Marelli Microplex MED 860A 1688

The Microplex ignition system on my 88 328 has been misfiring for some time and I was told it needs to be replaced. Problem is this model has been out of production for some time and those that are available are either used or rebuilt units being sold without warranty. Thought of relying on more recent 348 / 355 units were dashed when I discovered these moved on to Bosch Motronic....if any one have had experience, pleae share the lesson learnt. Thanks in advance.

Leo

First of all how do you know for sure it's the Microplex itself and not loose corroded wires or a bad ground?? Then, how do you know for sure it's not one of the more likely suspects a Coil Pack?

My own garage (who have fetted this car very competently over the past five years) and the franchised dealer share the same diagnosis.

When the "misfiring" comes, the engine feels as if it was a Fiat 500 unit and such "misfiring" occurs occasionally when the car is driven without letting the engine warm up fully for 5 - 10 minutes and usually cuts in a few minutes into the journey when I fined myself cruising at low speed in traffic. Where circusmatnces allows, stopping and re-starting always cured this "misfire". Once done, the misfire would not return for the rest of the day.

Last visit to the garage I had my mechanics measured the ignition of both cylinder banks and one side was found to be very weak and it was traced back to the MED 806A. I would not profess to be a spanner man but since this diagnosis was confirmed by the franchised dealer, I am assuming both are not wrong?

Best

I cannot remember ever seeing one of these 328 units laydown like you describe, however I have seen many instaces of one of the Coil Paks going bad over a period of time causing a sporadic )such as when cold) problems...in fact I found a sporadic miss problem earlier this year, that after considerable investigation & analysis, proved to be a Coil Pak.

Anyway...to answer your original question...if the seller will give you a minor warranty to nsure the used/rebuilt unit is in fact good, I'd readily go with either one without concern.

Regards, JRV

John,

I appreciate your analysis. Allow me to clarify one issue. Is your reference to "Coil Paks"refers to the ignition coil or something else?

I read the other thread in which you had earlier advised on the Digiplex on a BB 512i. From what I recall of my garage's explanation, their check on my 328's Microplex sounded very similar to Tom's description of checking the power output of his Digiplex which leads me to assume (rightly or wrongly?) that both my garage and the local franchised dealer are right......

Thanks for your guidance & best wishes.
Leo

Leo,

328's have a completely different system than other cars talked about previously. Although test procedures are simular.

Your engine has an ignition computer and Two Coil Units that sit on the left front engine compartment bulkhead. If your technicians are reffering to those two coil units, then they are correct. It's not that uncommon for them to fail as you describe.

They are not that expensive if I remember correctly, on the order of $450 approx. for a new complete unit.

Regards, JRV

>>Problem is this model has been out of production for some time and those that are available are either used or rebuilt units being sold without warranty.<<

Leo,

this is the part that threw me/throws me....the only part of the system that's rebuildable is the Computer...the Coil Paks (the microplexes) are readily avalible NEW for the $450 approx. I mentioned.

The transistor unit (trigger) on top of the Coil Paks (under the black shield) is reportedly the same as 4 cylinder VW's/BMW's and is the portion that most commonly fails and can be purchased seperately for about $60. Maybe by replacing the trigger unit someone is calling this rebuilt???

HTH's

I'll post some pics tonight.

Regards, JRV

John,

Thanks for your continuous help. The two ignition coils on my 328 as you described were in fact replaced by my mechanics 3 / 4 years ago and they remain functional. I called my mechanics yesterday after our exchanges and he has confirmed it is the Microplex unit that is giving me grief.

I contacted Perma Tune yesterday and they replied the Microplex cannot be rebuilt but offered a solution in the shape of a Plasma Drive model PD010 from Zims Autotechnics saying this can be triggered by the Microplex so long as it is still firing. I will find time later today to get in touch with Zims to find out a bit more.

In the meantime, I am eagerly awaiting to see your pics.

Thanks &amp; best wishes.
Leo

Leo,

I forgot to take the pics today sorry.

I don't think the plasma drive is well suited to your purposes. If Zims thinks it is, I'd be curious as to their feedback.

I still find it hard to believe a sporadic miss can be caused by a computer slowly going bad...just is not logical.

As these cars get older they have become notorious for bad and loose connections that cause these types of sporadic issues, or as the other gentleman found a faulty/weak flywheel pickup sensor, likely combined with dirty/loose connections. Of course if this sporadic problem of yours is suddenly cured with a new computer I'll be very very suprised.

For a used unit you should try Bill @ GT Car Parts. Din't have his number at home, but if you need it I'll post it from work in the morning.


Regards, JRV

John,

Thanks. I was building my hope on getting aftermarket replacement units from Perma Tune / Zims that I hope are built with more modern technology (if Ferrari passed on Magnetti Marelli and switched to Bosch from 348 onwards.....). I will let you know what comes out of the dialogue with Perma Tune / Zims.

I would like to hear your views on buying used Microplex. Maranello Autoparts has one on offer @ $ 11750 (ex 86 Mondial) while Italian Car Parts has one for $ 1250 but neither comes with any warranty and I am worried about the old cardinal rule of "buy cheap, buy twice". My local Ferrari dealer located an unused Microplex in Tokyo for $1700 inclusive (very good value by comaprison) but again no warranty is offered nor could they ascertain the date of manufacture of this unit.

Do you have any views?

Thanks &amp; best
Leo