Heroez Posted May 24, 2012 Share Posted May 24, 2012 (edited) Hi everyone. I used to get the normal fuel prime on my 280zx, but one day it just stopped working. Its causing the car to be hard to start. Curious, I took a voltage reading at the fuel pump wiring connector under the hatch carpet. As I turned the ignition on the voltage reading was not good. 2.5 volts for maybe a half second then back to 0. I repeated the test getting varied voltage like 2-7 volts for a fraction of a second. I was looking at the diagrams in the factory service manuals, and reading about 3 fuel pump relays. If I understood correctly, fuel pump relay 1 is involved in the fuel prime. So I remove the dash box liner and check the connection to the relay. I found it to look good, no corrosion or obvious red flag. So next I replace the relay there with a new one. Still no fuel prime! Am I overlooking something? Is there a fuse or other part I should look into? I dont see a timer unit mentioned, or the ECUs role. Any suggestions? Edited May 25, 2012 by Heroez Quote Link to comment Share on other sites More sharing options...
Heroez Posted May 27, 2012 Author Share Posted May 27, 2012 Anyone? Quote Link to comment Share on other sites More sharing options...
sqweekykneecap Posted May 28, 2012 Share Posted May 28, 2012 hey man, sorry to hear about a elec problem, just remember that (the majority of the time) its something REALLY simple. Now, i'm not insulting your intelligence, but did you check the battery voltage? Also, make sure your alternator connections are all secure, if not, your battery wont get good charge. hopefully this helps lol Quote Link to comment Share on other sites More sharing options...
Heroez Posted May 29, 2012 Author Share Posted May 29, 2012 Yes, the battery is new, and I was goimg to install battery cables too but the negative cable isnt readily available at the parts store. I did check the battery and got 12.5 volts. Went ahead with the relay tests in the manual. Fuel pump relay 1,2, and 3 tested good. I will look into my alternator connections like you suggested. Thanks. If I have trouble I will post again. Keep an eye on me. Quote Link to comment Share on other sites More sharing options...
Heroez Posted June 10, 2012 Author Share Posted June 10, 2012 Alternator looks good. All three fuel pump relays tested good. Ignition switch is good. I don't understand what to look at next. Quote Link to comment Share on other sites More sharing options...
Heroez Posted June 12, 2012 Author Share Posted June 12, 2012 Anyone? Quote Link to comment Share on other sites More sharing options...
Noddle Posted June 12, 2012 Share Posted June 12, 2012 (edited) Anyone? Do a search for the EFI manual, this will tell you how to do a step by step test of the EFI system, The link I have is no longer valid, sorry Nigel I found this will looking at the other threads, http://forums.hybridz.org/index.php/topic/107398-how-to-check-if-ecu-is-good/page__view__findpost__p__1004777 Edited June 13, 2012 by Noddle Quote Link to comment Share on other sites More sharing options...
Heroez Posted June 13, 2012 Author Share Posted June 13, 2012 Ive done the tests in the FSM, which consisted of testing the 3 relays, and checking pin 21 at the ECU. They passed testing, and no other mention of the 5 second fuel prime can be found in any part of the manual. That is why I made a topic on it. In case anyone can fill in where the FSM falls short. So what do I look at next? The fuel pump wiring traces to a bulb checking relay, and fusible link. I swapped out the fusible link with no change. Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 13, 2012 Share Posted June 13, 2012 (edited) Edit - Had some suggestions here, but they were random. Your best bet is to study the wiring diagram and figure out which circuit controls power to the pump and could be affected by a timing device, then focus on that circuit. The FSM may not mention the timer, but the wires still connect the various relays, oil pressure sensor and alternator. Edit 2 - By the way, 5 seconds of fuel passing through the rail will have little affect on "heat soak". Edited June 13, 2012 by NewZed Quote Link to comment Share on other sites More sharing options...
Heroez Posted June 13, 2012 Author Share Posted June 13, 2012 (edited) It greatly effects heat soak if you have a bad check valve on the fuel pump and the engine is heating gas vapor in the fuel rail, and its not cycled out by a fuel prime. A separate problem I know. I just want to fix a problem with the car. Im not positive but the prime stopped after my voltage regulator went bad and overcharged on the interstate. Melted my tail light bulb sockets too. Anyone out there have a suggestion on what may control the fuel prime on a 1980 280zx? Edited June 13, 2012 by Heroez Quote Link to comment Share on other sites More sharing options...
ctc Posted June 14, 2012 Share Posted June 14, 2012 (edited) If you have other wiring damage the wire itself may be bad. Two suggestions, 1) wire a light into the plug in the hatch, this will simulate a load. See how long it stays on. 2) inspect the wires from the plug back up the length of the car. Look for any damage or breaks. Or alternately run a second independent wire to the pump from a known good splice point. You didn't mention NA or Turbo or what year. Looking at the FSM from the 82 280ZX Turbo from Xenon S130, EF & EC page 66 notes 5 seconds of operation at the fuel pump relay. I would check for continuity across the relay when the key is turned. Also EF & EC page 67 indicate 9.8V applied to the pump expect under certain engine states. With a low battery this could translate to 7V where you measured. Just some thoughts. Edited June 14, 2012 by ctc Quote Link to comment Share on other sites More sharing options...
Heroez Posted June 15, 2012 Author Share Posted June 15, 2012 Good suggestions, thanks for taking it seriously. Its a 1980 deluxe, the base model. I see on page 6 a diagram that shows a relation between the relay 1 and air regulator. I was starting to think that a bad air regulator was responsible for the fuel prime not working. I did test all three fuel pump relays as directed by the manual, continuity and power switching. They all passed. So it's outside the relays. As for what's going on when the prime should happen, its a very brief low voltage on my meter. The relay 1 test directs you to testing the air regulator, so I may as well do it. Pin 21 checks ok. I will report my findings, so keep an eye out. If everything checks ok, it says check harness, like you mentioned. Thanks for all the replies on this topic from everyone. Keep them coming. I'm very surprised that this circuit is so unknown. Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 16, 2012 Share Posted June 16, 2012 That's a good find by ctc. Even better, the FSM seems to imply that the EFI ECU turns on the relay for a "few seconds", page 50 description of the earlier, non ECCS EFI. The diagram and table seem to say that the ECU "monitors" engine RPM by coil pulses to control the power to the relay, but that the relay is energized for a few seconds when the key is turned ON. Seems like the computer is the controller, at least for 1982. Quote Link to comment Share on other sites More sharing options...
ctc Posted June 16, 2012 Share Posted June 16, 2012 Ok, so if I read the table on EF-13 in FSM, the fuel pump should not be on with the key in the run position (Ign On) because there is no oil pressure or alternator signal. The test would be to start the engine, disconnect the oil pressure sensor and the alternator wire (I'd just take the belt off before you start it). The engine should die from lack of fuel, as the pump would shut off. Also, based on the 1980 NA manual off of XenonS130, I do not see anywhere where there is a prime function in the fuel pump. Maybe your pump is working correctly? Could it be that the relay was previously stuck "On" and is now working properly. Your hard start my be somewhere else. I'm stumped, unless I am reading the manual wrong! Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 16, 2012 Share Posted June 16, 2012 Page 50 and 66 (as you noted) say the pump turns on for either a few or 5 seconds. Those are the only two mentions of a "priming" function that anyone has found and reported. I'm assuming that when the FSM says the relay is on that it is feeding power to the fuel pump. Otherwise the pump would run when the key was off, since the circuit runs directly to the battery +. That's what the diagram implies since the pump has its own ground. It is a puzzle. Quote Link to comment Share on other sites More sharing options...
Heroez Posted June 16, 2012 Author Share Posted June 16, 2012 I did a poll here and other sites. All 280zx models 79-83 do have a 5 second fuel prime. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted June 16, 2012 Share Posted June 16, 2012 You can lose prime when something like a sensor has the ecu in crisis. Try unplugging all the sensors and all the actuators and see if prime returns. Quote Link to comment Share on other sites More sharing options...
cgsheen Posted June 16, 2012 Share Posted June 16, 2012 In an '80 280ZX, the fuel pump isn't connected to the ECU. It's powered through 2 or 3 relays (depending on manuf date or which FSM you look at) that only depend on: the start signal, the oil pressure switch, and/or the alternator signal. Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 16, 2012 Share Posted June 16, 2012 (edited) If you look at pages 50 and 66 in the Engine Fuel and Emission Control section of the 1982 FSM, you'll see actual words from Nissan of the fuel pump relay being "on" for either a few or 5 seconds. There is also a diagram on each page showing the ECU connected to the relay, not the pump. So far, it is the only official publication, described in any of Heroes' threads, from Nissan that verifies power to the relay that controls the pump for a short time without the engine running or in Start mode. No mention of why or if it has a purpose. State of the knowledge of the mystery. Edited June 16, 2012 by NewZed Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted June 17, 2012 Share Posted June 17, 2012 The two relays mentioned above are connected to alternator and oil pressure switch. Satisfying them is required to run the engine beyond the turning of the key switch. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.