jackrabbit501

Hey everyone, this is my first post on here, but ive been reading many posts for about a year on my problems. so heres my issues:

its a 1979 280zx non turbo, has a decent idle at 1000, and puffs black smoke out the back constantly. Ive read that the black smoke is too much fuel so here is everything ive replaced in this car so far:
-distributor
-fuel pressure regulator
-fuel pump
-spark plugs/ o2/ filters
-fuel lines
-CHTS
-starter
-all vacuum lines
-AFM

with all this replaced, it makes me wonder whether the rings are bad or the fuel injectors? along with this black smoke comes the sooted plugs and o2 sensor. would a valve adjustment be needed? im just so lost as to what i should do next, i dont have the money to keep replacing everything until it gets fixed, so a more directed approach would be much appreciated!

would some bad spraying fuel injectors cause black smoke? bad valves? thanks for reading!

NismoPick

Welcome to ZDriver!

Some follow up:

I thought the 79 didn't have an O2 sensor. Maybe CA model?

The 79 didn't have a CHTS... it has a coolant temp sensor in the thermostat housing. It's actually the same sensor, just different location. I suggest checking it's connection / ohm test.

I would also check the thermotime switch and cold start injector.

jackrabbit501

Hey nismo, this car does have an o2 sensor on the exhaust but no egr system. It also does have the chts under the 5th and 6th spark plug. But it also has the thermostat housing temperature unit with only 1 wire and thermotime above it. I was wondering why it would have so many coolant temp devices?
On a second note, the temp sensor under the thermotime broke the wire to it, didnt effect the running so i could tell but i cant find the correct replacement part. The repair manual shows a different shaped unit than what i have but the correct placement. So im not sure what to do about it... I can post pictures if its confusing, i havnt seen any similar pictures to what i have..

Also i was trying to find a source where it would tell me how to find the correct resistances for all these switches and units so i dont need to replace everything. Could it also be possible that the cold start valve would be stuck open, leaking into the intake? Let me know what u think.

Ps. Also i unplugged the chts and my car wont start, so i dont think the issue is with that.

jackrabbit501

Also ive tried unplugging thermotime/ cold start while it was running with no improvement or change in how it was running..

jackrabbit501

Im trying to research whether the injector rings and seats would have any effect on this? A while ago i replaced one of the plastic seats because it was split, but would bad o-rings on the injectors and seats cause it to run rich? Im thinking of having the injectors sent off to be rebuilt/serviced, is their any good place to get this done? New injectors would cost about $200 with some price hunting, but is it better to get them overhauled since theyre factory injectors or does it not matter? Sorry about all the questions, ive had them for months but i needed to make sure i had tried as much as i could with the diagnosing before i posted on here my concerns. Thanks in advance

SHADY280

Is be checking the temp sensors as well and see if your cold start injector is stuck open. Take the line off to it and stick a bolt in it so no fuel leaks. Also check the timing to make sure it's perfect at the stock 8 deg for now. Also you said you replaced the Afm. Every Afm has to be calibrated to the vehicle. Your old one could have been bad but unless the new one is adjusted the problem may stay the same. Try at last resort tightening the vane spring inside and that should lean it up

jackrabbit501

I got the car from a guy who owned a mechanic shop, he said they replaced the afm and tuned it so i havnt really touched it. when its at an idle i tried pulling the afm to the negative to run more lean but the smoke didnt clear up, only stutters the engine. my neighbor insists that its bad piston rings, but before i pull the engine i wanted to be sure.
I was thinking about that with the cold start valve, i guess thats the next step, ill give an update once ive done it.

I have the N-47 head on the f-54 block and during compression test, all cylinders stuck at 150 psi, sound about accurate? is it possible that some of the rings are allowing blow-by? ive checked the plugs after letting it run for a little and besides the build up of black crap all over them, a couple were wet, couldnt really tell if it was oil by the smell, or by wiping it off because it gets the rag black, but im not sure if it is oil? smoke doesnt look blue to me. could the pcv valve be an issue? that was the only vacuum hose i didnt replace because i couldnt get it off..

jackrabbit501

No change in the running condition with the cold start blocked off, just made for a rougher idle at cold start.