Suspecting problems with Marelli Plex - was with Crane 700

[alfacybersite <acs@domain.elided>]

Dean, everyone, want to apologize. I rarely send complete copies of
posts, let alone the post + answer, but: While no where near as serious
(hopefully) as Stefano's major cutting out on his GTV, I too am again
experiencing some periodic cutting out then fixing itself on my Alfetta
GT (with Marelli Plex).

Let's get the admissions out of the way first: Fairly recently had
similar symptoms but noticed (fortunately) on turning the ignition
switch, there was not that busy little bee of a sound coming from
underneath the car (electric fuel pump). So cleaned up all contacts and
car has been 'pretty' good since until just the past few days. I say
pretty good in that the car really needs to idle at least 1,400 minimum.
If even slightly below, engine gets Very lumpy, Very quickly. Now I do
have 12.0 cams, but car has always preferred a higher, rather than lower
idle. But lately it has become more demanding and literally starts to
shake if the revs drop only a few hundred rpm. Suspect timing and did
recently slightly retard which ever so slightly helped.

Rather than fighting the fuel and electronic ignition systems all at one
time, let's 'all' do the ignition / timing first. By coincidence I'd
just purchased a set of Bosch 4477's when on the way home it cut out,
pulled over to the side but illegally ran along the pull off area, she
cleared herself and I made if home fine. Changed plugs even though the
NGK BP 7ES's were very new and looked pretty good on all four. Pulled
the distributor cap and all looked fine. The gap was .018" which I
believe is correct for Marelli Plex's.

Now, short of gapping it correctly, how does one know they've properly
accomplished..."The trigger must be mounted very precisely, so that it
fires when the rotor is pointing exactly at one of the plug wire
contacts inside the cap."

All I can assume is (mixing apples and oranges here - or if you prefer,
killing two birds with one stone) should one do a slight variation on
your 'spark checking system' and position the crank on exactly the
correct static timing mark, then with the ignition, slowly moving the
distributor back and forth until (hopefully) one gets a big fat spark
when grounding the coil wire at the same time. If all goes well, one has
determined not only the fatness (quite technical) of the spark And have
the static timing properly set (after tightening down the 10 mm nut).

With me so far? Now if the spark looks either weak, or merely just
fairly good - then what does one do? Yes, have replaced both the
magnetic pickup and control module fairly recently along with new
ignition wires.

Biba (whose car always cuts out when she knows she's in for a longish
trip even though she should be on her best behavior so I won't worry).
Irwindale, CA USA

I agree, the ATS wheels do look great on Stefano's Alfetta GT.

**********

Hi Stefano:

First, the ATS wheels look great, and so does the rest of the car.

Second, I've had a Crane XR-3000 and LX-91 coil (very similar to your
setup) on my '74 Spider for a bit more than a year of driving, maybe 5K
miles.  I've never seen problems like you describe, and I couldn't be
happier with the improvements over the stock system.  I did however
install
the optical trigger in a Bosch 041 disty, and that was one major pain in

the ass, due to the tight quarters inside the Bosch.  Before the Bosch,
I
had the system in a Marelli S103BA, again with no trouble, and the
install
was much easier.

Checking the spark in the system is quite easy.  Position the crank on
the
engine so it's just before where the timing is set (i.e. 10 degrees
BTDC,
if your timing is set to 5 degrees BTDC).  Pull the coil wire out of the

distributor and place the end near (1/4 inch) a good ground, like the
cam
cover.  With the ignition on, grab the rotor and turn it clockwise and
watch for the spark.  The distributor shaft isn't really turning, just
the
top part with the advance mechanism.  With that coil, the spark should
be
pretty strong.

Your problem may be with what Crane calls "phasing" of the trigger
assembly.  The trigger must be mounted very precisely, so that it fires
when the rotor is pointing exactly at one of the plug wire contacts
inside
the cap.  If it's wrong, the spark will have to jump too great a
distance
inside the cap to the appropriate plug wire contact (which will be ahead

of, or behind, the rotor as it passes by), and the spark at the plugs
will
be degraded.  Same symptoms occur if the shutter wheel is positioned
wrong.  The blackening you described inside the cap may be an important
clue.  Is it possible that you have a mismatched cap and rotor?

I can't explain the problem that initially occurred after your long
drive,
but at this point your plugs may be fouled and might require cleaning or

replacement.  Perhaps something moved out of alignment, or consider that

the problem is not ignition related.  Crane has a hotline to call for
tech
support, and after you check the stuff I mentioned, perhaps a call would
do
some good.    I'm very familiar with the Crane stuff, so let me know if
there's anything else I might do to help.

Regards,

Dean

At 08:52 PM 8/12/2002, you wrote:
>Date: Mon, 12 Aug 2002 15:30:38 -0700
>From: "Stefano Iachella"<iachella@domain.elided>
>Subject: Suspecting problems with Crane 700
>
>Hey cats,
>
>Can anyone with experience with the Crane XR700
>system read this and comment please?
>
>I have a recent rebuild (under 350 miles so far)
>on my 74 GTV, and had my builder put the XR700
>kit on my Bosch distributor and a PS91 coil. I'm
>breaking it in, and it pulls great. I go on a
>100 mile trip this weekend, and on the way back
>I get some hesistating. This is about 300 miles
>into the rebuild. It feels a bit like the old
>low fuel pressure sputter. Just a slight
>hesistation, but I made it back home.
>
>I had seen this with low tank and bad filters, so
>I go to top off the tank, and it is sputtering
>bad at this point. No change. I am thinking maybe
>the little wheel or the optical mechanism is
>loose or dirty, so I pull the distributor cap off.
>First off, the 4 contacts inside are black - this
>is a new cap and rotor. I scrape the contacts and
>rotor tip off. The optical mechanism seems tight.
>The wheel seems to rotate a mm or two each way,
>but otherwise it seems secure.
>
>I start up, and drive around. Still sputtering,
>like running on 2 or 3 cylinders now. I shut down
>and let sit for an hour. I start up and it runs
>great. I drive around for 1/2 hour with no ill
>effects; it pulls like crazy again.
>
>This morning it was a very hard start and when it
>finally turned over, it felt like only 1 cylinder.
>I couldn't drive it. I shut it off and tried a
>few more times and couldn't get it to catch.
>
>Any ideas? Does it sound like something with the
>XR700 setup?
>
>Thanks,
>Stefano
>Oakland, CA
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