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Converting a 530i to L-Jetronic with Lambda Control

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Courtesy of Robert Bondi, Scott Stewart
Updated June 1, 2002

If you're starting with a stock 530i and wish to remove the exhaust gas recirculation system (EGR), regardless of whether or not you wish to convert the fuel injection system, see this section :  Removal of 530i EGR Equipment

If you have a 528i, you don't have to worry about this, but if you have a 530i, keep reading. The following describes the process of converting your fuel injection system to the later style Bosch L-jetronic with lambda control. (Scott Stewart)

The object here is to assemble a FI system that is properly tuned, provides good driveability, low fuel consumption, and has minimal emissions. (Scott Stewart)

I had my 530i checked for emissions after I retrofitted my L-jet with Lambda control FI system from a 528i. It's emissions are lower without a catalytic converter than what the original specs call for on a 1977 530i. The L-jet with lambda control FI system is leap years ahead of the one on your car now because it actually monitors the fuel/air (stoichiometric) ratio rather than assuming it is OK. My performance is up, driveability is much better (my car would flood at high RPMs when it was cold before I changed to the new system) better fuel consumption, and of course the lower emissions. (Scott Stewart)

Here are some reference resources I found useful if you want to understand what you are doing (Robert Bondi) :

1. • 1980/1981 electrical schematics                                                          http://www.bimmerparts.net/
   • All E12 Factory Manual                                                                       http://www.bimmerparts.net/
   • Bosch Fuel Injection and Engine Management book by Charles Probst      http://www.bmpd.com/
   • BMW Mobile Tradition Parts CD                                                          http://www.bmpd.com/
   • 528i Ljet Schematic in Adobe Acrobat Format

I acquired all my parts from about 4 different sources: (1) BMW dealer, (2) used 1980 528i, (3) BMP (http://www.bmpd.com/), and (4) Dealer Marketing (http://www.bimmerparts.net/).  I found Dealer Marketing was a great source for new and rebuilt OEM BMW stuff and typically a few bucks less than the dealers in many cases.

Table 1 is a detailed list of parts you will need for the conversion with comments. Later 530i refers to 1977 and 1978 models. Don’t be confused or think you are getting off easy with all the "optional" designations; it all depends on what year 530i you have and what system you want in the end. The reason for "optional" designation is included in the comments. There are also a handful of minor components you will need to or should considering replacing along the way, but are the same as your 530i, e.g. various gaskets, aluminum sealing washers, FI Temp sensor, distributor cap, distributor rotor, thermotime switch, etc....not included in the table. I will try to point out the various options you have along the way with comments. Some major choices you have include your exhaust set-up, fuel rail, and whether or not you go to the 1979 528i arrangement or the 1980/1981 system. The big difference here is that 1980/1981 systems use a modified auxiliary air valve vacuum circuit, eliminates the whole coolant chamber below your intake runners, and move some sensors out to the thermostat housing. (Robert Bondi)
 
 
 

A general hint: Clean everything that you acquire used, especially electrical connectors. I acquired a used FI and engine wiring harness from a 1980 528i. After a degreasing round of cleaning, I took apart many of the sockets to clean the terminals and replaced cracked boots and connectors. I also patched any imperfections in the insulation with either silicone or electrical tape. The two pole connectors and their boots are readily available from BMW and so is the AFM connector and boot. If you don’t clean the electrical connections, I hope you enjoy troubleshooting. (Robert Bondi)

You might consider acquiring a bunch of used parts from the appropriate donor cars which include the E12 528i and, in general, similar years of the E24 633csi and E23 733i. If you don’t like the looks of your used stuff, then you can always get new or rebuilt. A nice trick I used was to purchase a rebuilt ECU and distributor and send in my equivalent used parts that didn’t pass my standards as cores and got some nice refunds. (Robert Bondi)

Some anomalies to watch out for:

The 528i does not use a cold start relay or any injection resistors. That caught me off guard when examining the harnesses. The 528i engine wiring harness is much beefier with a few different connections than my 530i harness and seems to require a bit of time in working out a rational route for it on the driver’s side of the engine. The mystery black wire emerging from the FI harness near the firewall with the green O2 sensor wire is for the AC compensation valve. Connect it up with a wire carrying the signal to AC compressor. I believe the extra brown wire emerging from the engine wiring harness with the T gauge sensor wire is a ground and I attached the ring terminal under one of the 4 bolt heads holding the thermostat housing cover elbow. Brown is the universal ground color for these cars. (Robert Bondi)

Coolant return pipe:  If you go with the 1980/1981 FI, you will no longer need the coolant chamber below the intake runners, but will find yourself needing to connect the two dangling hoses that plumb the throttle body coolant chamber. The two options are to acquire the metal coolant return pipe and a new hose for the 1980/1981 528i or connect up your hoses as they are. I eventually replaced the metal pipe because it also appeared to harbor a bit of rust on the inside walls. My first solution was to acquire some fittings from the hardware store and join up the hoses. Get a hex coupler, one 5/16" ID hose barb, and one 3/8" ID hose barb. The 530i hoses are slightly different ID for some reason. (Robert Bondi)

If you purchase a new thermostat housing, make sure your thermostat fits in it. I purchased mine new and it had 5 threaded bosses and may be intended for a later model using the M30 engine, such as the E28. The thermostat was a little large, but initially fit; however, it did not function correctly. I had to remove the thermostat housing and do some aluminum grinding to solve the problem. (Robert Bondi)

You should consider installing an electrically-shielded cable of some sort for the O2 sensor; BMW did. It should help reduce noise, particularly near the spark plugs and since the signal is generally less than 1 V. Also, thermally shield your O2 sensor wire well. Don’t underestimate the heat of the exhaust emerging from the head. I had to revise the sheath I put on my O2 sensor wire twice because the sheath I had installed was deforming and melting. The flame retardant fuel hose sheath currently installed seems to be holding up. I also recommend installing a wiring provision from your O2 sensor signal wire so that you can easily check your sensor voltage signal while running closed loop. (Robert Bondi)

I see about 3 different options on exhaust, depending on where you are coming from: (1) acquire the stock 528i exhaust manifolds, downpipes, and catalytic converter, (2) get 528i headers with O2 sensor port, or (3) modify 530i headers by adding a welded port for the O2 sensor. I modified my 530i Stahl headers, but make sure you put the port in a section where the pipes have merged to get an average exhaust over several cylinders. BMP sells stainless steel O2 sensor weld ports and plugs. I plan to go with a heated O2 sensor in the future, but even though my O2 sensor is about 3 feet back from the head exhaust ports, my sensor does get warm enough to function after about 4 minutes or so. (Robert Bondi)

Your 1980/1981 engine wiring harness will have the following connectors: fuse box socket, combination relay socket, oil pressure switch female flag, three starter motor wires, two alternator wires, brown engine ground wire, temp gauge sensor female flag, 2 terminal distributor impulse connector, ignition control unit socket, two wires for the ignition coil, and three wires for the ballast resistors. I did that from recent memory, but it should cover most of the bases. (Robert Bondi)

Your 1980/1981 FI wiring harness will have the following connectors: 6 fuel injector 2-pole connectors (grey), 2 FI ground ring terminals, thermotime switch (brown) and FI temperature sensor (white) 2-pole connectors going to thermostat housing sensors, 4 wires for throttle microswitches, 2 female flag terminals for AC compensation valve, 2-pole connector for aux air valve (black), 35 pin ECU connector, 7 pin AFM connector, cold start injector 2-pole connector (blue), black AC compensation valve signal wire, green O2 sensor wire, and combination relay socket. This is also from memory, but confident it is most everything. You won’t have the little tack-welded bracket for the white O2 sensor connector, but this isn’t any real issue. (Robert Bondi)

Your 1980/1981 thermostat housing should accommodate 4 sensors/fittings: vacuum thermovalve (green), thermotime switch (brown), FI temperature sensor (white), and temperature gauge sensor. That white connector tends to look orange after 20 years of service.  (Robert Bondi)

You need to make one wiring modification suggested by Peter Florance. The 530i fuse box lacks a terminal and does not appear to use the yellow/green wire coming from my 528i engine harness. I believe this is the reason for the wire rerouting. Remove the purple/green and yellow/green fuel pump wires from the fuel pump side plug in your combo relay coming from the fuse box harness (easily done with a small screwdriver that will flatten the tab that holds the terminal in the plug). Remove these same two wires from the fuel pump side plug of the combo relay that came on the 528i engine wiring harness and replace these wires with the two out of your harness coming from the fuse box. Tie wrap everything down and tape up the old combo relay plug with electrical tape (the main power, red, wire still has power to it). (Robert Bondi / Scott Stewart)

The figures below contain some pictures taken during my lambda conversion.  The close-ups are probably most helpful, while the finished shot is maybe more for inspiration.

Figure 1. Valve Cover Area Under Construction (Robert Bondi)
 

Figure 2. Valve Cover Area Complete with Custom 3-port Hose (Robert Bondi)
 

Figure 3. Thermostat Housing (Robert Bondi)
 

Figure 4. Completed 1980/1981 Lambda Conversion Engine on a 1977 530i (Robert Bondi)

When assembled, try starting, but be prepared for tuning. Make sure you use properly-gapped 528i spark plugs, adjust the timing according to manual specifications, and be prepared for tuning and adjustments of the throttle body, AFM, and maybe aux air valve for 1980/1981 systems. Check the voltage output of your O2 sensor; if that is oscillating about the magic lambda = 1 (450 to 500 mV), you are probably not doing bad on tuning. My O2 sensor worked without much tuning effort, but the idle is currently requiring some work. (Robert Bondi)

I hope some of this helps you or anyone else brave enough to perform the upgrade.

Robert Bondi
Scott Stewart

Removal of 530i EGR Equipment

The EGR system was removed in 1980 from our car, but I'll do my best to differentiate between the expendable and not expendable parts.  Before performing this removal procedure, it is a good idea to check your state and local emissions requirements.  Removing this stuff could be a bad idea if your area has a visual inspection.  If the local inspection only checks emissions and you're converting to lambda L-jet FI, the lambda system should do a much better job than the EGR system.  Figure 5 shows a pictorial schematic of the U.S. 49 state EGR system on a 1977 530i.  Note that the California system (not shown) has slightly different connectivity, mainly because of a third electric control valve (12) not used on the 49 state version. Some of the other connections not designated in the vacuum hose color legend are also the skinny 3.3 mm ID vacuum hose; the non designated connections are usually black.  (Robert Bondi)

(Click on picture for larger version)
Figure 5.  EGR System Schematic of 49 State 1977 530i (Robert Bondi)

Table 2 describes which of the components shown in Figure 5 you can remove.  It is assumed you are stopping and staying with the 530i fuel injection for the components that you do not remove.  The lambda conversion will either remove the remaining parts or require replacement with the equivalent 528i part. If you remove the reactors, you should remove all things listed as expendable.  Without the reactors, these components have no function and are just cluttering the engine bay.  (Robert Bondi)
 
 

Most of the EGR system is a vacuum circuit.  Cap/plug anything that remains open.  There will be a few more ports to cap on the log manifold and cap the top little port on the throttle body that points to windshield (advance port).  You can make nice little caps for the small vacuum line by sticking an appropriate size wooden dowel stick or metal rod into one end of a short segment of the vacuum line and capping with a little silicone.  Figure 1 shows one of these caps made from some of the red vacuum hose. (Robert Bondi)

Whether or not you convert to the lambda system, you will need another exhaust solution with the reactors removed.  We used Stahl headers.  Others have used Paeco headers or Bavaria manifolds.  If you go onto a lambda conversion, it's a good time to consider you will need an O2 sensor close to the head in the exhaust.  (Robert Bondi)

Robert Bondi

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