nismo35 Posted September 5, 2005 Share Posted September 5, 2005 I think I have narrowed my long and exspensive list of FI problems down to a sensor near the throttle body, problem is I don't know what it's called. If you are looking at the motor from the front there are two sensors side by side near the top of the block. If I unplug one the rough idle goes away so I'm guessing it's the culprit. I have a haynes manual but it doesn't have any idiot pictures. It's a 1976 280Z. Any help will be greatly appreciated. Rondal Quote Link to comment Share on other sites More sharing options...
TomsCoupe Posted September 5, 2005 Share Posted September 5, 2005 when you unplug a sensor, the computer will go into "limp" mode. limp mode makes the engine run off of a bunch of preset readings. so that may not be the problem. Quote Link to comment Share on other sites More sharing options...
nismo35 Posted September 6, 2005 Author Share Posted September 6, 2005 crap! So should I disconnect the battery and see if that clears it off? I've replaced the tank, the fuel gauge sending unit, the fuel pump, all six injectors and all six injector plugs. This goes along with the usual plugs / wires / cap etc... Quote Link to comment Share on other sites More sharing options...
Gollum Posted September 6, 2005 Share Posted September 6, 2005 could be a fuel pressure regulator. Did you replace that? And yes, limp mode sucks. honda motors have CRAP limp modes. They run ultra rich and limit rev to 3k. It's basically made as a secondary mode in case anything stops working, so you won't loose your car off the side of the road. Basically, it's made to get you home, and then to the mechanic. But on some cares, it's not so bad. Quote Link to comment Share on other sites More sharing options...
nismo35 Posted September 6, 2005 Author Share Posted September 6, 2005 FPR? No, I haven't replaced that yet. It does start sputtering and backfiring a bit at 3500 rpm...I guess it's a good safety measure. I'll check the FPR today, I may just go ahead and replace both of those sensors as well, after 29 years it can't hurt I don't guess..... Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 6, 2005 Share Posted September 6, 2005 I hear references to this 'limp mode' all the time, but are you guys SURE that stock L28ET EFI *HAS* a limp mode? For instance, I run my car with both my TPS and O2 sensor disconnected, ALL the time (why I do this is a whole topic unto itself, but suffice to say that the motor has NEVER run right with either of those two sensors connected). Yet, my car runs great, starts right up every time, is great around town and absolutely FLIES on boost all the way to 6000rpm. I wouldn't call that 'limping'. It made great power on the dyno with a great power curve. I also run with the knock/detonation sensor disconnected, as many turbo guys do. Only problem as far as I can tell is it runs a bit rich and my gas mileage is a relatively sucky 17-19mpg (driven hard pretty often, about 1/3-1/2 on the street vs. freeway). Now, on the other hand, if I disconnect my head temp sensor, the car will just die. The only other 'sensors' I know of that are used by my EFI are the AFM, and it's built in air temp sensor, and the crank angle sensor. Obviously the car will die if either of those are disconnected... so what other sensors are there that can supposedly put the car into 'limp mode'? Quote Link to comment Share on other sites More sharing options...
Gollum Posted September 6, 2005 Share Posted September 6, 2005 'ALL' OBD1 cars have limp mode.... Now, the Z's don't fit that bill, although I believe my 81 ZX is OBD1. But I can't remember the year OBD1 was initiated. It's a valid point bastaad, and I can't believe I didn't think about it. So yes, it IS possible the problem is the sensor you were unpluging. Quote Link to comment Share on other sites More sharing options...
nismo35 Posted September 6, 2005 Author Share Posted September 6, 2005 Well I'm going to call MSA today and order them and new connectors..if's that's not it I'm going to invest in some of that Katrina priced gas and a book of matches! Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 7, 2005 Share Posted September 7, 2005 Z's didn't get OBDI until the 300ZX. My Sentra is a '91 and it's OBD1, but I can guarantee that 280zx's are not. Think of the nature of OBD... On Board Diagnostic. Usually involves the ECU's ability to diagnose problems for you and then give you a trouble code, either via a computer you hook up to the ECU, and/or usually, thru an LED on the ECU itself that will flash the codes to you. Now, the 280zx ECU does have an LED, but all it does is indicate that the O2 sensor is working and what it's reading. Also, all OBD cars have a check engine light, this is how the OBD lets you know that it has a problem and to check the code. The 280zx's have no check engine light. And given that this is my third EFI Z (had an '81 and an '82 ZX before this), and that I've run all three of them with one sensor or another disconnected (another long story), and each of them has run just fine, I'm inclined to believe that 280z-zx EFI has no limp mode. Quote Link to comment Share on other sites More sharing options...
Gollum Posted September 7, 2005 Share Posted September 7, 2005 ^^^ Words of a wise man. I wonder then, if I could get failed on a smog for the "sensor" light on the dash, even though it's not a "check engine" light. You know, what this really does is confirm my beliefs all along, if they want to smog cars this old, they should go purelly by emission levels, not engine codes and such. I could get a 5.0L ford motor over 500hp with less emissions as these cars, I see no reason why I should have to pass mustang smog specs if I'm putting it into a prefectly legal dirty car to begin with. Well, sorry for the slight thred hijack there, hope all goes well nismo35. Good luck with the issues. I've been having FI issues myself, very anoying. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 7, 2005 Share Posted September 7, 2005 the sensor light on the dash is specifically for the O2 sensor. As I remember it, that light is only supposed to come on once, when the car hits it's first 30,000 miles (I may be wrong on the number). Then when the O2 sensor is replaced I think you have to manually switch the light back off. After that I think the light is never supposed to come on again. Or maybe it's supposed to come on every 30,000? Not really sure on that part. But I am pretty sure that that light isn't actually an indicator that anything is wrong, rather it's just a reminder. This is all covered in the Haynes manual if I remember correctly. At any rate, yeah I'm pretty sure they can fail you for that light being on. Best just to get it completely disabled. Quote Link to comment Share on other sites More sharing options...
nismo35 Posted September 7, 2005 Author Share Posted September 7, 2005 Well the sensors are on the way so we'll see. I have a friend that bought a 77 that was already 90% restored and I gave him grief about "missing out on the experience" of re-building his Z....I'm not so sure he didn't have the right idea! ) Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted September 7, 2005 Share Posted September 7, 2005 you'll learn more this way, and NO stock l28e do not have limp modes or even check codes on the computers, they just anaylzye data and output, plain and simple. Quote Link to comment Share on other sites More sharing options...
Guest Loose_Screws Posted September 7, 2005 Share Posted September 7, 2005 Ithere are two sensors side by side near the top of the block. If I unplug one the rough idle goes away That is called the thermotime switch. If the head/coolant temp is cold, it tells the ECU to enrich. If the sensor is bad, it may be telling the ECU to enrich all the time, hence the rough idle. Unplug the sensor and connect the two bullet connectors coming from the ECU harness together. If she runs fine, it's the sensor. Now, if it is breaking up at 3,500 rpms, even if the sensor was bad, it would not be the problem. I suspect you have fuel problems. If you have a fuel pressure gauge, connect it up and drive the car. If fuel pressure drops, start checking for bad fuel filter or clogged lines, or even bad fuel. Z are notorious for rusty tanks and trash in the lines. Quote Link to comment Share on other sites More sharing options...
MikeK280z Posted September 7, 2005 Share Posted September 7, 2005 Unplug the thermotine switch and clean up the connections as best as you can. Use some Radio Shack Stereo Component cleaner and lube. Make sure it is tight fitting when you replace it. I friend with a '76 had a similar problem, it ended up not being the sensor, but the wiring harness connecting it. Quote Link to comment Share on other sites More sharing options...
nismo35 Posted September 8, 2005 Author Share Posted September 8, 2005 Loosescrews - I've replaced everything in the "fuel delivery" system but I probably do need to check the pressure..my luck it will be the lines from the tank to the engine compartment. The tank was full of crap but it was sandblasted out and coated with epoxy. MikeK280Z - That's going to be my project this weekend, A friend of mine just did that on his Z and he said it's made a world of difference on everything electrical related. Nismo280zed - I know but I have the world's worst patience...) Quote Link to comment Share on other sites More sharing options...
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