Ferrari Mailing List: Re: 308 QV emissions failure and possible misfire

[Jeff Greenfield (coyote]

Alex -  

A couple of things come to mind ...

First, check all the spark plug extenders closely. You could have one
starting to burn through, which could be causing your symptoms. Very common
problem. 

Next, check the carbon brushes inside the center of the distributor caps,
I've seen these break and/or wear down and cause problems. These brushes are
available as a separate part from the (expensive) distributor caps. 

Make sure that the oxygen sensor is working properly too. Back probe at the
single wire with the engine running and warm. You should see the voltage
swinging between 0 and 1 volt, averaging at .5 volts. This is best done with
an analog multi meter, or scope. A DMM may not show the voltage changing. If
the voltage seems stuck (not changing) then it could be the oxygen sensor is
dead. Low voltage below .5 volts would indicate a lean condition, higher
above .5 volts would be rich. 

If all this is ok, and you are 100% sure there are no vacuum leaks (the only
reliable way to tell for sure is with the use of a smoke machine ...
somewhere I have instructions on how to build one, if you or anyone else
wants them, LMK and I'll see if I can dig them up. If you are not familiar
with the use of a smoke machine, go here ... www.redlinedetection.com) the
next thing to check are the fuel pressures. 

CIS is VERY dependent on fuel pressure(s) and failed or gunked up control
pressure regulator with cause havoc with the system. This requires a special
fuel pressure gauge with a three way isolation valve that is connected
between the fuel distributor and control pressure regulator.

If the fuel pressures check out ok, then measure the duty cycle at the
frequency valve. Several QV's have been having problems with the duty cycle
at the frequency valve being incorrect. I have some PDF files that include a
diagnostic flow chart for this convoluted system. LMK if you (or anyone else
wants these files)

If the fuel injectors have not been replaced in the last 10 years, by all
means replace them with the upgraded injectors. CIS injectors are famous for
having poor spray patterns when they age. It may not solve this problem, but
it will definitely help to maintain proper running and will be a step in the
right direction.

Lastly, if anyone has measured the duty cycle at the frequency valve (or
better yet checked the signal pattern with a scope) under various conditions
on either a US QV or 328 I'd be interested in your findings. As my QV is
having a problem with this (duty cycle stuck too high all the time). I've
communicated with several other people who have been experiencing this
problem, and I have not yet found the answer. In my case I'm suspecting the
jetronic ECU, but have not made that leap of faith yet ...


Jeff



-----Original Message-----
From: Alexander Ishii [mailto:alexishii [at] mindspring.com] 
Sent: Thursday, December 23, 2010 1:01 PM
To: Jeff Greenfield
Cc: The FerrariList
Subject: Re: [Ferrari] 308 QV emissions failure and possible misfire


Hi Doug,

> Ahhh Alex - the ever wonderful world of CIS, the constant injection
system.
> VERY temperamental to air leaks.

Yup, I've looked over all the leak points that I can inspect without pulling
the major plumbing bits, and found nothing that looked suspicious (or that
had an effect on the idling when "wiggled").  My plan is to replace all the
hoses when I take the thing apart, just for good measure.

> Especially at the boot area.  The pop you
> hear may be a misfire fired off in the cat (shudder)

I also hope this is not the case.  I don't think it is, as the source of the
"pop" seems to be close to the engine, rather than back where the cat is.

> but most likely it is a
> lean mixture misfire spit back.

This certainly would mesh with the engine-temp issue.

> Do you have a method to check CO?  These systems are set on fuel pressure
> and CO.
> 
> What is failing on your smog report?  HC, CO, NOx (do you test for that?
> Needs a dyne to do it or the test equipment is shoved in your passenger
seat
> and your car is driven about - yes, they had that at one time)
> 
> Get me your readings - its like the engines blood test.

At idle the results are:

HC ppm  270     (pass is 220)
CO%     0.51    (pass is 1.2)
CO2%    14.6
O2%     0.5

At high idle the results are:
HC ppm  100     (pass is 220)
CO%     0.52    (pass is 1.2)
CO2%    14.5
O2%     0.3

Any thoughts would be greatly appreciated.

     Cheers,
     Alex

> ----- Original Message -----
> From: "Alexander Ishii" <alexishii [at] mindspring.com>
> To: "DOUG" <dnt [at] dock.net>
> Cc: "The FerrariList" <ferrari [at] ferrarilist.com>
> Sent: Thursday, December 23, 2010 7:58 AM
> Subject: [Ferrari] 308 QV emissions failure and possible misfire
> 
> 
>> 
>> Hi All,
>> 
>> So my 84 QV has been stubbornly failing emissions (in NJ), and after some
>> repeated assertions by my usual mechanic that "all seems to be well",
I've
>> found myself having to try and figure out the problem myself.
>> 
>> At the moment, the car is not idling right in my mind (despite what my
>> mechanic says).  For one, the idle speeds "hunts" a bit; not enough to be
>> seen on the tach, but enough to be felt as a slight change in the
>> vibration
>> frequency of the engine.  Second, every couple of seconds one gets a
>> just-audible muffled "pop" sound from the engine, accompanied by a slight
>> puff of extra exhaust out of the tail pipes (no sound out of the air
>> intake
>> system).  Also, the car is running sort of on the hot side (coolant temp
>> "idles" at 195).
>> 
>> Plugs and wires were changed not long ago, but other than that, nothing
>> much
>> has required much tinkering in many years.
>> 
>> The "pop" has me thinking than one-or-more of the cylinders is
>> intermittently misfiring and dumping some un-burnt fuel into the exhaust
>> manifold (where it is igniting and "popping").  Given the "every couple
of
>> seconds" nature of the problem, however, I have little doubt that all the
>> sparks will look fine when I try the usual tests.  Anyone have any
>> suggestions for how I might try and zero-in on the faulty system (short
of
>> swapping-out every part one-by-one until the issue goes away)?
>> 
>> Also, it has also occurred to me that the problem might be that the
>> injectors are not atomizing properly, and leading to an complete burn (in
>> turn leading to exhaust manifold ignition of the leftover fuel).  Has
>> anyone
>> seen symptoms like the above be remedied with replacement of the
>> injectors?
>> 
>> All thoughts/opinions/experiences would be appreciatively accepted.
>> 
>>    Cheers,
>>    Alex
>> 
>> 
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