1977 stock coupe runs then dies

[Orangys280Z]

I swapped the engine in my '77 a while back for another '77 280Z(both are CA cars) and kept the original ECU and wiring harness. After figuring out a few things I was able to start the car. When I want to start it I have to have the distributor centered(screw in the center) but when it starts, it idles at 1500+ rpm. I've turned the idle screw all the way down, and that doesn't help much. If I retard the timing 100% then it goes down to 900-1000 rpm idle, but if I turn the engine off and try to start it, it won't start. I've tried leaving the idle high to see if it still kills itself after a few minutes just like if I retard the timing 100%(still runs for a few minutes, then dies). Does anyone have any ideas on what could be causing this? ECU maybe? With my luck it'll be something obvious that I overlooked.....

[S30Driver]

Verify and set the timing with a light, 7 or 8 degrees advanced at idle, warm.

Fast idle is controlled by the AAR, maybe it is stuck open or you did not hook up its electrical connection for the heater in it.

[Powerglide]

B.c.d.d.

[ronroyboy]

put 12 volts to your bcdd wire see if it the idle goes down.

[Orangys280Z]

Ok, I'll try all that as soon as I can(next day or two if my schedule allows), but would the AAR and b.c.d.d explain why the car dies once it has some temperature? I DO have the AAR connected correctly though.

Edited June 30, 2010 by Orangys280Z

[KDMatt]

You check to make sure your auxiliary air valve is closing?

It's supposed to kick up the idle to like 1500 ish RPM when the car is cold, then gradually close off and bring it down.

How's your fuel mixture? Rich? Lean?

I'd be willing to bet your timing is OK ...

[Orangys280Z]

How would I go about checking to see if it closes? Last time I checked it seemed to be running rich. I checked the plugs after a couple runs and they were black, but still firing.

[KDMatt]

How would I go about checking to see if it closes? Last time I checked it seemed to be running rich. I checked the plugs after a couple runs and they were black, but still firing.

Rich hrm? ... Was this before or after you messed around with the timing?

You can pull the AAR off of the car and check to see if the flap is moving just by sticking a screwdriver into it and pushing it around a bit. You can also adjust it by undoing a locknut on the other side -- this will let you change the initial amount the AAR is open.

My car idled low and ran rich for years until I pulled off the AAR and adjusted it.

[Zed Head]

How would I go about checking to see if it closes? Last time I checked it seemed to be running rich. I checked the plugs after a couple runs and they were black, but still firing.

KDMatt might be on target. I have a spare engine that had a bad AAR and I could not get the idle down to where I wanted it until I plugged it off (it's a spare engine so I didn't replace it).

The FSM says to pinch the hose to the Regulator when the engine is cold to see if it is open. The engine idle speed will change if it is open. If the hose is old though it will probably split giving you a big vacuum leak.

You could remove it, plug the hose ends then see if the car runs differently. You might have to start it with a high idle screw setting when cold, then turn it down when it warms up.

If you do decide to remove it, for testing or whatever, be careful, there is a good chance that you will break off a bolt in the manifold and tear the guts out of the AAR when you're trying to remove the electrical plug.

Edited June 30, 2010 by Zed Head

[Orangys280Z]

I'll try pulling the AAR off tomorrow and try to find the one from the old engine to put on to see if there's a difference. I remember the old engine didn't have any idle problems(besides when it overheated and blew the head gasket due to a clogged radiator and I had to drive it for a while since I didn't have any other vehicle to drive to and from school 25 miles away). Though does anyone have any idea what would be causing the engine to die though? After I get the idle down through the timing, it would be fine for a few minutes, no backfires, no acting up, nothing. I have tried to advance the timing when it started to die, but it was pointless. Then couldn't start it afterwards, no matter what I did to the timing at least. Any ideas about that?

[KDMatt]

I'll try pulling the AAR off tomorrow and try to find the one from the old engine to put on to see if there's a difference. I remember the old engine didn't have any idle problems(besides when it overheated and blew the head gasket due to a clogged radiator and I had to drive it for a while since I didn't have any other vehicle to drive to and from school 25 miles away). Though does anyone have any idea what would be causing the engine to die though? After I get the idle down through the timing, it would be fine for a few minutes, no backfires, no acting up, nothing. I have tried to advance the timing when it started to die, but it was pointless. Then couldn't start it afterwards, no matter what I did to the timing at least. Any ideas about that?

Well, if we assume for a second that my assumption about your AAR is completely 100% right (which, odds are against us it will be) ...

BUT ... if this is the case ... what could be happening is that as your fuel mixture leans due to the rise in engine temperature, the AAR is still dumping all kinds of extra air into your manifold, creating a super lean mixture, which could, I suppose, in theory, kill the car and then make it hard to start again 'til it's cooled down.

However there are also a good number of other things that could cause that behavior.

[Orangys280Z]

Update on the Z:

I replaced the AAR earlier and the idle was at like 500rpm(with everything set from the other AAR) I messed with the timing a bit and opened up the idle screw and got it back up, but I need to figure out which plugs aren't firing now. I have quite a bit of smoke coming out the exhaust(cooling system not in car and only exhaust manifold is on with the intermediate pipe on, no cat or anything after). Sounds like 2 or 3 plugs aren't firing right now, so tomorrow when I get a timing light from my friend I'll clean up the plugs and set the timing to where it should be.