Good day community, I have encountered this some time ago, but thought examine some doubts before posting. Now the following observations: Whenever dropping to half a tank of fuel, the car starts acting as if it had a pitlane limiter engaged. For those that are not familiar with that device, it can be best discribed as a button that - when pressed - somehow limits the amount of ignitions per second, in order to reduce the revs. to an amount that holds a certain speed in the engaged gear. (Wish I had found an official text on this somewhere) The engine sound changes significantly: It gets a deeper tone, probably for missing every second spark. At the same time, you could press full throttle but the car will not accelerate any further. Now that I (hope I have) explained what it seems like, here is what my '92 US spec T is doing after driving excellently for the first half of the resevoir: Happily driving in 5th on the highway, you want to accelerate a bit. Pressing the accelerator normally would result in a nice push into the seat accompanied by the trumpet-like sonore that we are all so fond of. Now however there is no additional propulsion and the car sounds like someone is farting into a Tuba. It occurs only in the second half of the tank and get's worse the lower the level drops. At a certain point it will occur in any gear and the only way to get to speed is to accelerate VERY gently in any gear and changing at relatively low revs. For the record: NO LIGHTS are showing on the dash. Stopping the car, letting it sit for a while (no it was not running hot) solves the problem for a while, but then it comes back. Fueling it up to the top, solves the problem entirely - until you get down to the second half again. What the heck could this be ? If it were the fuel-pump, why does it only occur when half empty and beyond ? If it were the ECU's, again, why only at low level I could think of maybe the fuel getting hotter the less is in the tank, and thus causing bubbles of evaporation somewhere in the lines, but then this would have to occur on long drives only - but it doesn't Has anyone ever encountered something alike ? Best regards, Jan
The fuel pumps have to "lift" the fuel up into the pump, and the fuller the tank, the more the fuel in the tank helps to "push" the fuel into the fuel pump inlet -- i.e., if you had some sort of partial blockage in this inlet path = more fuel would get past the partial blockage when the tank is full. Also, if the partial blockage is bits of deteriorated rubber gasket = could be worse when the pump heats up (the rubber debris expands and get softer). Just bloviating, but you are still left with determining if it's fuel or spark. Based on your description of the symptom (consistently happening with fuel level), measuring the fuel pressure on each bank when things are OK, and not OK, would not be unreasonable IMO.
Old post, but I owed the solution: After I dropped both fuel pumps and cleaned the filters on them ( https://www.ferrarichat.com/forum/posts/149118193/ ) "cleaning the 348/T fuel pump assembly" I took the car for a nice 850mls road trip last weekend and can report: PROBLEM SOLVED !!!! Car has full power all the way down to almost empty (with the reserve-lamp on for already 50mls). .. and dude, it pulls beyond 5.500rpm, even in 5th ! Now all questions are answered: - It must have fed itself through the bypass straw whilst fuller than half - once below the straw, the pumps sucked more vapors than fuel as this was blocked up by the accumulation of gum >> causing the loss of power - when parked fuel must have slowly penetrated the blocked filters solving the problem for a short while I am so glad I found the problem, and to be able to give an advice to the community: If your car acts as describe in the initial post, or in anyway has different behavior once your fuel level drops below half, then it is worth dropping the fuel pumps and check their filters. If you do not account for the soaking and cleaning, this can be done in 3h time. Include the cleaning and it is an overnight job for the weekend. happy motoring, Mondi Cab
