Guest jjohart Posted January 18, 2005 Share Posted January 18, 2005 Ok, I've been over the rails with my local shop and the 280ZXT over the past week, with their hauling it in and out of the bays when they could to reasonably check all systems for a poor running condition, documented too many times here (yet again=car sputters/bucks/stalls/idles near death w.in an exact minute of starting, where it seems as if something is kicking in and changing throttle position and fuel amounts, and about a minute later, should I survive the bottlenecks by revving the engine to 2500rpm or so-not nice treatment, but it keeps me running-it quick as a wink seems to normalize, for the most part). They checked fuel pressures, injectors, vac. leaks, afm/ECU (I swapped in another one from autoecu.com, no improvements), and they DID find a faulty oxygen sensor. Replacing this and getting the car back means it doesn't stall out once the car is warm, but there has to be something else at play here, and it feels to me like it is something that is working either by electrical or mechanical DESIGN, but I don't know what's left to replace!! Does anyone know if the ZX cold start valve might somehow disengage in such an abrupt manner a minute after start up so that I'm suddenly running lean b/c the car is just too cold to have proper fuel flow at low pressure/throttle position? I have also added an adjustable FPR, and they set it a few points above stock, but I still hear backfire when I go off throttle at certain speeds (40-55), but I assumed that this was a negligible byproduct of the limitations of aftermarket 3 in exhaust kit-Magnaflow). Probably I should get a fuel rich/lean meter to see where it's at, but for now, the dial in of somewhat more fuel hasn't changed this one minute cycle of starvation I go through with this car every morning/or every cold restart. I know it sounds like I'm griping and should go out 5 mins early with a car this old to sit there and idle it out/warm the car up somewhat, but I've always thought it was better to drive off gently and do 30-40 without havoc. I've pretty much given up on what to do next, but if anyone has any comments on what, if any components might be producing this "memory-effect starvation cycle" (e.g throttle position switch, cold start valve, etc), I might keep my Ebay/used part search eyes open, as it isn't worth it for me to keep paying hundreds of dollars in tech time to garages, when it seems a real goose chase! Thanks John-83 280ZXT 5 speed, I/c, Profec B, 3 in exhaust, CAI, adjustable FPR. Quote Link to comment Share on other sites More sharing options...
Guest magnadyne Posted January 19, 2005 Share Posted January 19, 2005 First off to address your "back fire". Depending on how bad it is, it may not be a back fire. It may be the low restricting exhaust like you said. They are known to make a burble and/or small popping sounds right after letting off the gas. You can also make it do it if you are basically cruising, and you are barely on the gas. Keep in mind that these pops & burbles are pretty rappid in succesion, and only some what loud. A true back fire to worry about will be LOUD. (refferance the movie Uncle Buck ) For the idling problem, I am wondering if there is an idle control valve. I have worked on a lot of Hondas back in the day, and they have one. When they go bad, they run like crap, and don't idle. I do have an SR20DET, but have never run into any problems, so I have never had to replace anything like that or even look into it, so I can't even tell you if Nissan is using a system like Honda did. Maybe someone else knows on here. Also, did you replace anything right before this happen, or did it just start acting bad? Quote Link to comment Share on other sites More sharing options...
innerware Posted January 19, 2005 Share Posted January 19, 2005 don't know if this will help or not but here it goes. On my 78, I had a similiar problem when cold. I would get it started and it would backfire when I touched the throttle when cold. That is if it started. Finally I brought it in to the shop. This is what was wrong. I had accidentaly crossed my thermotime switch with my temp sender(the wires) I had replaced the wires a little while before when it was warm and the symptoms hadn't shown untill it was cold. My ecu was getting the wrong reading and was causing it to run lean or rich (not sure). So, check your wires and make sure they are going where they should be. Most shops don't know if they are wrong, but I had brought it to the Z Doctor and they having been a Z place for so long checked this after the first 1/2hour of testing. I got lucky. It was a cheap fix. And it really fixed the problem. Good luck, I hope it get fixed. Quote Link to comment Share on other sites More sharing options...
Len Posted January 19, 2005 Share Posted January 19, 2005 doesn't cost anything sometimes works....wiggle your plug (to your ecu especally the top one). Also unplug it then replug it in...the wires and plugs are over 20 years old...could be shorting in the wire somewhere. Quote Link to comment Share on other sites More sharing options...
Guest jjohart Posted January 19, 2005 Share Posted January 19, 2005 Yes, I have tried the removal and flex of the ECU cables, as well as spraying the hell out of them with electrical contact cleaner. Again, I may be wrong, but I swear this stall/lean issue occurs LIKE CLOCKWORK, within a minute of start up, as if there is something impinging proper fuel delivery, like a finger squeezing something tight, and then releasing a minute later! I know that sounds funky, cuz there probably isn't anything that kicks up and lets up in such a cycle from cold, is there?!!? John Quote Link to comment Share on other sites More sharing options...
Len Posted January 19, 2005 Share Posted January 19, 2005 I'll be honest with you...my car runs like crap until it warms up. I know this isn't solving your problem (just covering it up) but to help me on cold day starts; till engine warms up. I spliced into one of the two wires of my cold start sensor on passenger side of block...ran the wires into my cab and located a switch that I could flip when cold...just be careful to turn it off once its warm. Quote Link to comment Share on other sites More sharing options...
Guest jjohart Posted January 19, 2005 Share Posted January 19, 2005 Wow, that is a COOL idea...but what happens if you never shut off the cold start sensor? With my luck, it'll happen... Quote Link to comment Share on other sites More sharing options...
Len Posted January 19, 2005 Share Posted January 19, 2005 what your doing by flipping the switch you installed, is break the cold start circuit causing a rich situation...just like when you unplug it by hand. But once your car warms up then it will start to cause your car to run crappy rich lose idle etc. But will help you until it warms up. I forgot to turn it off a few times... once it warms up and starts to die at stopsign and generally run lousy then remind yourself to flip the switch....kinda like the old manual chokes in carb. cars. Hey you could even use a button to push (instead of switch) when your engine is running crappy cold ...till it warms up. then you'll just stop pushing the button once its warm. Quote Link to comment Share on other sites More sharing options...
Guest 240zJake Posted January 19, 2005 Share Posted January 19, 2005 You could wire the switch with a kill that would turn off the cold start when the car hit a certain temp.EDIT insert large grin here Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted January 20, 2005 Share Posted January 20, 2005 I hope everyone realizes that the cold start valve and the thermotime switch work together in a cold engine start condition. The thermotime switch is on when the cooling water temp. is between 57 to 77 degrees F. It sends a signal to open the cold start valve which causes fuel to be injected into the intake manifold independently of the injector operation so that the engine starts smoothly during cold weather. If either one of them is not working you will get the stumble and stall condition until the engine is warm. LARRY Quote Link to comment Share on other sites More sharing options...
Clifton Posted January 20, 2005 Share Posted January 20, 2005 Check the voltage of the O2 sensor when plugged in and up to temp and disconnected. Stoich is around .45v. I know Toyota uses a sheilded cable on there O2 wire. If the insulation becomes brittle, cracks and it grounds to the shielded wire the ECU will not read the voltage. I had this happen on mine and the a/f were in the 10-11:1 range until I found the short. If I unpluged it it would show voltage, the second it was plugged in it would show zero. Just a thought. The cold start valve on 7M's are just used to start. It isn't on when the motor is running. I don't know about L28's but I'm sure it would be the same. Quote Link to comment Share on other sites More sharing options...
Len Posted January 20, 2005 Share Posted January 20, 2005 I spliced into one of the two wires of my cold start sensor on passenger side of block...ran the wires into my cab and located a switch that I could flip when cold...just be careful to turn it off once its warm. Now I wasen't talking about the cold start valve..(mounted on the intake of pre 79 z's) I was talking about cold start sensor (or temp head sensor) located on pass. side of block screwed in the head... Quote Link to comment Share on other sites More sharing options...
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