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RE: '88 5000CD TQW engine knocking


Ya gotta be careful comparing two gauges.  

The digital gauge reads *absolute* pressure where total vacuum is 0.0 bar
and 1.0 (or so) with the engine turned off.  

Most mechanical gauges I've seen are *relative* gauges.  At total vacuum
they read negative 1 bar or -30 inches or...  With the engine turned off it
should read zero.

0 on the digital gauge corresponds to - 1 bar on the mechanical gauge.

Now another question:  Does Andrew have a digital gauge or a mechanical
gauge?  Andrew?

At 05:10 PM 2/12/98 -0800, you wrote:
>I think that the original poster is getting some excellent feedback on
>this problem ... but IMHO one thing is being left out.  That knocking is
>occurring because your ECU is getting a faulty input.  Knocking is not
>often a good thing for an engine; if you must drive the car, try to keep
>your foot out of it as much as possible.  Yes, it is true that the ECU
>should be getting the feedback that the engine is knocking, and back off
>the timing and then boost, but since you are noticing the knock it must
>not be able to turn things down enough (perhaps Orin can comment on what
>the code would do in this situation).  
>If you want to try to track this problem down yourself, I'd recommend
>that you "T" in a separate boost gauge as close as possible to the ECU
>(which is mounted behind the kick panel on the right side of the
>passenger footwell, in front of the door.  You should be able to remove
>the screw that holds the cover down and pull back the front door seal a
>bit to allow the cover to come off.  The ECU is in a little "shower cap"
>... it might be able to get at the boost line without pulling the ECU,
>or you might have to remove a couple screws to get the ECU out (hazy
>memory here ...).  You'll need to watch the other gauge when the display
>goes to "0" ... if both gauges read zero you've got a vacuum leak in the
>line ... if the analog gauge says you've still got boost when the
>display reads "0" you're going to need to repair or replace your ECU ...
>Steve Buchholz
>San Jose, CA (USA)
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