MAP sensor....what's a map sensor?

[seattle_fleetwood]

Here's another stupid question about my '91...I replaced the injectors on my '91 Deville and now it hesitates REAL bad when I start off the line (or when I try to merge onto the freeway). Before I replaced the injectors, it started without cranking the engine over, and now it takes 5-10 seconds of cranking before it starts, I had a couple error codes referring to the MAP sensor and the PCV valve, but they went away...would the map sensor effect the car hesitating so bad?

[Logan]

What kind of injectors? Why did you replace all of them? Injectors rarely go bad.

Did you reset the computer? Most aftermarket injectors have a very different flow rates compared to original units. I personally have seen lower flow rates as much as 30% difference. The ECM cant handle that unless its reset. You cannot replace just 1 or 2 injectors with aftermarket units. You have to replace them with GM units. The only way around is to replace all the injectors with the aftermarket ones.

As for the MAP sensor.....its for 'manifold absolute pressure.' It works exactly opposite of a vacuum gauge. Very rarely go bad.

[poopdeville]

I have a 90 Deville with a 4.5 L... I am guessing you may have the same.

I had a MAP (Manifold absolute pressure) Sensor go about 18 months ago. When it went, the car would start and quit all in the same 2 seconds. Having said that, if I "feathered" the gas pedal very quickly, it would stay running. I did exactly that in order to run it to my garage to replace the sensor. Hesitation is generally fuel or electrically rooted when there is a problem. I had a bad hesitation when my fuel pump was acting up and this would affect fuel pressure and could quite possibly return a MAP sensor code. Map sensors do quit quite regularly on our older girls though.

Mike P