ping

[Jeff M]

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
>
>