MAP sensor drift, is it common?

[grassulo]

is it common for the MAP sensors used in the TBI 2.8L S trucks to drift out of range? Mine gave me an intermittent code 34 this afternoon and I'm wondering if i should just write it off or replace the sensor, I think this may very well be what was causing that no idle when warm condition I was having, a heat soaked map.

-Garret

[geoffinbc]

If you have ever had a backfire or pop through the intake then it could be dead. If it is old it may be bad too.

[grassulo]

I'll look at the date code on the sensor itself, but im pretty sure its the original one, the truck is a 1987 GMC S15, so im pretty sure its the original, do these often fail at this age?

-Garret

[geoffinbc]

Yea the diaphragm inside gets fucked up. I can't say for sure if it is your problem. Do you have a vacuum guage that you can compare the map readings to?

[grassulo]

I'm going to replace it anyway, since this truck has to get me to work every day and I don't have another vehicle, better to replace it with a new one than have this one go completely and have to drive in limp home mode (and use all my gas).

-Garret

[grassulo]

I just tested the sensor, with 5 volts from my bench power supply going to terminal C, and its negative going to terminal A, and a voltmeter hooked across B and A. Initially it read 4.7 volts, an ok reading even though it should be around 4.5 cold, then i heated it with a hair dryer placed about a foot away and almost immediately the readings jumped to around 4.9 volts it didnt even need to be that hot to drift that much, this must be why the truck is so hard to start when warm, anyone else ever bench test sensors like this?

-Garret

[Juglenaut]

component drift is common but not to a point that it can not be compensated for upon manufacture. All electronic components have have there own so called finger print for how they act in given conditions, some last past warrenty some don't. A map functions very much like a Barometric device, if this is the case your map thinks it is lower in elevation causing the map to richen the fuel and take in air at your present elevation, this is a culprit of vapor lock and can happen under some conditions in TBI systems.