355 Cam phase sensor malfunction

You know, as an interesting aside, years ago when a friend and I were racing his corvette we used a magneto ignition. As I'm sure you know, the only real difference between a magneto and a battery powered ignition is that in a magneto a rotating magnet is used to generate the current in the primary. Other than that they function similarly. So the magneto was lying on a table with one high tension lead lying close to a cam shaft which was also on the table. My friend started turning the shaft of the magneto for no reason and next thing you know a spark jumped from the high tension lead to the cam shaft, maybe 1/4 inch. How could that happen? The was no connection of any type between them.

When the spark plugs aren't connected to a coil and you crank the engine does the potential not build up in the secondary? Why can doing this damage the coil? Why does a spark form in the first place? Why will a Citroen 2CV, 2 cylinder engine with wasted spark run on one cylinder if you pull one plug wire?

 

The "-" of the left (primary) coil is not permanently connected to the ground as you have shown.

The "-" of the primary coil is connected to the ground only from time to time, switched on and off, as the frequency of ignition requires (12V is permanently connected to the "+" of the primary coil). When the "-" is briefly connected to the ground, the primary coil builds-up a magnetic field around it. The secondary coil is electrically completely separate from the primary coil but it sits in the same magnetic field. When the "-" side of the primary coil is disconnected from the ground (the moment of ignition), the magnetic field collapses inducing HT current in the secondary coil which flows through its own (electrically separate from the primary coil) circuit - through the gaps of its two spark plugs.

In the classic single ignition coil, one side of the secondary coil is connected to the ground and the other side to the centre electrode of the spark plug. In this case, the HT current loop is closed through the ground, after it has jumped the plug gap.

This is the difference between the secondary (HT) current flows between the two ignition systems.

 

Ok, make it this. Again, the spark plugs are connect to ground.

Image Unavailable, Please Login

Yes, agreed that when the magnet field collapses a high voltage builds in the secondary. But no current flows until the gap breaks down. And the gap doesn't break down until the potential reaches a level sufficient to bridge the gap. How is that potential created? The collapsing magnetic field forces electrons to migrate in one direction along the coil. Since there is no completed circuit, this migration of electrons, or charge, is balanced by the development of an electric field along the secondary winding. These are transient effects. The migration of the electrons is a "particle current", what we typically think of as current. The time rate of change of the electric field, which gives rise to the high voltage potential across the coil, is a "displacement current". The total current, sum of the displacement and partial currents, is zero (conservation of total current, a law of physics). Thus no net current flows at this time. Nature doesn't like charge imbalances (witness lighting) so once the charge imbalance reaches a high enough level, i.e. the potential difference between say the + end of the coil, and the potential the head is at (ground) , a spark is formed. Charge (current) flows across this spark in an attempt to neutralize the charge imbalance between the hot electrode and the head and the field collapses and the spark dies. Likewise, when the potential difference between the - end of the coil and the head (ground) is sufficient a spark forms for that plug. But this time charge imbalance is opposite and current flow in the other direction.

 

John , you seem to be privy to some kind of electronic principle that none of us know about.

Why does a neon light tester work? It's not connected to ground.

The spark plugs are just two resistors in series joined by a conductor (the head) The collapsing field in the primary creates a potential difference at the opposite ends of the secondary coil. This causes a current to flow through the "resistors". You could substitute two neon lights for the spark plugs if they were able to take the current and they would flash..... just as the spark plug does.

 

Ah, thanks, Grant. I was actually after a picture of one of the other plugs, 41091 I believe. Anyway, I'll try to add a note to my diagrams of that blue/black colour difference. I assume there is only a wire colour change rather than a pin assignment change, but who knows.

Thanks, Grant. No real smoking gun yet. I assume the ceramic casings have no cracks. I don't suppose there is any point doing basic resistance checks on the leads and plugs. This stuff is only likely to break down with high voltage. I've forgotten if you did a push test on the coil pack plug centre socket to see if it moves?

I guess you could try Miro's testing technique and tying two inner (2/3) or two outer (1/4) spark plug pairs together with their casings touching, placing the pair on an insulated surface. Pull the fuse for the fuel pump to stop fuel spraying out the spark plug gaps (Fuse #21? Or is the F1 car different?). Maybe put a rag over the holes (if there is residual fuel or oil in the cylinders). Unfortunately, if there is no spark, it's not going to prove anything, because we don't know what's broken yet.

Miro, I understand (well) your point regarding plug pairs, but the likelihood of two components failing simultaneously in different circuits with no previous signs of a problem doesn't seem likely (to me).

 

Agreed. Grant should do a spark-watching test with the old plugs and then with new ones. The problem may not be in the plugs, but it is an easy and quick way to eliminate it.

 

It's hard for me to explain simply, mostly because I haven't looked at this since I retired 22 years ago and I've forgotten a lot of it.

The electric field around the ignition wire excites the electrons in the gas and ionizes the gas. When the electron drop back to their normal energy level the emit photons of a specific wave length (color) depending on the type of gas.

The point about grounding isn't about current flow. The plugs aren't resistors. They are more like switches that turn on once the potential across the contacts exceeds the required level. The problem is about the switch turning on, not what happens after they are on. The point about grounding is just that in the engine all plugs, installed in the heads, have the threaded end fixed at the ground potential.

Certainly the plugs will fire without the threaded end being grounded. That's exactly what I did in my bench test. But that is not the way they are installed in the engine and if I want to mimic the engine installation I want them grounded. A lot of this argument is the result of semantics. But, when I said the loop is completed by grounding the plugs, how can one argue that the plugs aren't grounded when the plugs are screwed into the heads which have their own ground straps to ensure that the heads are at ground potential. It's just nonsensical to say they aren't grounded.

And another issue is that current is about the movement electrons and changing electric fields. That is how this large potential is created in the coil with no net current flow. There is movement of electrons in the coil before the spark occurs. But there are no electrons flowing through the plugs. It's an open circuit. The magnetic field surrounding the coil makes the electrons in the coil move from being evenly distributed to accumulation at one end and depletion at the other. Electrons are moving so there must be a current. There is. It's the particle current. But this movement of the electrons is accompanied by the development of an electric field along the wire in the coil. That field changes in time as the electron concentration at any point along the wire changes. The time rate of change on the electric field is called the displacement current, for the obvious reason that it is dependent on the displacement of the electrons. The result is that the movement if the electrons (conventional current) is balanced by the development over time of the potential across the coil (displacement current) with no net current flowing through the loop.

Honestly, this whole thing has gotten way out of hand because I suggested a way to check the secondary side of the ignition while being disconnected from the car's primary side, thus possibly identifying where the problem is.

Let's all agree to move on.

 

Your description would be correct if the secondary coil was arranged as shown on this diagram. But it is not like that.

Image Unavailable, Please Login

 

I suppose moving the plugs also introduces the possibility that one or more of the spark plug leads has a weakness in it. Also, as you said, you removed the plug on the ECU for me. There could be a problem there. Wiggle the ECU plug wires to see if they feel like the conductor has failed inside the insulation. That wire on pin 49 looks kinked. Recheck those coil power wires on plug 41090. Engine outs cause stresses to wiring. There could also be a problem at the relay panel, but one thing at a time.

Fig11_1998_F355_F1_5.2_Engine_Control_System

Fig11a_1997_5.2_Injection_System_Ignitionv2

Miro blinked first )

 

Can't see the pin clearly on your picture but it is probably AMP Superseal 1.5 Series p/n 183025-1. I got some from https://www.ebay.com/itm/10pcs-AMP-Superseal-1-5-Series-Receptacle-Contacts-183025-1/252083028731?epid=1223679351&hash=item3ab151c2fb:g:GQkAAMXQWzNSnJur but you can also get them from a US seller https://www.ebay.com/itm/10-AMP-TE-AUTOMOTIVE-TERMINALS-183025-1-18-15G-SOCKET-1-5-SERIES-TIN/302196976431?hash=item465c57eb2f:gE8AAOSwImRYe6pW.

Compare your pins with the pic below and make sure they are same.

Image Unavailable, Please Login

 

Thanks, Grant. I'll try and make a diagram for you. Can you see if that's a brown only wire in the second picture or is it brown with a grey stripe?
On non-USA cars, the grey wire goes to a 3-pin (OBD2) diagnostic plug, but on USA cars, I believe the plug is under the dash (or is there a second plug under the dash?).

Engine Control Diagram (Grant)

I hope repinning that plug doesn't make the wire too short.

 

That's interesting since 5 & 8 are connected to one secondary winding and 6 & 7 are connected to the other secondary winding. Are you sure which leads you are checking?

 

Just a note. The engine will definitely run and start on one bank, and certainly would run on 6 w/o a problem. So what you are saying is that after 15 pages of gut wrenching, hair pulling, bare knuckles brawling, it isn't a spark issue?

 

How old are your plugs and what mileage have they done? I would replace all spark plugs just to eliminate them.

Long time ago, i had a Daimler Double Six (V12) which had compression 12.5:1 as standard - not an easy task for the spark plugs to ignite the mixture at such compression so the plugs for it were quite special, not used by any other car. At one point, as I did not have the specified plugs, I put in plugs which were for a Mercedes V12 engine. My engine ran well but for only a couple of months. Then, one morning, suddenly the engine would not start without any previous warning. Luckily, by that time, I already had the correct new plugs for the engine and, when I put them in, the engine started straight away and these plugs lasted for a very long time thereafter.

 

Keep in mind that there are fake NGK, Denso and any other brand you want plugs made in China so one has to be careful where one buys them (better not on Ebay).