[xj-s] Marelli question

I am getting help from Mike in Ohio in testing my 1989
Marelli ECU on his known working car. What I don’t know, is
what to do next, either way. I have isolated out everything
I know of on the Marelli wiring harness, to insure all
wiring is acting as it should. What happens with this car,
is that it turns over for about 3 seconds, firing BOTH coil
wires to ground, but then the B bank drops out. Every time.
Switch amps, same problem. Switch coils, ditto. So, HAS to
be in the ECU, right? However, one thing I found after
several hours of testing with a digital voltmeter, is that I
am getting 3.4 volts on the tach wire, that is on the A
coil! Anybody have a good grasp on Marelli? It seems pretty
straightforward, but I bought this car about two weeks ago,
and would love to get it going. Very low mileage car. And it
has been at the hands of what appear to be hacks at best. I
am just perplexed. The Marelli ECU has been changed as well,
and makes me wonder if the tach is backfeeding voltage for
some reason, and effecting the Marelli ECU.–
Gene Holtzclaw
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

// please trim quoted text to context only

In reply to a message from Gene Holtzclaw sent Tue 27 Aug 2013:

Gene,
Have you replaced the flywheel sensor? You may be able to
clean it enough to get the car to run. The end of the sensor
can get crud and metal dust on it that distorts the signal to
the ECU. Clean the end of it off and use some electrical
contact cleaner on the connector.–
The original message included these comments:

I am getting help from Mike in Ohio in testing my 1989
Marelli ECU on his known working car. What I don’t know, is
what to do next, either way. I have isolated out everything
I know of on the Marelli wiring harness, to insure all
wiring is acting as it should. What happens with this car,
is that it turns over for about 3 seconds, firing BOTH coil
wires to ground, but then the B bank drops out. Every time.
Switch amps, same problem. Switch coils, ditto. So, HAS to
be in the ECU, right? However, one thing I found after
several hours of testing with a digital voltmeter, is that I
am getting 3.4 volts on the tach wire, that is on the A


Jeff Schultz -1992 XJS 5.3L V12 -1995 X300 4.0L
Rutland VT, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from JagsinVT sent Wed 28 Aug 2013:

Thanks Jeff, I’ll take a look at
it. From what I’ve read, the
Marelli won’t fire at all with
either the crank, or flywheel
sensor not working–
Gene Holtzclaw
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

Gene,

I believe you are correct that the crankshaft and flywheel sensors are
not going to cause a problem that just affects one bank. I suspect you
have an ECU or wiring problem.

Your plan to have your ECU tested in a known good Marelli car is a good
one. The only other thing I can think of is an intermittent wiring
problem. You email said that you have checked all the wiring, however it
is always possible that you have an intermittent fault.

Have you cleaned all the ground attachment points?

I don’t think the tach could be causing the problem since it gets it’s
signal from the “A” coil (the lower one for the right bank) and your problem
is on the “B” side (left bank).

Is there any difference in how the engine starts runs with the Strategy
Selection Link inserted or removed. There really shouldn’t be, but at this
point I would try anything I could to see if it made a difference.

Regards,

Paul M. Novak

1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA
P.M.Novak7@gmail.com-----Original Message-----
From: owner-xj-s@jag-lovers.org [mailto:owner-xj-s@jag-lovers.org] On Behalf
Of Gene Holtzclaw
Sent: Wednesday, August 28, 2013 9:01 AM
To: xj-s@jag-lovers.org
Subject: Re: [xj-s] Marelli question

In reply to a message from JagsinVT sent Wed 28 Aug 2013:

Thanks Jeff, I’ll take a look at
it. From what I’ve read, the
Marelli won’t fire at all with
either the crank, or flywheel
sensor not working

Gene Holtzclaw

// please trim quoted text to context only

and makes me wonder if the tach is backfeeding voltage for
some reason, and effecting the Marelli ECU.

Just disconnect the tach, see what happens.

– Kirbert

// please trim quoted text to context onlyOn 27 Aug 2013 at 19:07, Gene Holtzclaw wrote:

In reply to a message from Kirbert sent Wed 28 Aug 2013:

This probably will not help you, and I believe some already
mentioned it in your previous post, but the Marelli V12 can
start and idle on one bank.

I have personally confirmed that I can disconnect
amp/coil/injectors for either bank A or B and can start the
engine without any problems. There is no power and you
cannot rev it, but it does start.

You mention no start, based on my experience, this cannot be
your problem.

Can you start it with a fluid sprayed into the intakes? Do
you have injector clicks? Fuel pressure OK?

Steve–
The original message included these comments:

and makes me wonder if the tach is backfeeding voltage for
some reason, and effecting the Marelli ECU.
Just disconnect the tach, see what happens.


'95 XJS V12 6.0L, saphire/tan
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from sbobev sent Wed 28 Aug 2013:

Alright, here’s a question for the Marelli guys. Is it normal to
have one bank cut out like that if the engine doesn’t start?

The reason I ask, I know the crank only has 3 fingers on the
harmonic balancer. That would only cover 6 cylinders when the car
is running. So, it would seem the ECU has to take the timing
trigger for the one bank and synthesize the ignition pulses for the
second bank. If this is the case, the logic may deduce it needs
more power to the primary bank after 2 seconds to get things fired
in case the battery is weak…and then restart the second bank.

I only conjecture here, because I still think you have a fuel issue
going on. You said it starts on ether, but won’t run…that usre
sounds like it is not getting fuel to me.–
John. '95 XJS 6.0L convertible. Southlake, TX
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from CJ95 sent Wed 28 Aug 2013:

John:
I don’t know, I can only speculate.
In the JDHT ROM they mention no difference in the A vs B
bank power module outputs. This is what the manual says:

EM11-9 Output B bank power module key on: 0.2V 1000 rpm:
2.4V 2000 rpm: 2.1V
EM11-10 Output B bank power module 20 mV @ 1000 rpm,
increases with rpm

EM11-14 Output A bank power module key on: 0.2V 1000 rpm:
2.4V 2000 rpm: 2.1V
EM11-15 Output A bank power module 20 mV @ 1000 rpm,
increases with rpm

This is for the 6.0L Marelli computer. Based on the above,
cutting one bank until the other picks up does not seem
reasonable

Steve–
The original message included these comments:

Alright, here’s a question for the Marelli guys. Is it normal to
have one bank cut out like that if the engine doesn’t start?
The reason I ask, I know the crank only has 3 fingers on the
harmonic balancer. That would only cover 6 cylinders when the car
is running. So, it would seem the ECU has to take the timing
trigger for the one bank and synthesize the ignition pulses for the
second bank. If this is the case, the logic may deduce it needs
more power to the primary bank after 2 seconds to get things fired
in case the battery is weak…and then restart the second bank.
I only conjecture here, because I still think you have a fuel issue
going on. You said it starts on ether, but won’t run…that usre


'95 XJS V12 6.0L, saphire/tan
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from sbobev sent Wed 28 Aug 2013:

First of all, I only have had this car start one time since
owning it for a little over two weeks, and that was very
briefly. I am trying to follow my grandfathers advice of
keeping it simple. Fire, Fuel, Air. In that order. Since I
KNOW the car isn’t firing properly, this is as far as I have
gotten. What I have done, is strip the Marelli harness wide
open. I have disconnected every component other than the air
temp, coolant temp, and speed sensors. i.e. the ECU, the
coils, the idle switch, and the power amps. I have inspected
every single wire in the harness. All grounds appear good.
Switching amps, coils, does nothing to change the situation.
B side fires about 3 seconds, and then drops out.

Kirby, there is a splice (appears factory) where the wire
feeding the coil changes colors before it gets to the Lucas
connector. This same connector supplies the power to the
Marelli system. My next step, is to first see if my ECU is
any good (thanks to Mike from this list), and if it is,
disconnect the tach, and see what happens.

Outside of that, I can only see replacing the wires that
control the B side. I am in WAY deeper than I ever imagined,
but having re-built a couple of V-12s, its not as scary as
it used to be, lol.–
Gene Holtzclaw
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from CJ95 sent Wed 28 Aug 2013:

‘‘I know the crank only has 3 fingers on the harmonic balancer. That
would only cover 6 cylinders when the car is running. So, it would
seem the ECU has to take the timing trigger for the one bank and
synthesize the ignition pulses for the second bank.’’

According to AJ6 Engineering, that would be a correct statement.
The sentence following that statement has no basis - there is no
such logic regarding power changing to either bank as a function of
time and battery voltage. See the AJ6 extract below:

‘‘Triggering is from a three toothed rotor mounted on the crank
pulley, providing a register signal via pin 1, for each A bank
cylinder at 8 degrees ATDC. B bank firing points are then
calculated via the speed signal, which is taken from the flywheel
teeth to pin 16. Both pickups are of inductive type and the air gap
setting is quoted as a rather unfussy 0.018 to 0.042 inches (0.45 -
1.0 mm).’’

Based on the last sentence of the AJ6 Engineering extract, there
really could be a problem (as suggested by a previous poster) with
the crank pickup and speed signal from which the B bank firing
points are calculated. It is apparently an intermittent problem
since the engine initially starts, but then looses the speed signal
and dies. Bad Senor or faulty Circuit?–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from lockheed sent Wed 28 Aug 2013:

It doesn’t start. It did one time, out of 50 tries maybe.
When it did start, I tried slowly turning the throttle
pedestal, and it promptly died. Never would start again. So,
I began with the basics. I checked the firing of the coils,
and found this problem. I also put the engine to TDC on the
compression stroke on 1A, and the timing mark on the
balancer seemed perfectly aligned. I then took the
distributor cap off, and the rotor appeared as close to the
center of 1A as you could hope for, the notch in the
distributor was aligned as well, per the AJ6 site. I also
found this 3.4 volts coming to the A coil via the tach wire.
This doesn’t seem right no matter what. If my ECU is bad, I
have a target. If my ECU is good, on a known working car, I
will still be a bit perplexed.–
Gene Holtzclaw
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

Gene,

How is your fuel pump?

Have you checked your fuel pressure with a gage on the fuel rail?

Maybe you have a bad fuel pump and/or a clogged fuel filter and there is
enough fuel to get the engine to run those 3 seconds on occasion but the
engine shuts down due to fuel starvation.

The archives are full of fuel pump problems, especially with cars that
haven’t run for a while and have been left outside. The tanks get rusty,
the fuel filters clogged, and the cars just won’t start.

Maybe you have a fuel delivery problem and an ignition problem.

If I were you I would check that the fuel pump runs, remove and replace the
fuel filter, and cut open the filter to see what’s inside.

I would also check the fuel pressure at the fuel rail.

Regards,

Paul M. Novak

1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA
P.M.Novak7@gmail.com-----Original Message-----
From: owner-xj-s@jag-lovers.org [mailto:owner-xj-s@jag-lovers.org] On Behalf
Of Gene Holtzclaw
Sent: Wednesday, August 28, 2013 6:13 PM
To: xj-s@jag-lovers.org
Subject: Re: [xj-s] Marelli question

In reply to a message from lockheed sent Wed 28 Aug 2013:

It doesn’t start. It did one time, out of 50 tries maybe.
When it did start, I tried slowly turning the throttle pedestal, and it
promptly died. Never would start again. So, I began with the basics. I
checked the firing of the coils, and found this problem. I also put the
engine to TDC on the compression stroke on 1A, and the timing mark on the
balancer seemed perfectly aligned. I then took the distributor cap off, and
the rotor appeared as close to the center of 1A as you could hope for, the
notch in the distributor was aligned as well, per the AJ6 site. I also found
this 3.4 volts coming to the A coil via the tach wire.
This doesn’t seem right no matter what. If my ECU is bad, I have a target.
If my ECU is good, on a known working car, I will still be a bit perplexed.

Gene Holtzclaw

// please trim quoted text to context only

In reply to a message from Gene Holtzclaw sent Wed 28 Aug 2013:

Gene:
Read Alan’s post above mine carefully. The Marelli computer
takes input from the idle-switch and air-temp sensors, as
well as crankshaft position and engine speed sensors.
If you are having problems with the latter two, this can
explain why your B-bank coil misbehaves the way it does. If
you look up crankshaft position sensor in the archives,
there are many posts where just cleaning debris from the
sensor brings the beast back to life…

I will repeat what I said in case you missed it – you can
disconnect the coil, the amp, the injectors to B-bank and
your engine should start on the A-bank alone (you are
certain your A-bank fires, right?).

BTW, where are you located? There might be a friendly JL
member nearby?

Steve–
The original message included these comments:

gotten. What I have done, is strip the Marelli harness wide
open. I have disconnected every component other than the air
temp, coolant temp, and speed sensors. i.e. the ECU, the
coils, the idle switch, and the power amps. I have inspected
every single wire in the harness. All grounds appear good.
Switching amps, coils, does nothing to change the situation.
B side fires about 3 seconds, and then drops out.


'95 XJS V12 6.0L, saphire/tan
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from sbobev sent Wed 28 Aug 2013:

Coming into this a bit late (on the list). I am the ‘mike’ Gene is
referring to, helping him out.

When his ECU arrives, I will be plugging it into my Marelli car
(1990) and seeing if it behaves, or not.

Right now, Gene’s cars’ problem is ignition- I don’t think he’s
been able to get to fueling, just yet, because he can’t get the
ignition to behave.

Again, as I understand it, he gets A bank to fire normally, but B
bank fires for only about 3 seconds after cranking begins. A
continues to fire.

My understanding of the Marelli ECU is that the crank and flywheel
sensors are primary inputs, and the ECU won’t output firing signals
(A or B) unless both inputs are present. So, the fact that A
continues to fire, and B drops after 3 seconds would indict the
theory that the flywheel sensor (or crank, if that’s your fancy) is
at fault.

Gene has played the game of swapping amps, and coils to see if the
problem changes, and neither of these produces a useable result.

He has peeled open the harness (under my advice; I have solved
problems on my car that could only have been solved by taking this
step, so actually SEE what is there), and he as been doing
continuity checks on the various connectors and the ECU connector
(and ground). We have concluded that he has a) good amps, b) good
coils, and c) circuit integrity from the various connectors back to
the ECU.

The ECU is in route (probably should be here today, I am hoping),
and I will check that.

The one theory I have been nursing, which relates to this thread
(and the other Marelli thread going on), is this: could the Marelli
ECU be varying timing in the first few seconds of cranking such
that the B-bank wiper of the rotor is in range of the cap contacts
at first keying of the ignition, but advances out of range after 3
seconds. Of course, the A bank wiper seems to be in range
throughout this.

Toward that end, Gene knows about the AJ6 page on Marelli
distributor alignment, and, having rebuilt a V12 for an E-type, he
knows how to find TDC for 1A, and has verified his distributor is
aligned properly.

This is leaving me to muse on the ECU. What this feels like is
that the ECU is driving AMP B’s input and then, the ECU output
overheats (I like the theory that it may be grounding somewhere),
and stops. When turned off, it cools enough to repeat this
behavior on the next keying of the ignition.

Any thoughts on this?

-M–
Mike, 1990 5.3 XJS Conv., 5-speed, SE-ECU, TT Extractors
Lakewood, OH, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from mike90 sent Thu 29 Aug 2013:

From my previous posting:

From AJ6 Engineering:

‘’’'Triggering is from a three toothed rotor mounted on the crank

pulley, providing a register signal via pin 1, for each A bank

cylinder at 8 degrees ATDC. B bank firing points are then

calculated via the speed signal, which is taken from the flywheel

teeth to pin 16. Both pickups are of inductive type and the air gap

setting is quoted as a rather unfussy 0.018 to 0.042 inches (0.45 -

1.0 mm).’’

Based on the last sentence of the AJ6 Engineering extract, there

really could be a problem (as suggested by a previous poster) with

the crank pickup and speed signal from which the B bank firing

points are calculated. It is apparently an intermittent problem

since the engine initially starts, but then looses the speed signal

and dies. Seems to me to point to a bad flywheel sensor and/or
wiring and circuitry associated with that flywheel sensor.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from lockheed sent Thu 29 Aug 2013:

I’m with Alan on this one. We rarely hear about Marelli ECU
failures, but quite often about no-start issues due to
sensors…

Gene has not indicated that either CPS or the engine speed
(flywheel) sensor have been checked.
They are both in places where dirt can accumulate rather
easily. The latter is close to the B-bank cat converter and
could be ‘‘cooked’’. Also, the connector from the CPS is
right next to the breather-elbow and could also be jammed
with dirt and oily residue.

The results from the test of the ECU will be telling, Mike
please keep us updated on your progress.

Cheers,
Steve–
The original message included these comments:

Based on the last sentence of the AJ6 Engineering extract, there
really could be a problem (as suggested by a previous poster) with
the crank pickup and speed signal from which the B bank firing
points are calculated. It is apparently an intermittent problem
since the engine initially starts, but then looses the speed signal
and dies. Seems to me to point to a bad flywheel sensor and/or
wiring and circuitry associated with that flywheel sensor.


'95 XJS V12 6.0L, saphire/tan
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from sbobev sent Thu 29 Aug 2013:

Good point…

It is not clear from the OEM jag manual that the ECU actually does
indeed require BOTH primary inputs to function. It certainly leads
us to believe that they are required for function, but it does not
say that, for example, if the crank sensor fails, the engine won’t
run, or, if the flywheel sensor fails, you will only have ignition
on A.

It simply says both are considered primary inputs, and things won’t
work if they are faulty or absent.

If I were designing the firmware for this ECU, I’d definitely make
sure that if one of these two primary inputs faulted, that the
ignition firing outputs would be inhibited. There’s too much
consequence if they’re not, as we’ve seen, and so such a
circumstance would be an additional candidate scenario for a
Marelli fire (and not only due to a rotor burn through, as is
universally touted).

Thing is, I’ve only ever seen posts in this list that refer to
crank or flywheel sensor failures as leading to the engine dying
out, and many of those are thermally-drive sensor failures (sensor
gets hot and the element goes open, only to return to continuity
when it cools down).

And, the trigger point of the front crank is referenced to a point
ATDC…surely one would want to compute advance for the A bank,
also, wouldn’t one? If so, one would need an engine speed signal,
so that the trigger on the crank merely starts the game off, and
the ECU, counting the teeth on the flywheel, now knows when to fire
A, and, again, knowing speed, can compute B as well.

Point is, A bank is not directly fired off the crank sensor, it
NEEDS the speed as well, or else the advance can’t be computed.

OK, I’ve come back out the same door I went in on this.

It would be a good exercise to verify this, and it is easy enough
to do.

When I look at my car this afternoon, I will start it, and then
pull the flywheel sensor connector and see if I lose the B bank, or
if the engine simply dies. I run TT pipes so I am not terribly
concerned about a CAT fire under these conditions, and in any case,
I won’t run it long that way.

I will also check the ECU that Gene has sent.

It happens that I have a crank sensor harness that I replaced
during the diagnosis of my own car’s ignition, and I since believe
that sensor to be good (certainly measures good on the DVM). There
were other problems at play that were responsible.

Both the crank and flywheel sensors share the same P/N, and so I
will send one of these down with the ECU when I return it to Gene,
and we can see what the outcome will be.

-M–
The original message included these comments:

I’m with Alan on this one. We rarely hear about Marelli ECU
failures, but quite often about no-start issues due to
sensors…
The results from the test of the ECU will be telling, Mike
please keep us updated on your progress.


Mike, 1990 5.3 XJS Conv., 5-speed, SE-ECU, TT Extractors
Lakewood, OH, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

As I understand it, the Marelli cars still suffer from the dreaded
coax wire problem. On the Lucas cars, this wire begins on the port
side rear of the engine near the Lucas AB14 amp and goes rearward
toward the firewall and then across the engine bay to the starboard
side. The section above the engine gets baked and dries out and
cracks, and then the shield makes contact with the core and the
engine comes to a screechin’ halt. I’ve been told that the Marelli
cars still use this wire, there’s just a signal wire that comes from
the Marelli ECU up to this same location and connects to the same
coax wire.

I dunno if that could be the problem here, but stranger things have
happened. That coax wire can go from OK to shorted with the
SLIGHTEST wiggle of pretty much anything, including the engine on its
mounts.

It looks like a normal white wire; it takes looking twice to notice
that it’s actually a coax wire. And you have to peel back the sheath
to verify its condition. If it’s all dried and cracked, it needs to
be cut out and replaced. Usually, the section of wire from the
starboard side of the engine all the way back to the EFI ECU in the
trunk is OK, it’s only the foot or so over the engine that’s toast.

– Kirbert

// please trim quoted text to context only

In reply to a message from mike90 sent Thu 29 Aug 2013:

''And, the trigger point of the front crank is referenced to a point

ATDC…surely one would want to compute advance for the A bank,

also, wouldn’t one? If so, one would need an engine speed signal,

so that the trigger on the crank merely starts the game off, and

the ECU, counting the teeth on the flywheel, now knows when to fire

A, and, again, knowing speed, can compute B as well.

Point is, A bank is not directly fired off the crank sensor, it

NEEDS the speed as well, or else the advance can’t be computed.’’

Mike,

I get your point, and understand the dilemma here as this process
is not fully explained. My guess is that the A bank will still
fire from the baseline trigger point (8 deg. ATDC), but crappy with
no advance, since it lacks the speed signal from the crank sensor -
which is also needed to compute any sort of spark for B bank. Why
B bank gets 3 or 4 sparks, in the first place, before quitting
beats me. Maybe there is some sort of time delay factored in here,
or it just takes that long for the fault in the speed sense circuit
to occur due to weakness or saturation, and the inability to
sustain any continuing load in the circuit and function properly.

Sounds as if your approach of substituting the Marelli ECU and the
crank sensor will hopefully shed some light on the problem.

Off the wall - some missing or short flywheel teeth??? But wouldn’t
that imply starter drive problems? I throw that out there because
I have had to change two Mercruiser 470 flywheel ring gears because
of rusted off or worn short ring gear teeth. What amazed me is how
short some of the teeth were before the starters failed to turn the
flywheels. Since this car sat for a long time, could it be that
some of the teeth may be rusted or worn short and the starter still
catches them, but, the sensor does not sense them because of
excessive gap??? If no other answer, maybe a check of the ring
gear teeth might be in order. I better quit now before I fall off
the edge - if I haven’t already.–
lockheed 92 XJS Cpe/97 LT1 Miami FL/ 96 XJS Cv 4.0 Austin TX
Austin, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only

In reply to a message from mike90 sent Thu 29 Aug 2013:

Any result is usable. What happened to the spark when the
amps/coils were swapped? If it stayed on A, then the ECU deserves
the attention. If it moved to B, then the amp and coil deserve all
the attention.

If it were pickups, I cannot imagine still having the A bank
functioning normally. Again, having A bank work fine would lead to
ECU/amp/coil problems.

It’s my understanding that he was checking the spark right off the
coils, so that would negate any distributor issues regarding
timing. I have never used that (coil straight to ground)
technique, as I fear drawing too much amperage from the coil. I
prefer to use a spark plug and hold it to ground to check for
spark. The B coil could be getting overloaded sending the juice
straight to ground.

If I misunderstood that the car started with ether, then that is a
check that has to be tried. If it starts for a few seconds using
ether, then you do not have a spark issue.–
The original message included these comments:

Gene has played the game of swapping amps, and coils to see if the
problem changes, and neither of these produces a useable result.


John. '95 XJS 6.0L convertible. Southlake, TX
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

// please trim quoted text to context only