Intermittent Stalling

[DoD70]

I am having a problem with my uS that is driving me batty. The unit is installed on my turbo-Hayabusa powered dragster and I am using it for fuel only at this time. When originally installed, I was using the tach signal from my MSD MC4 ignition system to trigger uS. Recently, I have converted to the stock Suzuki VR pickup utilizing a 24-1 wheel. It doesn't matter which system I use to trigger uS the problem is the same.

The problem is that often times while idling uS will just quit. This has happened while I had my laptop connected and I observed that the tach signal and pulse width simultaneously dropped to zero. The datalog from my LM1 clearly showed that the AFR went dead lean before the MSD stopped producing a tach signal indicating to me that uS is to blame.

Wiring is not an issue nor is the power supply, switches, etc. My uS is one of the orginal ten units that DIY Autotune sold when uS was released last year. The only updates I have made have been the VR diode and the bootloader wire is now tied to the 5v reference voltage through a 10k resistor. Both mods were made mere minutes ago based on what I have read on the message boards and neither helped or worsened the problem.

Another issue I'm having is that the motor will not rev past 5000 rpm or so immediately after starting the engine whether the engine is hot or cold. When the tach gets to 5000 rpm or so, it bounces wildly while the engine goes into a rythmic surging like you would get with a slow rev limiter. This goes away after 20-30 seconds of idling before hitting the throttle. I'm not real concerned about this second issue as it might just be a tuning issue. Maybe an overly rich after-start setting.

Any help or suggestions would be welcome. I have an exhibition race at Norwalk, Oh (10/11-12) and would really like to have this fixed by then.

Thanks in advance.

[Matt Cramer]

Do you have a data log of these happening? IF so, that would be very helpful for others to diagnose it.

[DoD70]

The datalog I have shows the AFR and RPM as flat and steady as can be. Then, the AFR goes dead lean and shortly after, the RPM drops to zero. The RPM signal being read by the datalogger comes from the MSD ignition system. There really isn't anything else that you can see in the datalog other than what I've described. AFR and RPM were the only channels that were recording at the time and I was watching the gauges on Megatune when it stalled. The tach and pulse width on Megatune went to zero killing the motor.

[SQLGUY]

AFR and RPM were the only channels that were recording at the time and I was watching the gauges on Megatune when it stalled.

I didn't know you could do that. When I've captured a datalog, it always included all the data points, and it was in MegaLog Viewer that I was able to select which values to view.

Can you post the log(s) anyway?

[DoD70]

My datalogs are done with an Innovate Motorsports LM1. I'm not datalogging with uS. I'll try posting what I have tonight but I don't know if it's going to be helpful.

[DoD70]

Just plugged my laptop into uS and datalogged using Megatune and was able to record an incident of surging while trying to spin the motor towards redline shortly followed by the infamous stalling problem. The datalog is attached.

[DoD70]

And here's the .msq.

[Matt Cramer]

I see an RPM breakup issue - something is wrong with the VR input. Try a 10K 1/4 watt resistor in line with the VR signal wire. Does that help?

[DoD70]

I'll try the resistor tonight but I thought the diode swap did the same thing. I'll report tomorrow. Thanks for the suggestion.

[DoD70]

I tried adding the resistor last night and it didn't change anything. Then I changed the MAP and TPS lag time to a significantly slower value which helped but didn't solve the problem either. More like masked the problem. The good news is that it only stalled on me once last night at the dragstrip.

I noticed while I hade my laptop hooked up to uS and had Megatune running, that the accel button on the bottom of the Megatune main screen flickers while the car is idling. Can it be that uS is adding fuel for acceleration while the motor is idling in sufficient quantity that it floods ands stalls the motor? If so, would that not be reflected in the O2 graph? When it does stall, it does so without warning. Just as if you shut the motor off with the main power switch.

Going back out for more test and tune tomorrow. Then I'll just have to go to Ohio with it like it is.