Rover V8 MegaSquirt P38 4.6 – extraEfi – 2

I’ve been working on the Megasquirt ECU for my 4.6 P38 Rover V8. Progress has been slow, partly because it’s summer but mostly because everything I do seems to get double and triple checked.

If you’re fitting a Rover V8 to a Land Rover, you’re in luck with several suppliers making parts, but if your car is something unusual, then most parts will need fabricating from scratch.

Surprisingly, given the amount of Megasquirt information on forums and in manuals, finding part numbers can be very time consuming.

Suppliers are understandably secretive of part numbers, thread sizes, tube diameters and wire sizes. Many offer different solutions, that might not be inter-changeable or cross-compatible. Finding just one tiny piece of info can be several evenings research, often with numerous answers. Narrowing down possible solutions, often involves purchasing similar parts, measuring and experimenting.

Rover V8 P38 Extra Air Valve & Manifold Air Temperature  Tube

I welded up a steel tube to mount the Manifold Air Temperature Sensor (MAT or ATS) with a 19mm outlet to the Bosch PWM Extra Air Valve (EAV).

For more info on these:

Rover V8 Megasquirt MAT tube

This tube needed a few tweaks and modifications to get everything to sit right. At the moment it’s just aerosol black but when finished, will be powder coated. The bracket mounts to the front of the passenger cylinder head, with an extra tab holding the Extra Air Valve. There’s a 20° bend to keep the tube under the bonnet. All of the threaded collars and hose outlets are all available on ebay for less than a couple £.

Rover V8 P38 megasquirt

The large tube is rock solid, but the Extra Air valve despite being held on it’s original front mount and by short rigid silicon hoses will get an additional bracket (just in case). 

As can be seen in the above shot, I’ve milled off the Land Rover Logo from the top of the plenum and machined flat the front face to take a right angled 19mm hose outlet.

Wiring loom

What’s hard to see is the wiring loom and that has taken quite some time. I’ve tried to keep all sensor wires in separate looms from injector and ignition wires. All sensor wires are twisted into pairs to create mutual inductance. This should hopefully help keep sensor signals clean and spike free.

Wires that run close to the block are passed through Braided Fire Sleeve, then through split conduit tube and finally wrapped in low adhesive wiring tape. The reason for the heat reflective sleeve is not just to protect the wires but also to reflect heat. As wires heat up, the resistance changes, although small this can cause fluctuations in sensor voltages, creating false readings.

Braided Fire SleeveSplit Conduit Tube

Each loom is held to the block with rubber insulated stainless P-clips. Where possible, I’ve tried to keep 20mm between injector/ignition looms and the noise susceptible sensor looms.

In the bottom right of the shot below, you can just see the sensor wire pairs are twisted together. It makes the loom much more bulky, but hopefully I’ll have less electrical noise and interference on those signals.

Rover V8 P38 Megasquirt Wiring Loom

Manifold Air Pressure (MAP) Hose

I’ve also drilled and tapped the base of the Inlet plenum to take a barbed stainless 1/8 BSP 3mm diameter hose tail. I used a 11/32″ Drill. On the driver’s side, there’s already one breather hose and 2 spare blanks in the casting. I drilled out and tapped the centre one.  Make sure you drill high enough for the new hole to clear the base inside. 

I also had a similar brass hosetail, but it wasn’t as long and the barbs were less defined. With the brass hosetail it was possible to ease the hose off with considerably less force.

Barbed Hose tail

To this hosetail, I fitted some 3.2mm I.D. 7mm O.D. thick wall silicone hose. Once on, the pipe is very hard to get off and realistically needs to be cut off.

After reading various forums where people had numerous problems allegedly linked to cheap thin wall MAP sensor hose that basically collapsed when hot or as it aged, I decided to go for thick wall silicone tubing. I chose silicone over rubber as it has better heat resistance. Silicone does not stretch or deform so well over barbs and fittings as rubber but, given the trouble I had removing the hose, I figured it was probably airtight. If I do have issues it would be easy to fit 7mm Spring band hose clamps. None of the factory fitted rubber breather hoses had hose clamps, so hopefully I’ll be OK without.

Rover V8 Megasquirt MAP vacuum hose

The plenum on my P38 Rover 4.6 wasn’t bonded to plenum base plate and there were no signs that it ever had been. However, I also have a couple other professionally tuned 3.5 units, where the top plenum was sealed to the base with blue hylomar type sealant.

The hard bit will be wiring up the 37 way D-type into the Megasquirt ECU. Where I’ve used Earth Star points, and individual wires to all injectors, there’s an awful lot of wires trying to go into a small space. The loom is 1″ in diameter.


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