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77 280z no power + backfires under heavy load

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Hey guys this is my first post and my first z car! I bought a 77 280z about a month and a half ago. It lost all power about a week after buying it. In gear it wouldn't go passed 1500rpm. I took it to the shop and they fixed some leaks and adjusted the timing and it worked perfectly for a few days. Now all of the previous symptoms are back with the addition of heavy backfires while going up hill.

 

I've been all over different forums looking for others that have had the same problems and testing my engine using the advice I found but with no luck. The previous owner and I have been brainstorming too.

 

-The timing is perfect

-coil was recently replaced

-fuel filter is new

-alternator was replaced along with the voltage regulator because I was running on 17-18v but now is stable around 13

-spark is good

-drained the tank in case of bad gas

 

I've had this car for about a month and a half and it's only been drivable for a week. Help please!! I don't know what else to look for. I just started to get mechanically inclined about a year ago so I'm still new. Any advice is appriciated!

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thanks for the feedback guys!! I've checked the fuel pressure and looked for vaccum leaks but with no luck. I took the car to a mechanic friend and weve been trying to figure it out a little. we've found that its definitely an electrical issue. the alternator wasnt charging the battery at all and that was because of a fryed fuse link. we fixed that but now its pumping out 16-18v which is really not good. the external voltage regulator is brand new. we even hooked up another new one and nothing changed.

 

so my problem is: The car is overcharging at around 18v. But its something other than the alternator or the voltage regulator.

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thanks for the feedback guys!! I've checked the fuel pressure and looked for vaccum leaks but with no luck. I took the car to a mechanic friend and weve been trying to figure it out a little. we've found that its definitely an electrical issue. the alternator wasnt charging the battery at all and that was because of a fryed fuse link. we fixed that but now its pumping out 16-18v which is really not good. the external voltage regulator is brand new. we even hooked up another new one and nothing changed.

 

so my problem is: The car is overcharging at around 18v. But its something other than the alternator or the voltage regulator.

Either your new regulator is bad, or one the wires at the T plug on the alternator is not connected to the battery.  

 

"checked fuel pressure" doesn't mean anything without numbers. 

 

Open the Engine Electrical chapter and get a multimeter.  You mechanic friend should have one.  Check the bottom (edited - said top before) of the T plug at the alternator for battery power.  Measure fuel pressure, according to the procedure in the Engine Fuel chapter.

 

Edit - actually, with the key on, both top and bottom contacts of the T plug should shows battery voltage.

Edited by NewZed

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