[Diagnosed] 2010 Dodge Caliber 2.0L Misfire, Scope capture analasys

Hi folks.,
Wanted to get your guys opinion on the following scope capture I took of a 2010 Dodge Caliber 2.0L.
This capture was taken from the tail pipe using a GM fuel tank pressure sensor (voltages are inverted for clarity: (+) Voltages = pressure)
I can see a definite pattern in the capture. I have done the following tests, Relative compression, and a Cylinder Leakage test. Customer has previously replace all plugs and coils, swapped injectors and replace crank sensor with an O.E. part.

The relative compression and leak down test resulted in nothing out of the ordinary. I also smoke tested the Intake and found no leaks. I also put a GM map sensor in the vacuum hose to the brake booster and didn't see anything that stood out.

Thanks

Crazy capture. :blink: :lol: I haven't done a ton of exhaust pulse testing, but I can speculate. For my info, is this running or cranking? When does it misfire?

Looking at the pressure peaks, I see a repeating low pulse every eight peaks in the second half of the capture. That'd be a misfire every other complete engine cycle. Not that I have an explanation, just what I see.

Looking at the lower half, with the vacuum pulses, is still kinda confusing. I can't decide if the .4V valleys are representative of the problem, or if the missing valleys are. :silly:

This was taken at idle

Got curious, had a look at some captures I took with a homemade FLS. In the exhaust at idle, with one injector disconnected.



They're not the same type of sensor, but this waveform suggests that the deeper vacuum pulses correlate with misfires. If that's the case, then this Caliber is barely running. :blink:

Nice captures guys --- really clean and clear

Not going to tag this a fixed just yet. It's almost time to go home and I wont be at the shop next Monday if the customer approves the work.

Looks like what I thought I had checked and what I had actually checked were two different things.

When I first looked at this vehicle a couple of weeks ago I could not get the engine to misfire. It wasn't until late in the day that it actually acted up and I was running out of time and the customer was here to pick up their vehicle. By that time I was into another job at the time and I had a helper swap injectors for me.

Fast forward two weeks later and I thought I had smoked the intake for leaks, well looks like that's the problem. blown out intake gasket near cylinder #1. SMH!!