Intermittent stalling - 308QV US

Hi Guys,
I posted this in the 308 forum, so apologies if it's redundant but I'm in a quandary.

A few years ago my 85 QV US developed an annoying, intermittent habit of stalling when dropping into neutral. Sometimes I could drive it hundreds of miles without it happening. Other times it could happen 5 times in a 10 minute drive. There would be two types of stall - 1) the rpms would drop normally when coming to a stop, but continue down past normal idle speed till it died. 2) when dropping out of gear from 4K or so, the rpms would drop like a rock to zero. Each time the car would start right back up. No rhyme, reason or advance warning.

In the course of maintenance and also with an eye towards resolving the issue, the following has been done:

New plugs and wires
New rotors and caps
New fuel injectors
Refurbished warm up regulator
New brake vacuum check valve
New crank sensors (all 3)
Grounded both digiplexes
Replaced spark plug extenders
New fuel pump, filter and accumulator
Full tune-up at Ferrari of SLC
New ignition coils

Now, something new has developed. After changing the coils, the car drove great for about an hour, and then exhibited the same stall at a stop. I restarted the car and drove a bit more. Then it started bucking like a bronco. It felt as if it were being switched on and off. Finally, it died and I couldn't get it restarted. By the time the flatbed arrived in 90 minutes, it did start but didn't run well. It was towed back to Ferrari of Salt Lake (who put the coils in). They said maybe the coils were n/g, and they reinstalled the stock ones. They took it for a test drive and after 15 minutes or so...the same problem. Car died and needed to be flat-bedded back to the shop.

They now tell me that the've lost the tech who knew how to work on classic Ferraris, so I'm kinda stuck. The only thing we haven't done is replace the digiplexes. Do you think those could be the issue? If I can't get this sorted, I'll have to ship the car to Denver or Monterey, where I know there shops who are knowledgeable about the 308.

Thanks for your input!

 

If you’re fairly certain that the FI system is OK, then you need to diagnose the ignition system.
When they did the work on the FI system, did they check the pressure in the fuel rail?

 

You've certainly fired the parts cannon at it . IMO, you (or the Shop) really need to do some diagnostic work to determine if spark or fuel. It could be the Digiplex(es), but their architecture is each one running 4 cylinders so your reporting that it won't run at all sometimes that seems unlikely (unless it's a common upstream power problem). As Bill wrote, if you put a fuel pressure gauge to measure the supply fuel pressure, that might help you rule the fuel side in or out -- i.e., if the supply fuel pressure stays the correct ~5 bar during the good and bad running (and the frequency valve always buzzes with the key "on" and safety switch unplugged = fuel pump running), pretty strong sign that it's not the fuel system.

What is the status of your fuseblock? Stock or aftermarket or modified? If still stock, one easy thing to do is ensure that the fuel pump fuse (#3) position is in good shape and not showing signs of frazzling/melting at the riveted connections of the metal terminal pieces at each end.

 

Thanks so much for your responses. A little more info...

As part of the full tune-up at SLC ferrari, they went through the fuel system, cleaned everything and calibrated it to spec.

The fuseblock is a birdman unit. I had an "interesting" experience soon after I bought the car when my wife noticed a burning smell and wisps of smoke rising from the passenger side dash. Changing that out was the first thing I did

I'm fairly confident given how it's behaving that it's an electrical issue. The on-off nature of the new bucking would be consistent with one bank going in and out, no?

Question...If one bank (digiplex) was out, would the car start?

I don't usually fire the parts cannon at things (though I love that term!). Most of what was done was part of general upkeep since the previous owner deferred a lot of things and the car has 70K miles. In the case of the fuel pump and accumulator, the pump actually died last year (fortunately in my driveway). I also replaced all relays. The intermittent and unpredictable nature of the problem has made it very difficult to devise a diagnostic plan.

I was content to live with the occasional stalling, but finally realized that needed to be fixed when the car stalled after dropping it out of gear on Guardsman Pass road. It's as amazing and potentially scary as it sounds. No engine = no brake booster .

Thanks, as always!

 

My failing coils where getting super hot (hard to touch) then would quit for 15minutes. Once they over-heat a couple of times, they are done. This being said a failiure of both new coils together would be extreme bad luck! (in any case check the temperature).

Installing a k-jet fuel pressure gauge and taking the car for a spin would allow to check the Fi system during a failiure.

While you were there in the maintenance, you should have replaced the intank fuel pickups: if the tank is full of crude, your new pumps won't last long (remember that filters are located AFTER the pump). Adding an ammeter would allow to monitor the pump amp-draw (lots of intank crude=high amps).

 

Good thoughts. Thanks!

 

Re-reading your post: your pump failiure last year is an indication that it may have swallowed debris from the tanks.

 

It would, at least, do an initial "cough" on start-up and try to run. Might not stay running as the idle speed will be quite low. If you'd like to have your Digiplex ECUs checked out, David Feinberg at Sarasota Italian Garage (https://www.sarasotaitaliangarage.com) can do so.

 

What does "calibrate to spec" mean exactly? What you are describing sounds like a mixture problem. More than likely a rich mixture.

 

My instructions to Ferrari of SLC was to assume nothing was correct and take everyting to factory baseline. They replaced the O2 sensor, set the idle and checked the mixture. They also cleaned and checked fuel distribution.

 

If you do have a k-jet with lambda, you should validate the ECU and frequency valve when during "hiccups". A non functioning valve can make the engine extremely lean. Here again this could be identified through a test of the control pressure (that should be way to high if the frequency valve quits).

 

Don't take this the wrong way. But I think your first mistake was to take it too the dealer. What you need to find is a shop who is familiar with vintage cars with C.I.S fuel injection systems. Porsche, Mercedes, VW all used them. They would be the best best to get your car set up and sorted out properly. Hate to say it, the dealers are fairly useless on the vintage stuff.

 

I agree. Usually the dealer is a last resort for me. I recently moved to the Salt Lake City area and have been trying to find a good shop. Posted here several times and in other forums. So far, nothing. Will keep looking.

 

PROBLEM SOLVED. And the answer was so simple. I finally found a great independent ferrari mechanic who took a fresh look at the car. He determined that the battery had one or more bad cells and theorized that it might be causing some gremlins. He replaced the battery and the car is now rock solid. SLC Ferrari had my car for the better part of a year and couldn't solve the issue (despite thousands spent on dead-end diagnostics). Kudos and thanks to Paul at Euro Planet!

 

I'm glad its fixed. However I find it hard to believe the battery in a 308 can cause all that? I would have suggested one of the protection relays on the right side of the trunk bottom are loose or not working. I hope its all good from here on out! happy driving.