91 Camry: Plugs wires firing inconsistently... How do I diagnose?

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Old 23 Oct 2003, 05:26 pm   #1 (permalink)
Al Kondo
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Default 91 Camry: Plugs wires firing inconsistently... How do I diagnose?

I have a 91 Camry LE with 180K miles. It recently failed the HC
portion of the Texas emissions test. As this is often caused by
misfiring, I connected my inductive timing light to each of the plug
wires. I found that there was a patterned miss in each of the wires.
This lead me to believe that there is a problem with the distributor.
My question is "What should I do next to find the problem?". BTW, I
changed plugs and wires last year when I passed the emissions test. I
would appreciate any suggestions.

Thanks, Al Kondo
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Old 24 Oct 2003, 12:21 am   #2 (permalink)
Philip
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Default Re: 91 Camry: Plugs wires firing inconsistently... How do I diagnose?

In news:3f985581.34310369@news.hal-pc.org,
Al Kondo <alkon@hal-pc.org> being of bellicose mind posted:
> I have a 91 Camry LE with 180K miles. It recently failed the HC
> portion of the Texas emissions test. As this is often caused by
> misfiring, I connected my inductive timing light to each of the
> plug wires. I found that there was a patterned miss in each of
> the wires. This lead me to believe that there is a problem with
> the distributor. My question is "What should I do next to find the
> problem?". BTW, I changed plugs and wires last year when I
> passed the emissions test. I would appreciate any suggestions.
>
> Thanks, Al Kondo


An inductive timing light is NOT a reliable indicator for locating a
misfire. Many inductive lights don't work reliably with high
resistance high tension wires and can be influenced by which way the
inductive clip is placed over the high tension wire (many have a
direction arrow on the clip).

Elevated HC that is due to misfire and will also have lower than
normal CO levels because .... CO is a byproduct of combustion. No
combustion, no CO. With normal CO and elevated HC, look for
excessive base ignition timing. BTW, you did not mention what the CO
reading was. That would be helpful. A very low CO with elevated HC
suggests excessively lean idle (vacuum leaks).

--

~~Philip "Never let school interfere
with your education - Mark Twain"




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Old 24 Oct 2003, 08:28 am   #3 (permalink)
Al Kondo
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Default Re: 91 Camry: Plugs wires firing inconsistently... How do I diagnose?

It was mentioned that my problem could be excessive base ignition
timing. I am not sure what is meant by this. Does this mean that
the timing is too far advanced? Please clarify.

Also, here are my HC and CO readings from my emissions test:
(the standard or passing reading is in parentheses)

Hi Speed Low Speed

HC (ppm) 207 (123) 415 (128)

CO (%) .41 (.69) .67 (.71)

Would these readings indicate that the fuel is inadequately combusted
or that there is a timing problem. By the way, my NOx were well
within acceptable range. I would appreciate thought about this.

Thanks, Al Kondo

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Old 24 Oct 2003, 08:47 am   #4 (permalink)
Philip
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Default Re: 91 Camry: Plugs wires firing inconsistently... How do I diagnose?

In news:3f992773.2138086@news.hal-pc.org,
Al Kondo <alkon@hal-pc.org> being of bellicose mind posted:
> It was mentioned that my problem could be excessive base ignition
> timing. I am not sure what is meant by this. Does this mean
> that the timing is too far advanced? Please clarify.
>
> Also, here are my HC and CO readings from my emissions test:
> (the standard or passing reading is in parentheses)
>
> Hi Speed Low Speed
>
> HC (ppm) 207 (123) 415 (128)
>
> CO (%) .41 (.69) .67 (.71)
>
> Would these readings indicate that the fuel is inadequately
> combusted or that there is a timing problem. By the way, my NOx
> were well within acceptable range. I would appreciate thought
> about this.
>
> Thanks, Al Kondo


"Excessive base ignition timing" simply means the ignition timing
when set at idle is possibly too far advanced. Put the jumper wire in
place as mentioned on the EPA sticker under the hood and recheck
"base timing."

If your NOx levels were well within range, then we will assume EGR
system is functioning correctly although.... too much base ignition
timing will raise NOx readings depending on engine load. Also, if
there was a CO2 (carbon dioxide) reading on your smog ticket, the
higher the CO2, the better .... indicating greater exhaust catalyst
activity.

The readings are the result of exhaust taken AFTER the catalyst
instead of ahead of the catalyst so diagnosis is a bit more
difficult. ASSUMING you find the ignition timing to be correct, the
next items to check are for really filthy (gasoline diluted) engine
oil, a failed O2 sensor, and finally a failing exhaust catalyst. O2
sensor life spans vary by a wide range in real life. Some fail by
50k miles while others may last 250k miles. It's all in the gasoline
quality and driving habits which vary a lot by region. Same to be
said for the exhaust catalyst.
--

~~Philip "Never let school interfere
with your education - Mark Twain"




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