Digi' gti wiring,

[autocad]

I am piggy backing a digi' loom off the caddy loom, the under bonnet bit is easy enough but i have a wire and i dont know what it is?

In the rain tray on the MK2 GTI are two connectors,

one has black and yellow - idle stabalisation relay,
Red and yellow to the fuel pump relay,

Red and white that just stops at a blanked plug,

Red and Brown with a yellow conector where it terminates at the fuse box- this does not appear on any wiring diagram

Any idaas what it is of where i could get a better diagram,

Other wise 2L AGG polished and ported is well on its way,

[Iowa Caddy]

autocad -- maybe this will get you on the right track? It's from US Mk2's with Digi II that were built in Germany, and which use the Euro-type fuse/relay block (as opposed to what is usually used in US/Mexico/Brazil-built), so is probably similar to UK wiring.

A 1.0 mm Black/Yellow stripe is the main power feed to the Digi Control Unit (brain) and to the injectors at the rail. The power originates at the output of the "Digi Control Unit Relay" and exits the fuse block at terminal R2 on the back of the fuse block. It is energized when the key is in the ON & START position.

The chassis end of that 1.0 mm Black/Yellow ends at a 2-conductor connector in the rain tray. The other conductor in that connector is a 0.5 mm Red/Black. It originates from the #50 "Start" buss in the fuse block, exits the fuse block at pin C18, and feeds the "start" signal to pin #1 of the Digi brain.

The following is a wee bit circuitous, so bear with me. ;)

In the Mk2 Digi's, the control side of the fuel pump relay gets it's earthing from the digi brain "engine running" signal via 1.0 mm Red/Yellow to pin D13 on the back of the fuse/relay block. The terminal connection in the rain tray is either 2 or 3 conductor, depending on the year. It is always "paired" at that terminal with (at least) a 1.0 mm Red/White that feeds power to the O2 sensor heater. The chassis side of that Red/White goes back to a single wire terminal (near the fuse block), that connects to a 0.5 mm Red/White which goes to pin E14 at rear of fuse block. At that pin, siamezed with that Red/White that powers the O2 sensor heater is a 1.5 mm Red/Yellow that feeds both the pressure fuel pump and the in-tank transfer pump. That pin E14 gets its power from the output of the fuel pump relay (which was energized via the earthing signal from the brain, and we're now back where we started this paragraph :)).

I don't have any indication of a Red/Brown wire associated with Digi controls, but I do re-call a couple of wires/terminals in the digi engine harness that were un-used when I did this swap (Digi into Westmoreland A1) for a friend last year. One was a 0.5 mm Green connecting to pin 16 of the Digi brain, which I believe is meant to be connected to the A/C wiring, giving a signal to the brain when the A/C compressor is running. (Maybe to bump up the idle speed? Or to defeat the ignition retard at idle?)

Are you swapping in the entire MK2 Digi loom, including the fuse/relay block? Or are are you only using the engine control portion of the Mk2 loom?

In the US, the fuel pump relays on Caddies (actually on most A1 chassis) are different, and operate differently, than the A2 (Mk2) Golfs, and do not need that 1.0 mm Red/Yellow from the Digi brain that gives the earthing signal to the pump relay. Instead, the "engine-running" signal for the pump relay comes from the #1 terminal of the coil via the same circuit that drives the tach. Therefore, that Red/Yellow wire goes un-used if we retain the original Caddy relay in the original fuse/relay block and chassis wiring.

Have you looked at this thread? http://vwcaddyforum.com/showthread.php?t=4764

edit -- added the following

After posting the above and while working on something else this afternoon, I've been mulling over in the back of my mind the elusive Red/Brown wire. Upon re-reading your post, I realize that I'm unsure of your description, so the above may not have been of any use to you.

Do I understand that you have two double (2-conductor) connectors in the rain tray? One has black/yellow and red/yellow, while the other has red/white and red/brown? Are these the wires from the engine (and brain) to the connectors, or from the connectors to the chassis? Is the 2nd "double" connector in the rain tray colored yellow, or does yellow describe a connector at "the other end" of the red/brown wire? Where exactly does it "terminate at the fuse block" ? (Letter/number designation where it connects to the fuse block would be very helpful.)

"Red and white that just stops at a blanked plug." Not sure what you mean by blanked plug. And is this "blanked plug" one of the 2 double connectors in the rain tray, or is it at either the engine end of the loom, or the chassis end of the loom?

Sorry for my confusion -- just trying to help you get that AGG in and running. :)

[autocad]

The rain tray connectors are red/yellow, red/white and black/yellow red/brown? and from the engine/brain to the fuse box the yellow connector is on the end of the red and brown wire at the fuse box.

Yellow and black is the positive feed to the digi’ unit, from the ignition via a control relay, correct? This is live when the ignition is activated

Red and yellow is the negative feed to the fuel pump relay, so if the engine stops it breaks the circuit cutting fuel flow to the engine bay,

Red and white is redundant as there is no emission control on uk trucks, hence there is no wire on the other side of the connector, it is in the engine bay loom but ends at the rain tray.

Red and brown starts in the under bonnet loom and terminates at the fuse box with a yellow connector, this may be the start signal to the brain, as its the only wire I haven’t found yet?

The easiest way to check may be to stick a volt meter on a friends gti and see what happens

I am only swapping the engine bay loom, keeping the caddy fuse box KISS style (Keep it simple stupid).

Thankyou for that,

p.p
The other thread was worth looking at i.e., they use the same fuse box, if that is so, I might swap it for that on golf, it might just then be a case of pushing missing the pins in to the base connectors at the fuse box? I have done this before on other engine/loom swaps,

[autocad]

i traced the wire it runs back to with the text on the top of the plug,
the bottom right hand pin of the main ecu conector positon 25?

[Iowa Caddy]

I think you're looking good.

"Yellow and black is the positive feed to the digi’ unit, from the ignition via a control relay, correct? This is live when the ignition is activated" Yup. Inside the engine loom, the Black w/Yellow stripe branches to both power the brain at pin #14, and to provide +12V to the injectors. Confusingly, the Black/Yellow connects to 1.0 mm Brown at the injector rail connector T2d/1 [* see below] on the earlier Digi vehicles, but to 1.5 mm Red on the later, but pre-Central Electric vehicles. (For future reference, on the 1990 up w/CE, the brain gets power from Black/yellow from the same "Digi Control Unit" relay through connection T6c/4, but the injectors get power from the Fuel Pump relay via connection T6c/5.)

"Red and yellow is the negative feed to the fuel pump relay, so if the engine stops it breaks the circuit cutting fuel flow to the engine bay," Yup, again.

"Red and white is redundant as there is no emission control on uk trucks, hence there is no wire on the other side of the connector, it is in the engine bay loom but ends at the rain tray." Sounds right.

"Red and brown starts in the under bonnet loom and terminates at the fuse box with a yellow connector, this may be the start signal to the brain, as its the only wire I haven’t found yet?" Looks to be correct. On my friend's swap, I used loom from a German-built Jetta, post VIN 1GKW40001, and the start signal wire was Red/w Green stripe. Looking now at schematic for VIN up to 1GKW40000 shows that indeed it is a Brown w/Red stripe that receives the start signal and connects to pin #1 of the brain. Sorry that I missed that.

"The other thread was worth looking at i.e., they use the same fuse box, if that is so, I might swap it for that on golf..." I took another look at it too. From Admin Al's post there "...to your existing wiring, this will be made even easier if the digifant is the pre 1990 central electrics model as the earlier ones share the same fusebox as the caddy." So apparently, all of your [UK] caddies have the same fuse/relay block as our German-built A2 Golf & Jettas and our Mk2 'Roccos (and Cabbies from ????). Our '79-'80 caddies have the early, corrosion-prone German fuse blocks and '81-'83's have the crappy US/Westmoreland design fuse block -- neither of which will easily interchange with the later stuff (without wholesale splicin' & dicin') because of completely different plugs and loom and wiring scheme. Lucky you. ;)

"I am only swapping the engine bay loom, keeping the caddy fuse box KISS style (Keep it simple stupid)." A man after my own heart. :)

"The easiest way to check may be to stick a volt meter on a friends gti and see what happens." You seem to know your way around a schematic and are probably familiar with proper test procedure, but a caution to others. Using a simple incandescent test light is fine for probing a disconneted loom. But on electronics, be sure to use only high-impedance test equipment, such as a resistored LED test light, or a multi-meter (VOM, voltmeter).



You probably know this, autocad, but for others' reference, a primer on VW wiring diagram nomenclature and terminology for "pull-apart" connectors/terminals. T2d/1 -- T2 means "2-conductor terminal"; d means it's the "d-th" (i.e. fourth) double-conductor terminal on this particular wiring diagram. The /1 refers to pin #1 of the two pins (not present on early diagrams. Started circa 1989.)

Likewise, T6c/4 refers to the #4 pin of 6 pins total of the "c-th" (third) 6-conductor terminal on that diagram.

It's important to note that a T6c on one diagram will not necessarily be the same as aT6c on a different diagram.

There's usually a key at the start of the diagram that gives the physical location of the "named" terminal. The circled numbers at the bottom, ground (earth) portion of the schematic are keyed for location, as well.

BTW, the color codes on the diagrams refer to the color of the wires, not the color of the terminal itself. I know of NO place where the color of the actual terminal is documented. Anyone???

[Iowa Caddy]

Sorry, your last post was made while I was composing. :)

"i traced the wire it runs back to with the text on the top of the plug, the bottom right hand pin of the main ecu conector positon 25?" I think you're looking at it bass-ackwards, or at least up-side down and/or in a mirror. ;) It should be pin #1.

Pin #25 connects via 1.5 mm Green to pin #6 of the Ignition Control Module. I don't have brain/loom handy at the moment, but if you look real closely, sometimes need a magnifying glass, you'll see numbers in the recess of the plug on the loom, or on the brain.

[autocad]

I used to have an Alfa Sud!

This is really useful!!!!!!!!!!!

The fuse box is the sams it has the same part number.

Black and yellow wire branches at the connector to the brain and to brown at the injectors,

The relay for the manifold heater is the relay for the injection system on the GTI so i can use that.

The fuel pump relay can be added back to the relay tray,

There is a spare yellow connector coming off the back of the loom, - this may be the start signal wire just needs testing, i presume this relays the starter signal and is off once you are running,

Thank you for the wiring explanation it was a bit of a mystery,

[Iowa Caddy]

Glad to help get your swap on the road. Keep us posted. Kudos for discovering the Alfa Sud cross-over, and for posting that info -- improves the database. BTW, in the US, all Mk2 Roc's, Caddies '82(?)-'89(?), and all German-built A2's until 1990 CE's, use the same part # relay/fuse block.

[Iowa Caddy]

autocad -- (clever screen name -- do you have an AT in your Caddy, or are you a CADD draftsman [draughtsman??] ) -- I just had another thought.

"Red and white is redundant as there is no emission control on uk trucks, hence there is no wire on the other side of the connector, it is in the engine bay loom but ends at the rain tray." "Sounds right." Maybe not. Even though your Caddy has no emission control, the Digi brain will expect an O2 signal to run properly (unless your UK Digi's are non-emission controlled??? :i_dont_kn ). I think you'll have to add an O2 sensor -- other-wise you'll be running in "limp-home"/open-loop rich mode all the time.

Did none of the UK A1 chassis vehicles have exhaust manifolds with O2 holes drilled and tapped? Maybe the later 'Rocs and Cabby's? Easiest/cheapest would be to weld a bung somewhere in the exhaust tubing. Closer to the manifold heats up hotter/faster to give an O2 signal sooner, and you wouldn't have to use a heated sensor -- only a single wire. Further downstream almost requires the 3-wire heated sensor. Some say the bung should be sniffing exhaust from all 4 cylinders -- others get by OK with a bung in only one of the 2 tubes of a dual-tube downpipe. Some of our (US) 4-into-2 manifolds (especially our non-O2 Caddies) came with the boss cast in for the O2, but un-drilled. Easy enough for a machinist to mill, drill & tap, but about as pricey as sourcing one already drilled. ($10 if you're lucky enough to find one in a boneyard -- $50+ on eBay.)

Are you sure you don't want to put just plain ole' K-jet (CIS) on that new engine? ;) It'll work fine. More emissions, and probably not quite as good fuel mileage as the Digi -- maybe not quite as good driveability. But K-jet is well known to be able to put out the HP -- maybe more if tuned to within 0.0001 inch of it's life.

[autocad]

UK GTI's dont have the CO sensor and there is no facility in the under bonnet loom or exhaust for it. So yes, no emission control! Emission control only came in ten years ago ish, pre 76 and specials are exempt.

The loom from the fuse box the connection but it ends at the rain tray connector (sorry i got this the wrong way round earlier).

I have a 205 GTi with bosch L-jet, later models of both this and the golf with the Cat have closed loop Lambda,

i think the V8 and V6 fords only pick up from one down pipe but im not sure?

I had considered the K-jet but i like the Digi unit and the way that it works, i am building another system on another car also, not a VW

P.S.
Ik ben architect,

[Iowa Caddy]

Hmmmm, a non-O2 Digi -- v, v interesting. I knew Germany and Switzerland used cats as early as 1985, and by at least 1989 they were on EC15.05 w/3-way cat. I guess UK and Italy stayed with EC15.04 for a while longer. USA didn't get Digi until mid '88, and I assumed by then VW would have standarized on emission controls in anticipation of all of Europe & UK requiring it. Now that I think about it, our first Digi's (in '88 ) were actually Digi II -- with Digi I coming in '91 (go figure!), but only on California 8V's for their stricter emission standards. Don't know the difference -- I'll go check.

According to the Bentley "The most significant difference in the Digifant I [relative to Digi I] system is adaptive circuitry for fuel metering. The system can adjust its own operating range in response to changing conditions brought about by normal engine wear, minor vacuum leaks, change of altitude, etc. There is little or no need for periodic mantenance adjustments.

"Another feature of the Digifant I system is self-diagnosis of system faults."

Hmmm, I wonder why those attributes were removed in Digi II? Maybe didn't self-adapt as well as planned? (morts -- maybe that's why your g/f's Digi was troublesome? Was it CA spec?)

So autocad, your Digi engine loom doesn't have a 3-conductor plug for the O2 sensor? Usually Brown/black to ground [earth], Red/white for heater, and Green for signal to pin #2 of the brain??? I've got 2 friends running Digi in their AutoX cars -- they might find this useful. How much would it cost me for one of you UK blokes to find one of these non-O2 Digi brains? How about a part number, autocad? Cheers.

[autocad]

Some one stole my brain!

I'm off to a breakers today to pick up a gearbox and new ecu so ill know by this evening, £20 - $35 max i would have thought?

If you get rid of self diagnosis you have to pay someone to sort it out,

There are no spare connections in the loom the 205 has dagnostics but the golf has nothing as far i can see,

Digi 1 does not have the knock sensor, digi 2 cuts fuel flow on overun to help economy - this is also eliminates the chance of a backfire on turbo'd engines,

One of my main reasons for using the Digi is i can run it on LPG - and switch between the two without effcting the performance of either system, gas is 115 octain so runs really well with high compression engines.

When it costs over $100 to fill your car you start looking at alternatives,

Petrol here is getting close to $5.5+ gallon (80% tax on petrol, soon to be 90!!!!!!!!!), LPG gas is $2.2 so it pays to use it, theres also something really satisfying about not giving the govenment all your money!

I could go on............

-----------------------------------------------------------
£25 for an ECU but unfortunatly he didn't have one,- He also produced a hall effect 4 blade dizi for use with a MK2 loom and AGG block, what this came off i do not know but it save a great deal of hastle,

[Iowa Caddy]

"I had considered the K-jet but i like the Digi unit and the way that it works..." Me too -- at least in theory. But remember KISS?? K-jet wins. ;)

"I am building another system on another car also, not a VW" -- but using Digifant? What kind of vehicle is it? Have you heard of and considered using MegaSquirt?

"Ik ben architect" -- and trained in Deutschland?

"If you get rid of self diagnosis you have to pay someone to sort it out." -- now, now -- don't be cynical. ;) But it could be true. :)

"One of my main reasons for using the Digi is i can run it on LPG" -- NOW you've got my attention!!! I'd really be interested in what you have planned. I've been planning a turbo'd LPG project for a while now. Use the Private Message function here on the forum and we'll swap e-mail addresses if you'd rather take it off the forum.

"...is 115 octain so runs really well with high compression engines..." . I converted a 5.7L SBC (Chevrolet V-8 ) back in '81 when our petrol got real dear. Dear to us, anyway -- not like what you guys have to pay. Mileage went down 5-10%, but LPG was 50-60% the price of petrol. Power was down (10-25% ???), because it only had 8.5 or 9.0:1 CR and didn't utilize the high octane. (I kept the original CR, because I was dual-fueling it.) I swore I'd do an LPG conversion again sometime, only do it correctly. I.e., at least 11:1, maybe 12:1, if N/A -- or slightly lower and lightly turbo'd. I still miss the sound, and crisp throttle response, of a high-compression engine.

"Petrol here is getting close to $5.5+ gallon (80% tax on petrol, soon to be 90!!!!!!!!!)..." -- Wow, I knew how dear it was, but didn't realize so much of it was tax! Actually, I think the USA missed a golden opportunity back in '83 when the price of oil started coming back down from it's historical high (petrol was about 50% higher here in '81 than it is now, when adjusted for inflation). People had gotten used to the high price and were finally conserving energy in many ways. If the gov't had raised the tax as oil got cheaper, we'd still be conserving -- not commuting 13mpg 7000LB SUV's with one person in them, and thus not have to spend 100's of Billions to try to continue controlling Mid-east oil -- and have some tax money to repair/maintain our abysmal roads. Anyway, I've thought 50% tax would be about right. "Oil companies - you can charge anything you want, but give us half of it to fix the roads, bridges, etc., and to clean up the drunken driver wrecks. If there's anything left, we'll use it to improve our infant mortality rate to something other than dead (pun intended) last of the developed countries." rant /off ;) :D


"LPG gas is $2.2 so it pays to use it, there's also something really satisfying about not giving the govenment all your money!" Is LPG so much cheaper than petrol 'cause there's less/no tax on it? Or is the base price that much different? Over here, "base prices" are tending to even out. I.e., if Natural gas gets a little cheaper (per Therm/BTU), electric generation gets shifted to natural gas, and price goes back up with the increased demand. To a certain extent, the same happens with LPG, coal, oil, ethanol, etc. Any un-eveness in total price tends to be the result of taxation/subsidy in-equalities.

Good luck on your hunt for an ECU. Do you need 2 for your 2 projects?

[autocad]

So do you benfit from the lack of self dignosis???

LPG is cheaper because of less tax. Compared to Petrol LPG produces almost no emissions so every car converted takes the government closer to its co2 reduction target, they will also give you a 50% grant toward the cost of conversion. I spend a lot of time in Holland where gas is only 35 euro cents/litre (so its Nederlands not Deutschland). So few people use LPG it is still a lot cheaper, but you are right as has happened with diesel the prices will even out.

Petrol tax and what do we get for it ……………………Speed cameras of course! Grrrrrrrrrrrrrrrrr!!!

I ran LPG in a Peugeot 205 GTI for a year, mid range was better but pick up and top end was a bit slow! This was using a conventional vaporiser with an emulators on the injectors switchable from the car. Its not a very sophisticated system. It bleeds gas through at an almost constant rate so runs rich at slow revs and week at high. Hence the performance profile. Fuel consumption was slightly less but not significantly.

The only problem i can see with Turbo charging LPG is that it can back fire, when it does its strong enough to blow the flap out of the flow meter.

It only happened twice, both on a hot day standing in traffic. Unfortunately it was at the airport. Imagine a very very loud bang at an international airport with a terrorism paranoia, If you think UK police don’t carry guns I can assure you they do, shiny black carbine rifles!

LPG injection may get rid of this problem, to be honest I don’t know enough about it.