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jersey280

I'm about push this in a lake..Plz help!?

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Hey guys,

 

I'm nearing my wits end with my car (76 280z with a 78 engine n42head n42block). 

 

The P.O seems to have deleted all of the emissions and most of the vacuum lines (egr, pcv, bcdd all blocked off).

 

I am having this issue now where i have back firing from the intake at idle (dozen or so per minute) and after warm backfiring out the exhaust and loss of power while on the road. Additionally, the car seems to start at a very high idle.

 

The fuel system is all custom cell with -AN set up (pressure great), valves adjusted to spec, injectors rebuilt with new gaskets, pintels, screens ect, Vacuum was checked and rechecked including with carb cleaner trick. Timing checked, temp senor replaced, all connectors replaced with new, all new plugs wires cap and rotor, new coil with internal regulator (external resistor bypassed), AFM checked for any possible signs of wear or anything, shows nothing looks great. TPS looks good, engages when suppose to. 

 

I am obsessive and have done tons of research and I cant seem to figure this out. Can anyone save this Z from being driven into a lake due to frustration? Thanks!

20200521_194805.jpg

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Posted (edited)
1 hour ago, jersey280 said:

 

I am having this issue now where i have back firing from the intake at idle (dozen or so per minute)

 

 

Sometimes that is caused by a flattened cam lobe.  The exhaust valve doesn't open all the way.  You might recheck your valve lash, examine the cam lobe quality, and also check your camshaft timing using the notch and groove.  Cam lobes have been known to go flat very quickly. 

 

"After adjustment" is good.  Make sure the drivers side of the chain is tight and the timing mark is on zero.  Use the cam shaft bolt to turn the engine.

image.png.a4bc9b70224f3af231ef204de896497d.png

Edited by NewZed

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Have you verified your plug wire order/ I tried to trace it out from your picture, but it's too low of resolution to make out for sure. It almost looks like your 3 and 4 might be swapped.

 

Timing marks look good, but to be extra sure you'll want to pull your #1 plug and use something to indicate that the piston itself is at TDC rather than trusting the damper, which can break free and move when extremely worn (and aren't 100% accurate to begin with).

 

How's the cam and valve lash look?

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Posted (edited)

Zhoob,

 

I checked with a screw driver down the plug hold and it definitely feels to be TDC. I also used the photo graph attached to verify. Is it possible my injector connectors got swapped? how can i verify?

 

edit: couple days ago I also adjusted all valves to spec, which werent off by much.

8.jpg

Edited by jersey280

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Injector order isn't really that important on these engines. I can't remember if the injectors are fired in 3s or all 6 at once, but either way it's not a precise event.

 

I assume the distributor rotor is pointing at #1 with the engine at TDC?

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16 hours ago, jersey280 said:

The P.O seems to have deleted all of the emissions and most of the vacuum lines (egr, pcv, bcdd all blocked off).

 

(76 280z with a 78 engine n42head n42block)

 

new coil with internal regulator (external resistor bypassed),

 

Burnt/bent/sticky valve maybe.  Have you done cylinder pressure measurements?  Should be at most 185 psi, depending on the gauge used.  Maybe the PO shaved the head.

 

Looks like you're doing everything right, for an engine with good working parts.  There a couple of odd things though, I quoted above.  1978 used the N47 head.  Why does yours have an N42 head? 

 

And what type of coil are you using, in detail.  The ballast resistor is actually a device that changes resistance as ignition dwell changes.  It's not just a resistor.  It's not a well-understood device, but pretty ingenious.  You might be overpowering the old 1976 ignition module.

 

Zhoob's thought that you might just have spark crossfire seems to fit.  Maybe you just have bad plug wires.  Move them around while the engine is running and see if things change.  Use an insulated screwdriver or wooden stick., or make sure your hands are dry. 

 

But here's some more possibilities.

 

- The PO left the PCV port under the intake manifold open, either at the manifold, or at the side of the block.  You missed a vacuum leak with your testing.

 

- The PO connected your vacuum advance to "always on'; vacuum instead of ported vacuum.  Check your timing at idle and disconnect the vacuum advance hose to see if it stays the same,  It should.

 

- The weights on your distributor mechanical advance have lost their springs and your timing is jumping around.  Again, check your timing and see if it advances with RPM like it should.

 

- the breaker plate in your distributor is gummed up and getting stuck at high advance.  Timing light should tell you what's going on in there.

 

 

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19 minutes ago, ZHoob2004 said:

Injector order isn't really that important on these engines. I can't remember if the injectors are fired in 3s or all 6 at once, but either way it's not a precise event.

 

I assume the distributor rotor is pointing at #1 with the engine at TDC?

 

They all go at the same time.

 

Another thing to watch is the tachometer needle.  If it moves smoothly with RPM that's good.  If it jumps around for no reason or reads the wrong RPM, that's a sign of ignition module failure.

 

The ECU's also go bad, usually running rich and rough, until they just die sompletely.

 

Have you tried to drive it yet?  These old AFM's are also known for running lean.  If that's the issue the engine will pop back through the intake and buck and jerk when you give it light throttle, under load.

 

http://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

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Appreciate all of the great ideas.

 

I had originally adjusted the valve lash. Drove the car about 70miles. Then issues had arouse on the trip home (loss of power, backfiring out exhaust). I checked valves again, appeared to be slightly off. I adjusted again to cold setting of .008/.010 and started her up again. I was able to eliminate the intake backfire by advancing timing to about 13BTC. Took her for a spirited drive, no issues. 

 

Car just seems to have a rough low rpm driveability, bad boy wants me to pedal down.

 

Wondering what would have caused the valves to go out of spec so quickly? 

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Posted (edited)
22 minutes ago, jersey280 said:

 I checked valves again, appeared to be slightly off. 

 

Car just seems to have a rough low rpm driveability, bad boy wants me to pedal down.

 

Wondering what would have caused the valves to go out of spec so quickly? 

 

Use more words! 

 

"Off" which way, loose or tight?  "Rough" how?  I mentioned the stumbling and bucking.

 

Pretty typical to work your way up to good-running, through many small improvements.  They're  easy to get running but take some work to get to perfect.

 

 

Edited by NewZed

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Most were too loose, I cant say by how much, i just corrected.

 

The bucking/stumbling is more accurate description then "rough". Ive read small things like pedal adjustment/replacement and throttle linkage repair or replacement may help, yet I feel its more deep the these adjustments. 

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1 hour ago, NewZed said:

Have you tried to drive it yet?  These old AFM's are also known for running lean.  If that's the issue the engine will pop back through the intake and buck and jerk when you give it light throttle, under load.

 

http://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

 

The low RPM driveability problem is super common.  Might be that /Nissan tuned the system to the edge for emissions on 1970's gas and it's too lean on today's gas.  This fuel tweak really works.  

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Posted (edited)

Was the temp sensor replaced by you or the previous owner? Also was it the temperature sensor or the temperature sender for the temp gauge itself? This sounds really similar to the temp sensor being bad.  Also I'm not sure if the 280z did it, but I know with the ZX up over a certain speed or it might be RPM the car goes into open loop where it reverts to just using the ecu programmed fuel maps and doesn't really use the sensors. Years ago my turbo ZX was running awful, but if I really got on it or on the freeway when you're cruising at over 65 (3-speed auto)/higher RPMs I'd suddenly notice the car ran really good. As soon as I went back under it started running rough. Reading through the FSM I found out about it using closed loop under lower RPM and open loop at higher.

 

Edited by DuoWing

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