Hyundai Excel Ambiguous Codes Read

I am trying to read the trouble codes on a 91 Hyundai Excel which,
incidently was induced to pass "aircare" vehicle testing a month ago
and has subsequently generated clouds of grey smoke. Compression is
175-185 (within spec)

On the subject, the procedure below, which is from Haynes and also a
discussion group, was followed with a scope in scroll mode to record
the pulses. Unfortunately, the scope display does not allow the whole
train of pulses to be displayed in fine enough detail, but it seems
that a string of 1 second wide pulse is generated as long as the
ignition is in start position.

how wide should the pulses (wide and narrow) be?
Terminals 8,9,A, 7, and E are present although I am using the
stipulated 8 (GND) and 7(SIG). Is a different configuratrion possible?

Thanks for any light.

(1) Locate the diagnostic connecter which sohuld be under the driver's
side kick panel.
(2) Connect an anlog voltmeter to the diagnostic connector ground
terminal
and MPI diagnostic terminal. See diagram below.
(3) Turn the ignition on
(4) Count the voltmeter needle sweeps and write them down for
reference.
Long sweeps indicate the first digit in two-digit codes. The short
sweeps
indicate the second digit. For example two long sweeps followed by one
short sweep indicates a code 21.
(5) To clear the codes, disconnect the negative battery cable for 15
seconds.

Diagram for Step 2

|_1_|_2_|_3_|_4_|_5_|_6_|_7_|
|_8_|_9_|_A_|_B_|_C_|_D_|_E_|

Diagram=diagnostic connector
8=ground
7=diagnostic terminal

wrote:
> I am trying to read the trouble codes on a 91 Hyundai Excel which,
> incidently was induced to pass "aircare" vehicle testing a month ago
> and has subsequently generated clouds of grey smoke. Compression is
> 175-185 (within spec)
>
> On the subject, the procedure below, which is from Haynes and also a
> discussion group, was followed with a scope in scroll mode to record
> the pulses. Unfortunately, the scope display does not allow the whole
> train of pulses to be displayed in fine enough detail, but it seems
> that a string of 1 second wide pulse is generated as long as the
> ignition is in start position.
>
> how wide should the pulses (wide and narrow) be?
> Terminals 8,9,A, 7, and E are present although I am using the
> stipulated 8 (GND) and 7(SIG). Is a different configuratrion possible?
>
> Thanks for any light.
>
> (1) Locate the diagnostic connecter which sohuld be under the driver's
> side kick panel.
> (2) Connect an anlog voltmeter to the diagnostic connector ground
> terminal
> and MPI diagnostic terminal. See diagram below.
> (3) Turn the ignition on
> (4) Count the voltmeter needle sweeps and write them down for
> reference.
> Long sweeps indicate the first digit in two-digit codes. The short
> sweeps
> indicate the second digit. For example two long sweeps followed by one
> short sweep indicates a code 21.
> (5) To clear the codes, disconnect the negative battery cable for 15
> seconds.
>
> Diagram for Step 2
>
> |_1_|_2_|_3_|_4_|_5_|_6_|_7_|
> |_8_|_9_|_A_|_B_|_C_|_D_|_E_|
>
> Diagram=diagnostic connector
> 8=ground
> 7=diagnostic terminal

Some thoughts:
Your one second pulses on the scope -- are you counting these when the
signal is high (12v)?

Is there any difference in timespans of any of the low signals (0v)?

Are these rises and falls sharp like square waves, i.e. transistor
switched?

Another possibility is that a continuous code one is simply a 'system
pass' code. You didn't mention whether the MIL is on or not.

Keep in mind that a (long) one flash followed by a (short) one flash is
code eleven, O2 sensor. A dead O2 sensor would be a likely cause of
the dark exaust smoke you are seeing. Scope the O2 sensor wire with a
backprobe in the connector, engine hot, just for giggles.

Before replying, I would suggest you try probing the '8' and 'E'
terminals. That's what my info shows for the Excel. All other models
show the '8' and '7' terminals as correct. It won't hurt or take much
time to try. If my info source is wrong, it wouldn't surprise me,
especially for makes such as Hyundai.

BTW, if I were in your situation (without an analog VOM) I would grab a
low current LED testlight first, rather than breaking out the scope
just to watch code flashes.

Toyota MDT in MO

Comboverfish wrote:
> wrote:
> Before replying, I would suggest you try probing the '8' and 'E'
> terminals. That's what my info shows for the Excel. All other models
> show the '8' and '7' terminals as correct. It won't hurt or take much
> time to try. If my info source is wrong, it wouldn't surprise me,
> especially for makes such as Hyundai.
>
> BTW, if I were in your situation (without an analog VOM) I would grab a
> low current LED testlight first, rather than breaking out the scope
> just to watch code flashes.
>
> Toyota MDT in MO

Thanks for the quick reply. I thought I'd reply and let readers and you
know that I plan to test all your suggestions within the coming week.
The vehicle has two O2 sensors and I'll test them both?

RR

wrote:


> The vehicle has two O2 sensors and I'll test them both?
>
> RR

On a '91 Hyundai Excel? That doesn't sound right... What emissions
package does it have (Federal, Canada, California, etc...)?

Toyota MDT in MO

Sorry for the delay in replying.

I was only going from the Haynes manual (which I may have
misunderstood) I had only found one at the time of writing (front of
the engine on the exhaust manifold) and was going to find the other
later. The setup is Canada. Thanks again. Tests this weekend.

I am hesitating to use a led for reading the flashes for two reasons;
- I can measure the signal more precisely with a scope or Labjack D/A
converter sampling every 0.05 s
- I think 10 V would overpower the LEDS I have handy

Would a led make a difference?

I analysed the signal from both pins 7 and E and it appears the same, a
continuous train of square waves with an (-10V?) x 300 mSec average
pulse or depending on how a threshhold is set for distinguishing
between short and long pulses, the codes 72 71 43 41 6 2 <many
pulsess>. Although repeatable, this may be an artifact of the
measurement process. In any case they don't correspond to the codes in
the Haynes manual.

I have disconnected the negative terminal of the battery for a minute
to reset and the results are the same.

Is this an indicator that the ECM is damaged? Or is this what a normal
"no trouble" signal looks like?

O2 Sensor
I will measure the O2 sensor response next week, however, I had not
done this already because disconnecting the sensor has no effect on the
original problem (rough idle and rich condition) and so I judged it not
to have a bearing on the problem? Could I be wrong here?

Thanks for all help.

wrote:
> I am hesitating to use a led for reading the flashes for two reasons;
> - I can measure the signal more precisely with a scope or Labjack D/A
> converter sampling every 0.05 s

I can see and process a light flashing once every couple of seconds
better than following a scrolling screen of square waves.

> - I think 10 V would overpower the LEDS I have handy

There's most likely B+ available at the diagnostic terminal. If you
read 10v with a 10Mohm input impedence scope, then you probably have a
weak battery. The signal *is* probably run through a resistor inside
the ECM so it can be pulled down easily, but that shouldn't affect it's
no-load voltage reading.

> Would a led make a difference?

I don't know enough about how the system works to be sure if the
impedence of a typical automotive LED test light (or high impedence
meter) would be adequate to initiate communication, but it wouldn't
hurt to try, and they're cheap. They're great to have in your tool
box, too. My guess *still* is that there is a constant pulsed
grounding of this B+ output at all times regardless of any load on the
circuit. That's why I suggested the low current test light, and feel
that the scope, while unnecessarily clumsy for this app, should have
worked as well.

> I analysed the signal from both pins 7 and E and it appears the same, a
> continuous train of square waves with an (-10V?) x 300 mSec average
> pulse or depending on how a threshhold is set for distinguishing
> between short and long pulses, the codes 72 71 43 41 6 2 <many
> pulsess>. Although repeatable, this may be an artifact of the
> measurement process. In any case they don't correspond to the codes in
> the Haynes manual.

I really don't know. I would be tempted to borrow an analog VOM at
this point and follow the directions to the letter.

> I have disconnected the negative terminal of the battery for a minute
> to reset and the results are the same.
> Is this an indicator that the ECM is damaged? Or is this what a normal
> "no trouble" signal looks like?

The ECM is likely OK, as they aren't major failure candidates.
Disregard that statement if this is a Mitsubishi ECM as they are
trouble prone. I don't know what ECM is in your 91 Excel.

> O2 Sensor
> I will measure the O2 sensor response next week, however, I had not
> done this already because disconnecting the sensor has no effect on the
> original problem (rough idle and rich condition) and so I judged it not
> to have a bearing on the problem? Could I be wrong here?

A normally operating system will see very low voltage (0.0 to 0.4) from
a lazy sensor and run rich for a while until the ECM determines this as
a problem and sets a code. Then it will run in 'backup' mode where it
doesn't rely on the O2 sensor input. Disconnecting the O2 sensor (0.0
volts constant) will expedite this process.

You've never mentioned anything about the MIL (check engine light)
being on. Does the MIL come on with the key on, engine off? Does it
stay on with engine running or does it go out? If it is working
properly and goes out engine running, then you have no current codes
stored. OTOH, if the light is inop, and you have a slurry of
nonsensical codes stored, I would be looking for a bad EFI ground.

If all of this is basically academic because you just want to learn how
to read codes on a car that has none, I would suggest that you
disconnect the coolant temp sensor and wait til the MIL comes on, then
check for code 21 (I think its 21).

Toyota MDT in MO