What is the minimum wiring needed to make it run

[sr20detmgb]

I have installed an s13 in my 1978 MGB along with the sr's trans, nice fit!!I have the mechanicals all taken care of and am on to wiring.I am using the chasis wiring for my starter, alternator, water temp and fuel pump. I have no AC.Do I need to have pesky little things like ECCU relay, water temp signal, tach signal and speedo signal?I want the bare minimum required to get it started and make it run.

[moyea]

I can tell you this, the ECU/ECM is going to want some of those signals or it might throw you into safe-mode or not run at all. Running a standalone engine management may be the best way to reduce the amount of wiring due to the fact that you can provide and program your own inputs. AEM, Haltec, etc.

[sr20detmgb]

Thanks for your reply,I see that you are with AEM and am guessing that your company makes a standalone system for the sr20det, correct?

If I were to use a standalone, how much of the original wiring would I need to keep? Could the original ecu be flashed to eliminate the need for the above mentioned devices?

In case you guys are wondering why I am doing this, with all of the work and expense it will still cost about $2,000.00 less than rebuilding the stock engine to give even 100 hp!! plus when finished the car will weigh around 1800 lbs. Should be fun.

[Hijacker]

There's going to be no bare minimum to get it running IMO. The 240's chassis wiring is about as essential as the EFI wiring to get the motor running.

I think your best bet would be to download an FSM and hit up the EC/EF section. Primarily the diagnostic area where it details out the wiring of each portion of the EFI setup.

You can use the USDM KA-DE FSM to get you started as the S13 KA and SR ECU share a similar pinout (wire colors are all the same). The primary difference between the two is the wiring for the coil packs and boost selenoid and lack of EGR.

I like the idea of an SR in an MG. I would just be careful with the original chassis harness. I have a feeling modern voltage requirements might cause Lucas to rear its ugly head

[sr20detmgb]

Thanks Bart,

I will check out the FSM section on what each circuit does.

Mr. Lucas and I have come to terms after 5 years with the car, most all of the original wires and bits have been replaced.

Talk to you soon and thanks again for your help,Dan

[Hijacker]

No problem. I don't know much about MG wiring (except that it's by Lucas and I'm surprised more MGs made it to today without burning to the ground).

I think the biggest hurdle is the fact that the ECCS and fuel pump relays are integrated into the chassis wiring on the S13s. Also, the ECCS relay is used to power more than just the ECU. It runs power for quite a few EFI components.

[IanS]

I think the biggest hurdle is the fact that the ECCS and fuel pump relays are integrated into the chassis wiring on the S13s. Also, the ECCS relay is used to power more than just the ECU. It runs power for quite a few EFI components.

Agreed, that part of the wiring will most likely cause the biggest headache, but its nothing that cant be done. I would just take the harness apart, label each plug, then begin separating out everything you wont need.

Sounds like a really cool project, you should post up some pictures of it.

[sr20detmgb]

Thanks Guys,

I have been tracing the paths of the wires and they are intertwined, looks like I might just be putting a coupla relays in this thing after all

[Hijacker]

No problem. Keep us updated!

[sr20detmgb]

This may seem redundant, everybody and his dog has asked this question but it's valid today, does anyone have a saved copy of the s13 wiring diagram? I have followed every link I could find and they are either "page not found" or corrupted and not usable.I have a diagram but I think it's an s14, are they different? I wanted to make sure I get things right.

[sr20detmgb]

using a different search engine, the 4th one I tried I found one,

http://jimwolftechnology.com/w...M.pdf

[Hijacker]

To date, there's no scan of an S13 SR wiring diagram online. The S13 was never officially released outside of Japan, so Nissan never made an English version of the service manual. Most people use the S14 edition for the mechicals as there was an English translation done for the EU.

The link from JWT you linked is the circuit diagram for the S13 as well as the ECU pinout. Both are different from the S14. I have a slightly better scan of the ECU pinout and the circuit diagram on my home computer. I can take a bit of time to translate them when I get home tonight.

I need to get off my lazy rear and finish translating the mechanical portion of the S13 SR FSM. I'm in the home stretch, but I got bored and needed to take a break. That break has lasted for 4 months now.

One of the moderators at SXOC.co.uk has access to the Japanese manuals and was scanning them. I got my copy of the mechanical section from him and he was working on the wiring section next. I'm hoping to have a copy soon.

But for now, you can use the USDM KA wiring charts to help you out. The S13 SR and KA are almost identical save for the wiring for the coil packs.

[sr20detmgb]

That sounds like a daunting challenge, lots of scanning and translating. I'm sure you will help a lot of people solve a lot of problems!!

I found your car and I stole its fuse/relay box!!! When I hit the U-Pull-it yesterday I came across a white convertable, complete, with no indication of why it was there! It's maf and ignitor were the only things missing til I nabbed the electronics next to the battery box.

In an S14 manual I downloaded was a page with schematics of the different relay pin outs. I am splicing my wiring into your fuse/realy box using that. It's slow and sometimes confusing but I am chugging away at it.

Maybe you can help me. When I look at the schematic I see wires with several others branching off at various points along their length. When I follow the wire from the ECCU it ends at a plug with no branches along the way. Am I to assume that the branching takes place all at the same place, the plug, despite what the schematic shows? And when I have a plug, like the one the ECCU Relay wire goes to, I don't have a clear Idea of what comes off the other side of the plug!

I read in one article or post I came across that the speed sensor wire comes from the transmission, goes to the speedo and the signal gets magically transformed into something the cpu can tranlate and use. If that's true does that mean I will need to have a 240SX speedo in my car? Tach too?

Wow, didn't mean to lay so much out in one post. Thanks again for all of your help.

Dan

[IanS]

I read in one article or post I came across that the speed sensor wire comes from the transmission, goes to the speedo and the signal gets magically transformed into something the cpu can tranlate and use. If that's true does that mean I will need to have a 240SX speedo in my car? Tach too?

As far as I know this is how the speed system works. I know that the speedometer reads a signal directly from the speed sensor, it then sends that signal to the ECU. Im not sure what, if anything, happens to the signal. It is possible that the resistance is changed, or the current is regulated down.

I can tell you this, I have an S14, with an S13 motor, when I originally installed it, I used the S13 speed sensor. That setup didn't work so well, my speedometer read about double what it should have, and when I reached 120 mph on the speedo, the speed limiter would kick in. Once I switched to an S14 speed sensor, the gauge read normal, and the speed limiter works as it should.

This leads me to believe that the signal being sent to the ECU is for the speed limiter, but I have found no test data to support this. Thinking about it, there isnt really much other reason for the ECU to see a speed signal. I have been meaning to throw an oscilloscope on speed signal wire before the the speedo, and after it.

[sr20detmgb]

Hey Ian,

I'm going to try runnig without speedo first and if something bad happens, or nothing happens at all (it doesn't run) I'll drop back 10 and punt.

Being all of the MG instruments are analog I'm going to need some new ones anyway. Something to think about.

I also noticed resistors in various places in the wiring spagetti, any info on the specs of each?

Thanks for staying with me on this. Once I figure out how I will post some pics here.

Dan

[IanS]

Hey Ian,

I'm going to try runnig without speedo first and if something bad happens, or nothing happens at all (it doesn't run) I'll drop back 10 and punt.

I ran without a speed sensor for a few days, I got sick of being limited to around 50 mph, I didnt experience any issues. I think you should be fine as far as starting, but you may run into runability issues later on.

Being all of the MG instruments are analog I'm going to need some new ones anyway. Something to think about.

There are some really nice aftermarket gauges out there, whether you're looking for an old school look, or something a little more modern. I personally thing Defi gauges are worlds ahead of everyone else, but they are a bit expensive.

I also noticed resistors in various places in the wiring spagetti, any info on the specs of each?

Only the FSM would be able to tell you that, I haven't delved that far into SR wiring. Resistors are universal though, by reading the colored stripes on their bodies, you can decode what resistance and voltage they are meant for.

Thanks for staying with me on this. Once I figure out how I will post some pics here.

Dan

No problem, Im always willing to help a fellow car geek, especially someone trying to take on a prodigious project such as this. If you need help with pictures, you can email them to me, I will host them and then post them here. My email is in my profile.

[Hijacker]

AFAIK there shouldn't be any resistors in the SR wiring harness. KAs had a resistor pack installed for the auto trans, but that was a pack that plugged into the harness (CAs use a similar resistor pack for their injectors)

Any other resistors I've taken notice of have been inside the brain boxes like the TCU, headlamp timer, etc.

The ECU has a speed limiter in it that reads the 5th gear sensor and the speed signal to cause a fuel cut. You will be alright with running without a speed signal going to the ECU. I would suggest getting a new speedo that can read a digital signal as I don't know of any cable drives that will work with an SR trans. Maybe the cable drive off an old Datsun 510, but that's a stretch.

The tach is driven from a signal derived off the CAS. You'll need a tach that can read a digital signal.

For working with the relays, I would suggest using the S13 KA manual. The relays are all in the same place between an S13 Silvia/180 and an S13 240SX. The only difference in relays is that the JDM models had an ignition coil relay mounted in the passenger side engine bay fusebox (we actually have a spot labelled on our boxes for it, we just don't have it). The black/red power circuit turns that relay on and it provides a dedicated battery source to the coil packs (blue/red)

As for the branching, it's hard to visualize where the branching takes place by looking at the schematics. The schematics are done up with space constraints, so they're only concerned with showing you that there is a branch, not where/how many. Nissan, however, likes to keep the number of branch offs to a minimum. A lot of times, they use crimp connectors to connect 4 or more lines together and then surround it with a putty like substance and wrap it in grey electrical tape.

Since you're rebuilding a functional harness, you can put your branches anywhere you like so long as you don't think it's going to hinder the integrity of the solder joint. Your primary concern should be to make the fuel pump work, the ECCS relay work, and provide power to the coils.

The plugs to be concerned with connecting the relay box to the EFI harness are the grey/brown plugs labelled as E9 and E10 in the KA manual. Those two plugs mate the EFI harness to the chassis harness and run the primary power wires (ECU backup, ECU power on, coil pack power, fuel pump relay signal). If you look at just about any wiring FAQ, those two plugs are the primary focus.

The S14 is a bad manual to use to mimic your wiring because Nissan changed its power routing for the 2nd gen. Those plugs don't exist on the 2nd gen chassis and Nissan opted to run them all inside the cabin in a big 48 pin dash connector plug. Also, the ignition coil and ECCS relay are mounted with the ECU on the S14s instead of being mounted in the relay/fuse box.

One other reason I prefer the S13 manual for wiring, it's so much easier to follow the wires as Nissan kept everything on one page instead of running it through multiple pages.

[IanS]

The tach is driven from a signal derived off the CAS. You'll need a tach that can read a digital signal.

I do believe the tach signal comes from the ECU, I think it interprets the CAS signal, then sends a signal to the tach.

[Hijacker]

You're right on the tach signal.

The ECU interprets the firing order and the spits out a signal from pin 3 to the gauge cluster.

I was thinking of KA harness which have two y/r wires (one is an incoming signal from the coil and resistor pack) and the other is the out signal. I've successfully converted some KA harness to run SRs (I don't want to explain that one) and for some reason always think I just bypass the ECU when I wire up the tach, when I'm really just changing the outgoing signal from pin 2 to pin 3.

The joys of having worked on too many weird combination of parts. I write my wiring notes down for a reason these days

[sr20detmgb]

Thanks for all the tips guys.

I have been out of town for a coupla days and maybe my brain has recovered enough to dive bacvk into this thing. I'll keep you posted and I'm sure I'll have more questions.

Thanks again,

Dan

[IanS]

We have pictures!

This think looks really badass, I cant wait to see it done, it looks like its going to be a ton of fun.

[Kalypso]

awesome,

I wish there was a sit down and read bible on how to start an SR,

mine is stranded just like yours... its a tough life.