Haven't posted in ages.
My 83 runs right on the stoic/rich line for 2 seconds then all the way over to the full lean side for 2 seconds when just cruising along. at any normal speed. I cant tell if it is still doing it when I am accelerating.
I can feel it when it goes lean, like a very slight drag, like I just let up on the gas slightly. (but I didn't) . every 2 seconds it switches back and forth.
Any ideas ?

 

First thing that come to mind for me is a vacume leak.

 

other than your AFR gauge reading funny does it drive normal?

 

It drives normal, but I can feel when it alternates every two seconds, like I let off the gas a touch, then back to normal. Its been like this for a year or more, I'm just getting a bit more time on my hands now to play.
I even have a spare computer (no differance)

 

How does it idle ?

 

Idle is a bit low at the moment, but it dosnt seem to do the hi/low thing then.

 

RCoble,
Funny you should bring this up as after reading this I realized that this sounds similar to a problem I've been having since I reinstalled my engine, however, my symptons only seem to occur under WOT. My plan is to check the vacuum this weekend, and then look at the fuel dampers. If I find something I'll let you know.

 

I thought this "hunting" was normal behavior, although at least on my LH cars, the period is less than 2 seconds (ARM-1 makes a full trip back and forth in 2 seconds).

 

On a car with an O2 sensor in closed loop, the AFR should be alternating between rich and lean, although it should be faster than one cycle per two seconds. That is probably your gauge response time though. AFAIK older 928's idle in open loop mode, so you do not see the swing at idle. When you go WOT, the swinging AFR stops, right? WOT is also open loop. The behavior you are seeing sounds normal, but the hesitation you mention does not. I would make sure there are no vacuum leaks. Then I would check fuel pressure and the ignition system for proper function.

Dan
'91 928GT S/C 475hp/460lb.ft

 

Those narrow band A/F meters are next to useless. I found them useful only on TurboCars, and only to confirm my enrichment under boost. But YMMV...

 

I know he guage is just referance, but I can feel it right along with the guage. two seconds on, two seconds off. It didnt do this years ago, Ive had the car for quite a while. I noticed it two years ago, but the feel is getting more pronounced, although still subtle.
I didnt think I have a vacume leak, (been checked under hood. disabled,plugged all those climate control till futher repair.

 

How old is your 02 sensor ?
How old/clean is your fuel system (filters, injector cleaning lately? )
Fuel pump relay and fuel pump connectors nice solid and tight?
Engine grounds?

I go in order of $$ so I think if it were my car I would start by cleaning and refreshing all of the connections for the fuel system and engine grounds to start. Run some Injector / combustion chamber cleaner.
Plugs, O2 sensor, then see ..