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Cadillac 1992 Seville, Past 1993 Seville & a 2006 STS V-6
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121 Posts
Discussion Starter #1
hello --- My tach "jumps" I don't know why the car is in park it is 60F - 60F in my garage all the time can this have something to do with the throttle body or oxygen sensor ?? This is a 1992 4.9 Seville.
 

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93 Sedan Deville 4.9L
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1,005 Posts
jump as in uneven idle? If so then clean your throttle body bores/blade0 with carb cleaners and the egr tubes below them using a coat hanger or the like to rod them out.

Then you can disconnect the battery to reset the idle or just wait a few days for it to reset itself.
 

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2008 SRX
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403 Posts
Just had two 92 Sevilles like this recently, one being mine. They mostly jumped on accel. Both had a bad injector. Do you have a miss?
 

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Cadillac 1992 Seville, Past 1993 Seville & a 2006 STS V-6
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121 Posts
Discussion Starter #4
no miss. only a weak water pump -=--- a fuel injector or fuel rail what is the difference my brother does the repairs he loves 4.9's
 

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76 Eldo (54k), 76 Eldo (52k), 78 Eldo (9k), 85 Deville (43k)
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668 Posts
A fuel rail brings fuel to multiple injectors, which actually squirt the fuel into the engine. On the 4.9, there are 2 fuel rails, each serves 4 injectors.

If you tach is jumping, but the engine is running smooth, you may have a weak battery (improbable), a bad voltage regulator in the alternator circuit (check the battery voltage in park to see if it's too high, i.e. above 15.5 volts), or possibly, a corroded electrical ground that is causing spiking voltage. Either way, I'd get it fixed quickly, otherwise you could burn out the computer and the IP cluster among other things if it is a voltage issue.
 
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