Hi
Phew, that's a pretty comprehensive list of replacements.
The rather random nature of the fault does suggest an intermittent electrical problem. As I'm sure you know, each injector has a flow and return wire to the ECU. Apart from checking the connections each end for tightness and lack of tarnish, you could check the continuity of each one with the ends removed. The easiest way is to use an ohmmeter with croc clips to keep your hands free, and set it to audible tone for continuity. Then poke, flex and twist the loom to make sure the beep sound does not falter. Also, use your eyes to check for any chafing damage where the loom is tied in place. You may find nothing amiss, but it's a process of elimination.
The reason for recommending the fuse check is that the ECU supplies the injectors, so it has a pulsed demand for high current. If the supply to the ECU has a slightly high resistance from a bad contact like a fuseholder then you can get a varying voltage drop. The ECU is fairly tolerant of this (it is internally regulated down from 12 volts to 5 volts) but if the supply volts seen by the ECU dips too low it will play up.
The lack of fault codes is a puzzle, so the other possibility is some interruption of the fuel supply. This would fit in with power loss for a second or two rather than a very brief jerk/"misfire".
The only other thing I can think of is that if the ECU detects that the footbrake is being applied at the same time as you have your foot on the throttle, it will deliberately cut power. The brake light switch has two sets of contacts, one for the lights and one to signal to the ECU. A bit of a long shot but worth checking that the contacts are doing their job and the switch isn't coming on when it shouldn't be.
Hi
As you say, the thermostat housing is clearly designed to blank off this hole. I suspect that it communicates with the inlet manifold, and will be full of carbon due to it being a "backwater" with no through flow. Also, the manifold carbon buildup may be more than usual in your engine if it has been run without a thermostat, as it will have been over-cooled to some extent for the whole time it has been running without one. Carbon/oil mostly condenses out from the recirculated exhaust gas when the EGR system is in operation. Why Fiat put a hole there can only be guessed at. Maybe for a sensor of some sort that was superseded ?
If you remove the throttle body from the top of the intake manifold (mind you don't shear off the bolts, stop if it looks corroded or they are very tight !) you will be able to look into the manifold and judge the carbon buildup. I suspect the passages are generously sized so a bit of deposit doesn't matter, but if it is seriously coked up you might want to remove it and get it cleaned out.
I'd recommend fitting the thermostat housing with a proper factory style solid gasket rather than silicone sealant which can break off and get lodged in the cooling system. Also, there is a small possibility that the gasket thickness will affect the thermostat operation.
I don't know the cause of your misfire. I would be inclined to carefully check over the ECU to injector wiring and connections (8 wires). Also, check fuses F17 and F22 that supply the ECU to make sure their connections are bright clean. Are any fault codes logged ?
Hello Anthony.
