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Ok I have a 87 2.8 with TBI. It has been running like crap lately and just threw the engine light this morning. I pulled the codes and came up with these.

12, 33, 45

I know 12 is the diagnostic code
33 seems to be a MAP high (manifold pressure)
45 O2 rich (oxygen sensor)

Does anyone know what route I should go? I do know that I have had the truck for almost 2 years now and it doesn't look like the O2 sensor has been replaced in the truck. Not sure if it is starting to go bad. Any help would be appreciated. Also can anyone tell me how many O2 sensors we have?
 

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i agree with bobditts, do the quicker stuff first, such as the O2 sensor
 

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I would find out why you have a code 33 first. Something as simple as a broken hose to the MAP sensor can cause this, or a broken ground wire to the MAP sensor, can also cause this.

Your code 45 will likely disappear at the same time. With the high manifold vacuum (really a misnomer), the ECM will add fuel, since it sees this as increased load on the engine, which means, according to the VE tables, that the engine needs more fuel. Feed the ECM a proper MAP signal, and the fueling supplied will go down.
 
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