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Why We Don't Use the Bosch ECM with Our Discovery 2 LS Conversions

Land Rover Discovery LS V8 Swap
One of our Discovery LS Swaps with a GM 5.3L V8. The GM ECM is in the upper left corner against the firewall.

This is a question that I get occasionally. We don’t use the factory Land Rover Bosch ECM to run the LS engine. We use the GM LS ECM. I figured that the best way to explain our reasoning for this is to explain how using the Bosch ECM to run the LS would work. This setup basically wraps the LS with all the sensors of the Bosch 4.0/4.6 setup. Here it is broken down by major alteration:

  • Crankshaft Position Sensor – The Rover has a different pattern and number of teeth on the crankshaft reluctor wheel than the Gen 3 LS engines. Gen 3 LS engines came with the reluctor wheel mounted directly to the crankshaft. The reluctor wheel is also unfortunately clocked differently on the Bosch Land Rover setup than it is on any GM products. To use the Bosch ECU with a Gen 3 LS, you would have to pull the crank, weld on the correct reluctor wheel, with the blank spot in the correct place and (maybe) rebalance the crank. After going to this much trouble, you might as well rebuild the LS, since the entire bottom end has to come apart to install the correct reluctor wheel. This problem is avoided in our kit using our electrical conversion parts.

  • Firing Order — The Land Rover 4.0/4.6 uses the classic GM firing order that is different from the LS. The LS has a 4-7 and 2-3 swap from the classic order. The Land Rover ECM is virtually un-modifiable and the firing order cannot be changed in the ECM – it is a fundamental part of the programing in the Motronic. Therefore, the only way to change the firing order of the LS is to have custom camshaft made so that it runs on the older firing order. This is expensive because it requires a completely custom grind. During a discussion with a cam manufacturer, the cost for this cam is over $700 (more than the price of many used LS engines!). You lose the LS efficiency advantage of the improved firing order. Furthermore, to do the cam right on the LS, you are also going to need to replace the lifters, which means the heads are going to be coming off – time to rebuild the top half too! Our kit uses the factory LS firing order, so no changes are needed here.

  • Camshaft Position Sensor – The Gen 3 LS uses a 1x cam position sensor setup. The Rover uses a 4x setup. The sensor outputs are similar however. You have to switch the Gen 3 LS over to a 4x setup. This will require a new front cover and timing gear. The front cover used could be the unit from a Gen 4 LS which has a similar 4x setup. The timing gear from the Gen 4 LS may be able to be be used, but the clocking is probably slightly different between the Gen 4 LS and Motronic setups.

  • Idle Air Control Valve/Throttle Body – The GM throttle body and idle air control valve setup is not compatible with the Bosch setup. Therefore, you will need to use the Bosch throttle body positioned on the front of the LS intake manifold with a custom adapter. You will also need to use the Bosch IAC valve to control idle air flow metering. It would have to go from the intake manifold on one side to the air intake tube on the other.

  • Knock Sensors – These must be in the same position as the Rover – on the side of the block – to work with the Motronic engine tune. The Gen 3 LS has these sensors in the valley between the heads. It would be best to use the Rover sensors bolted between the middle two cylinders on each side of the block, essentially emulating the Rover engine.

  • Coils/Ignition – The unreliable Land Rover coils would need to be used with the spark plug wires routed to the correct LS spark plugs. The LS coil per plug setup would be discarded, which is unfortunate.

  • Injectors - The Rover uses an EV1 injector plug. They make conversion parts to go from the LS injector (both of the main types) to EV1 Bosch for under $20. If the resistance is an issue, then switching injectors would be an option (unlikely to be a problem I think).

  • Purge Valve / Secondary Air Injection - The Rover purge value routed to LS intake manifold for vacuum. The Rover secondary air injection would have to be added back if present. This would mean needing to hook up vacuum line to the intake manifold, and the vent would have to be routed out through the exhaust. The O2 sensors front/rear would need to be left as they were in the Rover setup.

  • Wiring Harness - Some wires would likely need to be rerouted, extended, shortened, etc. However, generally all the sensors that came off the Rover would have to go back on the LS.

If you made it through reading all of that, you probably understand why we use GM electronics. By the time you add of the price of basically rebuilding the engine (the new crank trigger wheel plus new camshaft plus new front cover plus time to put it all together – not even including all the little custom brackets, etc), you end up with an engine that runs on the Bosch Motronic. However, you are stuck with the Motronic tune that is not optimized for the LS engine (and most tuners won't touch it). That also means you are stuck with the sub-optimal Rover tuning (including its excessive ignition advance and overactive misfire diagnostics) and can’t get all the power or efficiency out of the engine.

For the overall cost and time outlay of this, you could have a really nice rebuilt LS and a couple thousand more for "toys" using our GM ECM setup. And with the Bosch ECU setup who knows if your average mechanic could diagnose a problem – the engine is a hybrid of half Land Rover and half GM parts. You wouldn't be exactly running to the parts store to get some things because of all the custom internals and Land Rover externals like sensors and coil packs. There is also no way use a factory-built or rebuilt LS motor because of the internal modification requirements – so no going to a junkyard and plucking a used engine to use in the Discovery. A bunch of the advantages of the LS are gone...

The GM Gen 3 ECM is happy to work with our electronics to keep the other factory features of the Land Rover Discovery 2 running, but also is easy to setup and tune the way you want it. While one of the downsides of using the GM ECM is that there are slightly more wires in the engine bay (and its really only like 5% more than factory), we really think this is a small price to pay for gaining easy tuning, significantly more power, and aftermarket parts options. For the same price as all that internal engine modification, there are a lot of great mods you could do to an LS to get better reliability and performance. Looking forward as well, there is no way the Bosch system could be adapted to other transmission options or diesels. You also don't get some of the more 'fun' features of tuning the GM ECM setup that I'll be talking about in a later blog.

Although the hybrid setup is feasible – we definitely think using the LS ECM is the best and most cost effective option.

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