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1983 280zx Flooded so bad it wont start. ECU compatability, Diagnosis and fix.


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Greeting all. I recently purchased a 1983 280zx N/A manual Federal car that was listed as having a “reliability Issue”. The previous owner of the car had moved out of state and after spending an enormous amount of money and the car spending 13 months in 2 different shops he decided to wash his hands of the car. The PO was only able to drive the car 145 miles in a year and a half that he owned it!
Being a pretty good backyard mechanic and having owned 4 other Z cars I figured that I could have the car up and running in less than a day. I was told that the car was running extremely rich to the point it would foul the plugs in a matter of minutes. I purchased the car, which is very nice, and it would not start when I went to the local repair shop to pick it up.
I spent the next 2 weeks checking and re-checking everything on the car. I went thru the FSM diagnostic procedures 3 times. The timing and distributor position were way off so I pulled the front cover and installed a new chain and put the distributor drive shaft in the correct position. When I finished, the car did the EXACT same thing. I tried 2 AFM, 2 different ECUs, I tried 3 distributors, I tried 4 CHTS, I tried 3 ignition modules and different combinations of all of these and nothing changed.
I also own a 1981 280zx N/A manual California emission car. I removed all the sensors, with the exception of the ECU, from the 1983 and put them in the 1981 and the 1981 sensors into the 1983. The 1981 started and ran, it even ran when I put the 1983 distributor into the 1981. This distributor has the 2 plug Ignition module, but it ran, not well, but it worked . Still no start, super flooding of the engine on the 1983 car.
So, I was getting fuel and spark and air. That’s all you really need to get a car to run. I even tried to start the car on starting fluid and it would not run. In that 2 weeks I was only able to get the car to run 1 time and it ran BAD. It would only run with the throttle wide open. The car smoked, the exhaust stunk of unburned fuel and the spark plugs turned black. The car would not idle at all, it would die if the rpm dropped below 3,000. When the car finally died and I could not restart it, the plugs were soaked with fuel.
Check the grounds! I did. The repair shop that I picked the car up from is an old school shop. They had actually added extra body grounds from the battery to body and from the engine to body. The AFM and distributor were grounded. The 4 ground wires at the ECU had pigtails soldered to them and were body grounded at the ECU.
Now I start thinking bad ECU. How do you prove that if you don’t have access to a good ECU. The 1982-1983 ECU’s were upgraded with Heavy Duty internals so that the Dropping Resistor was no longer needed on the 82 and 83 cars. Try finding a 1983 ECU! They don’t seem to exist.
I spent the next week thinking and researching 1979-1983 280zx ECU. Who can fix them. Who can diagnose or test them, but I could find very little information on any of the S130 car ECU’s. I started thinking what is different amongst all of the 280zx ECU’s? I spent 12 hours digging thru all of the S130 FSM looking for the differences. How many of you know that the 35 pin connector on the 1979 thru the 1983 ECU’s change very little. The wires for the AFM, CHTS, TPS, Cold Start Valve, Thermotime Switch, Air Regulator even the wires from the fuel injectors on all of these cars stayed in the exact same place for all years. The 35 pin ECU connector does not change from 1979 to 1983 with the exception of adding a few things on these cars, even on the HD ECU 1982/83 cars. Here is the difference:
*Sometime in 1979/80 O2 sensors were being added (pin 31 & 16) to California cars and made their way to all of them by 1983, but the O2 sensor is in the same pin position on the ECU connector on all years .
*In 1980 there was a 2 wire plug (labeled “Not Used”) was added to the 35 pin ECU connector (pin 20 &10) but stays in the same place.
*In 1983 an altitude switch was optional and added to the 35 pin connector (pin 28 & 35).
That’s it! I researched all of the input sensors that feed info into the computer, and with the exception of the coolant temp sensor (1979) that changes into the CHTS after 1979, the specs are all the same on the CTHS, AFM, TPS, Air Temp Sensor, nothing changes from 1979 to 1983.
Remember that I am trying to prove that my ECU is bad on my 1983 car. I have access to a 1981 that I know works and there is a local wreaking yard with a 79 and 80 280zx there. Since nothing changes on these cars ECU pin out, why not put my 1981 into the 1983.
I got a Dropping Resistor and main wire harness from the junk yard and pulled out the positive wires and dropping resistor form the main harness. I added EV1 connectors (from an junk Audi) so I could hook up my makeshift resistor harness to the fuel injectors. I added spade connectors to the negative side wires on the EV1 injector connector so I could plug the negative wire into the original injector connecter so that I would be connected to the ECU for the grounding to trigger the injectors. I ran power from the battery to the dropping resistor. Now I had power thru the dropping resistor to the injectors. The makeshift harness was hooked to the ECU ground wore thru the original wire harness and I could now plug in my 1981 ECU and BAM!!!! The car starts and runs great! BAD 1983 ECU!
So if you are having the super flood issue with your 1982/1983 car and you have eliminated EVERYTHING else by following the FSM exactly, its probably your ECU. Remember a bad/disconnected CHTS can and will give you a super flooded engine also.
One interesting thing to note that while I was at the wreaking yard, the two 280zx that they have are close to the river and have been completely submerged several times during spring thaw flooding. I purchase one of the “been underwater” ECU, the one that had the O2 sensor input in the 35 pin connector, and took it home and opened it and cleaned out all of the dirt an muck with precision electronic spray cleaner. After running the 1983 with the 1981 ECU, I installed the 1980 “been underwater” ECU into he 1983 and the car ran great!
Shakedown run tomorrow! Moral of the story, check everything 3 times, beg and borrow parts from your friends, think out of the box and do your research. 5 weeks, countless hours of labor, $270 on parts and only $3000 purchase price for the car and now it runs great. I may just install the Drop Resistor permanent and keep the 1980 ECU instead of trying to find a unicorn 1983 ECU. Don’t give up! The answer is out there!

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All the way through reading the above I'm thinking "this is a flood car" and then your last paragraph confirmed it, the only way I can think of possibly solving this problem is to pull the entire wiring harness from stem to stern, lay it out on the shop floor, cut off all the tape and start cleaning, testing for continuity and resistance on every wire.  There is also the possibility the water has wicked up the copper wire under the sheath, has corroded the wire but is completely hidden.

It might be a better all round decision the buy one of the many aftermarket wiring harnesses kits and start fresh.

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Thanks for the reply. Let me give you a little more information. I have a 1983 280zx that I purchased as a "reliability problem" about 7 weeks ago. I have a 1981 280zx that I have had for several years.......and in the post I talk about the car that was under water in a local junk yard, 3 different cars. My 1983 car was never in a "flood". By "flooded so bad it won't start" I meant that the engine was flooded with fuel to the point it would not run. I have the car running great now.

While I was trying to figure out my issue I read a lot of posts on 3 different Z car forums. I gained so much information and am grateful to all that post on these sites. One thing that I did notice thou is that a high percentage of people who post their issues on the sites don't come back and post the final resolution to their problems. It's like reading a book and the last 2 chapters are missing.

With my post I figured that I would let everyone know what my issue was, how I went around trying to diagnose and fix the problem and the final chapter on what I did to finally get the car to run. My post is a "start to finish" problem solved post.

I can see where you might think it was in water flooded, I did get a chuckle out of that... and I actually did pull the entire engine fuel injection harness out of the car and unwrap it and check every inch for bad wires! It's not as hard as you might think.

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  • 1 month later...
On 9/17/2021 at 1:10 PM, grannyknot said:

All the way through reading the above I'm thinking "this is a flood car" and then your last paragraph confirmed it,

Not wanting to read it all again😨. To sum it up. The engine ran so rich it flooded with the 83 ECU. It runs well with the 80 and 81 ECU' s, but to use them you need to add dropping resistors to the injector harness.

Grannyknot. I think there are two kinds of flooded in the story, but I could have missed something on the way....

Interesting about retrieving the 80 ECU from a ZX that was in the river flood zone and therefore several periods under not so clean water. After cleaning it ran the engine.smiley_abuv - Copy.gif. Try that with a modern ecu. Ofcourse we are comparing analog to digital.

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Yep, you managed to sum up 7 weeks of diagnosis and putzing around with my car in 3 sentences. I guess I get a little long winded! Just noticed your "map location" had to look that one up! Have not been to the Netherlands yet. WIll be in Italy this spring. 

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14 hours ago, kickstand80 said:

Have not been to the Netherlands yet. WIll be in Italy this spring. 

Oh then your only... about a 1000 Miles off.. 😂


BTW.. as a electronic engineer i always have trouble with saying a 280zx has a ECU... it's a ECCS..  a analog computing unit.. it has no "clock" in it and no processor... thats also why it's so much more reliable then a ECU :pow:

(ECCS= Electronic Concentrated engine Control System)

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16 hours ago, kickstand80 said:

Yep, you managed to sum up 7 weeks of diagnosis and putzing around with my car in 3 sentences. I guess I get a little long winded! Just noticed your "map location" had to look that one up! Have not been to the Netherlands yet. WIll be in Italy this spring. 

We were in North Italy around Lucca, Siena Pisa etc in October for two weeks. We decided to jump in the car drive down and book B&B's or agriturismo's. Great time.





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