78 air intake probs

[ghetto_zhetto]

I just recently got my 78 280z running after taking everything off the intake. the first owner had left it sitting for years. The car runs great now but it will sometimes die while I am driving it. I found out that if I tighten the living crap out of my AFM it will run close to how it did before. And I will be able to drive it with no problems until it will randomly change back to needing less air.

Its getting really annoying

If anyone knows what it is dong it would be greatly appreciated.

Things I've done: removed egr valve, removed cold start valve, removed air regulator, new plugs/plug wires, fuel injectors from an 82

[Zed Head]

 if I tighten the living crap out of my AFM it will run close to how it did before. 

This level of detail will not work with the EFI system.  What does it mean?  What was tightened?

 

You have a long frustrating path ahead.  

[rossiz]

first thing i noticed is an un-capped vacuum port next to the brake booster.

vacuum leaks and crusty electrical connections are your first 2 biggest enemy.

the third is chopping up the system too much - all the sensors need to work together or you will not get good results.

[Zed Head]

Good eye.  I looked closer and there's a huge leak in the boot between the AFM and the TB.  Massive quantity of unmetered air.  I'm going to guess that "tightening" means adjusting the AFM cog for more fuel.  Probably didn't mark the starting point either.  More tears...

[rossiz]

wow... didn't even notice that big ol' open tube!

while you're at it, check the pcv hose (underside of manifold down to block) it runs right over the exhaust manifold and the heat bakes it until it cracks & disintegrates. another huge vacuum leak spot.  

[ghetto_zhetto]

I have the AFM boot to throttle body hose thing temporarily plugged with forma gasket

As for the little tube close to the booster I didn't feel the need to plug it as it had no change in idle when I would close it up

I may end up plugging it now anyways

[ghetto_zhetto]

And my pcv hose is brand new forgot to mention it

And thank you guys for the quick response

[ghetto_zhetto]

Just realized he may have been talking about this

[ghetto_zhetto]

And by tightening the crap out of it I mean twisting this gear that tightens the coil spring

[Zed Head]

If you tighten the spring the fuel/air ratio gets leaner.  Loosen and it gets richer.  Adjusting the AFM away from the factory setting should never be necessary on a stock engine.  Stock cam, head, intake system, etc.  If you can tell where the old marks are you should put it back to that spot.

 

The cover over the EGR port could be a problem if it leaks.  It's also possible that your EGR passage is corroded inside and leaking.  You should be able to see ii it is by looking under the cover you've applied.  Both of those will make things lean if you've also removed the EGR exhaust tube.  If the exhaust tube is still connected it won't be leaner but it will be weaker.

 

Can't tell from your picture also, if you blocked the CSV hole well or not.  Vacuum leaks can add up.

 

And when describing the problem, you should tell whether the engine is hot, cold or warm.  There is a temperature actuated switch that can affect timing, which will affect the way the engine runs.

[siteunseen]

There's a port vacuum hose off the bottom of the BCDD that drove me nuts, like a ships wheel.

The hose came off the BPT ? valve next to the EGR I believe. Plugged it coming out of the BCDDs bottom.

I looked at my '77 and that open bung you have goes to my A/C fast idle servo. I thought, for as long as it took to walk downstairs, it was for your FPR.

Edited May 22, 2015 by siteunseen

[ghetto_zhetto]

The engine is warm it doesn't get too hot

It just will randomly change its need for air