Question about 1990 Geo Tracker

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Why is the engine running erratically?

My tracker started running erratic the other day it would not run without pumping and revving the engine,the diagnostic code shows map sensor. i saw where a vacuum leak or fuel problem could cause this code so I installed a new fuel filter and also pulled the throttle body and put new gaskets on the it and replaced some deteriated vacuum hoses, also I installed new pcv valve, now it sometimes misses at idle or speeds up to around 3000 rpm's at idle and then starts running rich and smoking bad. thanks for any help you can supply. JR

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  • Geo Master
  • 20,706 Answers

The map sensor fail means (DTC code not stated sadly)
mean the voltage is stuck at 5v or 0v.
near
the ECU never lies about this, ever.
the ECU enters FAILSAFE mode , in this case. (limphome)
and runs rich has heck , horrid rich, misfires.
RPM limited
idle controls disabled.
and retarded spark timing.

pretty much worst of the worst for EFI ops.
all you need to do is post the DTC error. and all that is what matters.
new MAP time, or fix the vacuum hose. its clogged? cracked.
make sure the vacuum leaves the intake manifold (sucks) and
makes it all the way to the MAP on the fire wall and that the
tiny filter(check valve?) inline is clogged, (blown through it)

This is a G16A ENGINE, With an ECU that does not create or control spark, (old style distributor with mech, and vac, advance)

DTC 31 or 32??????????????????????
http://www.fixkick.com/CEL/CEL.html#OBD1codes

if vacuum line is breached to map , the vacuum is not 0" HG
the MAP outputs 3.9V

the ECU trip points i do not know. but
above 3.9 or below .5v it will trip... somewhere,

here is very good map , graph

http://www.fixkick.com/sensors/my-map.html


all testing of it is here
http://www.fixkick.com/sensors/tests/MAP-testing.html

with photos and how to back probe it with an volt meter.

Posted on Apr 29, 2015

Testimonial: "thanks for the info I will test asap. the obd code is 32, if any more info please respond."

  • 5 more comments 
  • _-__-___-_
    _-__-___-_ Apr 29, 2015

    in pure theory , an engines with horrid bouncing vacuum can fool any MAP sensor. (true on most cars made) so we always, (map fails) check vacuum first. with a meter. (gauge) 19" vacuum is normal at idle. not bouncing like a kid on a pogo stick. (ever change out the cam belt?)

    EFI systems cant run dead engines.
    or say one with cylinder 1, intake valve burned to crisp. see? that is because it makes the MAP go NUTS

  • _-__-___-_
    _-__-___-_ Apr 30, 2015

    pressure is too low 32DTC. so measure the green wire, pin 2. on the map. I think them mean that pin 2 is low voltage near 0volts, (a dead sensor) the correct voltage key , no started is 3.9v. that is the first check of any map sensor, keyon output. easy huh? just one check. and big clue. got a volt meter? any will work.

  • _-__-___-_
    _-__-___-_ Apr 30, 2015

    keyon, not started,pin 2 is 3.9V just like the graphic in link 2 shows.....

  • _-__-___-_
    _-__-___-_ Apr 30, 2015

    keep in mind the MAP is just vacuum gauge so the ECU can calculate air flow INTO the engine, so it can match FUEL to AIR flows. that is is Prime job, non trivial. if the map works, it will match the shop vacuum gauge attached. see? it's a simple analog, sensor, and linear, in actions. making it easy to test with simple tools. (volt meter)

  • _-__-___-_
    _-__-___-_ Apr 30, 2015

    when fixed, you will get back 28mpg again. imagine that.!

  • _-__-___-_
    _-__-___-_ May 01, 2015

    my guess, (tools in pocket) map connector fell off, or was broken at last engine pull (or map bad due to same reasons)
    maps almost never fail, only seen one, due to crashed at engine pull. (cracked)
    the code you see usually means , map dead. or not connected.

  • _-__-___-_
    _-__-___-_ May 01, 2015

    the voltmeter checks are supper easy.
    backprobing, skills?

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