Porsche Fuel Injection History

[Coastr]

This post is just a rambling round up of fuel injection systems as fitted to Porsches over the years.  It comes out of a discussion thread where I was rambling on the topic, others said it was (kind of) interesting and thought it would make a good post.  I'm not an expert, have never worked in the industry or studied engineering.  Just an interested person who likes to understand how stuff works and how technology evolves over time.  I'll write for the person who really doesn't know that much about it.  I'll have made mistakes and feel free to call out and correct them where they lay.  I know it's long - pixels are cheap and skip by if you're not the reading type.  I did take my basic knowledge and fact check, but as Abraham Lincoln said, don't trust everything you read on the internet.

For me, the interest in german cars in general and fuel injection in particular comes from my childhood where we had a 280 SE with the M130 straight six.  Car model names was a fascination for me - why did our family falcon wagon say 'Falcon GL' (answer: no reason), but the benz said '280 SE' (answer 280 [2.8 litre], s-class [sonderklasse], injected [einspritzen]).  Also why was the Benz faster than the falcon, and why did it run so much better (The Falcon, despite being virtually new, often wouldn't start in cold weather).  Lots of answers but I much preferred the look of the benz engine than the round-air-cleaner look of the 4.1 Ford motor.  I loved the benz and the way it buzzed up the road.  It was also air-conditioned, a real luxury at the time.

There's some deeper truth there about the fuel injection - why so many German cars were fuel injected back in the day when English, American and Australian cars were almost exclusively carburetted.  It actually goes back to Rudolf Diesel, who invented (perfected) the Diesel engine.  Despite him disappearing off the back of a boat while on the way to England to sell Diesel technology to the Royal Navy (no foul play, I'm sure!), the Germans took diesel technology and ran with it.  And while gearing up for WW2 wartime production, the Germans had to solve some issues.  The first was their crappy and limited fuel supply - no Saudi Arabia or Texas for them.  The Germans knew that any major war would result in them not getting imported oil, and their meagre domestic production of synthetic coal-based fuel and normal oils imported from Romania was not enough to win.  Diesel came to the rescue but is too heavy for planes.  Anyway...two things came together and the germans had pioneered fuel injection for diesel engines, and they needed to produce fuel efficient powerful aero engines.  So they started sticking diesel injector technology onto aero engines.  The more precise metering allowed use of higher compression with lower quality fuel, and they were more fuel efficient.  The Daimler Benz inverted-V12 engine used in me109 fighter used direct fuel injection with a modified diesel pump, that had compensation for altitutde, supercharger boost and load.  Famously the Spitfires used carburetted V12 merlin engines and couldn't chase the me109 into a dive as the carb float would lift up and the hungry engine woudl lose power.  The luftwaffe pilots soon learnt this and it became a standard manouvre for the fuel-inject me109 pilot to negative-g dive and get away.  Anyway, as we know the Germans lost - and as captains talk tactics and generals talk logistics the fuel situation was probably one of the biggest factors in them losing.

After the war was over the germans got their economy back on their feet.  They wanted to resume winning racing and mercedes benz came up with the idea of using the s-class engine, dusting off the direct-injection technology from the me109 engine, threw the carbs in the bin and promptly started winning endurance races.  Just like the aero engines, more power, better economy and allowing use of more aggressive cams got an extra 70hp over the standard engine.  This direct-injection mechanical pump was designed  from the aero engine technology.

Before going much further, let's talk about what fuel injection really is.  A carburettor relies on engine vacuum to suck fuel into the engine, and the throttle regulates how much air (and thus vacuum) is available to suck the fuel in.  It's a continual stream of fuel that goes into the intake and gets distributed to cylinders depending on whichever piston is on the intake stroke at the time.  It's cheap and simple and does the job, especially if fuel is plentiful and cheap (hello USA).  Fuel Injection, developed for diesel engines, injects a precise amount of fuel either directly into the cylinder (direct injection) or into the manifold (manifold or port injection).  For diesels the amount (and timing) of the fuel plays the part of both fuel amount and ignition timing (no spark plug and no throttle).  There are 3 main parameters for determining how much fuel needs to be injected : engine speed, engine load, and throttle position.  If there was no load, you'd just have a 2 dimensional map - like revving a car in neutral, it's just the throttle opening and engine speed.  Add in load (uphill, pulling a trailer, cruising) and you end up with a 3-d map of how much fuel is needed by the engine at any one time.  You've probably seen those contour maps.  Now, it's more complicated than that in reality but you get the picture.  Diesels do it all within the pump, and they're complicated and cost a fortune to fix.

Going back to post-war Germany in the 60s and a company called Kugelfischer took the diesel-pump-for-petrol idea but swapped to manifold injection, allowing the swirl of air going into the cylinders to help atomise the fuel, plus injectors needing less pressure (ambient pressure vs compresssion pressure in the cylinder).  Less pressure for the injectors = less fuel pressure = simpler and cheaper.  The 3d fuel map is still like a diesel pump and uses a plunger, weird-shaped cams and the engine driven pump to deliver the fuel in precise amounts.  In those days, the Kugelfischer injection was for high performance cars and race cars.  It was less about the abilty to get more war from measly supplies and more about getting more bang from the same size engine - plus fuel efficiency for endurance racing.

The Americans had a few goes at fuel injection (fuelly split-window Vette, anyone?) but abandoned it because, well, Texas has oil, just add more cubes and more carbies.  But the German company Bosch bought out Kugelfischer and starting selling to manufacturers, who wanted higher performance out of the same engines as lesser models, probably because Germany and other European countries had engine-capacity based taxation laws (that's why so many 2.8 cars)

Enter Porsche and our first fuel injected road car (not sure about race models) - the 1969 911 S, which used a Bosch Kugelfischer injection system, known in porsche circles as 'MFI' (mechanical fuel injection).  This allowed for more aggressive cams, higher compression and increased power by 60hp.  The MFI engines are beloved and the individual throttle bodies (ITB) setup gives that wicked flat six sound.  The throttle response is by the injector pump plunger and not by the throttle response (the two move with the throttle) so (apparently) gives instant throttle repsonse (never driven one - anyone want to give me a go?).  The other notable MFI car of the era is the BMW 200tii (why not 'e', BMW?), but the BMW crowd call it Kugelfischer.  Arguably the most famous is the 2.7 RS and it's successor the MFI Carrera.  The MFI pump works out the load (a calculation of engine speed and throttle) to a pre-determined formula based on engine speed. SOme version had altitude-sensors and like any injection system, has warm-up compensation.  MFI is a set-and-forget system so tuning a MFI car is left to engineers with very, very deep understanding - effectively the 3d engine map is encoded in a bunch of cam profiles, spring tensions and other craziness.

But dark clouds were looming on the late 60's fun, and that was the California Air Resources Board (CARB) and it's various me-too-ers worldwide.  New standards were proposed and then introduced in the early 1970s.  One of these was catalytics converters, and they don't like getting raw fuel dumped through them. The Americans responded by de-tuning their big engines, lowering compression and putting on anemic carburettors.  Embarassing power figures followed, like 130hp out of a 6.6 Pontiac Transam.  The Germans at Bosch dipped into their rich history of Fuel Injection and came up with K-Jetronic.  Now Jetronic is just a brand name of manifold-injection systems, and the various names (K,L,D etc) are different styles (Jet=Jetronic).

K-Jet was introduced in the 1973.5 911 and ran through until the end of the 3.3 Turbo 964 - a production run of 21 years or so.  K-Jet stands for the German word for 'Continous' which is why it's also known as CIS - Continuous Injection System.  It's a mechanical fuel injection system so like MFI it doesn't need a computer, but unlike MFI the fuel map is determined by the air flowing into the engine, not unlike a carb.  The airflow into the engine is measured by a flap that moves with vacuum - that then moves a plunger which determines how much fuel to deliver through the injectors.  There is no injector pulse as it just squirts - the injectors open at a certain pressure and off it goes.  The fuel pressure is delivered by an electric pump.  Again, more too it than that, but the basic idea is - put a vane in front of the airflow, as the throttle opens, the airflow increases, which makes the pump deliver more fuel.  Not unlike a big carburettor, which is why you can get backfires and the like, but much, much better at metering fuel.  It also made it much simpler to turbocharge, unlike blow-through or suck-through turbo setups.  But it was introduced for economy & emissions to an early-1970s market, not because it made more power.  MFI would no longer be sold in emissions restricted markets like the USA, because it, well, 'if in doubt, more squirt'.  The 924 and 928 also got K-Jet, like just about everyone german in the 70s.  K-Jet is virtually impossible to tune unless you rebuild the fuel distributor.  The later US/Japan SCs also had an analog closed-loop lambda system for precise control with an O2 sensor, but the car runs just fine if you unplug it.  CIS engines have funny shaped pistons and smaller ports to increase swirl, and lower rev limits.  But they are torquey off the line, but just don't rev like an MFI.  Plus they have a big fuel plate in the way of the intake, slowing down things somewhat.  They are reliable, though.

D-Jet was another Bosch acquired technology from Bendix, the American company.  It is different to K-Jet in that it is an analog EFI system.  D this time is for 'Druck' and as air-cooled 911 owners will know, Druck means pressure. The pressure was not related to fuel pressure, but to manifold pressure.  The D-Jet system worked out the load on an engine not from a vane in the airflow, but from a manifold pressure sensor, these days called a MAP sensor (manifold air pressure) (plus throttle and engine speed).  This was analog in the way your old guitar amp was analog - capacitors and transistors.  D-Jet was the system fitted to our old 280 SE.  The first Porsche to get D-Jet was the 914 2.0 liter.  But gone is the continuous spray of the K-Jet and in it's place electrically pulsed injectors, early predecessors of what we see in more recent cars.  However it wasn't full sequential and batched injectors in pairs due to low processing capability - fine for a 4 cylinder but not so good for a 6 or 8.

L-Jet was an evolution of D-Jet but went back to the vane-type of air metering, kind of like K-Jet.  It was still an analog system though, taking inputs and varying the injector spray width.  It was better than D-Jet but still crude.  The 928 got the L-Jet technology after a few years (first in the US, then ROW later).  You can tell L-Jet units for the big vane-measuring box in the intake path and general lack of wires everywhere.

LH-Jet was a further evolution again, being the first to introduce a digital ECU and hot-wire airflow sensing - known as a Mass Airflow Sensor (MAF).  This had a very early Intel microprocessor and eventualy on-board diagnostic functions.  This was included in 928s from about 82 onwards (don't know exact, Euro/Aussie cars different to US cars).

The LH-Jet was the end of the line for the Jetronic brand and Bosch switched to Motronic.  Motronic is all-digital ECU and debuted on the 944, closely followed by the 928 and then the 911 3.2 engine in 84 (Turbos continued with k-jet until 94, remember).  Motronic ran for years but in later models got to be known as the DME as fuel injection became less special and more standard into the 90s.  Early Motronic units used a vane-type airflow meter and the fuel map was burnt into the ROM (read only memory) of the chip.   This is why you can 'chip' a motronic unit by replacing the fuel map with a different one.

As Motronic went on improvements were added without new names or series.  The later 911s and 928s got MAF instead of vane airflow meters, got knock sensors and then integrated ignition timing control.  Because of the OBD regulations in the US, they started storing fault codes and got diagnostic ports.  By the time the 986/996 arrived there was variable camshaft control and then electronic throttle control (which measures 'load wanted' over 'load required based off throttle').  And all sorts of other wizardy like traction control but those interfaced with abs speed sensors.  Eventually the distributor disappeared and was replaced with direct fire coil-on-plug (COP) ignition, with the ignition completely controlled by the DME.  And things like automatically increasing idle when the air-con cuts in, and much better cold start, and on and on and on.

The Motronic party ended with the arrival of Direct Injection in the 997.2 motor.  We arrive full-circle back at the me109 because it uses direct injection, scrapping the manifold injections of the MFI-Motronic era.  Again very high pressures, but instead of a diesel-derived pump, we just get a very high pressure electric fuel pump and precisely controlled injectors with a very powerful ECU to figure out what used to be careful cam grinding and hole-metering.  Gone are the vane airflow meters and MAF hotwire and back to the idea of the MAP unit - but now reliable.  The computing power available and precise control from the injectors and feedback from knock sensors allows for monstrous amounts of boost in turbo cars and very high compression in naturally aspirated cars.  And nothing in the intake path means no restriction and max power.  A modern direct-injection turbo engine is a thing of joy indeed.  Still lots of emissions crap, though, like running rich when cold to warm up the cats more and stupid stop-start systems.

Identifying your Porsche Fuel Injection System

MFI - look for the injector pump and ITB stacks, and steel fuel lines to the injectors.  Unlike the BMW 2002, the MFI pump is driven off the back of the engine, using a toothed belt off the camshaft.

K-Jet/CIS - look for the big plastic airbox, which contains the fuel metering vane, and the fuel distributor, which has all fuel lines running out of a single head.  Early cars had plastic lines, later (about 79 onward) had steel lines a bit like MFI.  As time went on, they grew more vacuum-operated compensation devices and gadgets - all were aimed at reducing emissions, not increasing power.

Super early k-jet system.  

1983 CIS with more vac hoses and stuff, but steel lines.

D-Jet - it looks like K-Jet in that it has a central air intake and spider-leg intake runners, but is missing the trademark airbox and fuel distributor.  And it was only on 4-cylinder VW based engines

L-Jet - look for the classic spider-legs of K-Jet and D-Jet but absence of K-Jet airbox and fuel distributor, but still with hard fuel lines running to injectors.  Hard to know with a 928 because the classic CIS fuel distributor is hidden at the back in a 928.  

Motronic - easy to spot in a 911 due to the central throttle body and big vane airflow meter. Also the appearance of fuel rails over individual lines.

Again in the 928 they hid this underneath but gone are the spider legs.  You can spot the fuel rails peeking out though.

For later models it all starts looking the same - central throttle body, fuel rail on injectors.  The Metzger motors keep the same type of high-plenum and runners look of the 3.2 engine, like this 996 era GT3 motor.  You can see the COP ignition here, and fuel rails, though this engine still uses a fuel return line - eventually this would go to a dead-head system to prevent returning hot fuel back to the tank.  

ITB's never made a comeback, but lots of aftermarket injection systems use them (because they are awesome)

People building these types of engines these days use aftermarket ECUs, either coil on plug (COP) ignition or individual separate coils.  These are built without emissions in mind, but the precise metering of modern injectors and powerful ECUs make them run in ways the 1930's german engineers could only dream of.

 

More pics : me109 inverted v-12 aero engine (db-601) - injector lines visible

db-601 injector pump 

The son...Mercedes 300 SL Injector Pump  - remember not upside down

Porsche MFI injector pump...the distant relative

 

If you're still reading congrats on making it to the end and I hope you either learned something or at least enjoyed the process.

[Peter M]

When I saw the thread title I thought Bruce Buchannan had been left unsupervised again and I was consequently well ready for a long post! 😁

Our parents do have a lot to answer for.  Similarly my experience was growing up with a K Jetronic equipped Volvo 144 that I eventually rebuilt myself as none of the local mechanics my parents used seem to have the foggiest about it.  Again the improvement in cold start driveability was a revelation compared to the single barrel Stromberg Holdens we had previously. 

However my K Jetronic experience wasn't all positive with it's occasional habit to backfire and blow the intake ducting off the front of the manifold and pesky fuel distributor and WUR.  Accordingly when it came to deciding on my first 911, SC's were instantly dismissed because they had the same injection system and a 3.2 was the front runner as I wanted modern injection like a VL Commodore!  (Yes, that was the extent of my analysis.  I also dismissed 930's simply because they only had 4 speeds!  Wasn't that to turn out a financially short sighted decision as that was only a year or so before the great appreciation!)

I'd like to have a drive of a MFI 911 as well because of the legendary throttle response.  However I think that legend may be a result of comparisons to mid 70's CIS cars with crude and invasive emission tuning and may not stack up to what we are used to nowadays.  After following a MFI car, I suspect from the smell they are great at pumping in a lot of fuel instantly that doesn't necessarily get burnt! 

Just a small correction to your ME109 photo caption, those lines above the exhaust ports are ignition leads not injector lines. 

Cheers!

[Coastr]

Ah thanks for the correction on the DB motor.  It's very hard to get technical information of any depth on the internet for these motors.  Somewhere in my photo stash I have a photo of a DB aero engine injector pump from a museum (I think the boeing museum in seattle).  

I too wanted to by a 3.2 for the 'modern' injection but for reasons have stayed in the SC world.  I don't mind CIS so much, for me it has been very reliable and trouble free.  One day maybe ITBs and EFI or EFI turbo.  For now happy with original CIS.  

People still swear by MFI cars and they do command a significant premium.  Regardless of anything else the ITB design will give you better throttle response and higher RPM flow over single-throttle body designs as used for every 911 engine since.  If at the cost of a little overfuelling.  They say the air cooled engines like to run a little rich...'they' say.

[Mike D'Silva]

On 06/02/2022 at 13:29, Coastr said:

Ah thanks for the correction on the DB motor.  It's very hard to get technical information of any depth on the internet for these motors.  Somewhere in my photo stash I have a photo of a DB aero engine injector pump from a museum (I think the boeing museum in seattle).  

I too wanted to by a 3.2 for the 'modern' injection but for reasons have stayed in the SC world.  I don't mind CIS so much, for me it has been very reliable and trouble free.  One day maybe ITBs and EFI or EFI turbo.  For now happy with original CIS.  

People still swear by MFI cars and they do command a significant premium.  Regardless of anything else the ITB design will give you better throttle response and higher RPM flow over single-throttle body designs as used for every 911 engine since.  If at the cost of a little overfuelling.  They say the air cooled engines like to run a little rich...'they' say.

I'm waiting on some pistons for a 3.5 litre engine.... which will be for sale when I get my 3.0 efi'd and turboed..... just in case you wanted to upgrade.

[Peter M]

8 hours ago, Mike D'Silva said:

I'm waiting on some pistons for a 3.5 litre engine.... which will be for sale when I get my 3.0 efi'd and turboed..... just in case you wanted to upgrade.

Mike,

What's the spec sheet on the 3.5?

[Coastr]

‘One day’ - I have other things I’ve got to be spending my time on right now.  All the while the engine keeps spinning I’ll keep it buttoned up.