348 Difficult to start when the engine is hot

So the cranking is fine? Is there just a problem getting the engine to run?

Fuel pressure regulator?

https://www.ferrarichat.com/forum/threads/explain-hot-start-versus-cold-start.189204/

I had a problem on one car (not a Ferrari) where heatsoak was affecting the vacuum hoses and they were collapsing.

 

The engine is, for some reason, running too rich. A few things to check first:

1. Vacuum lines to the pressure regulators. If one or both vacuum lines are leaking or collapse (maybe only when they get hot and softer), this will cause higher fuel pressure.

2. The pressure regulator(s) themselves - you can check the fuel pressure if you rig-up an adapter. According to the manual, with the vacuum lines to the regulators connected, you should have 3.4 Bar (+/- 0.2 Bar) at idle and 2.7 +/- 0.3 Bar when you switch the engine off. If the vacuum line to the pressure regulator is leaking or is collapsed, you may get ~ 4 Bar at idle.

3. The coolant temperature sensors.

Other reasons could be leaking injectors but it is unlikely that many of them would leak, perhaps one or two which should not cause the kind of rich running that you have. Another possibility is bad contact(s) in the MAF sensors connectors - check them and clean them if dirty/corroded and do not use any dielectric grease on the pins.

 

What year 348?

Re fuel smell when followed. Does it have the cats on it?

 

Here is the fuel, vacuum would be 72.

I agree with Miroljub, sounds a bit like leaky/stuck injector or bad fpr. Any CEL lights? Are the working, when you turn the car ignition on but not start do they light up?

Double check loose fuel lines, injector rail, filters, fpr, cracked fuel line on filter, check for leaks around the pump, drain and in/out lines and eliminate physical leaks first, probably can only tell when system in pressurized you may smell it in the garage if it is a physical leak. If not and only when behind car, running rich is likely


Injectors, FPR, O2, MAF is the order I would start replacing. But that's me I replace everything. Its all due anyhow its a matter of time before you start getting stranded for all those items anyhow.

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If CEL's are working and your not getting a CEL due to rich condition, O2 or water temp sensor etc is likely a physical leak, or at lease I would suspect that first. That's for the fuel smell. Not sure how its related to hard start except perhaps low Fuel pressure perhaps.

 

Well, there's your eye burning, fuel stinking exhaust.

 

Which explains why mine did the same, but only somewhat. Turns out, I had one good cat and the other was empty. What's odd, they both seemed like they were there since the beginning (badly corroded mounting hardware).

 

On my non-Ferrari car, this vacuum line going to the fuel pressure regulator was resting on the engine in the "V", and got very hot which accelerated the degradation of the rubber. I don't know if it's the same on the 348.

Unfortunately, the Ferrari fuel pressure regulators themselves are hard to find and quite expensive. I see there are part number variations between cars (at least on USA cars).

 

The replacements are on rock auto and come from std products. The Bosch fpr new don't exist.

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The FPR is #1. There is one on both sides in that location.
#2 is supposed to be an IAC your car looks like its a vacuum can there. They look like this. Never seen a car with a can there like yours. Its's #13 in the parts diagram. They are way cheaper if you xref parts.



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Hard to say. For now, I would just be checking the vacuum lines to both FPRs. You won't know if an FPR is faulty until you check the fuel pressures. If you can pull the vacuum line off the FPRs, check for fuel in the vacuum line.

I can't figure out what "2" is. It doesn't appear in any of the parts manuals. Things like IACs and Aux air valves need an electrical connector.

 

The thing (#2) that looks like FPR is a "frequency damper" - it dampens the pulsing in the fuel line caused by the injectors. It is strange that you have the dampers as it appears that they were used only on 328s and Mondial QV. What is the Bosch numbers on it?

I have one damper (Mercedes, I think) with a vacuum port and the Bosch number on it is 0 280 161 007.

 

Not installed on 348 that I know of, no diagram show it either. Regardless I would replace it with the IAC as the Mondial T diagram shows the same IAC as the 348.

Good option = https://www.ferrarichat.com/forum/threads/iac-valve-options.616769/

You can also xref the Bosch part number it was used on Audi and VW cars as well then search for the Audi and VW numbers.

 

Looking at your picture, I just realised that the damper (#2) appears to be in the idle air line, not in the fuel line. If this is the case, this is somebody's idle air control re-engineering attempt. This thing is, on some engines, inserted in the fuel line to dampen (smoothen-out) the fuel pressure pulsing as the injectors open and close, not used on any 348.

On the 2.5 348, the idle air is controlled by a by-metallic device having a 2-wire connector:
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See this thread for more details: https://www.ferrarichat.com/forum/threads/fuel-pressure-regulator-348-tb-euro.569486/#post-145821210

With regard to the 2.7 348 idle control valve (motor) with a 3-pin connector (like the pic below), you cannot use it on the 2.5.
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Replace both.
You car is 30 years old = the fprs are 30 years old.
Time for some new ones.