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So this issue of EFIing an old M10 motor comes up repeatedly from time to time and so I thought I could bring my thoughts about this together. I don’t know if there’s already a blog entry or write-up, so… sorry if repeating. Please feel free to add all your info, opinions and experience to make this a helpful content for later readers!

Talking about the reasons for EFI doesn’t make sense here I think. Let the pros-and-cons discussion take place somewhere else.


Fuel supply

(This does not affect tiis with an intact system)



What kind of injection ever shall be installed, in any case you will need fuel supply. A 12 Volt electric fuel pump that provides a pressure of 2-3 bar (31-43.5psi) has to go into the car. I guess a lot of pumps will do this since various systems work with pressures in this range. You should find a good 2nd hand pump somewhere, so buying new isn’t the only option. Check for correct voltage, pressure, junction diameters and where to get connectors. Tii pumps have a delivery rate of 120ltr/hr and 1,5-2 bar pressure as the German manual says. These ones have an intake filter.

There are in-tank-pumps also. Use the search function for info about this, I haven’t seen the perfect solution yet. Be aware of the different heights the 2002 tanks have when looking for an in-tank. I prefer an out-of-tank pump because of better access and less fuel mess if to address.


Here are sending units. Left: roundies 46ltr.. 200mm. Middle: squaries 50ltr., 225mm. Right: tourings 51ltr/turbos 70ltr., 290mm.




The other ones are all mounted on the underside of the car as far as I have seen. You may install a tii or other fuel pump at the same spot where tiis have them from factory. Don’t choose an in-trunk-mounting. Some versions of foreign brands will require custom installation by fabricating brackets or clamps. Care for elastic elements to the body for noise reduction. Don’t forget an expansion barrel not too far away from the pump to smooth out flow and pressure impulses. Check if your pump has an integrated filter in the intake, otherwise install an in-line-filter before.


Feed line:

The next step is the feed line. Tiis and -seemingly- all US-squaries have a metal tube leading from the left rear axle mount to the front end of the left frame rail below the battery. 73+ euro automatics have this, too. For tiis this is the feed line from the tank to the filter next to the radiator, for the carbed cars it’s the return line from the carburetor to the tank. The plastic line in the cabin is return for the tiis and feed for the carbureted. Check this one for usability anyway, it will carry some remaining pressure later. In case of doubt: renew. Do not install another plastic line parallel! Fuel pressure lines belong under the car.

Cars that don’t have the metal tube from factory can be equipped with this (tii-) version but do not trust 50-year old material. Buy this new, the risk of losing gas through a leaky tube isn’t worth saving some $. Plan a fine filter at the engine end of the feed line. I relocated mine underneath the battery because there’s not so much heat from the radiator.



The fuel pump sucks gas out of the fuel tank. Tiis have a separate pickup unit including return next to the sending unit for the gauge cluster. In these cases, the sending unit doesn’t have a pickup but just the electric junctions of the sender.

You may now find and install a tii fuel tank with pickup together with sieve and sender. This is a pretty easy and quick solution but wait for it until your tank is empty. If you want to stick to your just freshly refurbished tank you can modify it for the tii pickup:




You may go this route as an option:




Means: Create a custom pickup (don’t forget a sieve) and using the sending unit as return. Remember the different lenghts of the sending units. Let the diameters of pump intake/filter and custom pickup match. Order new gas-resistant rubber hoses of required sizes, clamps etc.

Some squarie tanks should have a welded-in junction some similar to the one shown above, painted black. This one is not longer than its visible part and does not catch the bottom, so: useless.


To get from the inside of the trunk to the underside of the car you will have to drill holes (in a non-tii). Here’s how it is done in a rear differential support from factory:




The smaller tube is for the wires. Sorry for not sandblasting.


So here’s your route: tank pickup, holes, fuel pump and feed line. Free order of appearance. These can be done without setting the car out of order for a longer time, it will remain driveable. If there are open junctions after installation: plug blind safe as long as not needed.


Now be prepared to install a wideband oxygen sensor. Narrow bands are useless. A location for it may be in the downpipe after the junction of the two lines. After welding in the bung (it’s 18x1,5 at least for Bosch sensors), plug blind. Think about where to run the wires.

Keep in mind that the oxygen sensor will need a controller. So buy a sensor with integrated controller (expensive), an ECU with integrated controller or an extra seperate device. These sometimes have a 3-step output (cold/middle/hot) for exhaust gas temperature for an LED, maybe in the center console.


Well, this is the easier part and you will need it anyway. Now: choosing the EFI. It’s no good to look for a plug-and-play solution what simply doesn’t exist.


A. Yes, there are these 318i L-jets. To swap the entire intake seems easy indeed but:

- the 318i gets air from below and not from the side or above. It’s an updraft. There’s no space for the air flow meter and an airbox except you relocate the battery out of the engine bay. Some people don’t like this, metoo. Many custom holders, brackets etc. will be needed.

- fabricating a throttle linkage will not be done quickly. You’ll have to combine levers and cable roll.

- The RPM signal comes from #1 on the coil/dizzy. I’m not really sure if this signal coming from a dizzy with points is suitable or not. Worst scenario here: replace the camshaft including anti-clockwise dizzy by those ones of the 318i.

- last not least: the E30 intake buddha is a question of taste, of course. But in my opinion the optics of the tii runners have never been topped.


B. This Bosch LH 2.2 for Volvos.

There are some people who have done this swap successfully by using the 318i intake also. This means same part, same issues plus several modifications to the harness and more.

I went with an intake combi of 320i and tii but the required mods are still more. (didn’t get it to run)


C. Aftermarket ECU and EFI systems

These systems have their own universe. They offer the opportunity to take some kind of all-grabbing influence on your engine’s performance. Some are fuel-only, some cover ignition also. By this it should be possible to get a 76 to pass smog. If switching to another camshaft or a 4-valve head the ECU can be adjusted to these mods. Well, there is the learning curve, and it’s long: But however... Maybe you have to pay for a tuning shop.

The prices vary a lot. Think carefully about your engine hardware and if the software will be familiar with it. On the other hand, you don’t need an ECU with full sequential for a 12-cylinder.


Relay board:

You will quite probably need this. A relay board is a device for many aftermarket ECUs. It carries a main relay, a pump relay (even tiis don’t have these) and several fuses. There are omni-fit boards in the market that use high-power transistors instead of relays. I don’t have experience with these but on the pictures they look pretty tiny. Check.

Do NOT run the coil via the main relay! You will not be able to switch off the engine. I chose two small 4-fuse boxes with the same torpedo-style fuses as are in the car for symmetry. Look for space in your engine bay and think about where to locate this board.

Now you can run a 1.5mm2 (do not undersize) wire to the pump colored green/white, that’s original. You could go from the relay board through the cabin under the rear seat through one of the blind plugs for the lower seat belt bolts- if there are no belts. Look for a solid ground spot and run a brown 1,5mm2 wire for the pump to it. The ground wire for the rear defrost should be near. At this stage the car will still be driveable.


Decide: cover the ignition or not? I recommend yes. There is the chance to gain so much better torque at lower RPM that you won’t miss it if experienced once. You may start tuning fuel-only and add the ignition later but don’t buy an ECU not covering the ignition feature.

For this, you will have to have a trigger wheel. I’ve learned that a 36-1 is quite easy to handle since each gap has 5°. Which custom wheel and which sensor (hall or VR) you choose is up to you. Note: your ECU must handle your choice. Here are measurements of the tii crank pulley hub (for easier app'ing a trigger wheel) :




Note that there is a mark on the pressed-on ring that does NOT show TDC!


Inserting a very important fact here. The pairings of TDC marks of carbed engines and tiis do not match! If you have a carbed engine with a tii pulley hub in TDC the marks on pulley and chain cover will not flush. The difference is about 11 degrees. You'll have to add new marks on your own.


Don't you think all parts are the same in dimensions. I created all my injection action on a spare engine block on the table what was much more comfortable than diving in the engine bay all the time. I also installed a spare flywheel and bell housing to find exact TDC on the tii pulley I wanted to install later in ther car. The marks didn't fit. I don't know if it is about the crankshaft, the chain cover, the bell housing or the flywheel but I decided to align this on the engine in the car and not on a spare.


Now let’s come to the injection style: throttle body injection (TBI) or port injection. The base of the phrase is: where exactly are the injectors located? I’ve been told that both styles could be run with an alpha/n-only ECU but ask yourself if you really want to do that. Most ECUs offer certain additional inputs and it would be a waste not to use them for better performance.


When choosing a TBI unit you should check: number of injectors, flow rate, impedance (resistance) and throttle size. What about: air temp sensor (IAT), fuel pressure regulator, throttle position sensor (TPS) and an idle air control valve (IACV or IAV)? Is it pulse width modulation (PWM) operated or is it a stepper motor? Note that the to-be-chosen ECU must be able to handle all components! My UMC for example can’t deal with a stepper. Where to put a MAP (manifold absolute pressure) junction? Some ECUs have a built-in sensor and are connected by a plastic tube, some have electric input and need a separate sensor adapted to the intake somehow, but do check before.


Compare the questionable TBI units for hardware and think about where to install missing sensors (IAT in the airbox, coolant liquid temp =CLT in a 318i/320i divider, where to put the IAV). Don’t choose a unit without TPS, it’s a mess to adapt these later. Look if a universal engine wire set is available, these seem to be pricey. Otherwise you’ll have to buy all single wires of your color choice or de-knot a 2nd hand harness- what I did. Look for all required connectors and plug housings. Will your stock airbox fit onto the top? These and more questions have to be answered before choosing an ECU.


Some may want to have port injection. I see three routes: 318i buddha intake, 4-throttle intake with injector holes from an aftermarket supplier or 320i injector bridge with custom intake.

The 318i buddha intake has already been addressed.


If going with 4-throttles check if a TPS is included. Other sensors won’t be included, so prove where to get and and how to locate them. What kind of airbox may match? How to connect an idle valve or can a throttle motor be adapted? Does the ECU accept such motors?


The euro 320i with K-jet was offered from 1975 to 1977. In the US seemingly longer. Its intake injector bridges can be set with more modern electric injectors. Well, adding the intake there won’t be much space below:




The black square feed line is hardly visible. It has to be modified and it is really very tight there. The mounting of a TPS to the TB is hard.

You may have a custom intake:




Decide if you want to fire batch, semi- or full sequential. Yeah: do google.


Concerning the ignition: you may stick to the standard dizzy, some may upgrade to coil-on-plugs (COP). There are also twin modules with the ECU running in waste spark mode but then the dizzy has to be replaced by a blind plug. Where and how to install COPs? However: no way without trigger wheel. Check resistance of plugs, wires and coils. Either the modules need integrated drivers or the ECU needs them.


Choosing the ECU is easier at this point. It has to provide all your required inputs and outputs. Raise a list. I chose a pretty small one since it might find a place in the engine bay to avoid drilling a hole for the harness:



The model car has a scale of 1:43.


Be now aware of the mapping. Some have talent to think inside this stuff. My advice is: read, read and read. When finished: continue reading. Talk to as many people as you can find who know about this and like to share their experiences with you. Or: pay the man. These are pricey men.


This is just a short overview. Now feel free to add your thoughts, ideas and corrections. I’ve done the beginning. You’re welcome!!



Edited by Henning

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If you want sequential injection you will have to fabricate a cam position sensor. It cannot be driven off the crank sensor.   

A great write up! 

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