MSefi.com read only forum (Jan.15,2018)

Hello everyone. This is my first post on these forums. I have a decent understanding of EFI systems and tuning but the more I learn, the less I know.

Anyways, the test engine I'm using for my masters research is a single cylinder gasoline engine with identical cylinder geometry to the Ford Mustang Cobra engines. I've spent the last year getting it up and running but now that I'm ready to test I'm running into a few issues with the ECU/MegaTune. I didn't set up the ECU or do any of the wiring so I don't understand everything although I've been reading the MegaManual to try and become familiar.

The problem I'm having is that under certain conditions (this was steady state at 2000 rpm and an intake MAP of 54 kPa) the injector pulse width fluctuates. I had the engine running at around 13.5:1 AFR with an injector pulse width of 7.495 msec but every few seconds the pulse width would fluctuate to something around 12-13 msec (it was very brief). You can see the "clear needle" on the Pulse Width 1 gauge that shows where it would fluctuate to. Since the engine is running in the same cell for 2 hours at a time to do testing it messes up the results slightly.

I wanted to see if anyone has encountered this before and if they know of a solution. (Oh and ignore how ugly the map is- it doesn't really matter since we only operate in a few of the cells at steady state)

Are you running speed density or alpha-N?
If you are running speed density, it sounds like you are encountering wild swings in manifold pressure which is a problem with single cylinder engines.
Unless you sample MAP synchronous with the cam, you will see aliasing effects that come and go depending on RPM and sample rate of the MAP signal.

If you don't have a cam sensor, alpha-N is a simple solution.

If that's not the problem, look at the logs and see if you find a correlation between pulse width and sensor inputs, e.g. MAP, RPM, CLT, IAT etc.

Mr.D,

Your best bet is to post a datalog and MSQ.

Without seeing those, my first guess would be that accel enrichment is triggering. Increase the TPSdot (and MAPdot if used) threshold so this doesn't happen. There is more on this here: http://www.megamanual.com/ms2/tune.htm#accel.

Lance.