400i A ignition problems

Pictures indicate someone has been "playing" with the MSD system. Outside pic shows some corrosion around the main contacts. So, I would question integrity of the MSD unit. Coils are the easiest thing to change and test to eliminate that as the cause.

On the other hand, the symptoms seem like the distributor could be the issue. Who did the rebuild? Where both bearings and lower seal all changed? Did they provide a final advance curve? Who installed the distributor back in the moor and did you check idle RPM and the advance curve vs. RPM at he flywheel?

You have a witch hunt for sure. You may end up looking into the fuel system.....
Ken

 

Strange that the box is labelled 104bk as BK was for carburated Ferraris, not ignition. So whoever built this alternative had the carburated cars in mind.

If the guts is from an MSD unit, maybe it's toast (MSd recommends to add a big capacitor during installatuon in order to protect the unit).

If the module is so-so the transition from multi-spark to single spark would explain why ignition is weak under a certain rpm range and better once the unit has less sparks to emit?

 

The Clinique has all the right tools. They may have kept a copy of the final advance curve; remember it is in cam RPM's not crank.

I would use an MSD coil and ask them for their recommendation which is better.
Ken

 

Good day Jean-Michel,

I can fully appreciate the challenges to track down and remedy such as issue given the circumstances and that there has been a variety of attempts at trying different things in the hopes of resolving the problem. Unfortunately, I did not see a clear, systematic, an integrated diagnostic approach ... but more of a try this, replace that, test this, etc. As a result, it makes troubleshooting and identifying the problem(s) that much more difficult. I suspect that the distance between the owner and the shops is a factor as well.

MSD units typically work the best with MSD Coils, simply because the MSD Coils have electrical characteristics that are better/tailored to work with the output switching characteristics of the MSD ignition modules. Although most understand the basics of ignition coils, most do not understand the core electrical parameters that differentiate one ignition coil from another (e.g. inductance, breakdown voltage, etc) and it is these parameters that can play a significant role in a properly working ignition system including long term reliability. Inductance is very important, as it determines how fast energy can be transferred to the coil... and so too much or too little inductance can affect the resulting output (high) voltage that is needed for the spark plugs. Inductance is directly related to the coils internal design, but also to the internal wiring (number of turns, wire diameter, etc). The other important factor is the high voltage insulating characteristics... This is also very critical, as the high voltage created by the coil has a tendency to want to "spark" inside of the coil instead of where it is needed.. at the spark plug. To stop the internal "sparking", various insulators are used which historically relied upon an oil which filled the insides of the coil (oils have now changed because of environmental laws). Over time these internal insulators "break down" and so lose their ability to properly insulate the high voltage spark... and so some energy is lost and/or intermittent output voltage is available for the spark plugs. There is a bunch more I can say about all this, but I think you get the picture. So... it would make the most sense to use the MSD coil with the MSD ignition module, as using a different vendor ignition coil may not be designed to accommodate the resulting MSD coil triggering output... which could lead to abnormal spark output and/or reduced reliability/longevity of the ignition coil. Remember that most ignition coils were designed to only accommodate a 12V input voltage, whereas the MSD outputs a much higher output.... and because of this the resulting ignition coils output voltage will be proportionately higher (2-3x than what the coil was designed to accommodate) and so could easily exceed the internal breakdown voltage (e.g. fails to adequately insulate the coil's internal high voltage) which can result in intermittent spark output and sorter lifetimes of these ignition coils.

So... try the MSD coil and see if there are any changes... Good luck!

Cheers,

Sam

 

The BAE coil is meant to be triggered through one of its negative posts, whereas the MSD modulates the positive side. Not sure how the wiring was adjusted but let's hope this was done "properly".

The guts of the ignition module seem small, I would say this is from a cheaper "street" MSD?

Given what the owner has gone through, I would replace the MSD, the coil, install the recommended capacitor, and also replace the harness and eventually add a relay (current flows through the key switch).

Once all this is done, the last point of failiure would be the distributor itself, but in this case I would be more than happy to test it on my Sun tester....

 

Are we sure this is an MSD unit : here are the internals of the MSD 6AL and StreetFire, none looks like what's in @rovexienus picture.

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Before changing the coil, I would first identify what this unit comes from.