Map sensor Issues

[Trstrugar]

My truck is a 1994 k1500 with a 5.7l. I am throwing a code for a 33, map sensor voltage high. I tried replacing it, but it made no difference. The truck starts up rough and sputters for about 10 seconds, then it appears to run fine. When I unplugged the sensor it would start up fine, but run extremely rich. I have true dual exhaust and headers, and was running into o2 sensor issues, but after I re wired the IAC valve all the codes I was throwing went away except for map sensor. If anyone can shed some light on this and explain to me what the sensor actually is supposed to do I would appreciate it. TYIA!

 

[LostX]

You may have a vacuum leak, can you hear whistling suction sounds when it's running. Does that year have a mass air flow sensor?

 

[livelifewideopen]

No mass airflow sensor on that year truck. The map sensor throws codes due to the stumbling, because its sensing the vacuum drop. I had an identical issue on mine, turned out to be a bad cap and rotor. could also very well be a vacuum leak though.

 

[SwatDawg15]

On my 94 the plug was dry rotten. I replaced with an ACdelco pig tail and it cleared it up. Im betting yours in a vacuum leak somewhere.

 

[LostX]

Here is an emissions vacuum diagram for a 94 k1500 5.7l without the air system if you need it. If you have an air system I can grab that one for you.

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[Trstrugar]

Thank you I appreciate it! I will start with looking for a vacuum leak and see what I can find. I had also heard that the vacuum modulator on the transmission can sometimes cause weird issues.

 

[Trstrugar]

Found the vacuum leak. The map sensor vacuum line was connected incorrectly. I have a new issue now but it is for a different thread. Thank you for the help and diagrams!