MoTeC Global Forum

Hey,

since a while I am facing the issue, that the car jerks heavily when accelerating. Especially when shifting from 1st to 2nd gear and carefully pressing the throttle it feels like an escalating regulation. Sometimes still driveable, somtimes I have to press the clutch and try to release again.
By changing the injectors and some connectors it's still possible to put the car back to it's original control unit, where I don't have this issue at all, so I'm pretty sure it originates from the tuning and not the hardware.
In the logfile you can see the jerky behaviour in the lambda value (e.g. at 95 seconds or 168 seconds). The lamda oscillates around 3-4Hz in this case, however I don't see any regulation from the MoTeC neither in ignition nor injection with this frequency.
I would be very grateful for any help or ideas

Hi,

There are a couple of items to look at. Your Ignition Timing Man table has a large step in it that you are going into when you are accelerating, you Fuel Mixture Aim remains at Lambda 1.00 through the whole log where it should go richer under load. It laos looks like your Fuel Film Primary settings also need work, this covers your transient fuelling behaviour.

Thanks Dean. The ignition table was tuned using a pressure sensor for MFB-indication, however you're right that there is still a large step. I smoothened it a bit but it brought no difference.
I was mainly asking because I can only imagine the behaviour originates from a miss-regulation of the ECU, however I can't figure out where exactly it comes from in the log data. Probably the fuel film setting, however the oscillation remains, even if I deactivate the primary fuel film.

May I ask a couple of questions please...... Can I confirm this is a 4 litre 6 cylinder Jeep engine, naturally aspirated, manual transmission? And the alternative fuel is 100% ethanol? Also, can you confirm the throttle does go to 100% and you were doing this testing at around max 2/3 throttle? Thanks.

Edit, also, can I have some timestamps from the log pinpointing the areas where your problem occurs please?

Yes, exactly. It's a 4.0L Chrysler Engine, naturally aspirated, manual transmission. Only Injectors are new ones (and some additional sensors of course). Ethanol content is about 16% in the log file I sent above.
Possible timestamps are 195s, 168s, 200s.
I can confirm the throttle sensor is well callibrated, only lower range was used during the issue.
I appended another short log file, which shows the same problem at the marker, but with ethanol content 20%.
I know that perecise tuning with these arbitrary ethanol values makes not much sense, however I hoped to find at least the origin. You can see the oscillation even in the vehicle speed, but e.g. not in the injector duty cycle.
Thanks a lot for your help!

My next question, have you changed the ref and sync sensors and trigger wheels or are you still using the Jeep TJ stuff?

We installed a custom 60-2 trigger wheel with sensor on the front vibration damper (inner part, no connection with the rubber-buffered part). For sync I just spliced the original sensor signal, that sits in the distributor housing.