1977 280z Idle Fuel Pressure 28 psi - Factory Service Manual says 36 psi

[Zed Head]

I originally installed mine to see if I could fix the hot start problem by adding fuel (it helped the engine run better but you still had to wait for the injectors to cool down). Then I installed an AFM with a lean spot at low RPM and ended up using it to get rid of the lean spot. So I tune mine by throttle feel. A lean spot will feel like a lag in response followed by a surge as the AFM vane passes through the area.

Not the best fix, since it's probably rich in other areas, but it's a pretty handy band-aid.

[FastWoman]

@darom: Glad it all worked out for you! Nice implementation of the pot!

@Kjeese: I adjusted my pot on the basis of a few things: (1) Exhaust flow and smell, (2) idle vacuum/RPM, (3) off-idle vacuum under constant load (A/C compressor), (4) plug color. I found a happy, all-around middle ground that gave me good results on all of these.

[jkeese01]

Drove the Z today for the first time after adding the 5k pot. Car seems to run smoother when set at 1k. This mod is simple to build and definitely worth adding.

[78sid]

Very timely post for me. I've been rebuilding a Z for three years and I'm about to get it back on the road. The engine has been rebuilt and all the components tested per the FSM. In testing my engine which is almost completely stock for leaks and other issues, I've noticed that it runs fine until it warms up. Once it warms up, the idle drops and the car shuts off. If I hold the throttle only slightly, it will run fine, but if I rev it up slightly and back off, it shuts down immediately. I can restart easily with slight throttle, but I have to hold it.

I'm thinking I need to try adding this fuel pot, but I'm also wondering if the idle set screw could help. Turning that screw seem almost as hopeless as getting out a spindle pin. Any input would be appreciated.

78 280Z

[FastWoman]

Your idle screw won't turn? That might be all your engine needs.

[78sid]

I did get it to turn using vise grips, it is all the way down or at least the spring seems to be tight. It did improve if only slightly but the engine still slowly idles down to shut off once the engine warms up. I'm assuming that tightening the screw increases the idle speed. I was also wondering if I could adjust the idle screw on the AFM and get some results. I was going to try that before trying the pot.

[Zed Head]

The idle speed screw actually controls air flow through a bypass channel. Turning the screw out (counterclockwise) increases idle speed.

The AFM screw just controls the air/fuel ratio, at very low air flow (low RPM). It might affect idle speed but only indirectly and not much.

[78sid]

Thanks Zed!!!!! Holding steady and clean at 800 RPM's. Sweeeeeeet. I might actually get to drive this car on the road tomorrow after a three year rebuild.

[Captain Obvious]

the engine still slowly idles down to shut off once the engine warms up.

Look at the bright side... You inadvertantly also verified that your AAR is working properly.