Changed my Digiplex

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I noticed lately that my car (84 QV) has been running rough, miss firing during idling, and at steady speed, then yesterday on my way home from a car show, the missing or what seems like coughing has gotten worst, so I was thinking, I just replaced the plugs last week, wires has been replaced by Dave Helm about 5 years ago and so my extenders which was inspected carefully when I changed the plugs and saw no holes and no sign of burnt marks. Then I remember that I bought this Euro Digiplex (MED 803 A) to replace my stock US (MED 805 A) in case they went bad plus also to get get better performance.

Soon after I installed the Euro Digiplex, I took it for a test drive and at start up I can tell already the difference, idle went up about 250 rpm, the slow acceleration is a little bit more preppier as in it pulls stronger now and smooth, and also at high speed acceleration is stronger and smoother. I don’t know the technical curve specs difference between the two Digiplex but all I know is that this is what those who did this highly recommended it.

 

The timing curves are very different between the two types. The US version has much less timing advance at idle which would explain the idle rpm difference.The two curves are listed in the Mondial8/QV workshop manual. I can't seem to find mine now.I will post it for you when I find it.

 

Do you have cats on? The euro curve is for no cats and a different exhaust valve timing ....just saying. ....

 

That would be great, thanks Ron!

 

No cat for me anymore and the o2 sensor is unplug

 

I did this change over on my ‘82 2v Also adjusted the exhaust cam timing. Very pleased to say the least. I had mine rebuilt. FSoB they include a rev limiter. As you can zip up there quickly. Yes the limiter works.

 

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Hi Mike,

I believe the cams themselves are different for the Euro cars. Not sure how that would play into it.

Franny

 

Well actually the cams or valve timing is totally separate or different from the ignition timing, I’m only changing the ignition timing curve by switching to the Euro boxes.

 

This is very interesting Steve. I have an 84 as well and the idiots/cheats that almost wrecked my car and killed me and trashed the voltage regulator caused me to think that something as sensitive as the Digiplex boxes might be messed up.

Can you say where you got your replacements?

Thanks

 

Tim, ditch the Digiplex... go XDI. Do it.....

 

Don’t know what that is but I will sure research. I should be driveable in a week. Fingers crossed

 

Nicks Forza Ferrari sells a preconfigured, almost plug and play ignition system using the Electromotive XDI system: https://www.nicksforzaferrari.net/engine-management--direct-coil-ignition-systems.html

 

I swapped to the Euro Digiplex units on my 2Vi and found a similar result. For those considering doing this, it is a different model Euro Digiplex for the 2Vi when compared to the QV.

 

Attached is the ignition timing curves for US 2 and 4 valve cars. Also attached is the Euro 2 and 4 valve ignition timing. You will notice cars with cats (US) have retarded timing which increases exhaust temperatures and helps the cats to function more efficiently. This isn't the most effective timing for power or engine response. Notice the key/ graph in the top left corner. This is the key to understanding different timing vs.engine load. FWIW. I have a turbo QV with fully tunable EFI and found the Euro QV ignition timing to be very good starting point when not under boost. Hope this helps.
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Thanks for that graph Ron! That shows why I disconnected the vacuum hose for the Digiplex, it advances the timing by 4deg. With the Euro digiplex, I’m now running 14deg. BTDC

 

Thanks Gordon, I do remember looking into this a while back before I replaced my two cracked caps. I will revisit this after I get her running again.

 

Sent out my Digiplex units for testing and should have results on Monday.

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