Intermittent Loss Of Power-1972 240Z Stock

[AWAUDIO]

@blue  Without a dyno,  what I'm trying to think of is, what would cause engine stumble (not misfire or backfire), hesitation, and loss of power, under a load (running under power on the road) versus static revving?  I'm willing to start from scratch.  It's the load/no load that has me thinking.  What engine systems fail under load, rather that at rest (running in driveway)?  Will do the 3 steps I outlined above, but I'm thinking outside the box here.  Thanks,

 

Andy

[madkaw]

A bad coil is a good example of failing under load. A restricted fuel line will also probably be fine in the driveway , but under load the fuel amount would be insufficient.

My daughter's ZX turbo acted up mostly under load and would experience the symptoms you describe . I finally found an obstruction in the fuel sending unit that partially blocked flow. The tank was spotless, but something had lodged itself in the sending unit pipe and would close off fuel.

I've also have seen a loose connection on a dizzy act this way.

[Patcon]

Another area that I don't see mentioned is the carb inlet screens and the float bowls. If the screens are badly clogged they may not pass enough fuel and the bowls get low on fuel causing bucking or debris in the bowls that moves around and clogs up the holes. Another long shot is a piece of bad fuel line, internally collapsed, possible the lines under the carbs (this is not regular old fuel line)

C

[madkaw]

Good point Charles . I have had those float bowl lines collapse on me. I've also seen the rubber lines back by the differential get hot enough to get gummy and collapse

[siteunseen]

Another area that I don't see mentioned is the carb inlet screens and the float bowls. If the screens are badly clogged they may not pass enough fuel and the bowls get low on fuel causing bucking or debris in the bowls that moves around and clogs up the holes. 

C

1st page post #7 & #11. 

[AZ-240z]

@blue  Without a dyno,  what I'm trying to think of is, what would cause engine stumble (not misfire or backfire), hesitation, and loss of power, under a load (running under power on the road) versus static revving?  I'm willing to start from scratch.  It's the load/no load that has me thinking.  What engine systems fail under load, rather that at rest (running in driveway)?  Will do the 3 steps I outlined above, but I'm thinking outside the box here.  Thanks,

 

Andy

Andy,

 

I had a similar problem, though probably not as severe as yours.  There is a part on your dizzy called the "assy-terminal" mounted on the lip of the dizzy under the cap, part

# 22403-18005.  It is a white plastic isolator which makes the electrical connection to the dizzy.  If you remove this white plastic part and inspect it for cracks or deterioration,

you may find that with this type of deterioration, as old plastic is want to do, could be causing a random grounding issue causing this intermittent problem. 

 

Replacing this little plastic part solved my surging, bucking, power problem and may take care of yours.

 

FWIW,

Dan

[siteunseen]

Did that bad part make your tachometer gauge jump around?  When I bought mine that part was hanging outside the distributor and the black wire wasn't connected so I had no tach at all.  Grounded the black and it worked, didn't run right but the tach worked.  I moved on to a remanufactured ZX distributor with electronic ignition.  Not original but it cranks and runs much better.

[AZ-240z]

Did that bad part make your tachometer gauge jump around?  When I bought mine that part was hanging outside the distributor and the black wire wasn't connected so I had no tach at all.  Grounded the black and it worked, didn't run right but the tach worked.  I moved on to a remanufactured ZX distributor with electronic ignition.  Not original but it cranks and runs much better.

The tach jumped only to reflect engine misfire due to the intermittent grounding problem

with this faulty isolator/connector assembly.

[AWAUDIO]

Once again, thanks to everyone.  I replaced the hoses from the bowls to carbs with factory OEM hoses 3 years ago.  Will check again.  Will inspect dizzy for the cracked insulator.  I had a loose connection there once, and it was the screw holding the condenser and the terminal you describe.  I also crimped on a new connector (cheap insurance).  Then it's float bowl and screens.  Then it's up on jack stands for sender unit and flex hose to tank inspection.  I like the collapsing hose idea. Will report back before she goes on the jack stands.  AW  

[AZ-240z]

Once again, thanks to everyone. .  Will inspect dizzy for the cracked insulator.  I had a loose connection there once, and it was the screw holding the condenser and the terminal you describe.  I also crimped on a new connector (cheap insurance).   AW  

Crimping and over-tightening screws could very easily crack this old, brittle, plastic insulator.  I was amazed at how a little crack in this insulator caused such a profound

engine problem.  This would be an easy fix for a few bucks, and I think you can still find these connectors through Nissan, but not positive. 

 

Dan

[bartsscooterservice]

I think the problem is in the distributor, because you said in post 1 that when it starts acting up, and you check the points, it runs fine again for a while...

[gundee]

Did you notice if the tach is very eratic as well when this happens?

If so. Ignition for sure from my experience.