Solved - it was a vac line to the boost gauge.

I am slowly starting to lose my mind diagnosing this issue over the last few days. I didn't want to embarrass myself and come asking for help... but I think I need another set of eyes.

I was driving along on a pretty aggressive on-ramp around mid throttle when I experienced what sounded and felt like spark breakup. Upon leaving the off-ramp, I noticed my cruising AFR was pig rich (~9-10), they should have been ~15. When I pulled over at the next exit, the car went lean at idle and in non-cruise.

In the garage, the car struggles to idle and seems to be running extremely rich then lean... enough so that I'm seeing fuel out the exhaust.

I first expected an 02 sensor, but upon replacement, I am getting similar conditions.

Tested/checked

• Fuel pump works
• COPs are firing
• Compression 180 across.
• Replaced 02

My next guess is a bad CAS. I thought you can test CAS by viewing RPM movement with no spark or fuel. I have movement ~200 rpm movement during cranking... which contradicts my thoughts on that...

Heres the logs:

First is with cops unplugged, to test CAS/RPM.

The second one is a start and hold to 2k rpm for ~25 seconds, then I let it try to idle itself. Here you can see the AFRs at 7, then lean out to 18.

 

Without looking at the logs, I'll interject that if you run it rich enough to drown the spark, a misfire event looks lean - since no combustion, no oxygen gets consumed, which looks like unburned oxygen to the o2 sensor that can't tell the difference.

 

(looking at logs) And your MAP line is disconnected / poorly connected / has a hole. That's probably the root cause.

 

IAT? Interestingly enough I haven't checked that yet. I'll need to check in the morning!

 

The vacuum line that goes to the Megasquirt. You're only at 70KPA at 2k RPM which is waay high or you've got really aggressive cams in it.

 

^this. Your MAP is acting pretty strangely.
Before cranking, it sits at 95 which is fine, but then while running the engine from idle to 4000rpm it only varies from 73 to 85.
It seems like the vacuum line has a big leak in it at the MS end.

 

This is why I needed another set of eyes... I was focused on the sensors themselves.

My wife was in the car with me when this happened. She could have kicked the vacuum line going from under the dash through the firewall.

I will investigate and come back.

You guys rock - thanks.

 

Wife kicked my boost gauge vacuum line out during the turn. Just let me die inside in peace....

Thanks for all the help folks - clearly I'm an idiot.

 

Hehehe.. **** happens.