1977 280z lean in 4,5,6 rich on 1,2,3

[240zadmire]

Hi all

strange problem I encountered.

the engine idle, rev fine. Look at the spark plugs, 1,2,3 run rich and 4,5,6 run lean.

The spark plugs of 4,5,6 looked clean compare to dark smog 1,2,3.

1,2,3 engines look like this

4,5,6

 

whats I have done.

compression test

cold: 170psi on all engine 

hot after 30mins idle, 180 psi on all engine
 

new piston rings

new bearings

new gaskets

new vacuum hoses

new spark plugs, cap, spark plugs wire. All NGK brand.

new alternator

new ignition coil.

 

I’ve stripped down the engine nut by nut, bolt by bolt, suspensions, bushing.... except the transmission.  Anything replaceable where cost is not prohibit. I replaced.

the engine responsive but just notice 3 front engines are a bit rich.

 

any advice, would greatly appreciated 

regards

 

 

 

 

 

Edited August 23, 2020 by 240zadmire

[240zadmire]

I’d like to add is that the there is clear mpg coming of the pipe tail whether I start the car in the morning or when the engine is warm.  Understanding that lately, California is like 80f in the morning. There is no back fire or anything Iike that. 
 

Am I looking for trouble? Or just be happy with it?

im prepping her up for the smog in couple of weeks.  Waiting for the weather strip to put windshield ...

will have another thread about prepping before smog test.  So exciting!

[Captain Obvious]

Hmmm.... On the fuel injected cars, the only thing that is really split 1-2-3 and 4-5-6 is the ECU. Everything else is pretty much shared evenly between all the cylinders.

If you really think you've got an issue that is split like that, you could try swapping a couple of the injector wires. I think some of the wires have enough slack in them that you can move them around. I'm thinking you could swap the wires going to 3 and 4 to see what happens.

If you swap 3 - 4 and then find that your sooty plug follows the injector connector, then you might want to look into a different ECU.

Clean up those plugs, swap the wires, and drive around for a little bit and then pull the plugs again to see what they look like?

[Captain Obvious]

And as you mentioned, you might pass smog the way it is. I don't know the details.

[240zadmire]

@Captain Obvious

good suggestion.  Let try the easiest path by swapping the spark wires. I’ve switch the spark plugs but problem persisted.  
 

I did heard little “knock” noise when start the car.  Probably a second or 2.

 

about the injectors, they all old.  I clean, sprayed brake clean fluid while energize and all of them spray.  I didn’t pay much attention if the spray streams were consistent.  
 

switch wires is ok, but pulling the injectors out is going to be painful.

[240zadmire]

Another thing I notice is the smog smell.  Compare to my other sedan, the smog coming out of 280z is definitely noticeable. Stronger smell.  Not that smell like unburn gas or oil, just stronger.  The muffler and catalytic must have been decade old.  Read somewhere it might need to drive on highway hard to knock down those deposits in the pipe... kinda egg, chicken problem. I need to pass smog  before I can take it into high way.  Cannot driving around 25 zone to 60-70mph ? 

[rcb280z]

Maybe post pics of all plugs. Your idea of lean may not be lean to anyone else. 

I can tell you now you will more than likely have difficulty with the smog test with plugs that look like that.

Make sure the plugs are gaped right, the right ones, etc. Again pics are a good thing.

[Zed Head]

1 hour ago, 240zadmire said:

@Captain Obvious

good suggestion.  Let try the easiest path by swapping the spark wires. I’ve switch the spark plugs but problem persisted.  

CO said the injector wires, not spark plugs.  You can just move one plug over to the injector next to it and swap them.  They all fire at the same time.  If it's the ECU then the clean plug will get dirty.  Make sure you swap a clean cylinder injector plug with a dirty cylinder injector plug.  Switch injector 3 with injector 4, for example.  4 should foul, if it's an electronics problem.

[cgsheen1]

Injectors open for milliseconds at a time so wire resistance, oxidation, and/or corrosion in wiring and connectors can have an impact. Follow Zed Head's suggestion, and also double check wiring and connectors - including the "dropping resistor pack" under the left side inspection lid.

[240zadmire]

Hi all.  Seem like the problem is gone with swapping the #3 and 4

Isn’t the firing sequence 1,5,3,6,2,4

#3,4 is opposite isn’t it?

please see the photos with notes.

before swapped the wires of 3,4

 

 

after swapped the wires.

#1 look much better but number #2 still have smog powder on it.

 

I did gave a Deoxit gold 5 bath to dropping resistors, voltage regulator, passenger seat relay, all the injectors when I trace issue with fuel pump....
Basically all connectors I can get my hand on.  I will give all the injectors one more bath when the temperature is cool down a bit.  I sweat like a pig or windows were down and drive through the car wash, in under 5 minutes.  Having wearing glasses doesn’t help either. ?

 

will update later.

 

regards

 

 

 

[Zed Head]

Edit - Left out some zeroes below.  .032", .043" is correct.

 

Those spark plugs are much dirtier than they should be.  Looks like your EFI system is running rich, which is a very common problem with the 280Z's.

Have you checked the gap on the spark plugs?  It looks too big.  1977 still has the weaker electronic ignition system, gapped at ~0.32".  If your engine has the ballast resistor then gap to 0.32".  I haven't found an FSM that I'm sure is actually 1977, so there might be specs showing 0.43" gap.  But I don't think that's right for a ballast resistor system.

The firing order is for the electrical spark, not the injection.  The injectors squirt half of the required fuel on every crankshaft revolution, all at the same time.  Some cylinders have valves closed, some open.  The fuel just hags around until the valve opens and it gets sucked in.  But they squirt simultaneously.

 

Edited August 24, 2020 by Zed Head
vary>>>very

[240zadmire]

I never give a second thought of checking/adjusting the spark plugs gap.  Installed it the way they are when I bought the spark plugs.   I just ran the engine for half and hour and wait till it cool down a bit to open.  Too hot in the garage ?

the FSM says 0.39-0.43 gap should be good.  The gap does look wide.

 

learnt a new thing about fuel hanging around till its turn to get suck in and fire.  I kept thinking the ECU controlled when each injector open up and how much fuel....

so for adjust to run a leaner without tampering/fiddling the AFM, there is a screw behind the AFM flapper.  Is it enough/right place to add more air to trick the ECU running lean?

 

regards

 

Edited August 24, 2020 by 240zadmire