Re: Quad-4 (1228707 ECM) Rough Idle Problem

[Will Remaklus <remaklus@attglobal.net>]

david garnier wrote:

> I haven't been paying all the close to this thread, I
> appologize if I am off base...
>
> I have seen rough, unsteady or idle that never seems
> to smoothly come down, until maybe the engine starts
> to warm up.  Dumb question, when was the last time
> you removed your IAC and cleaned the pintle and
> mating seat with gas or cab cleaner?  I am amazed at
> the difference cleaing the pintle and seat will do on
> idling.

I pulled the throttle body about a month ago and cleaned
it and the IAC pintle.  There was very little build up
to remove and hence I did not get any improvement.

Here are some new findings on the problem:

In pursuit of trying to understand my rough idling problem I
decided that the 2X reference pulses from the ignition module
did not provide enough resolution.  Therefore, several weeks ago
I fabricated a 24 slot crank position sensor using an IR LED and
photodetector.  The .pdf file:

 ftp://ftp.diy-efi.org/incoming/Quad-4%20Idle%20Miss.pdf

shows the instantaneous RPM, that is RPM calculated based on the
time between two adjacent slots in the wheel, versus time.  I also
included the slot number off the wheel to aid in identifying the
relative position of the crank.

The first page is the engine at idle.  Notice that it appears
that all four cylinders fire, followed by two revolutions of
little if any power.  In contrast, the second plot, at 1900 RPM,
shows a much better situation: an increase in crank speed as each
cylinder fires.  At first I thought that the engine control
computer was causing this, but now I am pretty sure that is
not the case.

While surfing the net I located the following:

  Very high overlap cams will exhibit an "eight stroking"
  phenomena at idle where each cylinder will completely misfire
  on every other compression stroke...  This phenonmenon is
  responsible for the loping idle of the older hot-rod V-8s.
  Unfortunately, with every other exhaust stroke pumping out
  a cylinder full of unburned gas, hydrocarbon emissions soar.
  The over-rich exhaust will not contain enough oxygen for the
  catalytic converter to complete its breakdown of unburned
  hydrocarbons, so even with the cat in place it will become
  ineffective.

The above explanation seem to perfectly describe the problem
that I am having.  The exhaust is very rich, yet the catalytic
converter is not all that hot (or glowing red, like it did
years ago when I had an ignition coil go bad!).

Therefore, it appears that the problem is likely caused by
something in the top end.  When I checked the timing chain
several weeks ago I verified that at TDC the camshaft alignment
dowel pins went in easily.  As such, the only things left to
check are the lifters and the cams.

Any ideas?

-Will

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