Project EXI

The building of a Marlin 5EXi kit car, using a Seat Leon 1.8T 20v Donor

Frequently asked Questions

Project 5EXi - Questions and Answers

Q: Tacho fitting?
A: My taco isn't working
You may find that fitting a 3rd party after market taco does not work with your ECU. One solution is to create a current sink circuit. Ensure you have the correct pin on the ECU, for me this was 132/37 If you have access to an oscilloscope then I suggest you use that to check you are getting the correct signal from the ECU. If this fails, then you may need to connect to the coils, you can use 2 diodes with a zener diode and resistor. Support for this is not provided here.

Q: Injector coils?
A: Is the supposed to be a rubber o-ring around the injector coil packs?
Yes there is, but they are not fitted to most VAG engines. Im not too sure if they are fitted in the factory either. Most VAG mechanics I have spoken too do not fit them as part of normal servicing rotuines.
I would advise that you do fit them, as the cam cover is exposed on the 5EXi as it is directly below the rear bodywork mesh.
If you dont fit them, you may find your spark plugs housing filled with water if it rains. For the sake of £ get the o-rings from a Main dealer.

Q: Handbrake ?
A: What handbrake cable do I need?
The donor handbrake cable should be fine. You may find it a little long, but you can cut it to length as long as you re-mount the end "nipple" correctly.
Cut the cable to length, and with a small round brass bar, drill a hole the same diameter as the cable.
On one side enlarge the hole, to halfway depth
Untwist the cable, and fan out the splayed ends.
Fill the hole with solder so the splayed end of the cable is soldered in.
Heat the solder until it "floods" and bonds with the cable and brass housing.

Q: Vehicle starting?
A: Is there a proceedure I need to go through whe I first start up the VAG engine?
Yes, If you have had your ECU disconnected it may of lost all of itsl earnt values. To run efficently the ECU needs to re-learn how to control the engine and sensors.
1 - With everything turned off, turn the ingition on, but do not start the engine. LEave it for 5 minutes. 2 - Start the engine, and let it idle until coolant reaches at least 80C
3 - Apply at least 3,500rpm
4 - The engine should be responive throughout the rev range. If its not, check all sensors, pay attention to the MAF sensor on the Airbox, if you have a mid range misfire.

Q: Lighting connectors?
A: The rear lamps provided by Marlin are multi connectors, what pin does what?
Indicators - Pin 1 GND
Pin 2 Indicator +
Stop Tail - Pin 1 Stop Lamp
Pin 2 GND
Pin 3 Tail Lamp

Q: Swirl pot?
A: The Marlin supplied swirl pot fits into the space behind the rear bulkhead. Mount it to the rear subframe support member and the rear bulkhead. The tabs are small, so use an M4 rivnut and bolt on the top, and a button head M6 bolt on the rear panel.
Working down from top to bottom, fit the connections as follows.
Top Return feed to fuel tank.
Top-1 Return feed from HP fuel pump
Bottom+1 Feed in from LP pump
Bottom HP pump take off

Q: What Fuel pipe??
A: You will need 10mm rubber fuel pipe with 17mm clips, and a shorter length of 8mm fuel pipe.
Use the 8mm copper tube and route it around the drivers outside.

Q: Rear Drive plates??
A: You will need to modify your VAG front drive plates to fit on the rear, particulary if you are using rear VAG calipers and brake discs, the drive plate is 127mm diameter, this needs to be machined down to 124.5mm to accept the standard rear discs from the donor. Best results are acheived on a metal working lathe, to maintain optimum balance.
Once machined, get the rover rear bearing pressed home cleanly with a hydraluic press, mine took in excess of 5 tonnes of pressure to push home. Some others have acheived results, with a hammer. Once home press the modified drive plate into the center of the bearing

Q: Suspension spacers??
A: You will need to fabricate your own suspension spacers. These need to be made with a 1/2" bore, and be made to the correct length to ensure that the damper is 90degress to lower wishbone. The need to make contact with the rose bearing. The best material would be 316 Stainless steel, but also nylon solid bar may work just as well.

Q: Do the gaps between the top and bottom of the Dampers needs spacing??
A: Yes, make your own spaces 12.55mm Internal diameter, 14-15mm OD, to ensure the damper is 90 degrees to the wishbone.

Q: The VAG system uses two lambda sensors.?
A: The VAG has two lambda sensors, one before the CAT and one after that CAT. The one before the CAT is used to control the engine mixture, and directly affects the ECU. The one after is used to monitor only, and is there as a driver aid. The Post CAT sensor is not used on the Marlin

Q: VAG Driveshafts interface with Rover bearing on the Rear Hub??
A: Yes, the VAG hub needs modifying to fit into the Rover/Honda Hub, send of to Marlin for modificaiton.

Q: Accelarator mounting bracket, confirm homemade suitability. Side panel modification required.?
A: Home brew is fine but better solution. Marlin will modify pedal box to change mounting bracket, and support fixing of pedal. Mark to supply a new mock up, use my existing pedals, and retro fit. Me to create new side panel drawing to allow full pedal box access, once new pedal assembly provided.

Q: Master cylinders, top need to be below bottom of fluid house to avoid airlocks in feed tubes. Current fluid reservious stick up above chassis?
A: Yes yo bleed brakes/clutch, once bleed As long as fluid level does not drop below top of cylinders should be fine. There mount reserviour with removal fixings

Q: Master cylinders, ok to space away (with washers/nuts) from bulkhead or cut actuator thread length??
A: Use spaces, allows greater flexibity for any future tweaks. Bolt with M8 bolts and custom spaces.

Q: Engine hose replacements - Blue silicone ok for as new status??
A: Any colour is fine, blue is ok i

Q: Fuel tank does it need any additional Rubber support mounting??
A: Yes, good idea to prevent tank damage. Particulary at tank bottom.

Q: Front free spindles, mount from inside or outside front uprights, if outside safe to modify them to fit flush, remove ABS sensor hole (area)?
A: Fit from Inside, If you loose a bolt, the wheel wont fall off, no need to modify

Q: Radiator GRD1071 fitting in hole size 720mm?? How to??
A: Fit intercooler, Golf intercooler will fit accross gap, mount radiator on intercooler.

Q: Considering mounting fuses and relays on thin plywood, for ease of construction (ouside of car) and service.?
A: Mount it on an aluminium sheet, then mount that to the front bulkhead

Q: Intercooler side pipes, take into account doors are fitted.?
A: Twist the intercooler pipes to below the door level

Q: Fuel pumps, which is the HP? which is the LP? HP at front or back??
A: Gold one is a LP and goes at the front, photos to follow

Q: Clutch and brake pedal switch to ECU? When clutch is depressed the ECU backs of engine revs, is this required? When the brake pedal is applied, if the throttle sensor is giving a constant reading, the engine revs are backed off, is this needed? Both will affect the wiring loom.?
A: Dont connect it for now, but highlight it in wiring documentation, as to a user option

Q: Acitvated charcol canister, do we need it??
A: Nope bin that as well

Q: Secondary air on the APP donor engine??
A: Dont need the Secondary air pump, remove it, the ECU needs modding to tell it there is no 2nd Air pump.

Q: What Intercooler do I need??
A: from Golf 1.9 / 2.0 TDI 10/03 onwards size 615x407x31 OE# 1K0 145 803A, £ 145 inc VAT and delivery from

Q: Air intake into throttle housing is round the other way on Race Car pic, than on APP engine, will affect intercooler pipework setup.?
A: No, use different silicone hoses, to make the air flow down the passenger side through the intercooler and return on the drivers side and directly into the throttle housing.

Q: My Steering rack seems to short?
A: Get the Marlin supplied steering rack extension parts.