Model Range, Interest:1300cc 128 All- Enigmatic Fuel Starvation Problem
My personal '76 128 began to exhibit strange symptoms a few months ago- It ran great at idle, and under partial load. Under heavy load or accelleration, it would seem to starve out & die.
The engine could always be restarted, and driven, but would cut out intermittently until driven for a pace at very light load, or heavy vacuum
I began by doing a fuel pressure check, which came up low (.7psi at idle)- I replaced the mechanical fuel pump (lot's of 128's have been retrofitted to mechanical, including mine), which raised the fuel pressure to 1.8psi at idle. This helped, but did not eliminate the fuel starvation. I pulled the carb, professionally cleaned & rebuilt it twice, and this was no help either.
At that point my 128 was retired from the road for a while for some other necessary work. Now enter David Voss' '78 Rally Coupe. This car was equipped with a healthy electric pump, and exhibited the same symptoms... We started with another carb overhaul... No effect. Many conversations later, we finally obtained specs for necessary fuel pressure, and decided we were not getting enough fuel pressure under load. David's car was reading about 1.0psi fuel pressure at idle, and almost nothing under load. After long discussion & inspection, we found that the small check valve in the fuel return line had gotten weak, and was bypassing pressure back to the tank. David's valve was so weak that it could be blown through in both directions with about equal resistance.
So, after replacement of the valve, David's 128 seems to be cured- His fuel pressure readings are great across the board, and the car runs like a 128 again... I'll report back after I get mine off it's jack-stands & run it with a new valve, but I think we've finally gotten to the bottom of it. The check valve is P/N #7574103. It currently lists for about $28 through Fiat/North America, but it's money well spent if your 128 is exhibiting these symptoms.
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