'94 Plymouth Acclaim - 56k miles - 2.5 liter w/ 3 speed automatic tranny
& A/C. Car is in good shape and regularly maintained.
Here's the problem - I start it and everything is OK. I drive along at
highway speeds (55 + mph) and everything is OK. Then I begin to slow
down and as soon as I slow to 45 mph the "check engine" light comes on.
Doesn't seem to be related to engine rpm's (as I put it in neutral at 60
mph and let the engine fall to idle with no light). A code 13 is then
stored. I know this is a MAP sensor related code. My buddy (fleet
mechanic for utility company) gave me a new MAP sensor to try. I clear
the code and the same thing happens (always the exact same 45 mph). I've
checked the vacuum lines and associated wiring and they all check out good.
Why the re-appearing Code 13 ? What am I missing ?
Thanks in advance .........
My guess is you are missing vacuum!! just because you installed a new sensor
doesn't mean that the end of the vacuum hose that goes to manifold vacuum is
tight or not broken. Have you looked at that yet?
What I've done was to remove the vac hose from the MAP sensor and attach
my vacuum gauge to that. Then run the engine.
Vacuum readings appear normal and within spec. Hose appears to be in
good shape. Also have removed all the MAP related hose and plugged one
end with a golf tee, then used my little vacuum hand pump and tested the
hose. Hose checks out OK.
Do you know if I could check the MAP vacuum another way ?
Well first of all I don't know how you can get a good vacuum reading with
the map sensor disconnected!! The map sensor tells the computer what load
the engine it is under. In other words at idle the map wants to see at least
17hg (telling PCM its at idle) At wide open throttle the map sensor will
see 0 hg. By you disconnecting the map sensor and checking the vacuum with
it disconnected told the PCM that the engine was under extreme load (at
idle) 0 hg. It had to be loading up and running like crap!!! when checking
engine vacuum always tee into the hose.
Thanks for the advice Glenn. I've been restoring old MoPar muscle for
many years and am much more comfortable with the likes of my '69 GTX
than with my '94 Acclaim. I get a little frustrated with problems like
this MAP sensor business.
Anyway, you're right. It was not running well @ idle (with MAP
disconnected) so I was manually opening the throttle while watching the
gauge @ various rpm's. I believed I had a good hose + connection. But I
also removed the hose and tested it seperately and it seemed OK.
So a little while ago I went down to the garage and added a short piece
of hose + tee in that vacuum line and ran the motor (@ idle) and got a
steady reading of approx 18 hg on the gauge.
I'm wondering why the "check engine" light always comes on when my
speed comes back down to 45 mph (from, say, 60 mph) --- but --- the
rpm's don't cause it too light. Because I can get up to 65 or 70 and
put the car in nuetral and idle the engine and no light comes on. Then I
coast long enough all the way down to 45 and, bingo, the light comes on
and a Code 13 gets stored.
By the way, when I first start the car and drive away, there is no
check engine light. I have to get up to a high speed of 55 or 60 and
then slow down to 45 mph.
With a problem such as that you will almost need to have a scan tool
connected so that you can monitor what the sensor values are. Its possible
the map sensor your buddy gave you may be faulty.
I think I will need a scan tool. My buddy swapped the MAP sensor for
another one and the second one acts the same way.
Do you know of a reasonably priced scan tool that would work with my '94
Acclaim ? Since I plan to keep the car for a few more years, this tool
may come in handy.
Thanks again .........
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