with an ohmmeter or use a scanner to see what it's reporting to the ECM, but if it's looking old and cruddy you might as well spend a few bucks to replace it - buy a good one like a Delphi/AC Delco. These have a lot of power over your fuel mixture and when they go bad they tend to send a colder than actual temp reading to the ECM, making it richen up the mixture.

    Back to the MAP, a bad MAP or problem with the MAP circuit can have a profound effect on how well your engine runs.

    Richard

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    I couldn't get a themometer to read the thermostat housing but I did buy a new coolant temperature sensor and I still have the same problem,I cleard the codes and am getting a 45 code.The smog tech guy used a scanner to test the sensors.The map sensor code may show up when I drive it more later.

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    Without knowing your actual temp we're kind of shooting in the dark. I know not everybody has an IR temp gun in their toolbox since a decent one is $75-$100 but it's an extremely useful tool. Maybe you know somebody that has one?

    In a pinch I've seen people touch a meat thermometer to the thermostat housing but I really don't know how accurate a reading you'd get that way. Better than nothing I suppose?

    For the MAP - have you checked the vacuum line from the rear of the TBI to the MAP? The boot on it often gets dry/cracked and doesn't seal well. The MAP needs a solid, reliable vacuum signal to do its job right. Also check the electrical connection to it - the retaining tab gets brittle and may be broken off; letting the connector just kind of sit in there and it may not be firmly seated. If necessary, throw a small zip tie around it to cinch it up.

    Richard
    Last edited by someotherguy; 01-27-2010 at 02:02 PM.

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    I did use a voltmeter on the map sensor by back probing it with the positive to the connection green wire and turned the key to the on position not starting the motor and I get a reading of 4.98 volts, shouldnt it be 5.00 or a hair more?I did buy a map sensor and tried that but still the same problem

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    My upper radiator hose is collapsing when I rev up the motor.What could be the problem?

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    You sure you got the right water pump? Sounds like you got a normal rotation pump instead of reverse rotation. Serpentine belt setups use a reverse rotation pump.

    Richard

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    my truck had a similar problem turns out it was a valve
    1994 GMC K1500 Z-Z1 SLE Regular Cab Short Bed 350CID TBI 4L60E Automatic Transmission 3.73 Gears

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    I went back to the auto parts store and it is he reverse pump,so that's ok.The truck is a 89 GMC Sierra k1500 5.7 liter 4x4

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    Re: 1989 GMC Sierra K1500 4x4 5.7 Liter

    I have the same problem with my truck and i do not know what to ive tried everything tooken it to many differrent mechanics but the do not what to do. I need help of a speciallist for these type of trucks ?

 

 

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