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1978 280z Fuel problems


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#1 Lighft01

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Posted 23 April 2008 - 05:24 PM

Yet another datsun with a fuel problem. I think i read every fuel/my car wont start thread in this forum but, still cannot get my car running. Downloaded a efi "bible" but it was for a 75, as i understand it from reading the fuel injection in a 78 is different than the rest.

In the EFI bible it shows position of a fuel pump relay, and some dropping resisitors. I cannot find these in my car. The PO said that he daily drove this car before he parked it. It sat up for about a year before i got it.

Brand new battery plugs, wires. Originally i found out the fuel pump was running, so after i could not find any relays, i just bypassed it to a switched 12v source to see if i could get it to run. Now the fuel pump works, but injectors dont seem to be spraying. I know i have fuel to the rail, i pulled in inlet line off and watched fuel pump into a bottle. When you pull the plugs after trying to get it to start there is no fuel smell.

Do not get any voltage to the fuel injector plugs. Pulled the plug to the ecm and there isnt even a fuel pump realy pin in it. Well atleast not where the efi bible said to find it. Today i pulled the dash off, and found a silver cylindrical relay looking thing right above the hood popper. Should this be clicking when i turn the key to "on"? The ignition relay is good i put my hand on it and tried tried to start it and it is clicking. Im kind of lost now, dont know where to start or what. Can anyone give me a direction to go in?

#2 mom'sZ

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Posted 24 April 2008 - 01:20 PM

You've already made a good start at diagnosing the issue. Good move reading up and downloading the bible. It was released in 75 when the fuel injection was introduced in the first 280. The wiring harness changed slightly in 77 and 78 and automatic and manual trannies have a slightly different wiring but all the components are the same and functionally it is the same system. The bible is mostly good for understanding how the system works and providing simple test procedures that can be performed with a multimeter for all the different components. Getting a new battery helps because the system needs full voltage to function properly. Here is a link to an AutoZone site with wiring diagrams for all years
http://www.autozone....irInfoPages.htm
The first thing you want to check is the connectors. The fuel injection wiring harness is a whole separate harness from the rest of the cars wiring. The connectors get old and crusty and often the voltage and signals they carry can be mucked up by a bad connection at the connectors. There are only so many, disconnect each one, spray some contact cleaner in each one. Clean them up with a little brush if you have to.
The fuel injectors do not receive positive voltage to fire so you won't get anything by checking them for voltage. They actually have a constant positive connection and the ECU grounds them to fire them. To check if the injectors are firing you can hold a screwdriver to them, tip against the body of the injector and your ear to the handle and listen for a click click click. Or you can go to the autoparts store and buy a noid light. They are cheap, less then $15. Unplug one injector wire and plug the noid light in instead, then turn the motor over and see if the light flashes.
You seem sure you have fuel pressure at the fuel rail. The sytem actually needs 25 - 30 psi at the rail. A cheapy fuel pressure gauge tee'd into the rail works best.
The stepping resistors are located under the driver side inspection cover next to and behind the clutch master cylinder. I think on your car the fuel pump relay would be on the passenger side fender well on the metal bracket that also holds the voltage regulator. (not sure)
So, try some of the stuff I've mentioned and then report back on exactly what is happening. Does the car try to start at all? It turns over but nothing happens or it coughs and sputters but won't start or it starts but won't stay running? What? And of course check and make sure you have spark. Good luck, once it's running you'll love the sytem. Make sure the vacumn hoses are all brand new and the boot between the AFM and the throttle body isn't torn.
Help keep Zcars on the racetrack!!!
Save your old rear brake drums. Brembo has stopped making these parts and there are no OEM replacements available.
Parts I want to buy: 75 - 78 280z shells or parts cars (any condition) EFI harness AFMs, ECUs and throttle bodies. Non EGR intakes. 5-speeds. R200. N-42 heads. 75 - 78 Strut housings and control arms. 75 - 78 distributer. 75 - 78 big ugly bumpers f & r
Thank you HybridZ

#3 zmaster

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Posted 24 April 2008 - 02:00 PM

on my 75 280z the injectors were firing, and I could start the car with a switched 12volt source to the fuel pump, I pulled the EFI relay off the connectors, and put it bak on the connectors, and the injectors stopped workin. I later found out that one of the wires in the plastic connector was being pushed out by the pin, so I simpily pushed it back in the plastic, and WAMMO the injectors work again
[SIGPIC][/SIGPIC]I live my life a quarter mile at a time, and nothing else matters. For those ten seconds or less i'm free.

#4 Lighft01

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Posted 25 April 2008 - 04:03 PM

You've already made a good start at diagnosing the issue. Good move reading up and downloading the bible. It was released in 75 when the fuel injection was introduced in the first 280. The wiring harness changed slightly in 77 and 78 and automatic and manual trannies have a slightly different wiring but all the components are the same and functionally it is the same system. The bible is mostly good for understanding how the system works and providing simple test procedures that can be performed with a multimeter for all the different components. Getting a new battery helps because the system needs full voltage to function properly. Here is a link to an AutoZone site with wiring diagrams for all years
http://www.autozone....irInfoPages.htm
The first thing you want to check is the connectors. The fuel injection wiring harness is a whole separate harness from the rest of the cars wiring. The connectors get old and crusty and often the voltage and signals they carry can be mucked up by a bad connection at the connectors. There are only so many, disconnect each one, spray some contact cleaner in each one. Clean them up with a little brush if you have to.
The fuel injectors do not receive positive voltage to fire so you won't get anything by checking them for voltage. They actually have a constant positive connection and the ECU grounds them to fire them. To check if the injectors are firing you can hold a screwdriver to them, tip against the body of the injector and your ear to the handle and listen for a click click click. Or you can go to the autoparts store and buy a noid light. They are cheap, less then $15. Unplug one injector wire and plug the noid light in instead, then turn the motor over and see if the light flashes.
You seem sure you have fuel pressure at the fuel rail. The sytem actually needs 25 - 30 psi at the rail. A cheapy fuel pressure gauge tee'd into the rail works best.
The stepping resistors are located under the driver side inspection cover next to and behind the clutch master cylinder. I think on your car the fuel pump relay would be on the passenger side fender well on the metal bracket that also holds the voltage regulator. (not sure)
So, try some of the stuff I've mentioned and then report back on exactly what is happening. Does the car try to start at all? It turns over but nothing happens or it coughs and sputters but won't start or it starts but won't stay running? What? And of course check and make sure you have spark. Good luck, once it's running you'll love the sytem. Make sure the vacumn hoses are all brand new and the boot between the AFM and the throttle body isn't torn.


The car turns over fine, really well, but the engine never actually starts. Ive tested for spark, its fine, sparks good, and i just replaced the wires and plugs. Just bought a brand new optima red top when i got it so i know its not the battery. I took my dash off, to try and find the dropping resistors and EFI relay to no avail, someone on another site told me where it was, dropping resistors under driver side inspection lid, and realys in the relay box passenger side fender. When i turn the key to "on" none of the relays click or make any noise. Someone else told me my problem was not with the realys but with the wiring. I have another 78' that runs perfect thinking about pulling the FI harness out of it and swapping them to see if that makes a difference. Fuel pressure did seem kind of weak, ill have to get a gauge and check and see what it is actually running. If you spray starting fluid in the intake the car runs fine, as long as you keep spraying. I swapped the afm from my other car thinking it might be the fuel cut off in the original and didnt want to tear the AFM apart, made no difference. The car was sitting in the PO's driveway for a year, maybe some of the wires got crusty but none of them looked that bad. Ill go back over everything this weekend really well and let you know, thanks for the support.

#5 240swapped

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Posted 25 April 2008 - 06:01 PM

my 76 has the EXACT same problem. plenty of fuel pressure from brand new fuel cell and holley pump. NO INJECTOR PULSE. have replaced three of the injectors, the efi harness, the ecu, the AFM, the tps.....still nothing, next i'm going to replace the dropping resistor. my wiring diagnostics are limited, but i checked continuity according to schematics and everything should be working. at my wits end. it's about to get su's if i can't get it running soon.

#6 Lighft01

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Posted 26 April 2008 - 06:25 PM

made a little progress today, swapped the 4 big fusable links on the outside of the relay box with another car i have that runs good, and the efi main relay clicks now when you turn the car to on. Checked the timing just be sure it was right, got the #1 piston to TDC pulled the cap, and it was one cylinder off. So i fixed the plugs wires, and bam the first cylinder fires, and then the car just goes back to spinning. Let of the starter for a second try it again, same thing, trys to start and then goes to spinning. When i pulled the plugs to see if they were wet, some smelled of fuel, and some had a really faint smell. I dont think all the injectors are getting the same amount of fuel, im going to pull the rail tonight and put air through it.

#7 zmaster

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Posted 26 April 2008 - 06:29 PM

you should clean out the injectors, or you could get new ones for about 50.00 each from autozone, or advance auto parts. Here is a picture of my fusible links I upgraded the grren one is 40 amps, and the black is 80 ithink can't remember off hand. They also have these at the auto part stores for 3 or 4 dollars each. http://i296.photobuc...er/IMAG0026.jpg I had to put electrical tape on the black fusible link to make sure it doesn't contact the car and make sparks, or a fire......SAFETY FIRST thats how you avoid serious injuries.
[SIGPIC][/SIGPIC]I live my life a quarter mile at a time, and nothing else matters. For those ten seconds or less i'm free.

#8 MJLamberson

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Posted 27 April 2008 - 09:55 AM

check fusible links yet?
-Michael Lamberson
myspace.com/mjlamberson
1976 280z, parted out
1977 280z, RIP, PARTING OUT! TURBO STUFF!http://forums.hybrid...ad.php?t=150948



#9 Lighft01

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Posted 27 April 2008 - 04:59 PM

check fusible links yet?



I swapped the fusable links and entire realy box from another 78 that i have that runs perfect, and still nothing. The only fusible links i havent changed are the ones on the relay box that are closest to the battery. the two green ones. Even after i swapped the reley box, the fuel pump still will not work, im going to pull the fuel lines tonight and blow them out, and probably pull the fuel rail again, and blow it out. Probably should have done that to begin with.

#10 zmaster

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Posted 28 April 2008 - 08:06 AM

heres something you should try and do. Have someone crank the car and test the voltage directly on the fuel pump. Chances are there is less than 1 volt going to the fuel pump. that is the problem I am having in my 75. I tried to use a switched 12volt source the battery, and I keep running rich. I pulled the plugs and they were black with soot or ash can't remember, and they smelled of gas just a little bit.
[SIGPIC][/SIGPIC]I live my life a quarter mile at a time, and nothing else matters. For those ten seconds or less i'm free.

#11 mom'sZ

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Posted 28 April 2008 - 08:38 AM

Lighft01: both your cars are 78s right? Because there are different ECUs and AFMs from year to year and also different from manual and auto, so if you mix and match components you might screw them up. If both your cars are 78s and both manual trannies, you should be fine. The harness will plug into the ECU but the pin outs changed and you can fry the ECUs. If they are different years or trannies you have to swap harness, ECU, AFM and everything all together. (some of this I am pointing out just for others who may find this thread)
Because of the fact that you changed the fusible links and the relay started clicking shows the wiring is possibly crusty. The connectors are the real weak link. There may be no problem with the components, it could just be a wiring/connector issue. Check the harness visually. Look at it close, checking for fraying or signs of heat/burning. Look in the EFI bible for procedures for checking the signals or voltages at the connector for the ECU by unplugging the ECU. This way you are checking the component as well as the wiring. This way you measure what the ECU is seeing. Look at each connector. Unplug it and look for loose or crusty pins. Zmaster's example is a good example of the things your dealing with. These things weren't know for great wiring thirty years ago when they were new, and thirty years hasn't helped.
If you spray starting fluid in there and it tries that proves it can run and you have some spark, although I'd double check your timing. Also, from the sounds of the first cylinder firing then no more, maybe coil is going. Don't just go buy one, try to check it, swap it with known good one. Does it get really hot after trying to start?
On the fuel pump thing, remember the fuel pump only gets juice in the key switch start position. In the key switch on position, the AFM flapper must be open slightly to send the fuel pump juice. Remove the boot between the air cleaner and the AFM. Turn the key to the on position without starting the car, and then stick your finger in the AFM and lift the flap slightly off it's stop, you should hear the fuel pump run when the flap is open slightly.
One more thing, I think your fuel pump is the issue, but don't just go buy one, diagnois it. But how cold is it where you are? Because it is a starting issue, you may have thermotime switch or air regulator issue. Again, there are diagnoistic procedures in the bible. But I'm in Florida and don't need either, because it is warm.
240swapped: Don't give up!!! download the EFI bible and use the diaganostic procedures to check the components. Start a new thread with your info (year model mods) and symptoms and we'll try to get you going. ALSO, guys, try to post when you get them going with details of what fixed it so others can benefit from your experience.
Help keep Zcars on the racetrack!!!
Save your old rear brake drums. Brembo has stopped making these parts and there are no OEM replacements available.
Parts I want to buy: 75 - 78 280z shells or parts cars (any condition) EFI harness AFMs, ECUs and throttle bodies. Non EGR intakes. 5-speeds. R200. N-42 heads. 75 - 78 Strut housings and control arms. 75 - 78 distributer. 75 - 78 big ugly bumpers f & r
Thank you HybridZ

#12 mom'sZ

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Posted 28 April 2008 - 08:42 AM

I tried to use a switched 12volt source the battery, and I keep running rich. I pulled the plugs and they were black with soot or ash can't remember, and they smelled of gas just a little bit.

Zmaster, I'll check your other thread next but, having cured or at least worked around your fuel pump issue, it sounds like your water tempature sender is bad. When the water temp sender goes bad, the ECU just goes full rich. It is located in the thermostat housing and they are only fifteen bucks at any auto parts place. Go get one and try it.
Help keep Zcars on the racetrack!!!
Save your old rear brake drums. Brembo has stopped making these parts and there are no OEM replacements available.
Parts I want to buy: 75 - 78 280z shells or parts cars (any condition) EFI harness AFMs, ECUs and throttle bodies. Non EGR intakes. 5-speeds. R200. N-42 heads. 75 - 78 Strut housings and control arms. 75 - 78 distributer. 75 - 78 big ugly bumpers f & r
Thank you HybridZ

#13 Lighft01

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Posted 03 May 2008 - 03:24 PM

Ok think i figure out what was wrong. There was about 3 inches of crud in the lines right before the fuel pump. There is a strainer in the inlet line to the fuel pump and it was full of crap i got all the gunk out, and after a few minutes of running clean gas through the pump, its pumping out nice clean gas again. I need a new strainer though, does anyone know where i can get one?? Searched but all i found was about the strainer thats in the tank itself. Part number would help, or an equivelant strainer from another car. I checked my local parts store they did not have any. Im going to run down to autozone right now and see if they have one. Please help if you know i want to get my car running this weekend

#14 Lighft01

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Posted 03 May 2008 - 05:41 PM

Well its running now, i cleaned out the strainer and put it back in its old, and cracked and has some holes in it so if anyone has one they dont need ill buy it off of you, but thanks for all your help. Now that i know it runs, it will be easier to figure out why the fuel pump doesnt work off of the stock harness. Again thanks for all your time, i really appreciate it.

#15 AK-Z

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Posted 04 May 2008 - 01:30 AM

Are you talking about the fuel filter? I might have one. Can you post a pic so I know what I'm looking for?
[URL="http://www.zippyvideos.com/70747806453375.html"]

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[/URL]

#16 Lighft01

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Posted 04 May 2008 - 08:56 PM

It isnt a fuel filter its the strainer, it is inside the inlet pipe that is on the actual pump itself. I dont need it now though, my pump died on me today so i had to go and get a new one, and the strainer wont fit in it.

#17 AK-Z

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Posted 04 May 2008 - 09:48 PM

Oh, ok. that sucks. let me know if you still need it. Also have a working fuel pump.

just to clarify, is it located inside the fuel tank or right next to it?
[URL="http://www.zippyvideos.com/70747806453375.html"]

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#18 Lighft01

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Posted 05 May 2008 - 03:15 PM

Well my car started acting up again when it got warm. Stuttering, and missing, sounds like it has a cam. The motor seems to be getting really hot really fast. I think it may be running lean, so im going to clean the injectors out again.

#19 ema

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Posted 24 August 2009 - 05:38 PM

yhanks mom's! This has been very helpful. Good job there Lighft01. How was it now anyway?

#20 kciuq

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Posted 01 September 2009 - 05:21 AM

hi ...i bought a 280zx it never ran good after it was warm and bad startup. i found that the air bypass valve was knakkered (i could blow thru it easily when disconnected and out of the car )i swapped it with a rb 30 one (which i could only just blow thru ) which helped heaps...(note... the standard 280 bypass valve runs at 60ohms and the rb 30 bpv runs 75ohms but it will do for now) also my cam lobes (on top dead centre ) were a little off (left one (drivers side) slightly lower than the other) i had to put the cam sprocket to position 2 which helped again ( diagnosis... stretched timing chain ) now it ran ok but still sluggish so i checked my fuel filter which seemed to be clean untill i shook it and mud came out so i changed it (the difference between struggling at 5g+ to coasting past 5.5g revz ) so i took no chances and also changed my fuel rail regulator once again more & better performance ...even though ive done all this i cant seem to get my fuel pump to stop running constantly which affects my bcdd (i ran my bcdd line to the black white wire on my fuel pump relay box bcause it ran badly and had no other wire to monitor fuel usage in the harness to the computer ) just a few things in my experiances with my datto ...maybe something here will or might help you with yours




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