knock knock goes the jeep....

[John S. Gwynne]

Hi All,

Here's a problem that I'm working on....

engine: '88 TPI 5.0L with Vortech SC (FMU and MSD boost retard) running
'7730 with '92 axxc bin (nearly identical to anth etc..). This is in my
Jeep with an NV4500 trans (5-speed manual 0.72 or-so over-drive, 4.10
gears, 33" tires).

problem: 

I'm was cruising on the highway in 5th and started up a moderate grade
while following someone. As the person moves over, I
down shift into 4th (about 6845 sec on the tps plot of
<ftp://jsgpc.mrcday.com/pub/knock/tps.jpg>), delay a few seconds till
the road was clear and gave it some gas... heard it knock... I lifted then
tried again around 6850 seconds... still no go. At about 6855 seconds, 
I shifted back into 5th. From about 6855 seconds and on, it was in 5th and 
now knocking. It didn't fully recover until about 6960 seconds.

The spark advance is plotted in
<ftp://jsgpc.mrcday.com/pub/knock/sprkAdv.jpg>, and the rpm in
<ftp://jsgpc.mrcday.com/pub/knock/rpm.jpg>. As I went back into 5th at
6855 seconds, the knock sensor has pulled out almost 20 deg of timing
(the timing goes into retard and is also shown as such in MW1)
BUT... it's still knocking. no real boost at this rpm and something
that it would not otherwise do.

I believe this has only happened three or four times now. Each on long
trips and shifting down to fourth to pass.  Other than that, the car
has been running fine. Accelerating from a stop or slower speed has
not had any such problem.

Other plots:
<ftp://jsgpc.mrcday.com/pub/knock/afr.jpg>
<ftp://jsgpc.mrcday.com/pub/knock/inj.jpg>
<ftp://jsgpc.mrcday.com/pub/knock/knock.jpg>
<ftp://jsgpc.mrcday.com/pub/knock/map.jpg>

I don't see how it could knock with so little timing advance (more
like none) at times past 6855 seconds and shifted back into fifth.  Is
my interpretation of the data steam correct? bytes 39:40 of the ALDL
stream (0x3128 and 0x3129 in the 7730 memory map) seem to be spark
advance without ref and knock correction. bytes 41:42 (0x30bd and
0x30be) are relative to the DRP and include knock correction.

Any thoughts on what it is doing and how to fix it?

john gwynne