Diagnostic Tech: '92 Ford Tempo EECIV
We're going to need to set the Wayback Machine for 1992. Ford was
using Electronic Engine Control System IV, or EECIV. By today's
standards EECIV lacks sophistication but in its day it certainly
performed its tasks very dependably.
On the plate today is a 1992 Ford Tempo w/2.3 engine and automatic
transmission. The complaint is an intermittent Service Engine Soon
light on and a high idle speed at that time. This system does store
trouble codes in memory but should only turn the SES light while a
code setting condition is present. In this case it just seemed to me
that a test drive to verify the complaint was in order.
Initially the car ran fine. No light came on and even though I was
driving in stop and go traffic there were no idle speed problems. I
decided to return to the shop and just run the EECIV self-tests. When
I pulled into the driveway the SES light came on. The idle speed was
fine until I stopped and put the car's shifter into park position. The
idle speed went to around 2000 rpm and stayed there for about three
seconds before slowing back to normal. I had just verified the
complaint. Time for the EECIV checks.
The car's test connector is at the left shock tower, near the battery.
Technically there are two connectors. One is a single wire called the
self-test input connector.
I'm going to mention that there are alternatives to retrieving codes.
You don't have to use a scan tool. That being said, you will find the
scan tool method more reliable with less chance of misreading a code
number or accidentally clearing memory codes.
It is important to understand EECIV self-tests before using them to
find a problem. Ford has the car's computer run specific tests and
report back areas that failed the tests. The failures are reported as
trouble codes. Running the tests improperly can give you misleading
results.
A quick warmup cycle for the engine and I'll get started.
After connecting the scan tool to the test connector and entering the
car data I want to start with "Quick Tests" and the Key On Engine Off
tests. If a sensor fails the KOEO test then it should be repaired.
You'll need a "Pass" or a no fault found condition in the KOEO
self-test before any KOER (Key On Engine Running) tests can be
reliably done.
The KOEO running test results are called "On Demand" codes. In this
case I get a Pass code 111 which means no problems were found. After
the On Demand codes are displayed the Keep Alive continuous memory
codes will be displayed. The Keep Alive, or continuous codes are codes
from the car's computer memory. Codes that have set in the past. This
car has a 332 in memory. A 332 indicates insufficient EGR flow. I
don't think a problem with the exhaust gas recirculation system it
going to be related to the high idle or even the SES on at that time.
An EGR not flowing should not cause the idle speed to be higher and
since the EGR is not supposed to be flowing at idle anyway I don't
think it would turn the light on at that time. I'm going to move on to
the KOER tests because that test should be done before getting too
involved with Continuous codes. The KOER test will reveal any sensor
failures that happen during the test.
The KOER test codes indicate a 332 again. This time I know the EGR
failed a test in real time and currently has a problem. Again though,
I don't think it is related to the idle speed problem. Two more codes
do indicate a problem with idle speed control, a 412 and 411. These
codes indicate the car's computer not being able to control the idle
speed. These codes do not store to memory so without running KOER
tests we would not see them. If you think that was a lot of trouble to
find that something is wrong with the idle speed you have a point.
What was learned though is that the several sensors that contribute to
the computer choosing an appropriate idle speed do pass self-tests.
That means I should start by concentrating my efforts in testing the
computer's ability to control the idle speed. In other words, I've
learned that the inputs to the computer are likely to be fine but
there is a problem with the idle control output circuit.
It's a good idea, I think, at this point to check the base idle and
minimum air adjustment. Before any throttle adjustments are made I
want to be sure I have a clean throttle plate. I'll remove the air
intake hose, the MAF and the air cleaner cover as a unit. The throttle
plate actually doesn't look too bad. It's pretty clean on the air
cleaner side. The air filter looks good and the air cleaner housing
was properly fastened.
When I open the throttle fully and look past the plate I can see major
carbon buildup. I can even see why the EGR flow is low. The EGR
passages are just behind the throttle body and fully plugged with
carbon. The best thing to do here is remove the throttle body, remove
the EGR valve and do some cleaning.
While we are in the neighborhood, this is a good time to remove the
Idle Air Control (or Air Bypass Valve) and clean that passage as well.
The engine computer uses this valve to control the amount of air that
bypasses the throttle plate. The amount of air allowed controls the
engine idle speed.
Once everything is clean and reinstalled it is a good idea to clean
the MAF sensor or at least see if it needs cleaning. Two tamper proof
screws hold the MAF to the MAF housing. A torx T20H will fit the screw
heads. Carefully remove the MAF from the housing. With a magnifying
glass and a good light you can look for dirt on the two tiny wires at
the bottom of the sensor. If you see dirt, carefully clean it. These
days there are spray MAF cleaners on the market. That wasn't always
the case so I still use the same Berryman Spray Carb Cleaner that I
always did. For stubborn spots I use a Q-tip as well.
This particular MAF looked pretty clean so after reinstalling it I let
the engine warm up again. I know that I now have a clean throttle, a
clean MAF, a clean IAC and a clean EGR passage but what I don't know
is if I've fixed any of the complaints. It's time to run the KOER test
again.
After getting the same results with the KOER self-test as before all
this work, I decided to see just what was happening at the Idle Air
Control as far as the computer control was concerned. The voltage at
the IAC signal wire should roughly match the position being commanded
by the computer. A command to open the valve 34% would have 3.4 volts.
As a load is placed on the engine the command would increase, so a
voltmeter could be used to check the command to see if the computer is
trying to slow the idle speed during the high idle problem. Another
method would be to disconnect the IAC wire connector from the valve
and see if the engine slows. You see, the valve is spring loaded to
return to minimum air position without a voltage command to the
contrary. In fact, it is by disconnecting the IAC and adjusting the
throttle position stop screw that minimum idle air is adjusted. All I
have to do is wait for the high idle problem to appear. After a few
minutes of running time the engine idle speed begins to race. When I
disconnect the Idle Air Control the rpms do not change. The IAC valve
is bad. I suspect a vacuum leak within the valve is the problem.
After replacing the IAC valve I now have no more racing idle and no
more idle control related fault codes. One thing very good about the
EECIV testing method is that I can rerun the test after a repair to
verify the problem is fixed. The idle problem is fixed! BUT the EGR
problem remains. I still have a 332 fault code in the KOER test.
During the KOER self-test the ECM will open the EGR vacuum regulator
solenoid very briefly. This allows manifold vacuum to pass through the
solenoid to the EGR valve. The vacuum should open the EGR valve. The
pressure in the exhaust tube that runs to the EGR valve is measured by
the PFE sensor. If the ECM has commanded the EGR solenoid to open yet
does not see the PFE sensor voltage indicate a pressure change the ECM
will assume the EGR is not working and will set the 332 fault code.
For testing purposes I like to use a length of vacuum hose and bypass
the solenoid, feeding the vacuum directly to the EGR valve with the
engine running at idle. If the engine nearly stalls then the valve is
passing plenty of exhaust flow.
I started to do that here but noticed that the hose that feeds
pressure from the EGR exhaust tube to the PFE sensor was broken. With
a broken hose the PFE sensor would not be able to monitor the exhaust
tube pressure change and would indeed set the 332 code. A replacement
hose and another KOER test and this time the repairs were done! A
complete system pass. No more light, no more high idle, no more codes!
posted by Deranger at 10:00 PM
1 Comments:
Blogger Mike said...
Hey Deranger!
Nice one, very nice!
8:23 PM EDT
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