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 Subaru Conversion Information Resource Navigation Bar - over 160 pages of info on Subaru powered VW’s! :


Do you have a problem with a Subaru conversion? If so, the following FAQ’s detail some problems people have encountered, their symptoms, and how to fix them:

Q1.  Do you have a conversion with which will not run properly from cold, rather like trying to start a car with a manual choke with the choke in? Typical symptoms include stalling, running rough and having to restart a few times until some heat builds up on cold days, and the symptoms go away completely when the engine is warm/

Q2.  Do you have a misfire, probably intermittent, which probably starts out slight, but gets worse, affecting more than one cylinder, until the vehicle is undriveable, on either a naturally aspirated Subaru engine, or a turbo with a single coil pack? The getting worse part may take a long time, and it may well be worse in the wet, and triggers no error codes.

Q3.   You have installed your conversion which has a transponder key immobiliser system, and know for absolute certain that it has a matched set of immobiliser components, yet the system remains immobilised no matter what you do.

Q4.   You have a harness converted by RJES and find that your low speed radiator fan is on when the engine is cold.

Q5.   You are having trouble filling the coolant system

Q6.   Your starter motor does not turn when you turn the key

Q7.  Your conversion is difficult to start, most noticeable when the engine is hot

Q8.  Your conversion backfires / missfires, much worse at idle













A1.  You probably don’t have the wire to the starter solenoid blade terminal connected. If so, there is probably nothing wrong with your engine or it’s management system. This is almost certainly an omission by whoever installed the conversion. This wire sends a signal to the ECU that the starter has been operated, which puts the engine into cold start mode. Cold start mode basically does the same job as a manual choke on a carburetted car, richening the mixture and increasing the idle speed until it is warm. Reconnecting this wire gets rid of all the symptoms. If your wire is missing need to know which wire needs reconnecting, please get in touch, as it depends what ECU spec you have.
   There seem to be plenty of conversions in the UK which have this wire missing. Non of the harnesses with this wire missing were converted by RJES, as we have a policy of retaining every possible Subaru engine management function. However, it seems that not all UK converters are so meticulous. There seems to be one out there who follow a policy of ‘if we don’t know what this wire does we’ll cut it off any way’, or similar. We have now fixed, or helped the owners to fix 7 conversions suffering from this problem. On investigation not only is the wire disconnected - it’s not even there at all, cut off at the ECU, and sometimes with not enough wire left to re-solder to


   In the interests of preventing such poor workmanship ruining people’s enjoyment of their converted VW, and the possibility of Subaru conversions getting a bad name as a result, here are the details of how to fix it. The ECU’s used by the culprits (you know who you are - raise your game and do the job properly - I’m even showing you how) are usually the 1990 - 1995 Legacy ‘4 plug’ type, as pictured above). To fix the cold start problem, simply connect a wire between B56:10 and the 1/4” spade terminal on your starter motor.


A2.   This is probably a coil pack or ignition module failure. All EJ series injected Subaru engines have a distributorless ‘wasted spark’ ignition system. Failure of the ignition module (basically a small black box made by Hitachi, containing power transistors which fire the coils - doing the job of points on an older car) causes no error codes, and can affect either an opposite pair of cylinders, or all of them. Failure of the coil pack is most likely to actually be a failure of one of the coils in the coil pack. Each fires two opposite cylinder simultaneously, so a failure here is likely to affect two cylinders only. 


Coil Pack

Coil Pack

Ignition Module

Ignition Module

   A near identical system was fitted to most mid ‘80’s to mid - late ‘90’s VW’s (including the injected T25’s), made by Bosch. These fail with near identical symptoms. The Hitachi and Bosch ignition modules are not interchangeable, despite looking almost identical, as they have different plugs.
   Note that from MY00 --> Subaru combined the function of the ignition module and the coil packs into one unit. Failure modes are likely to be identical on the later models.



A3.   The communication between the transponder chip and the key is magnetic, and as such can be affected by ferrous materials or magnets in close proximity. If there is anything ferrous or magnetic near the transponder, remove it and try again.


A4.   Please check whether any of the relays in you harness are the ‘normally closed’ type (see below).
nc-no_relays   Having recently discovered that some Subaru relays are normally closed (normally open is very much more common), I’m pretty certain that I have used the normally closed type where a normally open type is required in the low speed fan application by mistake in two harnesses in the past. I have no way of telling whose harnesses these were. If your low speed fan is on when it should be off, then one of the harnesses with the incorrect relay is probably yours.
   Please check the relays to see if one is the normally closed type, as shown here.. Note the different connector orientation in the picture below. If it is, please get in touch, and I’ll send you a replacement relay, connector, and full instructions. Apologies for any inconvenience or confusion.





A5.   Please read and follow our filling procedure. This circuit is not difficult to fill - probably easier than the standard VW system. It needs no extra bleed points adding, but you will probably struggle if you are not following the procedure.
   We regret that we can not answer questions and help with coolant circuits other than the on described on pages ‘general schematic’ and ‘T25 Pipe Layouts’.


A6.   The starter motor circuit is not modified as part of a Subaru conversion. If the starter does not work after installing a conversion, then you have one of the following problems:

  • Flat battery. Sometimes the starter solenoid clicks repeatedly if the battery is too flat to crank the engine.
  • Loose / dirty / corroded connection. Check the voltage between the M8 stud on the starter motor and the engine block. Less than 11V isn’t ideal.
  • Missing / corroded gearbox earth strap. These can easily be missed out by accident if you’ve had the gearbox out. Fitting a new earth strap is highly recommended as part of your conversion anyway.
  • Disconnected starter solenoid spade terminal

A7.   The fuel rail may not be remaining pressurised when the engine is turned off. This allows vapour lock to occur, which gives the difficult hot starting symptoms. The pressure is retained by the fuel pressure regulator and the non return valve in the fuel pump, one of which is not working properly if your fuel rail does not stay pressurised.

A8.   Check for induction leaks. Most often they are caused by not having reconnected a hose, quite often despite the installer being convinced they have reconnected everything. The brake servo hose is a common one to miss. Block it off on a VW with no servo. If you think you have identified a small leak, spray the area with a little bit of something like carburettor cleaner with the engine running. If the revs pick up, the leak is confirmed.

 Inventors of the Subaru - VW conversion bell housing using Subaru flywheel, clutch and starter

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