How to: mk2 carburettor to injection conversion

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mr.brown
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How to: mk2 carburettor to injection conversion

Post by mr.brown » Thu Dec 10, 2015 8:45 pm

I'm sure lots has been written on the subject in various places but I'm starting this thread to post my own ideas - and yours hopefully. I'll edit this thread and add in diagrams/pictures as I go.

So, where to begin? For starters all Scirocco carburettored engines have mechanical fuel pumps attached to the front of the engine block that effectively suck fuel to the carb. The fuel supply and return lines enter through the fuel level sender unit at the top of the fuel tank (found under the rear seat base). The picture below is from a mk1 Golf but you get the idea..
g1fueltankcarb.jpg
For the injected equivalents though, it's a whole 'nother ball game (pictured below). Instead of a sender in the top of the tank, there is a combined sender and "lift pump" unit that pumps fuel out of the tank. The pump supplies a plastic fuel reservoir (19) that sits on the side of the tank - this also has a filter in it. This reservoir also acts as a swirl pot, feeding the main in-line pump (36) which then feeds the accumulator (35). The fuel return line (2) from the engine bay also goes into this reservoir and another line (7) goes from it back to the tank.
Screen Shot .png
As far as conversion goes, the easiest thing is obviously not to bother - just sell up and buy an injection! Realistically though, the supply of carb vs injection cars seems to be 10-1 at times so converting will often be the only option.

Second easiest thing then, get all the relevant parts off a donor car and copy the set-up? Again, not very realistic these days - see my point above about the supply of injected Sciroccos. That said, don't forget that 84-on mk1 Cabriolet GTI/Rivage have all the same parts as a later injected mk2. That enlarges the donor pool somewhat.

My personal thoughts are that the standard late mk2 injection is pretty complicated and the parts are pretty hard to get hold of. Besides which, If you are looking to switch to injection from carb, the chances are you'll be fitting a much more modern engine, e.g. 1.8T - so at least some of the original system can be ditched. This is what I'm going to concentrate on.

The first item on your shopping list will be the lift pump/sender unit. UK ebay prices seem to be ridiculous but they can be found for a lot less on Germany ebay. It also turns out that, with VW being fans of parts sharing across models, the VW Polo, from around 1991-94 had an identical lift pump/sender set up.

(Examples of the price difference - UK ebay Scirocco/mk1 Cabriolet £150(!!), German ebay £50 delivered, Polo unit £29 delivered)

Pictured below is Scirocco vs Polo lift pumps - pretty much identical as you can see.
IMG_0096.jpg
The Polo uses the same fuel reservoir as the Scirocco (part 19 above) but instead of going round the houses with all sorts of additional crap it has a very compact assembly consisting of reservoir, main pump (a BMW item here in blue) and main filter - all conveniently mounted on a "carrier plate". The blue line here is the supply line from the lift-pump.
DSC00390_2.jpg

As you can imagine, even these parts are becoming "rare" so another option is using a mk3 Golf fuel filter carrier. This can be bolted to the chassis and an in-line pump attached (along with reservoir) as pictured below. Here you see the reservoir supplying the (foam wrapped) main pump which then supplies the filter.
g1-2swirlpot.jpg
tbc
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Re: Late mk2 carburettor to injection conversion

Post by mark1gls » Thu Dec 10, 2015 10:24 pm

Good thread this and I expect there will be a few people interested in this. I've seen the polo lift pump fitted to a couple of golfs which have been converted to injection, you can have a problem with the electrical connector as it faces upwards instead of sideways like the scirocco/golf lift pump, You need to modify the electrical plug so it's angled or you won't be able to fit the black cover plate back on under the back seat.


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Re: Late mk2 carburettor to injection conversion

Post by mr.brown » Fri Dec 11, 2015 12:37 am

In addition to the above, there are several "all in one" units found on mk2 Golfs + Corrados. These also take a feed from the lift pump to supply a reservoir but in this case the main pump actually sits in this reservoir - Digifant version below does away with the accumulator
digipump.JPG
The issue with these units is size, there can simply be lack of space under the car - unless you get creative. Also, finding an uncracked one can be difficult and expensive.

I did also toy with modifying the tank to accept a later mk4 unit - which is truly an all-in-one - but as you can see, it's a tad too large.
IMG_0097.jpg
If the idea of modifying the tank doesn't phase you, you might be interested in this thread where someone has fitted a BMW pump with custom swirl pot

http://www.autostadt.ie/phpbb3/viewtopi ... 98#p155598
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Re: Late mk2 carburettor to injection conversion

Post by mr.brown » Fri Dec 11, 2015 11:50 am

mark1gls wrote:...you can have a problem with the electrical connector as it faces upwards instead of sideways like the scirocco/golf lift pump, You need to modify the electrical plug so it's angled or you won't be able to fit the black cover plate back on under the back seat.
Thanks for pointing that out Mark - hopefully there'll be a simple solution out there. Wiring in the pumps is the next step in the game - and I need to do some more research..



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Re: How to: mk2 carburettor to injection conversion

Post by MikeH » Fri Dec 11, 2015 3:19 pm

Or you could just buy the car you want, rather than building a car you can buy....

Anyway... I've heard of people using Mk3 golf in tank pumps on a Mk2 golf, but they probably won't fit in the scirocco tank, as the opening is smaller. In any case they probably don't have enough pressure for a KJet system, although they would work for an EFI setup.

The polo lift pump assembly looks shorter in the pic - might just be the angle, but have you measured it? You really want it close to the bottom of the tank to make use of the capacity, and avoid running the pump dry. If you wanted an inside setup, then the Mk2 golf one could work in the spare wheel well, (I'd want to seal it off from the passenger compartment in case of leaks) although from memory I don't think there's enough room under the car to package it close to the tank outlet.

Digifant and other EFI systems don't need an accumulator because they have a fuel pressure regulator on the end of the fuel rail to keep residual pressure in the system. Again, this would be fine for EFI but not ideal for Kjet.


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Re: How to: mk2 carburettor to injection conversion

Post by mr.brown » Fri Dec 11, 2015 4:56 pm

MikeH wrote:Or you could just buy the car you want, rather than building a car you can buy....
Which is exactly what I said in my post :vcool:

Back to the point, I think the mk3 pump sits somewhere in size between the mk4 unit above and the Scirocco/Polo unit. It's on my list of "things to get if i can get it cheap/free".

The Scirocco and Polo pumps pictured are identical - size and part numbers.

I've also got a Polo "carrier plate" on the way - I'm going to see if that can be jammed in somewhere underneath.



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Re: How to: mk2 carburettor to injection conversion

Post by unknownmale » Fri Dec 11, 2015 5:33 pm

Is it not possible to just add an inline fuel pump or do you have to have a lift pump inside the tank too?


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Re: How to: mk2 carburettor to injection conversion

Post by bengould » Sat Dec 12, 2015 11:04 am

You 'can' run just an inline pump, but it is not recommended.

I had my 20vt set up like this for a week, it didn't like it at all. It would starve the pump of fuel when cornering, accelerating, braking, going up/down hills. This causes the engine to run extremely lean which is really not good for your engine.

I put the lift pump from an injection car in and it was much better, but still struggled on long bends and roundabouts. Put a large (about 2 liter) swirl pot in and it now never starves the main pump.

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Re: How to: mk2 carburettor to injection conversion

Post by unknownmale » Sat Dec 12, 2015 7:10 pm

I was thinking of blocking off my mechanical fuel pump and just fitting an inline one with a reg, but assuming i'd have the same issue as running the MFI set up? Or is this just because the system requires pressure?


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Re: How to: mk2 carburettor to injection conversion

Post by bengould » Sun Dec 13, 2015 1:01 am

You would probably be ok doing this. The mechanical pump doesn't mind running dry as much as an electric one, also your carb has float chambers and a small swirl pot to help even out the fuel flow. But to be honest I can't see any advantage to doing it. Before I changed my engine I had a Weber carb and 285° cam with the fueling adjusted to suit and never had any issues with the mechanical pump.

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Re: How to: mk2 carburettor to injection conversion

Post by james butler » Mon Dec 14, 2015 4:59 am

mr.brown wrote:
MikeH wrote:Or you could just buy the car you want, rather than building a car you can buy....
Back to the point, I think the mk3 pump sits somewhere in size between the mk4 unit above and the Scirocco/Polo unit. It's on my list of "things to get if i can get it cheap/free".
thats funny i was just talking to TimR about this as i have a mk3 tank with pump for his mk2 golf to "upgrade" it.
i dont know if it is a myth but it seems a common mod to swap the whole tank with fuel pump.
i tried to make the plastic tank fit the crusty rusty rocket but it simply wont go in as its totally the wrong shape and would have resulted in cutting into the structural parts of the floor which was a no no for me.

that said i was really shocked how cheap custom alloy tanks are and wouldnt be suprised if the mk3 or even mk4 fuel pump gubbins could be incorporated into it.
http://www.alloyracingfabrications.com/ ... ersal.html


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Re: How to: mk2 carburettor to injection conversion

Post by Nate » Thu Sep 08, 2016 11:38 am

bengould wrote:You 'can' run just an inline pump, but it is not recommended.

I had my 20vt set up like this for a week, it didn't like it at all. It would starve the pump of fuel when cornering, accelerating, braking, going up/down hills. This causes the engine to run extremely lean which is really not good for your engine.

I put the lift pump from an injection car in and it was much better, but still struggled on long bends and roundabouts. Put a large (about 2 liter) swirl pot in and it now never starves the main pump.

Ben.
I ran an inline pump from a 3 series on my last mk2, feeding a 2E from a passat. I had no fuel starvation problems at all, but then I do tend to keep my tank full rather than always running on fumes. Planning to do the same on the mk1 and probably on the current mk2 if I can find another 2E going cheap


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Re: How to: mk2 carburettor to injection conversion

Post by Scalatron » Thu Oct 06, 2016 5:13 pm

Most people convert injection to carb but... best thing is to get a rotten donor car and swap the fuel tank, cylinder head, radiator etc over. Personally I think I'd go down the Megasquirt route as K-Jet has its limitations when getting more performance, but if you're bored it could be nice winter project.



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Re: How to: mk2 carburettor to injection conversion

Post by scrappy1382 » Thu Oct 06, 2016 6:08 pm

Scalatron wrote: Personally I think I'd go down the Megasquirt route as K-Jet has its limitations when getting more performance.
i agree to disagree on this one...
with the right knowledge you can get around the 150 - 165 bhp from a k-jet system. ok, there is alot of work needed, but it is possible. 2e bottom end, 421 downpipe p&p head, performance cam, blar blar blar.

cost wise - if your not on a budget, there are many options, most people now tend to be doing the 20vt conversions. i recently brought one already built, and like the more reliable / modern engine in a classic shell. ( nice sleeper car ) keeps up with todays cars with ease.
if you are on a budget - 2.0ltr 16v abf engine . catch 22 as its now an old engine, if your gonna go down this route , a rebuild would ideally be needed. tbh any engine over the 120k is a gamble.

but its personal preference...


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Re: How to: mk2 carburettor to injection conversion

Post by Scalatron » Thu Oct 06, 2016 7:42 pm

I was thinking of a bit higher than 150 odd BHP, more like 200BHP. Forced induction is good fun but I really don't think K-Jet would be able to supply the fuel for a 200+ engine. It does depend on money, another old school way is to use a 2.0 ABF with twin Dells for around 170BHP with KR cams and a great sound.