BlueKitsune

I'm not new to soldering but I'm not that great at it either. But I've read somewhere that if your ECU is acting up that you might want to resolder some of the connections on the inside of the ECU

Right now I have one ECU that will idle very smoothly but wont rev past 3K RPM (its like I turned the car off for a second when it does it)

My second ECU (which is in my Z now) Will rev fine with or without load, but has almost a kind of miss at idle and its not very smooth.

So I'm hoping I can solder up my spare so it will work right, Think it will?

WildmaN

I would assume you are talking about your 280zx ECU? Anyway, might as well try it. I know they are pretty simplistic inside. Although, I have never had to change one in any of my Z's. Those seem to be the last things to wear out, or malfunction. Good luck with that, and let us know how it turned out.

BlueKitsune

Geez I suck at soldering. But I can see that theres corrosion on the ECU board in some spots, mainly around the connector pins.

NismoPick

Pics!

Maybe your gun isn't hot enough? Is the tip clean? Is the surface you are trying to solder clean?

BlueKitsune

I'm using a "coldheat" soldering iron, and it has a brand new tip.

And why pics? I'm just trying to cleaning remelt the old solder so it will make a better connection lol

NismoPick

The lil battery operated soldering gun? Hum... that may be your problem.

BlueKitsune

I'm to lazy to get my camera out so heres a cell pic

NismoPick

Looks very clean to me. I don't see any damaged or overheated pins.

BlueKitsune

I wonder why it doesnt work then. this is the one that doesnt run past 3K rpm

NismoPick

How do you know it's the ecu and not a sensor? Swapping ecu's and still having problems (even just diff problems) would tell me it's NOT the ecu.

Have you checked / adjusted / swapped the AFM, TPS, CHTS, dizzy, coil, ignitor, and O2 sensor?

BlueKitsune

My current ECU just has a slight miss at idle. Thats it. This spare ECU will not even rev past 3K RPM. and I already tested everything in the way the FSM says to test it and its all good.

And I dont have an O2 lol

BlueKitsune

Okay after checking all the joints and traces and then going partly mad checking all the resistors my spare ECU now has a clean bill of health.

I'm gonna try it and see if the ECU still facelants at 3K rpm and if it doesn't then it makes me wonder why my other ECU doesn't do that was well.

According the the FSM theres no difference between a 79 ECU and an 80 (well a build date of mid 79) ECU. well obviously lol I'm confused now

EDIT: After going for a testdrive with the spare ECU, it now doesnt fall on its face at 3Krpm. but now after 3500 it misses horribly. then I put my normal ECU back in and its doesn't do that. but it still slightly misses at idle. Not as badly tho. I'm confused. Anyone wanna just send me a Z31 ECU, harness, and chopper wheel? lol Injectors too if there good, or and the MAF. or a MS system lol

duowing

I think you need to try wiggling your wiring harness while you drive and see if that makes any difference. Then go into your engine bay, unbolt all your grounds, sand them clean, and make sure they're all bolted down nice and tight. I had a similar problem, heck I still had it after I switched to the Z31 ECU/MAF setup. My car would randomly start idling horribly, I'd reach down, bump the harness and bam it would straighten right out. For a while my Z for some reason started acting up before this case where it wouldn't rev past 3500. It would fall on it's face, lean pop, act like the fuel was gone. Cleaned my grounds in the engine bay and the problem went away.

75280z

I had a problem very like this in my 75 289z and it was the AFM connections were wet under the hood and that was causing the miss, I had to dry the connections by separating and blowing air into the connectors.

duowing

As for resoldering the ECU that shouldn't be too much of a big deal. Heck I had no experience and I managed to desolder the EPROM chips from two different Z31 ECUs and then solder in a 24-pin socket so I could plug my Nistune board in. Not to mention on the one ECU I had to solder individual wires to individual pins on the processor...

BlueKitsune

All connectors and the harness itself is fine. I cleaned them all nice and shiny and the wires tested very good. and I FSM tested everything electrical under the hood and they all passed.

So it HAS to be the ECU

FricFrac

Please for the love of traces and pads on PCBs everywhere take a little time and read about proper soldering techniques. It's not rocket science but a few simple tips will go a LONG way.

First off never use a soldering GUN. They are absolute crap. You want a pencil iron with as big a tip as you can manage. Reason being is that you want a big hunk of metal (eg the copper tip) that will act as a heat resevoir. Most of the time people have too small of a tip for the job so the piece they are soldering to pulls the heat out of the tip and cools it below the melting point of the solder. Then they push harder and hold it on longer until the piece heats up enough to melt the solder. Bad idea. Not only is it frustrating but its going to ruin the piece you are working on.

The other thing you are going to want to remember is keep everything as clean as possible. I would suspect that 90% of the soldering issues you are going to have on your ECU is the connector because of the physical strain from the cabling. Use some desoldering braid to remove the bulk of the old solder. If it has heated and discoloured you want to get rid of it because it will never flow properly after it has been heated and oxidized. Once that's done just reflow new solder on each pin. It's really easy to do you just need to have enough heat capacity and a clean working environment and use just enough solder to make a nice fillet.

BlueKitsune

I know. I never used a gun (unless the cold heat thing is a gun *shrugs*) and I got a good soldering iron now that is a constant heat.

But before I did anything I decided to test all the connections and make sure they where solid. and sure enough they there. so I'm not sure what is wrong with my spare ECU.