Wild idle fluctuation then engine dies...

[hobieboy]

After getting the engine to start reliably from cold, I now have problem keeping the engine going when it is warm.

As the attached log shows at the beginning, the engine was happily idling steadily then out of the blue, RPM drops & MAP rises rapidly by itself. The engine did catch itself this time then recover to another steady idle. Another wild cycle can also been seen later at secL = 760 second. Eventually, the engine dies on its own.

EGT2 & EGT5 confirmed that cylinder temp is dropping so I assume that ignition really didn't happen / slow down when RPM drops.

I am dumbfounded about where to look... one theory I have is that when the engine is warm, there isn't enough fresh air supply (I don't have an idle air valve)? But this same mechanism setup had been working for years when I was running MS1

Only other thing I can speculate is that this problem seems to occur only if my WUE is below 115%. But I can't see how that affect things here.

Any thoughts?

[billr]

Post the MSQ.

[hobieboy]

Here's the msq...

[hobieboy]

Its a short test but I am 99.9999% sure the problem is now solved! It turned out that I have a faulty (leaky) injector.

I spent days trying to sort this out & started another thread (http://www.msextra.com/forums/viewtopic ... 34&t=62793) looking for advice to tune idle. What I ended up noticing was that by increasing idle PW to a large value (>3ms) I was able to keep the engine from dying even though it is running pig rich. That led me to think I may have an injector or injector driver problem. So, set up a temp injector test rig and quickly found a leaky injector.

I think what happened is that the leaky injector caused 1 cylinder to die "randomly" - at normal idle RPM, as PW oscillates below 3ms, the leak caused more fuel than needed into the cylinder and it starts to flood the cylinder. That causes the engine to stall, so MS adds fuel. This raises RPM for other cylinders and "re-activated" the flooded cylinder since we now have right amount of fuel. And the cycle continues.