I've done a ton of research into this, and for the life of me I can't figure out what's going on with this car.
I've basically done a full rebuild on this car, everything sans engine internals. Long story short, everything is back together, and the car will only run with the AFM unplugged. Everyone keeps telling me I have a bad AFM but I have tested them by the shop manual. I have also had some recent suggestions that it might be my ECU. While I plan to go MSPnP eventually, that's an expensive dice roll to throw at a car, which may actually end up further complicating an issue.
Any help is appreciated!
If I press the gas pedal too quickly when the AFM is unplugged the car will die. With the AFM plugged-in using throttle seems to make it die faster than the measly 1-2 seconds it'll "run".
- Car has no error codes
- Vac gauge reads about 22 in/Hg at idle (I am at about 1,300 ft elevation)
- O2 sensor reads rich at about 11 or 12 ratio
- I have NOT timed this using the CAS yet as I cannot get it to idle under normal conditions. (I moved the CAS until the engine sounded good)
- New aftermarket fuel pump and filter within last 500 miles
- Injectors, fuel rail, Fuel Pressure Regulator, CAS all pulled from a motor that was working about 4 weeks ago. They sat on a shelf until I put them on about 1 week ago.
- Head has been gone through by a local race shop: Cleaned, pressure checked, resurfaced, valve job
- Engine has ALL new seals and gaskets
Things I have done so far to try to fix this:
- Cleaned and re-tightened all grounds
- Re-Torqued Intake Manifold (thinking it was a vac leak)
- Swapped Fuel Lines to confirm proper routing
- Confirmed spark on all cylinders by pulling plug wires individually and observing spark
- Jumped the fuel pump in diag box
- Pressed the AFM flapper by hand (with AFM plugged in) to confirm the fuel pump kicks on: and it does
- Tested the AFM per the shop manual and resistances are within spec. (I even bought another one on ebay and it didn't help)
- Sprayed starter fluid in places I would suspect vac leaks (none)
- Tried unplugging my wideband O2 and plugging in the factory O2 into the harness (no change)
I am SURE that one AFM has never been tampered with (as it worked before I took it off the car 1 week ago). The new-to-me used one I recently purchased could have been, but from my closest visual inspection seems to have not been tampered with. I tested the units per the shop manual as follows:
I also referenced this thread: properly testing an AFM / acceptable values - MX-5 Miata Forum
But couldn't make much sense of the "reference voltage..." and whatnot. Not sure if my testing methods were proper or not but my readings on my AFM's are nearly identical to what the OP in that thread posted.
Here is the Image of the graph that the "output voltage" of the AFM should be....but I have no idea where/how to test these numbers in the car (since the car won't actually run).