My '81 which I have recently purchased has a wee
electrical quirk which I would like to iron out if I can. When you turn the ignition key on, but before
actually starting the engine, relays clatter away under the hood. Once I start the engine the relay clatter goes
away completely, and car runs just fine. One of the
relays clattering is the "air relay" mounted up on
firewall bracket on the drivers side. Previous owner has
removed all the emission stuff (Air Pump, etc) so I am
picking it is possibky related to this ? Any quick
pointers would be appreciated before I start the long
haul project with the workshop manual and wiring
diagrams !!!

The 81 has computer control.  The relays for the emission stuff are controlled by the computer.  If the air pump has been removed, and the air relay is kicking, just unplug the relay.  The computer is controlling it and you don't want to mess with the computer.  Use a electrical di-electric grease in plug so it won't corrode and ruin the contacts.  You might decide to reinstall it someday.

 

BUT, I don't think that's what you are hearing.  The chatter should be coming from the carburator.   ALL computer GM carb do this.  It's the mixture control solenoid in the carb.  Some carb models are fairly quite, but it's still there.  This controls the fuel mixture when the oxygen sensor is active.  Everytime you turn on the key it will do this.  It actually does it all the time the car is running, you just can't hear it over the engine.  If you put a listening device on the top of the carb, you will still hear it.   If the key is on for a period of time without the engine running, the clicking will stop.  It will restart when the car is started or the key cycled.

This is a normal and necessary part of the computer control carb function.  If you disable it, the car will run too rich, use a LOT of fuel, and may foul plugs in time.  It will not run better.  You will also get that annoying yellow "Check Engine" light on the dash.

Thanks for that Ken. The Air relay is definitely one
of the culprits. I've bitten the bullet and over the
past week or so I've popped the centre instrument cluster out, and sides/top of centre console between seats. Initially this was simply to replace a couple of dead bulbs in the instrument cluster, but of course once I had it all out a general tidy up was in order - birds nest wiring from past messy stereo installation, etc. Changed all the bulbs while I was in there. And that's when the plot thickened a bit... guess what ? Check Engine lamp had no bulb in it. So I fitted one. Have only just tonight put back together enuff to reconnect battery, and turn key. And guess what... check engine light goes on and off perfectly in time with the clicking air relay. So I guess I'm in for a little more snooing. Fortunately I used to be an electronics technician, so I'm not too fazed by things electric. Happy of course to take advantage of any existing wisdom rather than reinvent wheels !   Cheers, Chris D.

Turn the key on.  Short the A and B connector in the black 12 pin computer diagnostic connector.  Watch the check engine light.  It should flash once, hesitate and flash twice.  This is a code 12.  It will repeate this three times.  Then if another code is set, count the flashes.  It will repeat three time and go onto the next code.  When you see the 12 again, all codes are displayed.  If you get the 12 four times in a row, there are no codes set.

Let me know what codes you have, and I will tell you what they are, and how to track it down.

Ken, appreciate your input, thanks for taking the time !
With diagnostic jumper in I get code 12 over and over, no other code. But here's the fun bit... intermittently while its doing the code 12 thing, relays would clatter and the code 12 display would be interrupted - the check engine lamp flashes in line with the relay clatter, and then resumes its code 12 display. I pulled the 2 offending relays so that the only sound to be heard (apart from the fan) is the fuel solenoid in the carburettor. So this rattles away normally while the code 12 is flashing up nicely, then the fuel solenoid rattle stops for a second and simultaneously the code 12 stops. Then the normal rattle re commences and the code 12 display recommences normally as well. Until a few random seconds later this repeats. Good stuff huh ????
At this stage I'm picking either the ECM is suspect, or it is receiving input(s) which are abnormal giving rise to an abnormal response. I have a GM 1981 workshop manual, a Haynes, and a 1981 Corvette Assembly manual so no shortage of bits of paper here !!!

Cheers, Chris.

It sounds like you have an intermittent electrical connection.  This could be a power or ground to the computer.

Check the remote lamp driver that controls the Check Engine light.  It supplies a power to the Computer and will sometime create this type of problem.  Believe it or not, if the bulb is loose in the socket or the filiment is starting to break, it will act like this.  The bulb is required for the driver to complete the circuit and make the computer functional.

Remote Lamp driver ??? Haven't stumbled across that
one yet. Where is that found then ? If you happen to have a GM Workshop manual, can you give me a page reference please ?

Cheers,
Chris.

If follow the wires from the check engine light, you will find the lamp driver.   They only used them for a couple of years, but your 81 will have it.  It goes from the driver to the Computer.

Sorry, I don't have the manual.

Thanks, Ken.

I'm out of town for a couple of weeks on business now,
so will explore further when I get back, and keep you
informed then.

Cheers, Chris.

P.S. FYI the other thread I had going about the elctric choke thermostat which you also assisted me with, I concluded that it was dead and purchased a new one out of Australia for $AU56.00 which is about $US40 or therabouts. Got a new vacuum break unit from the same
place at the same time for about the same price, as I discovered it too was deceased. Big suck no move !
These arrived just today, so they will have to wait a
couple of weeks now for installation also. Don't you just hate it wen work gets in the way of fun ????? :-)

Hmmmm...I also have an 81, I'm reading this and am wondering...I don't have any clicking noise when I turn on my key. I wonder if thats why she runs so terrible till she starts to warm up. And how do you tell which are the "A and B" pins in the little do-hicky"...

 

Thanks all

Fred from Columbia City, Oregon