spanishfly Posted April 27, 2012 Share Posted April 27, 2012 I went to start my 1978 280z and after initial startup the fuel pressure drops from 40 psi to zero and the engine starts to die and then the pressure shoots back up to 40 psi.This keeps happening during warm up so I shut it off. I also notice one of the fusible link covers was dark gray,so I pulled the cover and the thicker fusible link was fried. From these two new problems is there a definite componet to check or a direction someone can point me in to help me remedy my new fuel problem. Quote Link to comment Share on other sites More sharing options...
Vonlam43 Posted April 27, 2012 Share Posted April 27, 2012 you might have to do some reading but it sounds like something is grounding out hopefully this link helps. http://atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf Quote Link to comment Share on other sites More sharing options...
spanishfly Posted May 13, 2012 Author Share Posted May 13, 2012 you might have to do some reading but it sounds like something is grounding out hopefully this link helps. http://atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf Quote Link to comment Share on other sites More sharing options...
spanishfly Posted May 13, 2012 Author Share Posted May 13, 2012 (edited) Thanks for the link,it has the same info that my 1978 280z service manual has. I read through the engine fuel section and checked for any disconected wires but found none.I replaced the fuel pump but still the same problem 40 psi before startup,the engine starts and then the fuel pressure drops to 0 psi and the motor almost dies before the pressure rises to 40 psi again. I pulled the metal box that houses the fuel pump relays and the fusible link holders to look underneath and started the engine,and the fuel pressure holds at 40 psi until I try to install the cover back to the chassis? I now know there is a short or one of the relays or fusible links has a short or something is grounding. Anybody encounter a problem like this and better yet the REMEDY? Edited May 13, 2012 by spanishfly Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted May 13, 2012 Share Posted May 13, 2012 How does the pump sound? If it continues to run as the pressure drops, maybe your fuel line is restricted, or your pressure regulator is failing. If the pump noise falls off as soon as you start supplying fuel, look into the pump or pump wiring as the issue. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 20, 2012 Share Posted May 20, 2012 Your fuel pump switch is opening and closing. On some models the AFM flapper has a switch and as the car idles down the pump shuts off, pressure drops, the mix gets right it fires, the AFM flapper moves the pump comes back on, goes rich from high fuel pressure and the cycle repeats. The later cars use an oil pressure switch which wasn't supposed to do that, but... Like SleeperZ suggests, find out if your pump is turning on and off. With 40psi you may also have an obstruction in your return line---blow through it to check if it's clear. Once you know what the pump I scoring, you then just need to see why, which is straightforward, not much in the system. Use the CORRECT FSM DIAGRAM! Like i said, the control circuit changed in 76 I think, so early books won't reflect way is in the later two years of production. Reading the right manual saves a lot of headaches!!! Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 20, 2012 Share Posted May 20, 2012 I mean, it almost sounds like as you get oil pressure your safety switch is opening and stopping your pump. It's supposed to pump in the "crank" position, and once it fires, the oil pressure switch is your hold-in as it closes with 2-3psi. You do have a two-prong oil sender on the engine, right? That is where I would snoop, personally. Good Luck! Quote Link to comment Share on other sites More sharing options...
spanishfly Posted May 21, 2012 Author Share Posted May 21, 2012 After reading my factory service manual(1978 280Z) fuel section a dozen times as suggested I started the various electrical component checks, not far along I noticed green patina on most of the connections(both sides male & female). So I broke out the electrical connector cleaner and a tooth brush and cleaned all electrical connections under the hood. Even after the cleaning the car ran fine until I tried to install the metal cover that houses the relays and fusible links to the side of the engine compartment. It just so happens that up the road is a 1978 280Z sitting and rusting in an open field. So I took a drive up to it and removed all four of the relays that are housed in the " black box." I replaced the largest relay a five pronged(fuel pump control relay) and the other four pronged (fuel pump relay) and secured the "black box" back on the side wall via the four bolts. I said a quick prayer and turned the key and just like magic the car now runs fine. I have spent the rest of the weekend searching the internet for info on how to repair automotive relays. Re-soldering the pins on the electrical board is free while most ebay sellers of these relays want $100.00. Thank you all for all your input. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 22, 2012 Share Posted May 22, 2012 Interesting, relay failure, have you opened to find what went wrong? Quote Link to comment Share on other sites More sharing options...
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