3 Plug to 4 plug MPFI Sticky thread needed ?

discopotato03 · Post by **discopotato03** » Wed Feb 27, 2008 7:44 am

Hi all , I'm wondering if the moderators think a thread dedicated to converting L series and Vortex 3 plug MPFI ECU engine control to the later 4 plug and Hot wire MAF engine management system is valid .

People say that we have more 3 plug injected L's and Vortex's in Australia than the later system so if the conversion was shown to be affordable and painless more could use the superior system .

My personal interest is in manual and turbo though I think people who run Auto's and non turbo (or any combination really) wouldn't mind sharing their knowledge and experience .

A place like this could easily grow to include a carb/injection conversion section though I really think buying an EFI car is the way to go .

What do we think Subaphiles ?

Cheers A .

Suby Wan Kenobi · Post by **Suby Wan Kenobi** » Wed Feb 27, 2008 9:38 am

Just waiting till the thread runs its course then i edit the thread and place it in the tech manual.

discopotato03 · Post by **discopotato03** » Wed Feb 27, 2008 12:33 pm

As most know I have an 86 L RX Turbo and would prefer to have the later 4 plug computer system running my engine .

This is mainly because when an engine management system is using a Mass Air Flow (MAF) sensor it has a much more accurate and faster reacting engine load signal than either MAP or Flap AFM systems can provide .
Also this 4 plug system takes over control of the ignition timing so the computer can do things timing wise that are impossible for the earlier systems mechanical bob weight and pressure diaphragm can .
Mainly this shows up as more light load and cruise ignition advance and that's where fuel economy and throttle response gains are to be had . The later system also has the knock sensing circuitry in the main ECU box so its all localized .
One other thing too , when ignition timing changes all else being equal air fuel ratio (AFR) does as well . With the early or 3 plug system the fuel injection computer hasn't got a clue where the timing actually is , all it knows is the engines rpm signal (single yellow wire off the (-) side of the coil) and a signal from the knock sensor if the engine is detonating . The Oxygen sensor will tell it idle and light load AFR's via its old slow narrow band probe but its all very crude by today's standards .

The 4 plug system uses a optical crank angle sensor that hides under the cover under the dizzy cap . This is a thin metal disc with 360 fine slots towards its outer edge , in closer to the centre are four wider slots . Under the CAS/distributor body is a gadget with two LED's and sensors in line with
the two rows of slots . The 360 outer slots tell the computer where the crank is in crankshaft degrees and the inner ones provide a reference pulse so that the computer knows when the engine is approaching No 1 top dead centre (TDC) on the compression stroke . One it gets this reference or "sync" pulse signal the computer just counts in the firing order from there on engine start up .

The transistor (high speed switch) is the gadget near the coil on 4 plug cars and it just tells the coil when to discharge and the current flows from the dizzy caps central electrode to whichever pole and spark plug lead the rotor button happens to be pointing to .
So in this area you need to supply the transistors signal wire and run it back to the relevant ECU plug (details later) . You also need to run the four wires from the CAS/dizzy back to the ECU as well .

The engine harness works a little differently on the four plug cars because the throttle position sensor is different , also there is an injector current reducing resistor in circuit on their positive side - probably easiest to run the 4 plug engine harness because it logically plugs into the later TPS and has provision to plug in the injector resistor .

Its going to get a bit more involved inside near the computer but not too confusing if approached logically .
Being basically the same car/engine a few things are identical ie the ignition switch and most of the ECU's power and earth requirements .
It seems to me that you have to get the ignition transistor wire plus the four CAS wires to this location and the TPS and injector ones as well .
A lot of other stuff is common ie Ignition and Fuel Pump relays and auxiliaries like control of purge and EGR switches and the cold air valve which sits on top of the thermostat housing . Also coil tacho signal wire . Can re use power and earth on (+) and (-) side of the coil .
I haven't got too deep into the boost pressure switch (on drs side front shock tower) or boost control as these can come later .

I need to sit down with the two manuals and sort which wires to join from the early ECU's 3 plugs to the newer 4 plug sub loom .

Just on this I am prepared to murder a 3 plug ECU for its female plugs , once I do this I can plug my unmolested three plug loom to it and patch the ecu side of the plugs wires across to the relevant wires on the later systems 4 plugs . These four plugs will naturally already have the wires from the transistor/CAS/injectors/TPS and will be powered up earthed and switch all the other gadgets via patch wires to the murdered 3 plug sockets and on via the cars original 3 ECU plugs .
I want to go this way because if for any reason I had to re run an early computer it could be easily reversed - well under the dash anyway . Still have to change back engine loom/TPS/AFM/dizzy .

Sound simple or is everyone aslee z z zzzzzzzzzzzzzzzzz .

LOL Cheers A .

Gannon · Post by **Gannon** » Wed Feb 27, 2008 6:26 pm

You're a sucker for punishment. Its gonna be a big job.

I agree that the 4 plug system is far superior to the 3 plug one.

You seem to have most of it under control.

Two things... the 4 plug ecu doesnt use a boost or vac switch. Its fuel cut is activated when the AFM reaches a certain limit.
And the boost controller, car will run fine without it.
It doesnt make much difference, it simply bleeds a little air from the wastegate line between 2000 and 2400rpm to keep it closed and increase boost response.

I converted my carby car to the 4 plug system, if you have any questions, dont hesitate to ask

discopotato03 · Post by **discopotato03** » Wed Feb 27, 2008 7:41 pm

In time I'll post up the patch wire colour codes and look at the gearbox switch issues .

One thing I did notice is that the knock sensor wire is shielded on the early and possibly not on the late one . The loom I'm using funnily enough is a 4 plug auto N/A one so may be missing a few things for a turbo manual .

Knock sensor , same 3P/4P MPFI -T ?

Cheers A .

Gannon · Post by **Gannon** » Wed Feb 27, 2008 8:12 pm

Gearbox shouldnt make a difference to the ECU. More likely the other way around, i.e. using a 4EAT tranny without the 4 plug EFI

The 3 plug knock sensor is a 2 wire device, the 4 plug one is a single wire.

The wire is shielded all the way from where it enters the engine manifold loom to about 6 inches before the ecu.

The knock sensor is in the NA MPFI loom, its just turned back just before one of the two engine plugs (the big round ones near the airbox) Pretty sure its a white wire

discopotato03 · Post by **discopotato03** » Thu Feb 28, 2008 6:54 am

Ok so the knock sensor wire should be in the main harness from one of the ECU plugs to just before the relevant engine harness plug .
I haven't looked yet but I guess the wire may not be there also between the large plug and the knock sensor plug either .
I think I have a 4 plug turbo auto Vortex loom in the cave and possibly a 3 plug turbo auto Vortex engine loom so I'll see what I have and what can be patched together .

One challenge I can see is getting the 4 plugs systems extra wires in side the car , may have to look at where the gearbox/pressure switch wires come through at that horizontal grommet behind the off side strut tower .

With the gearbox switch stuff I mean the I think neutral/4th gear switch wires ? The 3 plug system uses clutch and acc pedal micro switches though it must have wiring /switches for reverse lights/ 4WD and low range .
I'm trying to use as much of the cars original stuff as I can and only add where the 3P/4P systems are different .

I don't expect an answer to this one but initially my problem was trying to figure out how it works rather than how just to make it work .

Life's a learning curve , cheers A .

Gannon · Post by **Gannon** » Thu Feb 28, 2008 8:11 pm

The neutral switch (and a clutch switch in some markets) is a switch wired in series with the starter motor switch wire, so the engine cant be cranked while it is in gear. Has nothing to do with either ECU.

4th gear switch has something to do with engine/gearbox temp.
The ECU will hold the 4EAT in 3rd for a few minutes so it warms up the engine/gearbox quicker. If you have a 3sp auto or a manual, i wouldnt worry about it.

discopotato03 · Post by **discopotato03** » Fri Feb 29, 2008 6:28 am

Interesting , so if not wired into the ECU plugs it should work just like my 3 plug manual RX does now - it starts in gear though never tried to start it in gear with the clutch engaged . Stall recovery ?

I suppose the wiring diags show gearbox wiring because it comes inside and lights up the dash lights in 4WD and low range .
Possibly OT but do the full time L box plugs connect and show up as 4WD in the cluster when the center diff locks engaged ?

Cheers A .

subanator · Post by **subanator** » Fri Feb 29, 2008 12:01 pm

From my previous car, I remember that it was originally a stock MPFI Tourer - a 4 plug ECU, this is the donor model you want, all the wires in the main harness are the same as the Turbo one, even if unused.
Mine had a EA82T put in, Turbo ECU changed also and I sourced a Turbo engine harness that had the wiring for the knock sensor, but being JDM, it did not have our emission control wiring crap, but the main connector plugs are the correct pinout.
If you get these items, its just about plug n play!

Gannon · Post by **Gannon** » Fri Feb 29, 2008 3:26 pm

I did the same as subinator, (i used an 89 tourer and a 88 vortex turbo) and worked prefectly. Only thing i had to do was fix the wire for the knock sensor at the round engine plugs, and run a wire for the boost controller. Easy as

discopotato03 · Post by **discopotato03** » Tue Mar 04, 2008 3:12 pm

The next stage will be to strip the 4 plug N/A auto loom of everything but engine control stuff .

Was going blind today looking at the microscopic 4 plug diagrams but this is the next job .
Basically start at the transistor and CAS plugs and work back towards where the large round plugs head towards the engine . Then I suppose I strip towards the plugs till I find that white knock sensor wire , will have to see if the engine harness half has the wire and plug to the knock sensor .

For me the difficult thing is trying to work out the minimum number of wires to run between the main junction and back inside to the computer . I can double up on things like the injector wires and keep the 4 plug loom sort of factory or splice into the originals before the ECU plugs and again before the injector dropping resistor .

One thing I don't know either is the Turbo/NA and Auto/Manual discrimination business at the computer . Can someone tell me how to set it for turbo and manual or if its a factory set thing in the ECU's .

Also will be splicing into the wires behind the original 3P ECU plugs , wires at the back of the ecu socket plugs would break too easily over time I think .

Cheers A .

Gannon · Post by **Gannon** » Tue Mar 04, 2008 7:05 pm

There are 4 different types of ECU (not including geographic location, ecu's of different regions are tuned different to accomodate for climate and avaliable fuel quality)

There are...
Turbo Auto
Turbo Manual
Non turbo Auto
Non turbo Manual

There is bugger all difference between auto and manual ECU's. Not worth bothering about unless you have a 4EAT (4 speed Electronic Auto Transmission)

discopotato03 · Post by **discopotato03** » Wed Mar 05, 2008 11:00 am

I have an Aus spec spider/turbo/manual ECU so thats what I'll use .

Since so many power (WB and BW) and earth (BR and B) wires splice together for the various engine sensors/solenoids within the looms I think I'll just run the all through to the computer .

Cheers A .

discopotato03 · Post by **discopotato03** » Thu Mar 06, 2008 7:11 pm

I could not find the white knock sensor wire that's supposed to terminate before the white body side loom plug . The 87 factory WSM colour codes do not match the body loom at this point .

Cheers A .

Gannon · Post by **Gannon** » Fri Mar 07, 2008 4:51 pm

Have a look at the white round engine connector, pin 14 is the knock sensor wire. Upon closer inspection of mine, maybe it was already there. I cant remember.

Here is a diagram of the white connector, body side. Pin 14 isnt labelled but that is because the image i got it from was the 88XT Mpfi service manual. Pin 10 is the shield for the knock sensor

discopotato03 · Post by **discopotato03** » Sat Mar 08, 2008 11:12 am

That makes a bit more sense , my 87 factory WSM shows the knock sensor as pin 15 of the round white engine harness plug (body side) and a "shield" as pin 16 . I have noticed in the past that American online WSM's used slightly different terminology (slightly more specific) , also they appear to be 88-89 era .

I traced the pin 15 wire back to an injector pin it seems .
I dug out a turbo vortex 4P loom the Cruisingbrumby sold me a while back and at least its mostly tagged so lots of spare wires and plugs so to speak !

The one thing I don't have spare is the knock sensor wire and plug on the engine loom side of the white plug . They aren't normally on non turbo engine side harnesses are they ?

Anyway , taking these looms and car to a friend of mine today . He's been a mechanic for many years and no stranger to aftermarket computer conversions . Far better with a multimeter than me so should be able to sort lots out .
He wants to look into running tap wires off behind the 3P's ECU plugs to a multi connector , who's other half has the connecting wires to the 4P ecu plugs .
Its still going to have to have all the extras to the CAS/Transistor/AFM plus the Injector dropping resistor on the drs side tower .

Another one I'd like to know about is are the 3P and 4P turbo injectors all the same ? The fact that the 4P system uses an injector dropping resistor could be because they are different or just that the injector drivers in the 4P ecu are different . If the turbo injectors are all the same then its just to suit the 4P computer .
I'm not sure if he will want to double up on the wiring between the ECU's and the injectors/solenoids/sensors and have basically two looms , two sets of body side engine harness plugs . If this is the case then the only shared wires between the 3P/4P ecus will be power and earths - and the permanent fusible link power that only the 4P ecu has - for AFR learning memory I would think .

discopotato03 · Post by **discopotato03** » Sat Mar 08, 2008 1:43 pm

I found I had made a copy of that US edition 1988 XT manuals Fuel Injection System section . It covers the N/A XT4/XT6 cars , the 4 cylinder version being the Spider manifold one and why I printed a copy .

That particular N/A XT4 didn't use EGR by the looks of things .

An interesting thing is that the Aust 87 WSM shows one of the engine loom to body loom connectors as sort of square while the XT manual shows them as both round . This is truly weird because every 4 plug MPFI car I've ever looked at has two round engine loom connector pairs .

Actually all the wires have been moved around in the XT's engine harness plugs . At least the ECU pin outs are the same .

Does anyone have a factory 89 L Series WSM Fuel Injection System section ?

Cheers A ..............

Gannon · Post by **Gannon** » Sat Mar 08, 2008 1:44 pm

Dont forget that 87 wiring systems are different to 88/89 4 plug systems.

If you have an 88/89 MPFI, the knock sensor will be at pin 14, with its shield at pin 10. That wire should lead back to pin 36 at the ecu

Just noticed you posted while i was writing.

I got all my info from a blury 88 SPFI/MPFI turbo FSM.pdf and that XT/XT6.pdf one you mentioned

Yeah there are a few differences between the 87 and 88/89 4 plug systems.

The 88XT diagrams will do the trick for an 89mpfi.

discopotato03 · Post by **discopotato03** » Sat Mar 08, 2008 2:13 pm

Always the way isn't it ...

I have an 89 L Series PDF manual which shows everything nobody wanted to know about SPFI AND Turbo EA82 but no engine loom connector details .

Ah well , this means we have to trace everything from the ECU plugs to the wires devices .

I know how Wally Binghamton feels , cheers A .