348 Hot Start Issue: I Have Tried Everything!

You haven’t been mimicked the hot start problem . Only proved the injectors work and don’t leak .
I am new to 348 s but had a long conversation with a highly regarded U.K. Ferrari Indy who was around when the 348 was born .
He told me the car I purchased from him , he’d serviced it the past 10 yrs , looked after it and at some stage retro fitted aftermarket the fuel pressure regulators ( its a 94 ) bcz of a known hot start issue that creeps into the OEM regulators .Also fuel starvation at the top of the rev range is another issue they end getting as they age .

Sort of pointing at them in a proud kinda way saying “ it won’t cause any of those issues “
“ those issues “ being head straching hot starting amongst others .
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Although it should not be relevant in the case "pre and after re-learn" starting, perhaps you should try starting, after re-learn, by first priming the fuel system.

Otherwise, one thing that affects the mixture at cold starts is the resistance of the CO screws on the MAFs. What resistances are you currently having?

NOTE: Turning the CO screw Clockwise (Higher Ohms) will make the mixture Richer.

 

I've tried priming by clicking the key to on 3 or 4 times before starting, no change. I haven't measured the MAFs, but no idea how that would matter pre and post learn cycle. Anyway, I'm at peace with it at this point, roughly every 5 years I mess around with it. There's a thread in here of other 2.7 owners with the same problem so I think it's just a quirk of the system.

Op may have something similar going on, the fact it starts when floored is what's interesting. Maybe TPS issue or temp sensor causing idle air control to be off when hot? How does it idle hot? What rpm? Maybe before starting hot, click to run and cycle the tps once or twice before starting and see if that helps.

 

You cannot prime the fuel system by turning the key to "on" (whether once or many times) because the fuel pumps do not run at ignition "on". The fuel pumps will only start running when you start cranking the engine.

It is possible that the ECU, for the first start after its reset, does not refer immediately to the ohm value of the CO pots (uses its default tables) but adopts this value during the process of re-learning. If so adopted ohm value of the CO pot is too low, it will cause somewhat leaner mixture at subsequent cold starts which could potentially be your problem.

NOTE: the CO pot resistance does not alter the MAF signal (the pot is not connected to any part of the MAF circuitry); this resistance value is used by the ECU to trim the fuel mixture.

 

I have a 2.7 456GT that for the last 6 months has been having the same hot start issues intermittently. 27k miles on the car too

Currently have all 12 injectors out to Mrinjector for service and have replaced both coolant sensors. Beyond that, I have gone thru most of what else is on the list above to check. Hoping once it's back together this may be cured.

Also have a COP ignition I added, but had been running a few thousand miles on it already when problems started.

 

Could be...but the 2nd time it starts flawlessly. I would have thought failing FPR or something if it didn't always start perfectly after an ECU reset. I have video of when I did the major after it had been sitting for 3 years and it fired almost immediately. I was shocked as I figured it'd need time to fill the new filters, prime the rail etc. but it fired right up and idled.

If the MAF value was off you'd think it would always be difficult to start once it did the learn, unless there's also a routine in the ecu to ignore the trim value if it fails to start or something....

 

Yes, it is possible that the ignition "Power Modules" are somewhat playing up when hot. These modules do not control the ignition timing, only switch the ignition coils on and off (electronic switches, equivalent to old school contact points). The ignition timing is controlled by the engine ECUs (the large boxes behind the seats).

I have not experienced electronic ignition switching modules playing up when hot (only experienced their sudden complete failure) but I did have a couple of cases on my other cars where the engine would start misfiring and die when its ignition coil heated-up. It would not restart immediately but after some half an hour when the ignition coil cooled down a bit. Pouring cold water over the coil also helped.

So give it a try with new ignition modules but be prepared to also replace the ignition coils. Luckily, the coils are used by many other cars and are not very expensive. Here are the cross references for both, ignition coils and ignition modules:

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You can get the "feel" of the coil prices here: Spareto

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You don't want to have at least one more try with new ignition coils?

 

When car is hot and not starting will you humor me and spray some starter fluid in the intake opening behind your head and the start car and report back here.

 

So it will start on command if you use starter spray. You can repeat that? Your problem is electrical. We battled these ghosts almost from delivery! Let's see if we can prove it? There is a round connector from the FI harness that 3/4 turn locks into a female near the oil filter. Get a poker and bent the living fu8k out of the pins so when reassembled you can guarantee a decent contact as the male and female pins scrape corrosion off each other and contact.

There is another round connector driver left at about the rear shock tower. Do the same thing with that connector. Now start car tell me what happens? Let's see if we get lucky.

 

I don't have a 348 in front of me. I could be confusing a different model with round connector by shock tower behind and sort of under. My memory is not good anymore.

 

It's a circular 9 pin connector made of plastic. Here's a modified one...

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Just near the rearmost point of the back window.

Miro @m.stojanovic regularly posts a pinout of the plug. Later models have more robust rectangular plugs, but I don't think yours is late enough.

I can't think of anything on this plug which would produce your issue though. Alternator?

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Also known as plug 115.

Coolant temp is for the instrument panel gauge only

 

The fuel pressure is controlled mainly by the FPRs and "trimmed" by the intake vacuum (higher vacuum, lower pressure) so the difference you are having could be due to some difference/tolerance in the (cheap) FPRs you are using at the moment or due to somewhat different intake vacuum LH to RH you may be having. It could also be due to your RH fuel pump being unable to deliver pressure higher than the FPR pressure. Anyhow, not critical for the diagnostics you are performing, unless you measured the mentioned difference only soon after starting a cold engine and not also later after the engine has run for some time.

The reason why I mentioned checking the fuel pressure after the engine has run (idled) for some time is because I had a case on my 348 that the engine would start fine but, after 3-5 min. of idling, it would display the CEL on one bank and start running uneven. As I (luckily) had fuel pressure gauges installed (pics below, 3.0 Bar fuel system), I could see immediately that the fuel pressure was initially equal L & R but, after some time of idling, the pressure at one bank would start dropping from 42 psi down to ~ 20 psi. I ran the pumps "manually" and could hear that the pump for the offending side was making strange noises.

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Yes, bad contacts in this connector will not affect starting and running of the engine unless the bad contact is on the thick white wire (Pin 8) which goes to the starter solenoid. However, this will cause no cranking (turn key to "start" - nothing).

 

Hot starting , have you tried just turning the ignition on for 20 secs then starting ?

To prime up the fuel regulator (s) . Thinking like a carb F car if left for a while you have to prime the bowls in the carbs .