Corporate Hippie

First off, happy thanksgiving!

I just picked up a 93 with a Greddy kit yesterday, awesome Craigslist find, $2100 with 118k and a hardtop, but it also came with some issues. The transition from vacuum to boost is far from smooth, and the car seems to have little to no power when part throttle from low RPMS. I've had a 1.6 N/A before and it feels slower than stock when accelerating before boost. If I hold 25% throttle from a stop, it feels almost as if it's missing or starving for fuel up to about 4500 RPMs, bogging all the way there, then full power comes on as if there was never an issue. If I take off agressively, the car usally does better too. But my low and midrange suck. If I go into a corner and try to apply throttle the car does next to nothing or bogs a little bit, until the RPMS are high enough.

I thought maybe the Vortech FMU was bad, but it doesn't make sense if at full throttle/high RPMs it's fine?


Did a compression test last night to see the overall health of the engine and I got 175psi across the board.

Here is a quick video of my CEL Codes:





If I translated that correctly, it's

1 - Ignition pulse (No Igf signal)
8 - Airflow meter open or short circuit
17 - Oxygen sensor unchanged after 1500 rpm

Any help is appreciated. I have another AFM from a swap I'm going to throw in when I get a chance to see if it makes a difference, and am also ordering another 02 sensor to see if that helps.

Corporate Hippie

Also want to add, occasionally it will idle high or idle almost as if it has an aggressive cam.

AdamC

Sounds like a faulty/worn o2 sensor. Its like its too rich at low RPM causing it to bog and feel slugish. Do you have a wideband setup?

Corporate Hippie

Putting a wideband in it this weekend, my symptoms sounds exactly like the ones in the following thread which was resolved with a new fuel pump, hoping that's not the case.

https://www.miataturbo.net/ecus-tuni...4k-rpms-60504/

Going to try disconnecting the 02 completely right now, then tps, then both to see if it runs any better. If not I have another AFM I'm going to try, and if all those things don't work I may have to bite the bullet and order a fuel pump. Is there any way to test the factory pump before I commit to a walbro? Why would a bad fuel pump work well at high RPMS but not low RPMS?

**Checked the plugs too and they still look new, I know if it was running too rich it doesn't take long for them to get sooty. **

Corporate Hippie

Did some troubleshooting and I think I can rule out the pump at this point.

The car runs BEST with BOTH the TPS and O2 Sensors unplugged, any hesitation/bogging issues are gone at that point and it transitions into boost much more smoothly. I would say in this state it runs well 90% of the time. The other 10% it will still hiccup and have the hesitation issue but nowhere near as badly as with both sensors plugged in.

If I run with JUST the TPS unplugged, and the O2 connected again it's 50/50 as far as the issue coming up, and a horrible idle of course.

If I run with the TPS connected and the O2 disconnected, the issue is still 100% present.

I have not tried swapping in another AFM at this time, but going off those symptoms does anyone have any suggestions?