knock knock goes the jeep....

[Carl Summers]

Hi John,
    I have had similar problems in a supercharged app as yours.  It always
seemed to happen at around 100-110 kpa....I never had the opportunity to
scope it out and see what was happening but I had noticed that it never
happened when the boost retard was at 0....something weird seems to happen
to the msd unit as it moves from no boost to low boost levels.  After
removing the msd unit I had no more problems, I only had 8 lbs of boost so I
was able to get by adjusting the 100 kpa spark settings.  Hth's point in the
right direction.
-Carl Summers

-----Original Message-----
From: owner-gmecm at esl.eng.ohio-state.edu
[mailto:owner-gmecm at esl.eng.ohio-state.edu]On Behalf Of digi
Sent: Wednesday, December 29, 1999 3:13 PM
To: gmecm at efi332.eng.ohio-state.edu
Subject: Re: knock knock goes the jeep....


Sounds similar to a problem I had, is it running a bit lean?

My fuel pump was dying, it was running a bit lean, and it would heat up
the plugs and ignite the fuel, tried the highest octane/zero advance/etc.

It may be worth a shot to check the fuel pressure, can't hurt and isnt a
hard thing to do.
- Brian

On Wed, 29 Dec 1999, John S. Gwynne wrote:

>
> 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
>