ping

[Jeff M]

I did not stick on my sillyscope because I wanted to get this guy back out
on the road running right but it would of been interesting to see what would
of showed up.  Jeff Middaugh


> I'm always amazed that automotive ECM can work
> reliably with such high impedance sensors. The
> underhood environment is very hostile and noisy. I
> have a hardware and software background, with some
> aeronautical and communications thrown in. Noise
> management was always a problem.
> I worked on a computer once that was located in the
> offices of a TV station. They were getting
> intermittent memory parity errors. I put a scope on
> the +5V buss, and was seeing 3V p-p of RF modulation!
> We added a fistful of bypass capacitors and shielded
> the case to solve the problem.
>
> Maybe we should be using BNC connectors and such.
>
> --- Jeff M <tystorm at email.msn.com> wrote:
> > I had an interesting time working on a friends Turbo
> > Grand Prix.  It came to
> > me with a rough idle so, slapped on the Diacom and
> > found a consistent line
> > of 7 degrees knock retard all the time, cool, a new
> > one on me (just wait).
> > No engine noises and all things are fairly new on
> > this car (I put in a while
> > ago; new injectors, some sensors and such), so I
> > swap out the ECM with a
> > known good one (that is easier than swapping the
> > knock sensor) and still 7
> > degrees all the time.  Swap out the knock sensor and
> > still.  Pull out the
> > (single) knock wire from both connector ends and ohm
> > it out, good wire and
> > not going to ground, even when shaking the engine by
> > hand.  Check volts out
> > of ECM, fine here.  Pull out wire and visually
> > inspect its entire length,
> > good again, check wire loom and no pinch or running
> > near anything that could
> > cause a false ?  Tired of this stuff I just grab
> > some twisted pair/shielded
> > cable and run a new wire in a new wire loom and in a
> > different location and
> > presto, 7 degree knock gone and been so for 8 months
> > (also tested it still
> > work by the usual thump test, and some higher boost,
> > as we tuned up his chip
> > for 100 octane).  I also took the braided shield of
> > this wire and on one end
> > (did not want to create a ground loop) secured it to
> > a good ground, with
> > other ground wires.
> >
> > (always up to a new challenge)
> > Jeff Middaugh
> > tystorm at email.msn.com
> >
> >
> > > You need to watch the timing with some type of
> > scan tool.  I would do this
> > > before spending money on anything else.
> > > Mark  By the way, I know why you would twist the
> > wires.  I have just never
> > > heard of a problem with rfi on the knock sensor
> > circuit.  The ecm is set
> > up
> > > to look for specific frequency so I doubt rfi
> > would trigger knock retard.
> > > Mark
> > > -----Original Message-----
> > > From: David Mulvey <kd6bzn at QNET.COM>
> > > To: gmecm at efi332.eng.ohio-state.edu
> > <gmecm at efi332.eng.ohio-state.edu>
> > > Date: Monday, August 23, 1999 11:36 PM
> > > Subject: Re: ping
> > >
> > >
> > >
> > >
> > > > It sounds to me like the knock sensor is NOT
> > working and/or egr problem.
> > > The
> > > > best way to check the knock sensor is to take a
> > plunger handle, and drop
> > > it
> > > > with it's own weight only onto the block near
> > the knock sensor.  Watch
> > the
> > > > timing, (Scan tool) and make sure the ecm is
> > pulling some timing out.  I
> > > > have never heard of twisting the wires.  I have
> > ALL the tech bulletins
> > on
> > > > the L98.  I have tuned the knock sensor a bit by
> > using a bit of teflon
> > > tape
> > >
> > > The twisting of the wires is just a simple way of
> > keeping some low
> > frequency
> > > RF from resonating on a stran of wire.  As long as
> > the
> > > wire twists the RF has only very small untwisted
> > sections to resonate.
> > >
> > > I checked the EGR valve and the EGR solenoid and
> > the voltage to the
> > > solenoid.  All Ok, a good vaccuum to the egr valve
> > caused the
> > > motor to idle down..  I cleaned out the EGR
> > solenoid gave it a test on a
> > 12
> > > volt power supply. So EGR I think it fine.
> > >
> > > I do have one old injector on the side of the
> > engine that doesn't have the
> > > O2 sensor. Could be a suspect.  I have 3 old
> > injectors on
> > > the O2 sensor side, and do not get any mixture
> > errors.
> > >
> > > I was wondering about the Knock sensor too.  I do
> > get error 43 which I
> > think
> > > is the code showing that the knock count exceeded
> > it's
> > > limits. An audible ping/knock is also heard at
> > this time.  I guess I was
> > > wondering if the knock sensor maybe was only
> > working a little
> > > not detecting the all of the knocks then causing
> > the computer not to
> > adjust
> > > properly then setting off the MAF voltage too high
> > and/or
> > > too low..  Kinda getting complicated at this
> > point.
> > >
> > > I still need to check the ground to the MAF
> > sensor.
> > > I still need to give the knock sensor wires a
> > couple of twists.
> > > I want to replace the 4 old injectors I have,
> > (short on funds at the
> > moment)
> > > AutoZone has injectors for $35 each.
> > > Am I buying crap or are these things workable?
> > > AutoZone also has MAF sensors for $139,
> > > $80 core charge. (got one the other day, same
> > 'ping')
> > > practically everything else is new except for the
> > ESC module.
> > > I figured the ESC is probably working since
> > > I do have a car that runs.. Good assumtion?
> > > I need to see if the knock sensor is working using
> > the plunger stick test.
> > > I haven't gotten into changing ECM values yet.
> > Will not hesitate if
> > nothing
> > > else seems to work.
> > > "PE vs. RPM table"  =- What's 'PE'?
> > >
> > > For the Knock sensor test would I notice a timing
> > change using the plunger
> > > handle and a timing light? I got one of those..
> > >
> > >
> > > end
> > > ----
> > > David Mulvey KD6BZN
> > > Lancaster, CA
> > > (661) 723-0352
> > >
> > >
> >
> >
> >
> >
> >
> >
>
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