Map Issue - I Think

[flint54]

Just when I thought things were running too good to be true.

 

Started running like crap the other day, with A/F ratio wild swings.

Fault codes listed:  12, 13, 14, 13, 55. (Not sure why 13 shows twice).

All this started right after I replaced my old tired battery,

 

Checked manifold vacuum, it's solid 20 with thottle-induced swings as should be.

 

Installed new MAP sensor.  No joy.  Motor sputters and fouls out when A/F is overly

rich (as one would expect) and and stalls out, with high RPM cutout, when overly

lean (as one would expect).  And once in a while it runs fine.  

 

My O2 sensor was replaced just a few months ago, the A/F meter runs off a

separate sensor.

 

Suggestions?

[flint54]

And I don't know why this posted three times???

[cruiser54]

MAP sensor on the firewall? If so, how is the vacuum going to it?

[HOrnbrod]

Also, what's your MAP input voltage reading? As referenced to the MAP sensor ground pin, not chassis ground.

[flint54]

Yes, the MAP sensor on the firewall.  Vacuum supplied via hard plastic tube directly

from the manifold, connected with two very short rubber hoses.  These are all new.

There is nothing else tied into that line. 

 

MAP sensor input voltage, referenced to the MAP sensor ground pin, (and measured

with plug connected through the wire jacket) is 4.95V, very close to what it should be.

 

Also, the ECU connector was recently (last fall back) pulled, cleaned, and pins checked.

[Akula69]

One item that I found when this was "my" problem was that the throttle body had fouling the area where the hard line went into rubber fitting. It was interfering with the vacuum going to the MAP.  Cleaned using carb cleaner and re-installed.

[HOrnbrod]

I had a code 14 for awhile (input voltage was 5.1V) but a new GM MAP sensor, not aftermarket, got rid of that code. I've never had a code 13 though. You have probably done this already, but how are the MAP output voltages while running, and did you check for continuity between the MAP output connector wire and the ECU pin?

[flint54]

Had to set this aside for a while, but back on it now.   The MAP sensor voltage

output is 4.83v, way too high.  I suppose it is possible for both the original and

the replacement sensor to be failed, but seems unlikely.   I'll check the line

continuity tomorrow, but doubt that would explain the high output voltage.  The

vacuum is good, right at the sensor.     I'm seeing A/F around 8 until warm, then

12-14 except when thottle is closed then it goes full lean (18).