Click, Click, Click: from under the dash while coasting

[sscanf]

Hi All,

I have been making some more progress on my 1976 280Z. I'll be posting an update soon (I have the aux air working now!)... Anyway, I recently noticed that if I put my foot on the clutch to coast down a hill, my RPM's drop pretty low (like to may 500 RPM) then recover to about 800 RPM which is where my idle is set to. All the while, there is a relay clicking away under my dash. Everything is otherwise fine - its actually running great, just the click, click, click that seems to happen when the rpm's dip low.

Maybe the fuel pump relay? Is it the fuel cut-off switch in the AFM? If so, what is the correct fix? What could be causing the excessive dip in RPM's while coasting? Does it have something to do with the fact that I have both the TPS and the BDCC (BCDD??) disconnected. I did try reconnecting both but still suffered from the RPM dip (but either or both of those components may be misbehaving). Or do I need to make an adjustment to the fuel cut-off switch in the AFM?

Other relevant info:

Rebuilt AFM

Rebuilt ZX Distributor/Ignition Module/Coil (along with appropriate wiring changes)

New FJ707T Injectors

Just added Temp Sensor Tweak (resulted in a huge improvement in cold engine performance)

BCDD sort of repaired (at least no vacuum leak any more)

Thanks,

Dan

[siteunseen]

I think it's called a dash pot, the round thing with the whitish plastic that serves as a shock absorber for your throttle linkage. They're adjustable, https://www.google.com/search?q=280z+dashpot&source=lnms&sa=X&ei=kzKXU6GRIubLsATjt4HIAw&ved=0CAcQ_AUoAA&biw=1280&bih=620&dpr=1.25

[Zed Head]

I've had the clicking under the dash and it was the fuel pump relay being kicked on and off by the AFM switch. I believe that I removed the clicking by adjusting the metal arm in the AFM to where the AFM vane could close farther before hitting the switch. But the low RPM on closing the throttle still happens, when the engine is between cold and fully hot. I found that the RPM drop got worse as I advanced my timing set point, and since I removed the other pickup coil that kept timing advanced while cold (that's contradictory but idle speed has to be reduced after advancing the static timing, the second pickup coil was for cold engine only, run off of a temperature switch). At this point I just live with it during warm up, since the engine doesn't die and it's only there for a few minutes. After the engine gets warm the issue goes away.

The dash pot adjustment helped, but it lasts for longer than the dash pot can stay up. It still bobbles around at ~600 RPM for a second, when the engine is cold and the AAR has closed before rising to 900-1000. It's a weird thing, I think it might have to do with cold air and fuel. Maybe the cold enrichment formula in the ECU is off or, the 10% ethanol in the gasoline is screwing things up.

Newer cars control idle speed via the ECU by changing timing and/or an idle air control valve (edit - actually called an idle air adjusting (IAA) unit. Idle air control is our AAR. Browsing my other car's manual).

Edited June 11, 2014 by Zed Head

[240260280z]

Check alternator output too. If the voltage drops under low RPM then relays can click however I think it is what Zed Head mentioned.

[sscanf]

OK. I'm going to try a dashpot adjustment first. I checked my dashpot and it seems to be in great condition - it actuates easily unless I block the plastic tip on the other end. It has been adjusted by a prior mechanic to have no effect.

Given that my RPM's seem to bounce back up within a second or two, I'm hopeful that this will do it. I'm still messing with my "Temp Sensor Tweak" setting too. All I had on hand was a 5K pot so its a little touchy.

We'll see how an adjustment goes - I'll let you all know.

Thanks!

[sscanf]

I Made the dashpot adjustment last night. Went out expecting it to sake 20 minutes but it was done in 1. I took it from all the way out to most of the way in and .... No more clicks, click, click!

The RPM's still dip when I coast but not quite as far, maybe 600 RPMs vs 500 before. So, fixed. Thanks!

[siteunseen]

Maybe if you plug the BCDD back up it'll keep your RPMs steady when coasting. If I remember right, on mine, the bottom nut turns out counter clockwise for more RPMs. Take it out 1/2 turn at a time and test drive it. If it's worse then I'm backwards, go clockwise. Good luck.