Software patch needed for 1500 RPM cranking XFI spike!


Classic fast, XFI, SPortsman & MS3 programming
May 25, 2001
The issue with the 1500 RPM spike ant 100% duty cycle effects many buick users, and is a mystery why it can;t be sovlved. Can Fast please make a software patch that limits the injector duty cycle when in start mode (under 400 RPM)..
I'm still not convinced it causes and issues. I'm also thinking it may be beyond a software patch anyway. If I remember correctly it seems that the spike occurs when the ECM commands the fuel pump on and the noise is probably internal.
Not sure on its cause, but i don't like it.....
This is my friends car with a msd crank trigger on a v8..
These look like display artifacts calculating RPM when accelerating from or decelerating to 0. The ECU calculates RPM by measuring the time between any two successive crank pulses. When first cranking or stopping cranking there isn't really a stable starting or ending pulse as the engine quickly accelerates up to cranking speed or decelerates to a stop. The occurrence of these artifacts can also vary by where the reluctor is in relation to the sensor when starting or stopping, the sensor reluctor air gap, or even the initial cranking speed as it relates to battery voltage. Once either a stable succession of pulses is received or the ECU decides that there are no more pulse coming, the trace will appear stable.

Regardless, these are display artifacts, not a real indication of what the ECU is doing with regard to fuel delivery. The actual rpm measurement is not used for cranking fueling nor is the injector duty cycle used for anything other than reporting and diagnostics. The injector duty cycle is simply calculated from the rpm (time available to inject) and injector pulse width. The important variable here is the injector BPW. This is a true indication of what the injector is doing every 4 crank pulses (for a V8) when cranking (always B2B when cranking).

There might be a way to improve the appearance by averaging during cranking and if there is, I'll see what I can do to implement it but I don't think this is a real fuel calculation problem; simply an aesthetic one.
Well said and good explanation. My car has this same spike but never seemed to effect anything.
So Lance, how about using your pull to get some Dash updates? Would be nice to be able to log more XFI parameters such as clutch flag to sync up the data as well as some other parameters that would be handy like can sync. As of now my XFI is loaded with other more important stuff and would like to depend on the Dash to log the rest.

Sent from my iPhone using Tapatalk
Thanks Lance, as long as its not dumping fuel in , which some people have claimed its happening, then its not that much of an issue. I know many people including me have spent hours, re-grounding , relolcation the ecu from sources of noise, and even running the starter from another source of power to eliminate this with no -success, a software patch would be a good solution.
Kind of funny, but not really.

Working on a older Ford and seeing the exact same thing. 1500 RPM / cranking spike, timing jumps from 11 to 28, and fighting the starter.
During the same cranking cycle, RPM spiked to 9100 RPM / 34 timing. Screenshot attached.
I have send the logs to XFI support and they claim this to be electrical interference, recommending rewiring switched power. After reading this, I am no longer convinced that is in any way a valid solution.

If my understanding is correct, there doesn't appear to be a definitive solution other than taking the XFI out and replacing it with something else?

View attachment
You have too much timing in it on the start up, what is the ignition system, the spike has no effect on start up that I have encountered. It will go to the lowest rpm cell at 99 kpa and reference that timing on crank, unless you have an ignition module with est and bypass control, then it will use the timing base set in the module.