BMW: E30 TDC sensor on M20 engine

In article <qhf5b.879$tsnz.net>, Steve Burley
<net.nz> wrote: 

IIRC, it has no function in the running of the engine - it's just used for
diagnostics. With L Jetronic, the dissy times the spark via an impulse
generator within it. It's on later Motronic systems where the spark is
timed from a flywheel position sensor. It's pretty obvious, though, as the
dizzies are different. The TCI type has a trigger wheel and pickup head
which are situated under a dust cover. The Motronic dissy has only a rotor
arm as all it does is switch the spark to the correct cylinder.

With the TCI system fitted to the L-Jetronic, the timing can be adjusted,
with the Motronic it's mapped and can't.

Hope this helps as I've not had one of these for ages.
 

You've checked the timing and dwell?

--
*If you try to fail, and succeed, which have you done?

Dave Plowman co.uk London SW 12
RIP Acorn

Thanks for reply Dave.
I can't check timing properly due to no start, but I have checked TDC on the
front cover alignment and made sure the rotor is lined up with the TDC mark
on the distributor body at the same time, which is all fine.
Will car start if ECU is fryed? I think it only controls power and economy
through timing, as I'm still getting good spark.
If I can't find anything else this morning I'm going to hang my head in
shame and get it towed to the local unauthorised BMW mechanic.

Steve Burley

"Dave Plowman" <co.uk> wrote in message
news:co.uk... 

In article <iVq5b.982$tsnz.net>,
Steve Burley <net.nz> wrote: 

You can still check it while cranking with a timing light.
 

That only shows the timing is approximately correct.
 

If you've got L Jetronic, the ECU plays no part in the ignition timing
whatsoever.
 

--
*The colder the X-ray table, the more of your body is required on it *

Dave Plowman co.uk London SW 12
RIP Acorn

Hey Steve, now you've got three different subject threads going here for the
same problem. It's getting hard to keep up with your latest efforts vs what
you've already reported to have tried.

Now, are you certain what vintage of engine management system you actually
have? Last week you stated 'early Motronic', now you're nominating
L-Jetronic. If you have a distributor cap with spring cap retaining clips
then we have to assume that L-Jetronic is the answer. My experience is all
Motronic related, so I'm a bit out of my depth with the L-Jetronic stuff.

Also, that your Haynes manual is number 1948 - RHD 3- and 5-series, and that
you have worn out pages 4.21 thru 6.8 over the past week Problem with that
manual is that it covers (jumps back and forth amongst) so many models that
it sometimes leads to utter confusion. But, like me, you need it for your
RHD E34, too. Our Yank newsgroup readers in the USA (yeah, and you too, Max
in Canada) won't have seen that manual, nor some of the engine variants
included in it like the 2.3L M20 that you have - so they won't have a clue,
unlike Dave and others in the UK.

Maybe by this time you have confirmed your ignition timing while cranking
the engine on the battery, as Dave suggests. And it's running again. If
not...

What have you eliminated, so far? Let's see:

Not a stripped valve timing belt - you have tested for normal cranking
compression with a gauge (not just by holding the tip of your finger in the
sparkplug hole), and have watched the valves going up and down by peering
through the oil filler while cranking the engine. (been there done that -
stripped mine on my E34 M20 in March this year - cost me 12 new valves, just
to start the list)

Not a kaput fuel pump - you smell fuel in the exhaust pipe after vainly
cranking, the ends of the spark plugs are wet with fuel (not, coincidently,
water or oil from a blown headgasket) after vainly cranking, maybe hired a
high-pressure fuel gauge to test pressure at injectors. (been there done
that, cobbled together a fuel pressure tester from the water pressure gauge
on the swimming pool filter to be sure I had fuel pressure, last month - see
next item)

Not a dead ECU nor associated sensors - you are getting full spark to all
plugs, indicating that the ECU hasn't shut down the ignition system due to
wrong input from sensors (an assumption on my part here, Motronic system
shuts off ignition if it can't sense crankshaft rotation from pulse
generator (crankshaft position sensor)) (been there done that - half-severed
cable to pulse sensor lead to intermittent engine shutdown and miraculous
resurrection ten-minutes later, about every twenty minutes in peak Sydney
traffic)

Where does that leave you? If you have compression, fuel, spark - all in
adequate measure, then IMHO Dave is leading in the right direction in
keeping you focused on ignition timing. Have you had the distributor off the
engine during this time? Might you have put it back on 180 degrees out of
synch? I'm grasping here, don't know if you can physically do this with a
BMW M20 engine, you can on old VWs and MGBs (again, been there done
that...).

The abovementioned Haynes manual (ref TCI system para 5-5, page 5.3)
mentions that this distributor has a mechanical (centrifugal) advance unit,
as well as a vacuum advance unit. Again grasping here, is it possible that
the mechanical advance is stuck fully advanced? Maybe with a piece of the
stuff that was gouged out of the distributor cap when this saga began. This
could conceivably leave the total initial timing advanced too far to start
the engine. Have you tried setting the static timing of the distributor with
some marginal retard (somewhat off the TDC mark, on the early side), to rule
that out? (been there done that, too, paid 'squat' for the MGB because it
wouldn't accelerate. Drove it slowly home, 20-minutes of work on the
distributor with WD-40 to free the rusted advance mechanism and it ran like
a champ - once I got the distributor back in the right way around)

Damn, I'd hate to hear that you had to tow it to a garage after all of this
effort.

Just some Trans-Tasman lateral thinking, from an DIY-er ex-pat Yank living
in Sydney. Hope it might help.

Bill K
E34 M20B25 525i
E36 M43B16 Compact 316i



"Dave Plowman" <co.uk> wrote in message
news:co.uk... 
mechanic. 

Steve, if you are using the Haynes 1948 manual for RHD 3- and 5-Series cars:

I suggested last week in the "E30 323i electrical problems" thread, when you
thought you had an early Motronic system, that a stuck idle control valve
can manifest itself in the problems you are experiencing. Now it appears
that you have an L-Jetronic system. The Haynes manual indicates that the
L-Jetronic system also has an idle control valve, but calls it the idle air
stabiliser valve - see Haynes Manual 1948 para 4-21, page 4.19.

Have you checked this out, yet? Someone else may have some experience with
this little bugger in the L-Jetronic context, but I can state categorically
in a Motronic M20 context that even if everything else is checking out on
spec, you can crank until the cows/sheep come home and it won't start if the
ICV doesn't want it to.

Bill K 
same 

In article <3f56c131$0$6527$optusnet.com.au>,
Bill K in Sydney <com.au> wrote: 

Other thing is that with the L Jetronic, the dizzy controls the timing and
is driven off the cam. If the dizzy jammed as said, it's possible for a
loose cam belt to jump a notch putting both valve and ignition timing out.

Might help if we knew the exact age and model of the car to determine
which system it uses as they're rather different...

--
*OK, who stopped payment on my reality check?

Dave Plowman co.uk London SW 12
RIP Acorn

Cheers for replies guys.
I had wrongly assumed car was Motronic because that's what one of my
American manuals said it was, but closer inspection revealed it to be
L-Jetronic.
The body is 1983 E30, head is original 320i, block is an unknown year 323i
with Isuzu pistons (same diameter as 323 but different crown shape). ECU is
original from 320i. Getrag 5 spd is hooked up to LSD back end off another
E30.
Compression was checked on gauge with all plugs removed - 150 PSI on all
cyclinders except #6, which was 140 - I'll worry about that later.
I have found 2 of the plug leads are a bit dodgy when twisted so have
ordered another set. Doubt very much this is the problem though as the car
has run rough for about half a minute when started from cold for a while
now.
Will check the Idle control valve - don't have the Haynes manual mentioned
but will look out for it. Probably could have saved alot of time if I
hadn't spent hours looking for sensors and such which aren't even on the
car...

Steve


"Dave Plowman" <co.uk> wrote in message
news:co.uk... 

here's a link to a pdf version of the Haynes manual, your informed
commentary lead me to believe that you were already working from it...

http://dl.bmworg.ru/book/haynes

Bill