Re: [DML] Question about the Oxygen sensor and Bosch adjustment

["content22207" <brobertson@xxxxxxxxxxxx>]

Some explanation (references turned around for our backwards oriented
engines):

The two shear head screws Martin mentions are balancing screws for the
manual idle speed circuit. They balance air to the driver's (middle
screw) and passenger (rearmost screw) cylinders. Until the foremost
most screw is opened they have no effect.

The slotted head screw he mentions lets air into the manual circuit.
However much air it meters is then routed to either side of the engine
according to settings of the shear head screws.

There's an annotated diagram on Page D:01:13 of the Workshop Manual.

These brass screws are built into every K Jetronic PRV. Many DeLorean
owners view them as "forbidden", but Peugeot, Renault, and European
Volvo make active use of them (only on 1981 & later North American F
series were the balancing screws "shear head" style -- designed to be
intentionally snapped off). In fact for many vehicles they are the
only means of idling the engine. My adjustment method differs somewhat
from Martin's, but I fully support his willingness to use the manual
idle speed circuit. 

Except for their shear heads, balancing screws are identical to the
metering screw -- anyone using this circuit may want to replace them
with metering screws for easier adjustment (or simply get a complete
set of non-shear head screws from a 1980 & earlier junkyard car).

Word of caution: O rings on these screws may be shrunken and dried
out. If you're going to open them, I'd recommend replacing the O rings
to avoid a potential vacuum leak.

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, Martin Gutkowski <martin@xxxx> wrote:
> 
> Get your money back.
> 
> Doing this will put the Lambda system ito "limp" mode and will run
rich. 
> Specifically it affects the gradient of the fuelling curve (it Air to 
> fuel ratio). The mixture adjustment screw adjusts the offset of the 
> curve - the two are not mutually exclusive but must be balanced. Get a 
> new lambda sensor in there.
> 
> If your engine stalls when you rev it then it's likely the idlespeed 
> motor is not centred properly - this is quite common and the way -I- 
> compensate for it is as follows. And yes I know this is not the way the 
> manual tells us to do things but the manual doesn't account for 
> variations in the idlespeed valve.
> 
> With the engine hot and idling, but minimum load on the alternator (no 
> AC, stereo, fans, anything) back the rearmost two brass adjustment 
> screws off by 2 turns each. These are the two that don't have a flat 
> screw head in them. They're 11mm BTW.
> 
> Then unscrew the front one - the one with the screw head. Keep undoing 
> it until the idlespeed starts to increase. When this happens, screw it 
> back in until the idle returns to normal, then another 1/4 of a turn. 
> Your engine will now no longer stall.
> 
> Martin








To address comments privately to the moderating team, please address:
moderators@xxxxxxxxxxx

For more info on the list, tech articles, cars for sale see www.dmcnews.com

To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/dmcnews/

<*> To unsubscribe from this group, send an email to:
    dmcnews-unsubscribe@xxxxxxxxxxxxxxx

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/