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Random Bogging / Loss of Throttle


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Hey all -
 
So here's my problem with my 1976 fuel-injected 280z (in all it's layers). My car has been suffering from a rough start-up lately, where the car has trouble turning-over, until it eventually fires with just enough power to get the motor running. A few blips of the throttle helps the car find a steady enough idle that it runs smooth enough to drive. And until the car is warm, the car comes close to dying when not under load (again, I tease the throttle a little to keep the car alive).
 
Then, it all seems to even out -- for a while. Then, a few miles into my drive (or after running strong for about 15min or so), the car will bog when I go to touch the throttle. The car will idle, but as soon as I go to give it gas, there will be no response whatsoever - almost as if the car has shut off, but it hasn't. Sometimes, if I turn the car off / on right away as I notice the problem coming on, I can get power back out of the motor enough to pull over and wait it out.
 
Turning the car on / off a couple of times usually gives me enough second chances to where I can limp the car home. But WHAT THE **** IS GOING ON?
 
 
If it's worth mentioning, I've only done so much as intake / exhaust on my car. I upgraded my coil, thinking this was the culprit, but the problem hasn't changed at all. Also had my tank refreshed / fusable links upgraded. I've changed my fuel filter, and replaced my plugs. My timing is correct (except for when it misfires when this particular problem arises), and my battery / alternator are up to snuff.
 
What could this be?
My next suspect in trying to track down the issue was going to be my fuel pump - is what I've described symptomatic of a failing fuel pump??
 
Any amount of help would be a big help.
Thanks in advance.
 

 

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UPDATE:


 


Decided to drive up to Yonkers from Brooklyn yesterday (followed closely by a friend in the event of something happening) and much to my surprise, the car made the entire trip without issue. That's 20 miles on the highway, through all gears, without any bogging whatsoever. Even at the toll plaza halfway through the trip, idling went without incident.


 


Once in Yonkers, I drove the car around all weekend: maybe 30 miles, give or take. Again, no issues.


 


Then, on my return trip this evening, upon reaching the toll plaza halfway into my trip, idling for the toll became an issue. I bogged at idle, and when I feathered the throttle to get some life back into the car, the response was flat. I turned the car off / on, and upon restarting, I was able to rev the car back into some life in order to make it through the toll.  Then, for the rest of my trip, the car ran strong through all the gears.


 


ALSO WORTH NOTING: when the car was bogging at the toll plaza, I noticed a significant drop in oil pressure. What might this be symptomatic of?


Also - even though the car wasn't bogging like it had been, the car does have a bit of a sputter when trying to get rolling in first gear. (?)


 


 


Any input??


Thanks!


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UPDATE:

 

Installed a fuel pressure gauge after my (relatively) new fuel filter today under the hood.  Drove around without incident for a little while, and when the car started showing signs of bogging, I popped the hood to monitor the gauge.

Even as the car bogs (power cuts off sharply), the fuel pressure gauge reads a steady 28psi -- obviously low because the car won't rev past the bogging / loss of throttle.

 

When the car is running correctly, it idles around 28-30psi, and when revved, the pressure jumps to around 40psi (which I understand to be correct pressure readings for the 280z).

 

 

So now what!?

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