76 280z computer problem - please help

[aaron-san]

i looked at my computer on my 280z because i noticed two wires cut coming from the harness, but they only turned out to be control unit check wires, but i also noticed two wires on the harness, (#20-21 circled in red) dont have a corresponding pin on the computer, and these wires go to the fuel injection relay, and my cars fuel injection system is running a little weird. if anyone could help me by checking their computer. preferrably someone with a 76 just to make sure its the excact same. i appreciate any help.

comp.bmp

[wal280z]

electrically, pin 20 is connected with pin 36 at the FI relay, and pin 21 is connected to wire #46 at the cold start valve.

This was looking at both a '75 FSM wiring diagram and a '77 FSM wiring diagram. Sorry, don't have a '76 at my disposal.

Have you taken the FI relay out and clean the external pin contacts?

Wayne

[aaron-san]

look at the picture i attached, theres no male pins on the computer, so the wires (#20-21) in the harness plug into nothing, and thats what concerns me. i have a chilton guide and am looking at the wiring diagram. 21 goes through a cold start valve and then to the electronic fuel injection relay, 20 goes straight to the relay. but when i checked i think 21 actually only went to the relay, i'll have to look at my car again. i just need someone with a 76 280z to pop off the harness and tell if there are pins on the computer for 20 and 21 on the computer.

[aaron-san]

also mine doesnt have a 36, the highest is 35. i looked on the wiring diagram for 75 and 77 and they dont have one either, are you sure you got the right numbers? thanks for replying though.

[wal280z]

electrically, pin 20 is connected with pin 36 at the FI relay, and pin 21 is connected to wire #46 at the cold start valve

Pin 20 is connected to wire #36 at the FI relay

My computer has pins at all 35 connections, and has the same type of connections that your picture shows at the harness.

also mine doesnt have a 36, the highest is 35. i looked on the wiring diagram for 75 and 77 and they dont have one either, are you sure you got the right numbers?

Yes, I'm sure I have the right numbers. I assume you are still referring to the connector at the computer.

Back to the original question, those wires terminate at the computer connector, and are not actually used by the computer.

Have you cleaned all your connectors relating to the FI system?

Wayne

[sblake01]

Take a look at your connector. It shouldn't have terminals at the positions that correspond to the 'missing' pins on your computer. Don't confuse wire numbers with pin numbers. As wal280z said, some of the wires join at the connector and complete their particular function without going through the ECU. Whatever problem your're having, I wouldn't look to the ECU. As long as you have the one that belongs in that car and the car does run, I would just make sure the contacts are clean, plug it back in and then look elsewhere. (Relays, sensors, switches, etc.) I would also recommend a FSM rather than Chiltons, Haynes, Clymers, etc.

[aaron-san]

ill check to make sure the contacts are clean tomorrow.so your saying that even though the wires run up to the harness for the computer they may not be actually used by the computer? doesnt really make sense why they wold wire it like that, but then again it doesnt really make sense why almost every wire in the car would be white. my problem is my car runs rich, but then after 4000 rpm it loses power, badly, as it actually decelerates if i floor it. im thinking its just the air flow meter. im new to the z world, so im still learning a few things. sblake01, im the one that you helped with the afm adjustment. do either of you have any idea what could be wrong. thanks to both of you for your help. aaron

[sblake01]

Nissan's wiring logic on these cars has always seemed somewhat strange to me. I noticed on my 78 that all 35 pins are there like wal280z says on his 77. I have also noticed on 75 and 76 cars that there are a number of missing pins. (junkyard research) My 79 810 also has missing pins but not as many as a 75-76 and the 280ZXs and RWD Maximas are also slightly different. There is a warning label on the ECU to not use it in certain year cars. Each one is unique to the car or group of cars it was designed for and the harness will correspond to that particular ECU. Its not really a 'computer'. It can't be 'chipped', reprogrammed or modified. All it is capable of doing is what the various switches, sensors, and relays tell it to do. They very seldom go bad. When they do, it's usually due to moisture. All that being said, I'll move on to some other possible causes of your problem. Timing, vaccuum leaks, PCV valve, AFM, fuel pressure. It's a step-by-step process of elimination. Checks and tests of these things are outlined in the FSM. That is why I earlier suggested obtaining a FSM. It is more detailed and specific than Chiltons etc.

[aaron-san]

wheres the best place to get a FSM? i got the chilton because i needed a quick vacuum line diagram, which also proved to be useless, so i basically wasted $25. ive checked the timing with a timing light. it has brand new injectors and plugs, wires, etc. but the boot between the afm and throttle body is a little worn, do you think that could cause a big enough difference. also i forgot to mention, it does it mainly in 2nd gear and up. first gear it does ok, but after that, it sucks. i geuss i'll check all the things you mentioned, thanks for all the advice.

[ecp48]

aaron-san

The place to purchase manuals is ebay.

You can also buy the factory manual on CD Rom from Courtesy Nissan.

I got both a CD Rom and a Paper manual for my 78 on ebay, after a number of bidding exercises. From memory, my original 75 280Z manual was about $75 dollars at the dealer (bought in 1979). The '78 280Z manuals have been going for 70 to 100 dollars on ebay. The other year 280Zs have been going for less.

good luck!

ecp48

ps: I also tried the on line used book sellers without any luck.

[sblake01]

Originally posted by aaron-san

the boot between the afm and throttle body is a little worn, do you think that could cause a big enough difference.

By 'a little worn' do you mean it's split and sucking air? If that's the case it is definately a problem! That would mean an intake leak and would throw off your air/fuel ratio.

[wal280z]

There is a warning label on the ECU to not use it in certain year cars

to what Sblake said, not all the ECU's had warning stickers.... I did take a look at the two dozen or so a buddy of mine has, mostly late '77s and later have the clear sticker with the warning on it. Also, take a look at the little metal tag / sticker on the box... (going from memory here)... the color of the tag may or may not correspond to the identical type tag on the AFM.

A buddy of mine was working at the local Datsun dealership when these first came out, and he would always use a 'matched set'. I dunno how true this is, I found it interesting to say the least 'cause I never noticed that before.

Wayne