For my sins (and the sins of my parents, and my parents parents) I have an X1/9 fitted with a 1,500cc single point injection engine from a Regata 85S. It's complete with standard Bosch ECU and Marelli digiplex, pictures attached. It's perfectly fine except there's a rev limiter that cuts in at 5,500rpm, which is annoying. Two questions a} is the limiter in the ECU or the Digiplex and b} is there a simple way can I delete or modify the rev limit? FWIW the engine was came from a 1989 85S automatic. I've also tried a spare Uno ECU but the rev limit is still there. Also FWIW the Uno didn't come to Australia. And, finding someone with a scanner that can read the ECU is proving impossible, which is character-building. Thanks in advance for any insights
Technical Where's the rev limiter please?
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Technical Where's the rev limiter please?
Rev limiters from that era normally operate by cutting the ignition spark rather than by cutting the fuel supply. Were this a carb as opposed to an SPI then this would definitely be the case. The Digiplex was used on both carb and later fuel injected models.
On our Regata 70S, Uno SX, Tipo 1.6 ie (SPI) and Strada 130TC we (as far as I can recall) have never hit any rev limiter. You mention Automatic. Was the Uno spare Digiplex unit also from an automatic Uno? Could be that the units for automatics had rev limiter function because over reving an automatic box can be very expensive!
I suspect the rev limiter is in that paticular 434 unit and not the Bosch ECU.
You can check this with a simple meter (suggest analog needle type). Measure the voltage on the Digplex output drive. It will change with rpm and when you get to 5500rpm is there a marked change in the reading?
If it is in the Digiplex then I doubt there is anyting you can do about it. I know that on the Tipo one of the spare pins retards the ignition by about 5 degrees when grounded. Could be that one of the other pins enables/disables rev limiting but you would need to check all the pin wiring against a 'normal' Digiplex setup.
On our Regata 70S, Uno SX, Tipo 1.6 ie (SPI) and Strada 130TC we (as far as I can recall) have never hit any rev limiter. You mention Automatic. Was the Uno spare Digiplex unit also from an automatic Uno? Could be that the units for automatics had rev limiter function because over reving an automatic box can be very expensive!
I suspect the rev limiter is in that paticular 434 unit and not the Bosch ECU.
You can check this with a simple meter (suggest analog needle type). Measure the voltage on the Digplex output drive. It will change with rpm and when you get to 5500rpm is there a marked change in the reading?
If it is in the Digiplex then I doubt there is anyting you can do about it. I know that on the Tipo one of the spare pins retards the ignition by about 5 degrees when grounded. Could be that one of the other pins enables/disables rev limiting but you would need to check all the pin wiring against a 'normal' Digiplex setup.
Thanks for the insights. It at least narrows down the target. I tried a spare (Uno) ECU, I don't have a spare Digiplex. If the rev limit is still there with both ECUs it reinforces your message
Info I have is: (Note Strada = Ritmo)
Yours = MED 434M (Digiplex 2)
From my resources in Fiat Manuals
Regata 1300ES = MED 405A
Regata 1600TC = MED 406A
Strada 1100ES (to 1985) = MED 404A
Strada 1100ES (from 1985) = MED 414A
Strada 1500 = MED 416
Strada 105TC = MED 406A
Strada 130TC = MED 408A
From the Internet (could be wrong)
Strada 125TC = MED 407A
Croma 1600 CHT = MED 412A
Croma 1600 CHT = MED 416A
Croma Centralina = MED 419A
Croma 2000ie = MED 419A
The problem you will have with using another model number Digiplex is that the ignition timing advance curves and possibly the static advance values will be different. Car performance could be seriously affected.
I've never opened up a Digiplex unit to see what is inside. The whole innards may be potted hard resin or possibly a softer rubber/bitumen compound
thanks again! I think maybe my 434M might be the softest tune there is, given it's a US spec emissions engine
