Lambda Goes Lean on a Twinspark with Emerald ECU
I've been running my Twinspark on an aftermarket ECU for a while. It's an Emerald K3. I have Spica Throttle bodies and no AFM or MAF. Using MAP, but currently I am not doing anything with the signal. I have a Wideband 02 sensor with a PLX controller to do adaptive (learning) mapping. So currently the car is mapped with RPM and TPS.
Every week for that last few, I've been reading the adaptive corrections and writing them to the fuel map. That's going OK. There are a few edits as I go through different driving conditions.
Last week I experienced a bit of stumbling at low throttle positions. RPM between 2500 and 3500. Sort of like when cruzing, easy on the pedal. I opened up the live screen on the laptop and when this occurs, the Lambda reading goes full lean. This week when cold it is very bad, but settles into only stumbling a little when fully hot.
Did a search here and online and found many people who have seen this say the sensor goes bad this way. Especially with the type of sensor that I have. It's the LSU 4.2 variety which is prior to the 4.9 which is longer lasting and more reliable. I got a new one. This did not change the stumble.
To verify, I turned off the adaptive mapping and the closed loop mode and am just running on my fuel map, open loop. The 02 reading should not affect the running of the car. It still stumbles.
Others have also mentioned air leaks. Exhaust leaks would affect the 02 reading, but not the running of the engine if the 02 is disabled, as I have it. Intake leaks would affect the running if the intake air were metered with an AFM or MAF since the ECU would have a false reading. I don't have metered intake air. I think air leaks is not my issue. Is my thinking sound here?
I am left with thinking that one or more injectors is not squirting. What do you think of my conclusion?
If that is the case, are there any suggestions on how to determine this? I have a fuel pressure gauge near the FPR and the fuel pump is a loud one. The fuel pump sound is constant when the stumbling happens and the guage reads fine 41-44 PSI all the time.
It could either be a fauly injector or an intermittant signal to the injector. Does a fauly injector behave this way? I don't know injectors all that well.
I am doing batch fire, so there is only one wire from the ECU firing all injectors. I did it this way because I am using the stock harness and the Bosch ECU fires them this way. The Emerald folks suggested that I use separate wires, but said one driver could handle the load of 4 injectors with no problem.
Is there a way to measure the signal to the injectors while the engine is running to associate the dropout to the injector signal?
Hoping this is common enough to have some simple solutions.
iachella [at] gmail [dot] com