I finally bought the Z car I always wanted (well I can't afford a 240) a 1979 280ZX (which was the year I went in the Navy and while other guys had Z cars I had a 1974 Ford Country Sedan Wagon . Just drove it home and after running fine for about 20 minutes when I got on the freeway it started to "jerk" by losing power going up a slight incline and then surge back gradually going from 65 to 40 mph. I tried to nurse it home but it got worse until it was doing it on the level road and I finally pulled over and got a tow. Called the guy I bought it from and he suggested the fuel filter which looks new (he took the car on trade) but I'm going to go get one and replace it. A couple of injectors were replaced recently. Has anyone else had something like this or have ideas?

Excited to be a part of the group!

Read your 12/2017 post: (Car LosingPower,CuttingOff)! I've had em all, built em all!  NOTE: The EFI system in the 280z/zx's (non-turbo) are as bullet proof as everything else in the zcars! Same goes for the fuel delivery system's components (I.e. fuel pump, filter, fuel pressure regulator, right down to the injectors! NOTE: Before any fuel even reaches the cylinders it has to past through three filters: (1st)filter in fuel pump,(2)GasFilter, and (3)Filters in Fuel Injectors.  No Dirt,Crud in tank can reach Injectors, hinder them! You said in your post how Car was fine until you "FILLED" the tank with "CHEAP" "GAS". The 280z,zx's require a min 90 octane fuel per the manufacturer! So the lower you go in octane (89,87) to save a few pennies will cost you in the end (i.e. car runs weaker, slower, and certainly it will start"CuttingOut/ Coughing (aka cold backfiring) out the intake)! 89 octane fuel is the lowest a ZCAR will safely tolerate!  I use the term "Safely Tolerate" due to the fact that using a cheap fuel (below 89oct) can cause damage to the flap/plate inside the "AIR FLOW METER" when the engine (coldbackfires) though intake, throttlebody! Putting backwards airpressure/force upon flap inside the AIRFLOW METER bending it/damaging it, jamming it!  Not only will cheap gas cause your issues, and also damage the "AIRFLOW METER" in the ZCAR, so too will a "Vacuum Leak" regardless if your using high octane fuel or not!  As a Vacuum Leak will lean out the air/fuel mixture too much and the engine will jerk,cutout, "COUGH"! Check TBody rubber boot to AFM as their know to develop large cracks, especially underneath. As for the Bosh EFI system used in z cars is a "Low Pressure" (38psi). The Fuel Pressure regulator is controlled by the amount of Vacuum applied to it which results in regulating the fuel pressure at the Injectors! Higher  pressure=more fuel out of injectors!  At idle (high vacuum) pressure is lowest at injectors due to the FPR is allowing fuel to bypass back to fuel tank via return gas line! When gas pedal is pressed vacuum drops at the FPRegulator resulting in higher fuel pres at injectors/more fuel!  So Check For Vacuum Leaks, and check all hoses, Throttlebody Boot! You can also safely block off all the vacuum hoses attached to the intake, "BUT NOT THE HOSE TO BRAKE BOOSTER"!  Check the "PVC valve,  The EGR valve also for vacuum leak. I eliminated BOTH and rerouted pvc crankcase ventilation as the older 240,260z had it, much better!

Car sitting for an unknown amount of time is a big clue. Addding fuel as you did probably stirred up years of yuk in the tank. When you buy an old car / classic like this you have to expect the worse. I went thru a similar issue and it turned out to be a clogged return line on the pick up tube. The fuel sending unit looked new when I pulled it out of the tank but the return had gunk in it and barely flowed and it would shut completely and it made the engine studder

Hello Madkaw, read ur post/reply! I'm new to this posting/reply stuff so bare with me! After reading your post I'm not clear if ur describing current problems with ur z or just replying in general to this topic! I've had many of these zcars, (240-280's) and being new to the Classic zcars forms, too which I read em and see zcar owners needing help so I'd like to help! There's not a part on a zcar I haven't had in my hands, apart/reassembled or replaced so I'd like to help anyone having zcar issues! In the fuel delivery system (on these zcars) from tank to engine and back via "ReturnLine"! If your not aware, "Gas" has a limited time before breaking back down to it's initial state "TAR"!  Thus, when anyone encountering a car that sat for long time (2-5years or more) the first thing he "must do" is drain/check tank, check pickup tube & screen: "ALWAYS BEFORE EVER TURNING THE ENGINE OVER"!!!! Secondly, "Regardless" if ur inspection of the gas tank, pickup tube/screen/sending unit looks good, your next move is to disconnect the returnLine coming off/from the Fuel Pressure Regulator then the Fuel delivery line to the gas filter to check if clogged or gas flow being hindered (slow flow)! If OK, great;  but both lines ("Plus the TankVent Line Going To The Emission Canister") should be blown out by air hose/pressure)! NOTE: The Fuel Line has to be disconnected at three location's due to having 3 separate lines! (1)Line at Tank to fuel pump, (2) Line from pump to Filter, (3) Filter to FuelPressureRegulator! The Fuel return line and Emissions VentLine can just be blow out! Next is the Fuel pump, which is also bulletproof! The pump, if it's turning/making sound then it's working! But since it's cooled only by gas flowing through it simply attach a fuel line from a gas container that has clean gas "90" octane mixed with "Marvell's Mystery Oil", (great stuff that clean's/lubricates entire fuel system, injectors, intake valves,etc)! Also add it to the new oil, which you must change also regardless how oil in engine may look and feel! Oil is gas and Gas is oil, they both break down over time! Once you have fuel line attached to the Fuel pump your ready to test it/allow it to clean itself of all the old gas and or gunk into another catch container so you can see it!  Once all above is done just inspect all rubber lines,  clamps, rubber seal at gas tank sending unit and replace anything bad if needed! I advise to change all the rubber gas lines, old clamps, and tank rubber o-ring seal with new ones since ur there and due to Old age of the rubber lines, seal! Then reassemble everything, add 5gal's "90" octane mixed with MARVELL'S MYSTERY OIL! Since the Fuel pump is only activated when cranking the engine I simply run a Hot Wire from battery to pump + wire and just let the pump do it's job, pumping fuel up to Filtef, thru the FPR and back to Fuel tank via returnLine! To see if fuel is flowing simply redirect the fuel return line into a container (AWAY FROM ENGINE COMPARTMENT TO PREVENT ACCIDENTAL FIRE")! Fuel will, ("must be seen") coming from fuel ReturnLine into container! Yes, the next test is the fuel injectors! Simply try to start engine ("Only if you've already freed up the engine!i.e. oiled cylinders then turned engine by hand!)! It will start, if not, make sure you have spark at plugs! All plugs! If there's spark then you have to remove fuel rail to examine injector's spraying fuel when cranking engine and or you can also activate the fuel pump, let it run, and with another hot wire simply remove wires off injector's and hot wire them one by one, "BUT BEWARE" you can only tap the hot wire to the injectors for a "mico second"!!!! Just tap the injectors to see if their spraying or clogged! The too have a very fine screen inside them! If they're spraying Cool, If not check ECM Fuse Relay for power, and fuse in box under dash on passenger side wall!  

Ummm- I was responding to the OP - and relating what I found to hope help him .

All good info and should help OP

 

And welcome aboard - we always need fresh help 

Edited April 7, 20186 yr by madkaw

Jacob Silj just joined!   Welcome JACOB!  It looks LIKE you've worked on these cars BEFORE!

Yea, I've owned/built zcars from scratch but I'm new to this Classic zcars forms/posts so I'd like to ask ya:

Is posting and replying to post same as "Texting" back and forth or is everything posted where all to see?

It's posting to threads that all can see.   There is also a feature to send messages privately between forum members.

Yes, we can all see the posts.  Hold your cursor over a member's name and the option to send a private message will appear.

By the way, tapping a hot wire to an injector will not cause them to open.  They are opened by grounding the power that is already there.  So, if you take the plug off then you need to supply a hot and a ground.  A 9 volt battery is commonly used, or you can ground them at the ECU connector, individually.  Just sayin...