AF DROPS AT THROTTLE, IDLES great

[John1978s30]

hey gang, recently re-aquired my first car (78 z 2+2 manual). it ran a little choppy until I replace the air flow meter and ran great for a week, then choppy again. Since the AFM was from a junkyard in AZ, i again assumed that was the issue.

...Log story short - I decided to purchase the FAST EZ EFI system from z-car depot, also replace the exhaust manifold (rusted and cracked), powercoated the valve cover and intake manifold, deleted and plugged the egr...blah blah blah.

Now, with everything installed and new ecu wiring harness and sensors, it idles great, all readings look fine <attached pic is warming up>

Once it warms, if I touch the throttle, it wants to stall and I hear a small hiss. IF i hold throttle far enough to not stall, say 1400 rpm's, the Air Fuel ratio drops way too much.rather than increasing as it should i.e. 8 or less.

fuel pump and pressure regulator are not that old. fuel clog?

[Patcon]

block off any vacuum ports you can, like the brake booster and see if that helps

[Captain Obvious]

Still early in the investigative process, but a hiss sound just off throttle sounds like the ported vacuum that drives the distributor and CARB can.

Did you remember to hook that little vacuum line back up after you were done messing with the AFM duct to the throttle body?

[chaseincats]

On 9/24/2019 at 8:11 AM, Captain Obvious said:

Still early in the investigative process, but a hiss sound just off throttle sounds like the ported vacuum that drives the distributor and CARB can.

Did you remember to hook that little vacuum line back up after you were done messing with the AFM duct to the throttle body?

I second this.  This vacuum line only receives vacuum when the throttle pedal is pressed.  If you are hearing a hiss (vacuum leak) only when the throttle is pressed then it should be this port.

If the vacuum line is indeed connected to the bottom of the throttlebody then it might be the distributor's vacuum advance pod's vacuum bladder is dead (this was the problem with my car.  Cap off the vacuum port on the throttlebody and see if that changes anything (if thats the problem, that will be all you need to do to fix this).

Edited October 22, 2019 by chaseincats

[John1978s30]

Thanks all for the replies, some good info in the thread that I didnt know.

Update: The hiss was from the new IAC I installed to communicate with the new ECU. Vacuum system was sealed and good to roll. The vacuum source I had hooked to the MAP sensor was too weak to register with the new ecu (notice in the pic above it's pegged at 100). A speed shop noticed this and hooked it up to the brake booster instead. I toned the accel fuel dump way down (was AFR was way too rich) they did some config on the injectors and boom. Car is running solid and now a good daily driver w 50k original miles!