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Hey guys i’ve been chasing this flashing rabbit hole, So far i’ve replaced all intake side gaskets cleaned injectors replaced spark plugs and tested coils, Installed a catch can (high crankcase pressure) And cleaned Grounds. Also did a compression test which all came back good. Forgot to mention the Car is Cammed so a lot of usual tests become a lot harder. The car is tuned so no concern there.
Im leaning either a cam or crankshaft sensor but i dont want to jump to any conclusions so im reaching out to anyone who has maybe encountered a similar situation.
A flashing MIL is a “cat damaging” misfire so you don’t want to be driving it around like that for too long…a compression tests only shows a cylinders ability to “seal” but not move air in and out of that cylinder…my advise to a DIY’er chasing a misfire is other than changing plugs and wires you don’t possess the advanced diagnostic equipment to diagnose this so you are just wasting your time and money…find a diagnostic shop in your area that has this equipment !!…BTW, how did you test your coils and do you know which cylinder or cylinders are misfiring ??…which tests become harder with a “cammed” car ??
Well the car doesn’t have cats and the rear O2 Sensors are tuned out, Now does that mean my car might be acting weird, maybe so i’ll take a look, and with a cammed car, audibly it’s harder to hear a clear missfire but actual diag wise when a cammed car gets tuned they raise the car stock values to adjust for the cam, Map and spark plugs advance which can both be useful, Map being higher combined with other things at least from what i’ve been told by people who have been doing it for awhile, Can make the computer not see smaller misfires, and spark plug advance can help see if the car is pulling timing but on cammed cars the number is usually All over the place. Part of me feels like it could be a crank/cam position sensor that’s on its way out but i’ll recheck over my O2s.
Ok, first thing the crankshaft position sensor is the engines’ “misfire detector” so when a misfire occurs the crankshaft slows down and when a certain threshold is passed a misfire will be seen…MAP being lower on a cammed car with higher valve overlap or even a higher MAP reading has nothing to do with misfire detection…to verify a cylinder is misfiring and positively identifying which one I use a pressure transducer in the tailpipe to see this and the misfire will produce vacuum in the combustion chamber instead of the exhaust gassed being “pushed out” of the exhaust manifold…this vacuum (circled below) can be seen in my waveform below….I can run a car for hours until I might see a misfire and yes some misfires which are called “phantom” misfires can be set by the ECM…I don’t know if all this started after your engine work was done but a “crankshaft variation learn” should have been done by whoever did the engine work…a crank position sensor change also requires this procedure…any vibration like worn torque tube bushings can also set a P0300 since these vibrations also cause the crankshaft to slow down….if I were you I’d get it professionally diagnosed !!
I highly doubt your tuner will be able to diagnose your misfire…you need more than just a scan tool !!…if he does attempt to diagnose it let us know if he is successful and how many parts he changes.
Sorry i say tuner becuase Thats usally all he does for me but he's the owner of a few Normal Mechanic Shops, Used To Be Peformance, They Have Everything they need for this.
I just ran my last test, and I'm 99% sure I found out what it is. I reconnected the rear 02s and took it for a drive. There was no flashing light, and the car definitely Drove Better. There was only one cold start, so there is always a chance of it coming back, but as of right now, I believe it is fixed.
The rear O2’s only monitor how the cats are working and have nothing to do with the fueling “schedule” and whether the car is running rich or lean…keep looking !!
Okay so quick update I Got the test done the one you recommended there was no loss the line was straight across, So i replaced plugs and coil packs issue still persists, Replaced the heads partially because i had an issue of spark plugs having a slight wiggle to them even after torque. and a new intake manifold both mostly for power but also to knock out more problems. issue still persists i’ve cleaned grounds, the only other issue that popped was a loss of ecm contact that came and went, The car is currently untuned so possibly could be the problem but i have a feeling it’s not, Do you have any other ideas?
My only idea is to take the car to an automotive diagnostician…you will only be replacing more parts and sometimes you can even “build in” another issue with a “bad” new part…you need to test each new part after installation…if your tuner has “everything they need” for this they should be able to diagnose it…if they don’t use a labscope they won’t !!
C6 Corvette Blinking Engine light
