Hello all. I have a 1986 Ferrari Mondial. Bosch K-Jet with lambda (lambda disconnected). The car has a hesitation under load since I bought it in June. The hesitation gets gradually worse as the car warms up. Eventually, after driving for perhaps 60 minutes, it becomes extremely rough and undrivable. Runs fine again after its cooled off overnight. Already changed lots of stuff - fuel filter, fuel pump, coils, coil-transistors, leads, plugs, battery. I've also checked all the grounds, the distributors, and the alternator function. Tested fuel pressure: cold control pressure is 28 psi, rises to 50 psi warm. Warm system pressure 70 psi. I have now bypassed the Bosch Jetronic ECU with a 50% duty cycle driver that provides a signal direct to the frequency control valve, so Bosch ECU and lambda function is out of the picture entirely. There is no catalytic converter. I have put an oscilloscope on the secondary ignition, and the waveform shows a lean condition while on throttle and hesitating, so I do suspect a fuel problem. I have done a smoke test, which found a few minor vacuum leaks that have been fixed. I have installed a wideband O2 sensor into the exhaust. This showed the car is about 13.7 AFR at idle. It got a little richer on steady throttle (about 12.5), and then jumped momentarily very lean (> 20) under increased throttle application while hesitating, but only at the moment of hesitation. I guess this could be a 'fake lean' spike caused by an ignition misfire. Just today replaced a suspect frequency control valve, which has made a big difference - car now idles at an AFR of 10.5 when cold, rising to 12.5 after the WUR reaches operating temp. Once warm, the AFR dips to about 10.5 on throttle, and she sounds a bit rough. So changing the frequency valve has had the effect of a much richer mix. Wondering if the previous owner had the mixture screw turned up rich to compensate for a weak frequency valve? Any ideas?
I am curious, where did you have vacuum leaks? Failing crank sensor can respond poorly to heat and cause ignition timing issues?
Leaks from the mixture screw hole (was unplugged), also from memory- around the large intake hose (needed a little tightening). OK crank sensor is a possibility. But my oscilloscope shows no ignition events are missing. The ignition pulse is steady. The individual spark lines do look lean though…when the car is hesitating.
