g0dsmack Posted November 18, 2008 Share Posted November 18, 2008 When I bought the car it ran great, but the shortly there after the thermostat went out. I replaced the housing, thermostat, and thermo gauge sender since it was stuck in the old housing. Since then it wouldn't start. I replaced the plugs and wires since one of the wires was grounding and finally got it to start. Since then it runs great... once it warms up. Once I get the beast to start it has intake backfires between 1.5K - 2K rpms and will idle then die at 600 rpms if I let off the gas. After ~20 seconds it will idle fine at 800 rpms but will still sputter at around 2K rpms until the temp comes up. I basically have to give it a bunch of gas to get it started and then maintain >2.5K rpms for those ~20 seconds. I have read around that it is probably a problem with the thermotime switch or the cold start fuel injector. Can someone give me some ideas of how to track this problem down. Quote Link to comment Share on other sites More sharing options...
woldson Posted November 18, 2008 Share Posted November 18, 2008 What engine? Quote Link to comment Share on other sites More sharing options...
g0dsmack Posted November 19, 2008 Author Share Posted November 19, 2008 Sorry about that, L28. It is a 1975 280Z 4 speed manual CA car. Quote Link to comment Share on other sites More sharing options...
Powerglide Posted November 20, 2008 Share Posted November 20, 2008 Clean and reseat EVERY engine low voltage electrical connection including injectors. Clean the ECU connections. Replace EVERY vacuum line in/on the car. Make sure hose clamps are clamping. Check running (34psi+) fuel pressure. Check the Aux Air Regulator for proper functioning. Replace the factory fuel filter. Install a G3 filter between the tank and the fuel pump. Set static ignition timing to 10 or 12 degrees BTDC. Check for proper centrifugal/mechanical advance. Set valve clearences cold...then recheck HOT. Put a vacuum gauge on the motor and verify at least 16 inches of vacuum at 900rpm idle. Quote Link to comment Share on other sites More sharing options...
woldson Posted November 20, 2008 Share Posted November 20, 2008 ^^I'm going to copy that and reuse it, if that is ok? Quote Link to comment Share on other sites More sharing options...
Powerglide Posted November 20, 2008 Share Posted November 20, 2008 Of course. Quote Link to comment Share on other sites More sharing options...
g0dsmack Posted November 21, 2008 Author Share Posted November 21, 2008 Clean and reseat EVERY engine low voltage electrical connection including injectors. Clean the ECU connections. Replace EVERY vacuum line in/on the car. Make sure hose clamps are clamping. Check running (34psi+) fuel pressure. Check the Aux Air Regulator for proper functioning. Replace the factory fuel filter. Install a G3 filter between the tank and the fuel pump. Set static ignition timing to 10 or 12 degrees BTDC. Check for proper centrifugal/mechanical advance. Set valve clearences cold...then recheck HOT. Put a vacuum gauge on the motor and verify at least 16 inches of vacuum at 900rpm idle. Alright... All the electrical connections and been cleaned, electrical greased, and reseated. No change. I replaced all of the vacuum lines, none of them needed it, but I did it anyways. /. side note ./ Something odd, my anti-stall pot doesn't have a vacuum line going to it and I havn't been able to find out where it is actually suppose to get it. Still no change. I don't have a fuel pressure gauge so can't check that. I have a hard time believing that to be the problem since my problem is a transient cold start problem. Fuel filter was replaced, it did need it. Still no change. I will check the vacuum at idle but the rest that was mentioned I either can't or do not have time to do. In any case those would not lead to an intermittent problem. I believe this problem comes from the cold start system; cold start injector, thermotime switch... something along those lines. I just don't know how to test the system or where to start with it. Please keep in mind the problem lasts for <1 minute. Quote Link to comment Share on other sites More sharing options...
Powerglide Posted November 22, 2008 Share Posted November 22, 2008 The Thermotime switch simply provides a ground for the cold start valve (7th injector). Depending on water temp it will only activate the 7th injector for a few seconds to aid start up. It shouldn't operate at all at temps above 60 degrees or so. Once the engine starts, the water temp switch will alter injector pulse via the ECU to enrichen fuel flow according to the needs of the motor. I suspect your AAR (aux air regulator) is either not functioning or leaking air. It's only function is to add additional air into the throttle body which raises idle RPM during warm up. If it fails, malfunctions or is marginal---you'll have to manually raise idle RPM to keep the motor alive till it warms up a bit. Your water temp sensor is probably out of spec as well. Suggest you test and/or replace both. How much initial lead does the motor have? Is the centrifugal advance in the distributor working smoothly? GOT NGK plugs, gapped properly? Rent a fuel pressure gauge from Autozone and test running fuel pressure! Quote Link to comment Share on other sites More sharing options...
DStegs Posted July 3, 2009 Share Posted July 3, 2009 Got this site for the EFI PDF booklet from thetremendoustim and it helped me with some terms and of course, testing the system. It helped me a lot and it leads you through almost all of the EFI system component testing. all you need is a little time and a volt/ohm meter to do the checks. Mine is also a 75 280Z with EFI. I still have a few things to replace but it helped get me to at least one of my major problems and ruled out my thermotime switch. You can download it and print it if you want. It is easier than taking the desktop into the garage. Good luck. Dave http://atlanticz.ca/zclub/techtips/e...ectionbook.pdf Quote Link to comment Share on other sites More sharing options...
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