355 5.2 coil resistance values and procedure

Primary, depending on which pins you measure between, around 1 ohm or less. Secondary, 13k.

It would seem unlikely both coils would go at the same time. FYI, these coils are very common. About $50 or $60 in the US. Same as Land Rover Discovery and Range Rover 1998-2002.

 

Paul, I can't see how both coil packs would fail at once and both un-fail on the next drive (or vice versa). Remember that each coil pack has two sets of coils and, depending on the defect, it may take up to four coil pairs to fail simultaneously to stop all 8 cylinders firing. Generally, how do the coil packs look (clean and dry?)

According to the wiring diagram, the coil packs do have earth wires, but I can't figure out what they do (as the diagram shows them not connected to either the ECU or the coil circuitry). Perhaps they are part of the shielding system (but would a shield fault affect spark plug firing?).

The manual probably expects you to check the voltages coming from the ECU or going to the ECU from the crank sensors with a cathode ray (or digital) oscilloscope. I see pocket digital types are available for less than U$100 on eBay, but I don't know how you would tap into the wiring to use them. Why don't you compare the resistances of the left coil pack with the right coil pack? Coil pack technology is very basic (and common to lots of different cars). There are plenty of YouTube videos on how to check the resistances of coil packs. e.g.



The primary coils are checked using the small plug (use pin 2 as the common... this is the 12v power in). Set low range on your multimeter if the multimeter doesn't have autoranging. The secondary coils are checked using the big output plugs. Expect a high resistance on these.

Note that coil packs are not terribly expensive (e.g. UKP66 plus postage), but I still think the problem lies elsewhere.

(EDIT: Sorry cross-posted with John... but he's basically saying the same stuff)

Cheers

 

Are you positive your grounds are good? Again when my major was done, one bank would not fire. We chased it for days, checking coils, crank sensors, wiring fuse box etc. It came down to one bad ground on one side. I have a 2.7 and have more grounds, two to each head. Ground was not tight on one head so that side would not fire. Do 5.2 have one ground for both banks?

 

The grounds on the coil are just it being bolted to the frame. No wires. The coils function from the signal to the ECU. There are 3 leads to the ECU. The center pin is connected to 12V. Pins 1 and 3 are controlled by the ECU which makes and breaks a ground though a circuit, which I presume is equivalent to the ignition power modules found on the 2.7 cars. Paul previously said that he has 12V at the coils so it would seem that there is something that is preventing the ECU for doing its job to fire the coils. As I posted earlier, there are 4 separate connections to the ECU for this and it would seem odd that all 4 connections are intermittently faulty at the same time. I would be looking for something that has some singular control.

 

Does the 5.2 have one ground to each head or just one ground for both? All I know is one bank would have no spark and would not fire until the ground to the head was tightened.

 

I don't know about the 5.2 grounding, but it's possible that what you say could happen. I'm a little suspicious though, because that would be on the high voltage (secondary) side of the circuit and, again, both sides being intermittent at the same time. Sore of against the odds. But worth checking. I'm also suspicious about the fact that Paul could previously connect to the diagnostic port and now can not.

 

Doesn't the secondary side earth through the spark plugs (i.e. to the engine head)? Wouldn't that mean the engine to chassis grounds would have to be checked?

If the coil packs don't have an earth wire (as shown in the wiring schematics), perhaps cleaning the mounting bolts would help.

Diagram:

RH Coil Pack

 

Image Unavailable, Please Login Here is the ground that caused my problem. Make sure it is clean and tight

 

I'm curious to know what the difference is between these devices. Don't they do a similar job? (or does the continuity tester include a megger function or super low ohmmeter function?)

I assume you mean visually inspected. Some comfort, but it would still need a full electrical check if other components prove to be ok.

By this, do you mean open circuit (infinity ohms or "OL" on some displays)? Note that the resistance between the secondary coil pairs is normally quite high (as mentioned in the YouTube video). However, I'm not sure which coil output pairs on the Ferrari coil pack produce this resistance (as per the wiring diagram). On the left coil pack, did you get a high resistance between the upper and lower outputs or Left to Right or perhaps even diagonal? (and open circuit with other combinations)

Of course, the secondaries normally have some super high voltages in them. It may not be possible to check the coils completely with simple ohmmeter/continuity checks.

Sorry, my car is still in the shop so I can't do a comparison (more problems found... more broken gears and the clutch is almost at the limit.... Still cursing the PO and the "expert" who did the PPI)

 

I don't think so. Look at the 2.7 diagrams. Same coil. No ground shown. I'm not sure why they even show it on the 5.2.

Make sure you check between the correct pins. Remember there are two primary and two secondary winding in each coil. To check the secondary winding you need to test between the top and bottom terminals. To be clear, the terminals where the plug wires connect. But again, that both coils packs, a total of 4 different windings, would fail intermittently just doesn't make sense. Somewhere this has to come down to a single point IMO, like getting power to the coils or the ECU. If you have power to the coils when you have a no start situation it would seem like the problem is in the ECU or getting power to it. If no power to coils when no start, you would need to chase down where the coils get power. (????, Ian???, Anyone???)

Looking at the 5.2 ECU pins, pin 26 should be 12V, fused, which looks like power to the ECU. Pin 54 is 12V which powers various sensors. Power to the coils is not defined on Ian's diagrams, but it probably comes directly from the ignition switch or immobilizer, or a relay controlled by one of them. I guess not much help now that you have things apart.

 

Thanks, John. Good to know. So no continuity from left to right or diagonally.

Good point. Unless it's because the 5.2 system needs shield earth wires (The signal from the 5.2 ECU to the coil packs may need some shielding). On the 2.7, the ECU signal only goes as far as the power pack. The power pack then triggers the coils. Paul, can you confirm there are no earth wires around the coil packs? Is the wiring on the small plug shielded?

Power comes directly (no relays) from the ignition key via wiring in the passenger footwell relay/fuse panel. From wiring checks on my car (without pulling the plugs on the fuse panel), I found that it's either plug D (pin 1) or plug I (pin 9). I couldn't narrow it down to only one of these as they are hooked up in parallel inside the relay/fuse panel. I think Paul has already checked the wiring for from the fuse panel to the coil packs (?).
Power from the ignition key goes into the fuse panel on plug A (pin 8). i.e. a single wire.

(EDIT not sure how that pic got itself attached)

 

There is no separate grounding of the secondary coil circuit and the HT flow does not rely on the engine block or heads being grounded. The HT simply flows from one coil HT pin, through the first spark plug, through the cylinder head, through the second spark plug and then back to the corresponding second coil HT pin.

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