Megasquirted 1973 BMW 2002

At the Oktoberfest 2002 autocross. Pic by Zenon Holtz.

!! NEWS FLASH !! More pictures added below, and . . .

The evolution to Megasquirt II with coil per plug / EDIS ignition

The distributor has been retired


I had two friends with ‘02s in college. We had lots of fun in them, some great road trips, and one was even pressed into beer ferrying service. It may be a small car, but it can carry 5 half barrels!

So, when I was looking for a 4 seater to complement my impractical assortment of vehicles (a Triumph TR-4 and a Miata), I remembered those good times in an ‘02. I bought this car in the fall of 1992. I probably should have tried to find one in better shape, but there were not many ‘02s on the market in central Wisconsin where I lived at the time. Also, way back when, the very first ‘02 I saw was atlantik blue. So when I went to look at this first ‘02 to turn up in the Madison newspaper and it happened to be an atlantik ’73, I succumbed and bought it. The car was in typical midwest 100k mile shape, but I had fun fixing it and using it as my everyday 4 seater. One day I blew the head gasket driving home from work. I removed the head, but the engine was crusty enough that I knew it would be more than a simple gasket replacement to properly get it back on the road. So it sat in the garage for a few years. An Audi 4000Q took over the everyday 4 seater duties.


Anyhow, fast forward to 1998 and I decided to get serious about fixing it up. I tore into the rusty body, fixing all the usual places including: new front fenders, welding in new rockers, rear fender lips, and about 50 other patches! The suspension was next, receiving Eibach springs, Bilstein sport shocks, and the usual parts. Later, I added Ireland Engineering fixed front camber plates. I also installed a rebuilt stage 2 motor. The motor has a ported e12 head, 9.5:1 CR, and what is supposed to be a 292 cam regrind (it says 300 on the cam nose). It has a lumpy idle, but sure is strong. A BMP big radiator kit keeps it cool. I was using a weber 32/36 carb at first. Exhaust is a new tii manifold, stock BMW downpipe, and the Ireland Engineering 2 ¼” muffler setup – very nice. Ignition is a Crane XR3000 with PS60 coil. Wheels are vintage 13 x 6 revolutions with 185/70HR-13 Bridgestone RE92s.

I drove around in it like this until I found a friend willing to do the paint work. That happened in the summer of ’99. I helped out with the messy grunt work -- lots of block sanding! Next was a Weber 38/38 carb and tweaking the ignition. I did a few iterations of recurving the distributor for the modded motor. I ended up running about 18deg. advance at 1000RPM idle and 34 degrees all in by 3500RPM with a 10 degree vacuum advance can.

New atlantik paint! Artsy pic by Gary in Colorado.

Time for efi:

Getting started: I had been looking into efi for some time. I’m an electrical engineer and have worked in the automotive industry, so I'm very familiar with the systems and had become used to the drivability and performance of more modern cars. My engine was different enough from stock that the carb and ignition were way off. I was able to improve the tune quite a bit, but I guess I am too picky. It still had some cold running and starting problems, poor idle fueling with the cam, surging at cruise, etc. I built a diy wide band o2 sensor and used it to dial in my carb some more, but I still thought it could be better. Then the first Megasquirt group buy came along. I signed up and started collecting parts. I had a copy of Pete McHenry's article from the Roundel (BMW club magazine) and liked the look of the 320i intake manifold with its curved intake runners and general resemblance to a 2002tii -- the factory mechanically fuel injected 2002. I ordered a ’77 320i intake, ‘84 318i water outlet and fuel rail from Al Taylor.

I was very impressed with the Megasquirt kit. Bruce Bowling and Al Grippo did a great job designing it and then sharing it with the diy community. Mine went together without any problems and tested out fine on the stimulator.

After a few months hacking: My original Megasquirted 2002 engine

Intake manifold and fuel rail: Modifying the intake to accept the efi injectors in place of the CIS mechanical ones was a bit more difficult than I expected from Pete’s article. But then I have met Pete at the BMW club's 2001 and 2002 Gateway Tech events in St Louis, and he struck me as pretty much a genius when it comes to BMW motors. Following Pete’s suggestions, I used the 318i fuel rail. It needs to have the fuel pressure regulator mount sawn off and sealed up, and a new fitting added for the fuel return. This rail holds the injectors at the same angle as the injector ports in the stub manifold. However, if I had it to do again, I would seriously consider using the 318i intake manifold and Mustang throttle body like Zenon describes in his website here.

The Bosch efi injectors need to be sunk much deeper into the stub manifold in order to provide enough clearance for the curved runners and plenum to clear the fuel rail. I was wondering how I was going to do this until I ran across these SDS efi tech info webpages on fuel rails and intake manifolds. There is tons of other good info on the rest of their tech pages – well worth reading through.

The SDS pages describe how to seal an injector to the manifold by boring it waaay out and using a standard, larger o-ring to seal the manifold to the body of the injector instead of the nose. On the 320 stub manifold, this required some fixturing to get the angles right (since the injectors are tilted in two dimensions from the face of the stub manifold). With the injectors mounted so the injector body is just above the stub manifold there is just enough clearance to fit the rail. You still need to modify the bottom of the plenum a bit and notch the rearmost runner support to make it fit. And make two brackets to hold the fuel rail to the stub manifold.

The large hose fitting on the bottom of the plenum needs to be removed for clearance. It twisted out with Vice-grips, and I replaced it with a bolt and some large washers, sealed with grey silicone. There is also an aluminum nub on the bottom of the plenum that hits the fuel rail. I filed this down at an angle so it helps retain the rail down against the injectors and into the stub manifold. For injectors, I’m using 19.8lb/hour ones (Bosch 0 280150 714) from an ’87 535is. These are close to perfect for my motor.

Throttle Body: For the throttle body (TB), I didn’t do anything real scientific. I selected it by wandering around the area pick-n-pull, looking at TBs that had a diameter that would have an area equivalent or bigger than the 38mm two barrel carb that I was running. This comes out to 53.74mm. I found a ’91 Honda Accord 4 cylinder TB that measured 56mm. It has minimal junk on it and was the biggest diameter TB that they had that would fit between the runners of the 320i manifold with a resistive throttle position sensor (TPS). I fabbed an aluminum adapter plate that used the 3 studs from the manifold to mount to the manifold and then bolted the TB to the plate. I did have to do a bit of modification to the TB to make it fit as well, it is pretty obvious.

To adapt the throttle linkage, I followed pretty much what '02 efi pioneer Larry Harris did. I changed the effective travel of the pedal to the shorter travel of the throttle cable with some simple brackets and a lever assembly that mounts to the brake booster bracket.

Believe it or not – there is a fuel rail under all that aluminum!

Here you can see the throttle linkage lever and cable bracket, the new fuel line coming up from under the car, and the relocated fuel pressure regulator with gauge

Fuel system: Some people track down a tii fuel tank and the external pump – but I wondered if there was a simpler way. I was stumped on what to do until I went to the 2002 Midwest 2002 fest where I talked to Ben Thongsai, Austin Bader, and Matthew Jeffrey. Austin and Matt built and ran an '02 in the 2002 One Lap of America. Ben set them up using a ’88 and up fuel pump from a 325i/is. It is a high pressure efi pump that drops right into the 2002 tank and even the fuel gauge sender works! For an early tank, a 1991 318i/is pump is even better because it has a fuel return fitting in the pump/pickup/sender assembly. This will save some work if your tank does not have one (like mine), but they are harder to find. So, I got a used 325 pump from Vines and brazed a return fitting into my tank. Some later tanks can be slightly deeper (230mm) than my 210mm tank. The e30 pump is the same depth as the 200mm deep pickup that was in my tank. I’ve heard that this pump still works fine in the deeper tanks, you just have a bit more fuel in the bottom of the tank.

I ran a new steel 5/16 line for the fuel feed up to the engine compartment and used the old steel line for the return. It may not be as big as the typical BMW fuel filter, but a Fram P/N G6567 fuel filter from a mid ‘90s Dodge efi V8 truck has 5/16” hose inlet and outlets – and has a nice bracket to mount it under the trunk panel next to the gas tank. The fuel pressure regulator has to be mounted somewhere, so I thought I would be clever and buy a fancy Mallory 4305M hot-rod grade adjustable regulator. This did not work well. It leaked fuel and vacuum and did not accurately control the fuel pressure. I finally made up an adapter block out of aluminum and used a BMW 3.0bar regulator. It flows enough fuel for an e28 M5 so it will work fine on this motor!

I also added a Ford fuel pump impact cut-off switch to the car. This is a switch that is wired in the + power lead to the fuel pump and mounts in the trunk. When a stout impact occurs (like an accident), it shuts off the power to the pump and keeps it from pumping fuel when the fuel plumbing may have been damaged. It is a small black box, mounted vertically, with a red button on the top. Push the button, and it resets the switch. These are in the trunk of all the '90s Fords I've seen in the junkyard, mine was $2 and came from a Taurus. They don't want a repeat of the Pinto -- and I sure don't either. Neither should you. It makes a nice anti-theft system too. Give it a thwack when you're getting your luggage out of the trunk and no one will be able to start the car.

Miscellaneous: The battery has obviously been moved to the trunk to make room for the Mitsubishi eclipse/Eagle talon airbox. They have a nice, big, readily available filter element and can flow enough air for the 200hp turbo cars, so again, I think it’ll do. The same car donated the rubber air hose, and it fits onto the Honda accord plastic elbow. For cold idle air bypass, I’m using the auxiliary air regulator from the 320i and wired it to the switched ignition.

Tuning and performance: The car started right up and within a few minutes was idling well. I had a few teething problems with ignition noise, which was not unusual for an early v1.01 installation. Moving the megasquirt ignition signal from the coil to the Crane ignition optical pickup (with the optoisolator return signal) and using shielded cable fixed this. My initial idle pulsewidth was on the low side (1.6mS) so I added the active flyback clamp from the v2.2 Megasquirt. Now I am up to 2.6 – 2.7mS with better idle control. Another interesting thing I was seeing was some low pulsewidth operating conditions where the O2 sensor reading was not stable in closed loop mode. The 0.1mS step resolution was too big and the O2 reading would go from very rich to very lean with just a 1% change in the VE table. The high-resolution code really helped this.

Eric Falgren’s Megatune and Darren Clark’s MSTweak3000 have been a great help in tuning. In fact the datalog picture on the cover of Darren’s MSTweak3000 user manual cover is from this motor and it was really neat to see the low RPM torque peak that the tuned runner intake manifold produces. I have not seen this peak on dyno charts from '02s with independent runner manifolds and sidedraft carbs. Tuning is kind of a never ending process. You can get the car running quite good in a short time – much better than with carbs in my case – but there is always some little area to adjust or experiment with. The car is much quicker now and drivability and idle are better than with the carb. With the Weber 38/38 carb, I ran a (average of 4 runs) 60 – 80MPH 3rd gear acceleration run in 6.71sec. With the Megasquirt I am now at 5.63sec!!

The next step is improving the ignition. With the megasquirt you can really see how crappy distributors are - especially at high revs (over 4000RPM). Mine seems to have lots of spark jitter and inaccuracy. And this is with a pretty new distributor with the Crane optical pickup so there is no point bounce. Some timing jitter could be seen with a timing light, but that is nothing like driving along, looking at the Megatune tuning screen, and seeing the green dot shake more and more as the revs go higher. I've been looking into the Ford EDIS stuff for a while, I got the parts in February 2002.

The story continues:

The evolution to Megasquirt II with coil per plug / EDIS ignition

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Email me at: tskwiot at hotmail dot com.

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Originally Created Feb 3, 2003

Last updated Jan 15, 2006

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