1975 280z coughing

[montyd]

Hey guys, I'm new to the forum and Datsun for that matter. I'm trying to revieve a 75' 280 for a friend of my dads. The car sat for almost 10 years. I drained the fuel, changed the filter and some lines got the pump freed up and she fired up. Freednup the clutch and went for a ride. I no more got to the end of my driveway andit started running rough and coughing. If I let it idle it runs fine and will pull itself in gear back into the garage. Any throttle and it coughs. Get back inside and its much better but still coughs and back fires through the intake. I have my fuel pressure gauge in line after the filter and have 28-30lbs at idle and it climbs with rpm. Minorly adjusted the tps so the second set of points touches on the second ramp. The AFM appears normal under the cover. I'm wondering where to go next. I've checked vacuum lines fuel lines etc. I'm wondering if all the injectors should be rebuilt and new plugs put on since the boots are dry rotted. The connectors on the coolant sensors are dry rotted also but seem connected well. Any thoughts?

 

P.s. its 70° inside and 15° outside. On a 30° day it was better outside but still got in drive able within 4-5 min

Edited March 1, 2015 by montyd

[NewZed]

Sounds lean.  I've had several old AFM's that run lean.  The simple fix is to add a potentiometer in-line with the coolant temperature sensor wire and raise resistance to add fuel.  But I also have had bad/clogged injectors, that ran lean.  Vacuum leaks will also cause a lean condition.  Could be any, all, or a combination of.

 

On an EFI car that has sat for a while, it takes some time to go through all of the basics of fixing vacuum leaks, cleaning connectors, tuning up, etc.  Download the 1975 FSM and read the entire Engine Fuel chapter, you'll understand a lot more, like how to properly check fuel pressure (and what the number should be).  Also read Engine Electrical and you'll realize that you shouldn't have points, and that the second set is only used for a short time anyway.  They're for emissions, not performance.

 

http://www.nicoclub.com/FSM/280z/

[Pac_Man]

The fact that it ran fine until it got to the end of the driveway makes me think it's fuel related. When my fuel pump was going bad, the car would randomly start to struggle even at idle and pressing the gas pedal down didn't do anything. You'll have to do resistance testing to be sure if the AFM, TPS, etc. are off. The FSM has readings for all of the EFI components and you can download it for free at xenons30.com or probably find them posted somewhere here.

 

Honestly with how long it sat you might be best off pulling the fuel rail off, having the injectors cleaned and rebuilt unless you would rather just replace them, blowing some air through the hard lines, and then see how it does. Of course I would suggest checking for vacuum leaks and EFI component failure before that as you don't have to tear into nearly as much. The garage mechanic way of checking for vacuum leaks seems to be spraying starting fluid around various intake components and listening for idle surge. You could also use a smoke machine or figure out a way to do it with a cigar or something.