boostfed Posted January 11, 2016 Share Posted January 11, 2016 Hello Everyone, after selling my 69 camaro, I've purchased my first Z car, a 1975 280z. I'm the second owner of the car with supposedly 73k on the clock. The car is in pretty good condition and a perfect platform for a beautiful cruiser Z. The car has a few issues that I'm hoping experienced owners can help with, I've done some basic checks on the car but the issue still persists. When I first picked up the car, the owner took me on a "test drive". The car will start but will stall out immediately, if the throttle is applied at the right time, the rpm's will climb "until the car warms up" and the car should be fine, not the case. The fuel pump was replaced with an off brand and is very very loud, the pump is ziptied to the frame and no insulation was used, Ive purchased a basic unit and will replace it soon, though i'm not completely convinced . Also on 75-76 280z's, theres a water temperature on the side of the coolant housing that is busted, from my research, the car can run reliably without this sensor, though a little more rich during cold starts, but would still allow the car to run and drive. This sensor is discontinued and i've yet to be able to source one , still up in the air about replacing it. Doing some testing according to the EFI bible, most readings through the ECU harness have returned normal, though the AFM tests are reading fairly high. EFI bible called for 100-180 ohms for different AFM readings, mine measured well over 200 on all of the measurements, even close to 300ohms during some test. I know the AFM turns on the fuel pump when the car is off (pushing the AFM flap while key in the on position), though during the test drive I'll be able to hear the fuel pump cut on and off, most of the time I wont be able to hear the pump while trying to start the car now. Fuel/Power relay works as expected as well, clicks on at the right times. Up until now, while trying to start the car it'll have ignition, stumble and die. The fuel pump is fairly intermittent though I believe the issue lies within the fuel pump signal, not the pump itself. Usually when I hit the gas the car will die. The AFM to Throttle body elbow is also ripped, I'll likely have to replace this, not cheap My goal is to get the car running reliably around town, its still in very good shape , hope you all can help! Excuse the lengthy post but I'm hoping to get this beauty back on the road! Quote Link to comment Share on other sites More sharing options...
NewZed Posted January 11, 2016 Share Posted January 11, 2016 The car will start but will stall out immediately, if the throttle is applied at the right time, the rpm's will climb "until the car warms up" and the car should be fine, not the case. Also on 75-76 280z's, theres a water temperature on the side of the coolant housing that is busted, from my research, the car can run reliably without this sensor, though a little more rich during cold starts, but would still allow the car to run and drive. This sensor is discontinued and i've yet to be able to source one , still up in the air about replacing it. EFI bible called for 100-180 ohms for different AFM readings, mine measured well over 200 on all of the measurements, even close to 300ohms during some test. I know the AFM turns on the fuel pump when the car is off (pushing the AFM flap while key in the on position), though during the test drive I'll be able to hear the fuel pump cut on and off, Up until now, while trying to start the car it'll have ignition, stumble and die. The fuel pump is fairly intermittent though I believe the issue lies within the fuel pump signal, not the pump itself. Usually when I hit the gas the car will die. The AFM to Throttle body elbow is also ripped, I'll likely have to replace this, not cheap There's a sender and a sensor for coolant temperature. One's necessary, one's not. But your research conclusion isn't right, either way. You can get a new sensor at Motor Sport Auto. Maybe even your local Nissan dealer. Do the coolant sensor test shown in the Guidebook first. You might have a ZX AFM on your Z. They have different resistance specs. Find the part number and post it. Not clear if you actually did get the pump to run with the AFM vane or just repeated something that you read. ZX AFM's don't have the switch, so if you have a Z AFM, then those resistance numbers are a problem. The fuel pump should run all of the time that the engine is running. 99% of the air must pass through the AFM. Any leaks after the AFM will cause problems. You might try flexible tape or shoe goo to fix that rip. No holes. Sounds like you have a typical set of 280Z problems. Try using the FSM in addition to the "Bible". Quote Link to comment Share on other sites More sharing options...
boostfed Posted January 11, 2016 Author Share Posted January 11, 2016 (edited) Hey newzed, Thanks for the response! Sorry I should've specified, its the water temperature SWITCH, the one on the side of the coolant housing pointing towards the drivers side of the vehicle, searching online (and on msa) has shown that the part is discontinued, i'll double check with my dealers (P/N 22120-N4202). The AFM p/n : a31-060 001 for the L28. I got the pump to run by switching the key to the on position and pressing the AFM flap, the fuel pump is very loud and pretty hard to miss, during cranking its not turning on, it'll just come on and off intermittently. I've read that if the car runs better with the AFM unplugged, then the afm is the issue. I tried this test and the car started even worse. Edited January 11, 2016 by boostfed Quote Link to comment Share on other sites More sharing options...
boostfed Posted January 12, 2016 Author Share Posted January 12, 2016 hopefully someone can chime in, I'd hate to pull the trigger on a new AFM and have it not be the problem. Has anyone ever seen higher resistance numbers while testing at the harness? Or seen similar symptoms? Quote Link to comment Share on other sites More sharing options...
NewZed Posted January 12, 2016 Share Posted January 12, 2016 The switch just controls the other pickup in the distributor. It advances timing when the engine is cold. It's not necessary. Post better information on how you're testing, pin numbers with resistance readings, and what tools you're using. You didn't say if you tested the AFM itself after you tested "through the harness". Assuming that means at the ECU connector. Could be that you just have a dirty connection, or a bad meter. They'll still be there after you buy a new AFM. Some of the tests don't matter for engine operation, some do. Need the exact test with exact numbers. " most readings through the ECU harness have returned normal, though the AFM tests are reading fairly high. EFI bible called for 100-180 ohms for different AFM readings, mine measured well over 200 on all of the measurements, even close to 300ohms during some test." Quote Link to comment Share on other sites More sharing options...
boostfed Posted January 12, 2016 Author Share Posted January 12, 2016 Here are my readings at the ECU harness: AFM resistance 1 ( pins 6/8) , efi bible suggests 180ohms : 234ohms AFM resistance 2 ( pins 7/8) , efi bible suggests small resistance: 212ohms AFM resistance 3 ( pins 8/9) , efi bible suggests ~100ohms: 250ohms I cleaned the carbon track and connector pins on the AFM before taking these readings, it was pretty dirty but the numbers are still fairly high. I did a small experiment while I was out there, I'll only hear the pump kick on while the key is in the start position, once it returns to the on position the pump will cut out the car will normally die. I depressed the flap in the AFM to keep the fuel pump on and started the car, it'll be able to hold an idle but it'll die once i hit the gas pedal (theres no afm -> TB boot installed on it yet). Methinks its the AFM causing issues Quote Link to comment Share on other sites More sharing options...
NewZed Posted January 12, 2016 Share Posted January 12, 2016 Methinks you need to remove the AFM and test at the pins. You'll be removing it anyway. Maybe you've already had it sitting in front of you. The pin numbers are molded in to the connector base. Test resistance right at the pins of the AFM. Do it before you buy another. Besides that, you're not understanding how the AFM works at all. How will the vane in the AFM move if there's no air flow through it? Logic it out. "(theres no afm -> TB boot installed on it yet)." Quote Link to comment Share on other sites More sharing options...
boostfed Posted January 12, 2016 Author Share Posted January 12, 2016 I'll test it at the afm, always hated those things so they were the first to go I owe you a beer newzed, next time im in the PNW I'll be sure to let you know. AFM boot is still on the way , i'll try to fix the one that was on there before but its in pretty bad shape, tattered is putting it lightly. Quote Link to comment Share on other sites More sharing options...
boostfed Posted January 13, 2016 Author Share Posted January 13, 2016 measurements at the afm connector is still consistent , not much variation besides between pin8/9 : AFM resistance 1 ( pins 6/8) , efi bible suggests 180ohms : 234ohms AFM resistance 2 ( pins 7/8) , efi bible suggests small resistance: 236ohms AFM resistance 3 ( pins 8/9) , efi bible suggests ~100ohms: 130ohms Quote Link to comment Share on other sites More sharing options...
GeeZ Posted January 13, 2016 Share Posted January 13, 2016 Man, you should have kept the Camaro. Quote Link to comment Share on other sites More sharing options...
NewZed Posted January 13, 2016 Share Posted January 13, 2016 measurements at the afm connector is still consistent , not much variation besides between pin8/9 : AFM resistance 1 ( pins 6/8) , efi bible suggests 180ohms : 234ohms AFM resistance 2 ( pins 7/8) , efi bible suggests small resistance: 236ohms AFM resistance 3 ( pins 8/9) , efi bible suggests ~100ohms: 130ohms I have one that has about the same 6-8 and 8-9 values. 234/130 = 1.8, as does 180/100. I'm not an expert on what the ECU does with the values but the ratio is is the same. Get the AFM boot connected, and check the wring harness from the AFM to the ECU. There must be some resistance along the way. It will probably at least control the engine if you can get those same values at the ECU. Then you can decide if it's bad enough to need a new one. The old AFM's tend to run lean, popping back through the intake and hesitating when accelerating. There's a fix for that. The fuel pump problem would probably have something to do with your EFI / fuel pump combined relay. It's a 1x1x2" silver box above the hood release handle. Above the driver's left leg. There's a test procedure for that in the books also. Quote Link to comment Share on other sites More sharing options...
boostfed Posted January 13, 2016 Author Share Posted January 13, 2016 (edited) Man, you should have kept the Camaro. I should've, still love the car but I got annoyed with the "classic car tax" that those cars get tacked onto them. Parts are pretty ridiculous , just because its a 69 camaro. Plus id be just as happy with a Z car and would be able to build it for a lot less. Both good looking cars, both different beasts @NewZed : Thanks, I should be able to get around to a tune up of the car within the next week or so, hopefully the afm-tb boot shows up at the same time. The fuel pump relay works as it should, 1 click for on and 1 click for start, so I know the relays are getting energized properly. Edited January 13, 2016 by boostfed Quote Link to comment Share on other sites More sharing options...
NewZed Posted January 13, 2016 Share Posted January 13, 2016 , I'll only hear the pump kick on while the key is in the start position, once it returns to the on position the pump will cut out the car will normally die. I depressed the flap in the AFM to keep the fuel pump on and started the car, it'll be able to hold an idle but it'll die once i hit the gas pedal (theres no afm -> TB boot installed on it yet) The AFM pump relay switch needs air flow also. Get clean wires from the AFM to the ECU on that high resistance 8-9 circuit, and the hose, and it will probably run fine. Quote Link to comment Share on other sites More sharing options...
boostfed Posted January 17, 2016 Author Share Posted January 17, 2016 (edited) AAAANNND she starts and runs great! replaced the ripped afm-TB boot with a universal silicone hose , did a quick ignition tune up (plugs, wires, cap / rotor). starts and runs like a dream, drove it for about 15 mins around the neighborhood and we're looking pretty good, thanks for the help newzed! hopefully others will be able to find this thread useful in the future. the water temp switch doesnt seem to have any affect on the car besides cold idle, though its not bad. idle on a warm engine is about 700-800 rpms. Thanks again everyone! this will do for now until its ready to get swapped out Edited January 17, 2016 by boostfed Quote Link to comment Share on other sites More sharing options...
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