1985 308 Running Issue - Digiplex Going Bad?

Hello all,

I am wondering if you all might be able to offer some thoughts. I have a 1985 308GTSi QV Euro. The car runs great but after it warms up, one bank (front bank) cuts out and is running on 4 cylinders. It happened quite often and you could almost count on it happening when the engine warmed up. Checking it again more recently, it will not do it again. Ran and drove the car for awhile with no issues. Then, parked the car for a bit and got back in to drive and it did it, but only briefly.

During that brief period I unplugged the Digiplex boxes, swapped them and the same box seemed to be the problem. Could not investigate much further as the problem stopped and would not do it again.

Measure ohms on the 2 crank sensors and RPM sensors and were all about 750-760 ohms cold and 820-828 ohms warm. I was hoping to find one that was way off which could be the culprit. All 3 sensors were replaced by the previous owner not long ago. I also regrounded the Digiplex boxes with a hard wire to the engine.

My question is.....can these ignition boxes do this and fail intermittently? Or, do they usually hard fail and not work at all? I drove the car all day yesterday without a problem. I believe I have checked all of the main items to check. The wires, caps, rotors and plugs are all recent new parts. Any input on what you think may be the issue would be really appreciated! Thanks.

 

Oh, and if anyone might have a spare Digiplex that they would be interested in selling, please PM me. Thx!

 

Swap the digiplex units and see if the problem follows the box. Electronics can fail in all different manners.

 

Yes, both . You might want to contact David Feinberg who has made a business of fixing/improving Digiplex ECU as a comparison to buying a second-hand stock one:

https://www.sarasotaitaliangarage.com/ferrari-parts/

 

Few years ago one of my Digiplex went bad and the symptoms I had was the idle is very rough and eventually the engine dies, but if you keep the RPM around 3k then it will stay running and as soon as you let the gas pedal go, engine idle rough then die. I change one of the digiplex after diagnosing which one is bad and my QV has been running great since. So, in my case, it ran bad as soon as the engine started, it didn’t have to wait till it warms up.

 

Given the symptoms you describe I would be more inclined to think it is a crank position sensor that is failing. As Steve suggested, swapping the Digiplex units will help identify whether its the sensor or Digiplex. If the bank that drops out follows the Digiplex then it is that, that is faulty. If fault stays with the original bank, highly likely to be the sensor

 

Please reread the OP's post #1 -- he already swapped them, and indicated the problem followed the "same" Digiplex ECU.

 

Ahhh yes, apologies

 

Thank you everyone for your input and thoughts.

Thanks Steve for suggesting David Feinberg. I am actually in contact with him now. I didn't even realize that anyone rebuilt these boxes. David seems to really do a good job, and even updates the internals with modern electronics. I have heard good feedback from him through others people as well, This is a great contact!

Thank you rjlloyd. No worries, my opening post was kinda long and drawn out. I don't blame you for not catching all of the details. I do the same thing sometimes and have also responded to threads with the wrong info. The problem seemed to have followed the Digiplex box, so I am thinking that the crank sensor is okay. It has 2 crank sensors, one for cyl 1-4 and another for cyl 5-8. It only has 1 RPM sensor and if that one goes bad, does it feed both boxes and the car does not start at all?

 

Very interesting. Thanks for sharing your experience with that. I am learning that these boxes can fail in a number of different ways. Glad to hear that you got it figured out. My first thought that it might have been a suspect RPM sensor that maybe wouldn't put out the correct signal at lower RPM. Obviously something in the Digiplex didn't like low RPM's. Mine doesn't seem to have a known condition on when it acts up. Like I mentioned, I drove it all day on Saturday and there was no problem. I expected it to start acting up when the car got warmed up. Maybe the ambient temperature has something to do with it deciding to fail. I suspect as time goes on, the problem will get worse and worse until it completely fails. I definitely wanna fix it before I get to that point though. It's no fun when you worry about if your car is going to start and if you're going to get home okay!

 

If those boxes were in my 84 QV, would I tell a difference if it were already running fine with the originals?

 

Depends. Feinberg indicates on his website that the ignition map he uses is "smoother" along the intake vacuum axis, and the map could be different, if desired. Wouldn't be a super huge difference (and probably less if you already have euro version Digiplexes).

 

Do euro version digiplexes make any difference with US spec cams? (I am assuming the cams are different between ours and the overseas models)

 

I believe the cam lobes themselves are the same for the US and euro K-Jet equipped F models (but the exhaust cam is set slightly retarded on the US models). Feinberg would be a better reference for what the changes would be if you take a US engine and just change the ignition map to euro (or something else).

 

I'm asking because these types of mods interest me - but not at a great deal of expense and permanently changing perfectly good ignition parts that are not readily available to go back to if something goes wrong.

In other words, if you cannot feel ANY difference in the car's performance, what would be the point in sending mine in unless they have failed and I may as well gut them and start over since they need to be repaired in the first place?

 

I've already done this, swapping the old USA 801's for a pair of Euro 802's, keeping the OEM USA cams as is.

Not a night-and-day difference, but it seems to run a bit smoother, with a higher idle speed due to the advanced timing.

Worth doing if you can find the Euro boxes cheap enough.

 

Yes, when my original 84 QV US Digiplex (805-A)went bad, I went ahead and replaced them with the QV Euro (803-A) Digiplex. Since the Euro has a bit more advance in ignition timing, you can feel that it’s more snappier or it takes off better off the line.

 

David says that over time, the ignition accuracy and timing curves can deteriorate from the factory specs. With his rebuilds, all of the electronics including the vacuum sensor is replaced. All connectors replaced with more modern design ones. It seems that the whole box is gutted and the original case is the only thing that is re-used.

 

Interesting. That was one of my next questions, was if the US spec and Euro versions were interchangeable and what the difference was. I suspect the US versions were mapped out to comply with emissions as is usually the case.

 

The timing curve are definitely different between the US and Euro. There are some good information here when I changed my Digiplex: https://www.ferrarichat.com/forum/threads/changed-my-digiplex.577465/

 

This is what I was wanting to hear.

Back in 2015 I had an 81 GTB for a little while that had a very primitive EFI. It was from about 92 and the shop that put it in didn't even have a laptop that would communicate with it anymore.

The engine was basically stock except for this - and it was totally different than my QV. It would pull instantly from a dead stop. Like night and day difference from what I was used to.

It probably didn't have **** for extra hp but the timing advance made every bit of difference.

It was like someone woke that thing up. It was fun

 

Great thread! Thank you! The timing curve is the main difference, and that was definitely a nice "upgrade" to go with the Euro boxes like you did. Reading that one post confirms exactly what I thought.....retard the timing to run warmer for emissions compliance. Nice to see those graphs! Definitely a negative on the performance and probably overall life of the engine too.

You were pretty smart to buy those 803A boxes ahead of time just in case your 805's went bad! Searching for info online, I've heard it said more than once that finding the 803A's are like finding hen's teeth. In reality that's not so true as anyone can send their US spec boxes into David, and tell him to map it with Euro specs and you're done!

I see you're located in CA. Does you car pass smog okay with the 803A's? The smog tech usually verifies timing and it needs to match original timing specs for the year/model of car in the database. Are they okay with the advanced timing? Or, do you have to go back to 805A's during smog tests?

 

What is the approximate cost to mod these boxes?

 

I talked to David about a year ago and he quoted me something like $2400 for the pair but then when I talked to a Ferrari shop owner, he said if you are a shop owner it’s like $2000 for the pair, so if I need to send mine, I will have the shop sand it for me save a few $$. David also told me that you can send your old boxes weather is good or bad as he only needs the casing out of it because he has a whole new circuit board with all new components to go in the old boxes. You also have a choice of either a US or Euro version. That’s all I know for now.

 

I wonder why would anyone pay that and request "US Version"