3.0CS DUAL CARB TO L-JET CONVERSION

by Jim Ockner

March 15, 2002

 

References

www.firstfives.org - The pictures and FAQ's were quite useful.

Peter Florence - He is a 528i electrical polymath and is amazingly prompt and consistent answering emails and has written several very useful FAQ's. Must be one very efficient and motivated individual.

Carl Nelson at CNPR/La Jolla Independent BMW (800-466-8184) - Excellent parts source. He's done many conversions and is very familiar with the pieces and parts you'll need.

Maximilian Imports (800-950-2002) - Really nice guy with tons of knowledge about coupes. Excellent service.

AllOEMBMWParts.com - If you know the part you want, this one of the cheapest online sources for parts I've found. Example: aux air valve (80-81), dealer $99, alloembmwparts.com $42, cheapest my mechanic could give me $55.

BimmerParts.net/bmwpart - These guys have factory service manuals available and the electrical schematics (listed under the service manuals section). They also sell the Bosch manual and probably any parts you may need. I found out about this site after completing the conversion so I haven't checked their prices.

How to Understand, Service and Modify Bosch Fuel Injection & Engine Management - By Charles O. Probst. (ISBN 0-8376-0300-5) I'd highly recommend getting this book and reading the sections on pulsed injection.

BMW Fuel Injection, An Enlightened Approach - by Jim Blanton (formerly of) and Jim Rowe (currently of Metric Mechanic, Roundel advertisers). It is amazing how simple things seem and how logical troubleshooting can be when using this manual. It i$ out of print but occa$ionally Jim Rowe can be per$uaded to $end out a photocopy of it, if you catch my drift. I'd have to $ay it was worth the co$t.

Gasoline Fuel-Injection System L-Jetronic, Technical Instruction - Inexpensive 37 page manual from Bosch that has no ISBN. Can't remember where I got it but the Probst book is more inclusive anyway.

 

Parts List

From a 1979-1981 528i:

• I'd really recommend getting the system from an 80-81 car with the newer style auxiliary air valve mounted on the valve cover by cyl 5.
• injection system including ECU - save lots of time later by labeling connections as you separate them
• ignition control unit with adjacent ballast resistors
• coil
• distributor
• new cap, rotor, and, if needed, wires
• complete intake
• combo relay
• possibly diagnostic port (see end of section on engine plug)
• main fuel pump (ideally new), filter (new), pump/filter ass'y bracket, and bracket that is spot welded to the car (see pics below)
• pre pump - get custom unit from Carl that fits CS tank - see section on fuel tank and lines
• new fuel injection grade hose - about 5m will take care of all 8mm hose replacement
• new fuel injection grade hose - 1m larger ID (14mm, I think) from tank to main pump
• bunches of new hose clamps from Carl - he's got good German ones & the hose he sells is BMW hose that's less expensive than NAPA - which Carl politely says is a place to buy wine not auto parts
• t-stat housing if 80-81 model
• new gaskets, t-stat
• valve cover if 80-81 model along with air bypass valve and all hoses
• new valve cover gasket
• single wire O2 sensor (from Auto Zone or wherever, generic Bosch ~$20)
• Because of a problem I have yet to diagnose, my O2 sensor is currently unplugged and I'm getting 16-17mpg.
• 13 ft 5/16" OD stainless steel tubing for fuel supply line available at any hydraulic supply store - may also want to check if the CS steel line is available new through BMW which might be a much simpler solution
• cable clamps, assortment of heat shrink tubing (Radio Shack), variety of butt connectors & terminal ends (NAPA is great for these), black zip ties (1/8" wide ones, Home Depot is cheapest), good quality electrical tape or (something which I use almost exclusively now) silicone fusion tape (Radio Shack or Home Depot), wire (use appropriate gauge & try to use appropriate color when possible)

 

Removal of Carbs & Related Stuff

Label the wires you disconnect. Some get reconnected and a little labeling really helps. The relays for the automatic chokes and the associated harnesses can of course be discarded. These relays are on the bracket attached to the brake booster. Save the bracket to use as a pattern later. The speed relays for the pollution controls (silver boxes under the coil) can be discarded. Remove the fuel pump from the head and put a cover plate over the hole. Carl Nelson may be able to help you out with this. I didn't have this problem since my head was not bored for a mechanical pump.

 

Throttle Linkage

The rod I had that went from the pivot point to the new throttle body had to be shorten by 1.25". The die to cut new threads is 5.0 x 0.8mm.

 

Fast Idle Air Bypass for cold engine warm up

 

I used a 1979 528i system, which uses the "Jules Verne" device (probably so called because it looks like a periscope and most of the damn thing is 20,000 leagues under the intake runners) for the fast idle air bypass. It is properly called the auxiliary air slide valve. A much better system comes from the 1980-81 528i and mine had been converted to this by the person who provided me the EFI system. This requires the 1980-81 valve cover with tapped holes at the top rear to mount the newer style auxiliary air valve (AAV). Also, the Bosch number on the ECU should end in 122. If you do this, one wire from the AAV goes to ground and the other goes to the exciter tab (upper - term 15 (16 on coupe diagram), the one that doesn't engage the starter gear) on the starter with the 4mm red wire. You will also need the air hose that comes off the throttle body and splits going to both the AAV and the A/C idle compensation valve. This hose is NLA (pn 11.61.1.271.604) so get it from the car you snag the AAV and valve cover from. The air hose that goes from the AAV to the cold start injector is available as is the air hose from the A/C idle compensation valve to the intake plenum.

As for the Jules Verne device, dump the auxiliary air filter (if present) and the air hoses going to it from the throttle body and from it to the intake plenum by the cold start injector. The connection to the thermo-time switch should be left. The temp sender connection must be left as well because it provides coolant temp info to the computer. If you want, you can dump the whole device, run coolant directly to the idle air warmer circuit at the bottom of the throttle body, and move the coolant temp sensor and thermo-time switch to the thermostat housing. This would require a t-stat housing that accepts three sensors (ECU coolant temp sender, thermo-time, & dash temp gauge sender), a readily available junk yard part that would also be on the car you get the AAV, valve cover, etc from.

 

Electrical System

 

Without the wiring diagrams from both cars, I would not have been able to do the conversion without asking millions of questions of those who had done this conversion before. I will describe everything I did but I highly recommend obtaining the diagrams, enlarging them on a photocopier and getting them laminated. Please note that there is a mistake in the 528i factory manual's engine electric diagram. It shows a wire going from term 1 of the engine plug to term 1 of the ECU. This is wrong. It should originate from term 5 of the plug as it is the pulse reference from the negative (term 1) lead of the coil.

Peter Florence has posted an engine electric diagram on the First Fives site. It looks to be excellent.

 

Starter

 

When looking at the connectors on the starter, the top is terminal 15 (16 on the coupe diagram), the bottom is terminal 50, and the right (toward the driver's side as it sits in the car) is term 30. On the left is ground and nothing is connected to this as it is grounded through the engine block. I assume this is a standard arrangement.

If you have doubts which is term 15 & which is 50, hook up the main power lead from the battery and apply another power lead to one or the other of term 15 or 50. If the starter engages, it's term 50. If nothing happens, it's term 15.

Term 15 (16 on the CS diagram) takes a black/red lead that goes to the resistors positioned by the ignition control unit (ICU). This is also where one of the leads to the auxiliary air valve goes (see section on aux air valve). The CS starter wire (blk/red) to this term should not be connected. It would go directly to the + coil lead and therefore bypass the resistors needed on the 528i system.

Term 50 is the starter engage terminal and takes a black/yellow lead. This lead needs its power from term 50 of the ignition switch (black), which comes through term 1 of the engine plug. Because this lead does need power when the engine is cranking connect both this and the original CS starter engage wire (2.5mm blk) to this terminal. The 2.5mm blk CS lead comes directly from term 50 of the ignition switch. There should be two spade terminals at this spot on the starter, so it's easy to do.

Term 30 takes the big lead from the battery and a 4mm red lead in the 528i loom that then goes to the alternator. In the CS, the lead to the alternator comes directly from the battery, which does not need to be hooked up.

 

Coil

The coils from the CS and 528i are different because the 528i uses a higher energy, transistorized ignition. Use the 528i coil. Externally, the 528i coil is smaller so I put a piece of cut old radiator hose partly around it to take up the slack in the CS mounting clamp. The only coupe wire that remains on the coil is for the tach pick up on the negative term. It is a black lead. Mine is composed of three wires but only one is shown on the CS diagram. I assume one is for the speed sensing relays for the pollution control valves. These are the silver boxes mounted under the coil and can be unplugged and tossed. I assume the other goes to the CS engine diagnostic port. My coil also has an extra lead from the positive term of the coil going to an aux cooling fan a previous owner installed.

If you have A/C, you'll have to remount the receiver/drier and coil. I haven't completed this part yet but it looks like I'll move the coil forward as far as it will go, right between the cold air intake port and inner fender wall. This should leave room for the receiver/drier between the coil and air filter box. Others have put the receiver/drier below the coil. If you replace any of the A/C hoses, do it after you've mounted the coil, drier, and air filter box to make sure they are made to the correct length.

 

Combo Relay & Engine Plug Socket

I mounted this on a bracket I made in place of the bracket that attaches to the brake booster about even with the forward end of the coolant compensation tank. The original CS relays that mount there are not needed as they supply current for the automatic chokes and carb related stuff. To make the bracket, I used a piece of 1/16" aluminum 4x10" in size which is readily available at any hobby shop. I simply traced the pattern of the original bracket with the angled side touching one edge and the long straight side parallel to the other side and extended it up 2 3/4". The extra material on the straight side is folded over at a right angle to provide rigidity. By means of a second much smaller bracket, I also attached the socket for the engine plug. Also on this large bracket are attached fuses for the combo relay (30A), fuel pumps (20A), and ignition control unit (15A). I believe the wiring diagram does not show fuses for the combo relay or ICU but my mechanic friend says there are fusible links.... The fuse holders are available at most any car stereo store. They would not be on display as they are what the installers use and cost about a dollar each.

The leads for the engine plug are as follows:

1. (see note *) starter engage wire (blk/yel) to term 50 on ignition switch

   Power will come from the CS 2.5mm blk lead where they both connect at term 50 of the starter. See the section on term 50 of the Starter section.

2. fused power with ignition on (grn/yel) to the pre fuse side of either fuse 6 or 7 where the grn ignition wire (from term 15 of ignition switch) comes in.

   Run a 12ga wire from behind fuse 6 or 7 through the firewall and butt connect it to 2 12ga wires. One will go to a 30A fuse and then to the grn/yel wire. The other will go to a 15A fuse from lead 4 (grn). While you're under there with the under dash panels out, take out your clock and fix it if it is the electromechanical type or send it off to North Hollywood Speedometer if it has white plastic glob coming off the back meaning it's a quartz movement.

3. (see note *) alternator exciter wire (blu)

   Not needed. It goes to the dash alt telltale. You will just use the existing CS plug to the alternator.

4. (see note *) fused power with ignition on (grn) Power to ignition control unit (ICU)

   See explanation for lead 2 above.

5. (see note *) to tachometer & ECU term 1 (blk)

   For the tach, you will simply use the existing CS wire, which is the group of 3 black leads that connect to the neg (term 1) lead of the coil. For term 1 of the ECU, run a black 16ga wire to the stubby wire coming out of the cable next to the plug for the ECU. It provides the pulse reference for the ECU and the car won't run without it.

6. temp gauge (brn/wht)

   Not needed. This is for the gauge on the dash not the ECU. Use the existing CS wire at the t-stat housing.

7. oil pressure sender (brn/grn)

   Not needed. Use existing CS wire to sender above and to the rear of the intake for cyl 6.

8. fused power to fuel pump (grn/vio)

   Take this wire from the engine plug run it into a 20A fuse and then back through the car (14ga) to the fuel pumps.

*NOTE: If you're somewhat fanatic and want to hook up the 528i dx port, these leads go to it on terms 7, 8, 2, and 9, respectively. Term 1 to + battery, term 3 to brake fluid level switch, terms 4-6 empty.

 

ECU Mounting & Firewall Access Hole for Cable

The hole that will fit the grommet on the main cable is oval and measures 1.5" x 2.1". Position it just above the spot welded attachment for the glove box hinge at its medial aspect. This should be between the two hard lines to the A/C evaporator. I made a little paper template, taped it in place, traced the shape, and started drilling and grinding.

I mounted the ECU horizontally under the horizontal portion of the dash with the socket facing laterally. It is mounted quite firmly and won't budge when plugging or unplugging the cable. Refer to the pictures and pay attention to the distances so you don't do what I did and have to remount the computer when you discover that the glove box won't close. If it were mounted much further laterally than I have it, it would be difficult or impossible to plug or unplug the ECU cable.

 

Ignition Control Unit (ICU) Mounting

I mounted this low and very near but not on the front of the inner fender. Just be certain that there will be enough clearance between it and the A/C hoses below it so you can insert the plug from the wiring harness. The pair of resistors needs to mount close to the ICU so wiring loom will reach. I put it several inches below the upper right radiator mount.

 

Distributor

Get a new cap and rotor. Plugs and wires too if needed. Set the engine to TDC BEFORE removing the CS distributor. On injected cars, the rotor should be pointing almost straight forward (3 o'clock when standing at the right fender looking across to the left side of the car) at TDC with the adv/ret vacuum pot at about 12 o'clock. Make sure you're not 180 degrees off by checking the position of the valves to the #1 cyl when the valve cover is off. If you are off 180 degrees, you're liable to blow the AFM off the t-body and into the sidewall of the garage. It makes for a pretty cool explosion but it can damage both the AFM and your paint. I had mine almost right the first time but the car wouldn't start and there was some backfiring through the intake. This backfiring was sissy stuff compared to what happened when I reversed it.... What turned out to be wrong was the position of the distributor. I don't understand why this matters but it does even though I had cyl 1 timed at TDC.

 

Fuel Pump & Lines & Injectors

 

Tank & Pre Pump

Starting at the tank, first make sure the tank is in good shape. I cleaned and lined mine with a 3 step process from POR-15. A presumably similar process that several people on the CS Registry have used is available from Eastwood's (www.eastwoodco.com). Using pre- and main pumps is recommended. Carl Nelson at CNPR (800-466-8184) makes a custom pre pump that will fit in the CS tank. Be sure to request the associated sender unit with new gasket and the plug ends for both the sender and pre pump.

 

Main Pump

I'd also recommend getting the main pump new. The main pump is located on the left side of the car lateral to the differential and behind and lateral to the rear brake apportioning valve. From the trunk perspective, it is located on the panel under the forward trunk floor board. This is where the CSi ass'y goes and it works well because there is an existing hole in a 1.5" vertical portion of the trunk floor through which the larger diameter pre pump-to-main pump line goes. You'll need an appropriately sized grommet here. From your choice of many older 5 series, you will need the bracket that is spot welded to the underside of the car and holds the pump/filter ass'y . This ass'y has its own bracket which then mounts to the spot welded bracket. I ended up having to order this ass'y bracket new. The junkyard guy will have to cut the spot welded bracket from the donor car. You'll need to cut away the excess metal and bolt it to your CS. Spray some undercoating on it before and after mounting it up.

 

Fuel Supply & Return Lines

at right against firewall - lower is supply, upper is return.

This required a lot of grunt work. The stainless line I got at a hydraulic supply company took some time to bend into shape with a little tubing bender. I was lucky in that I had a spare (rusty) line to copy from my parts coupe. You should check if the line is still available new as that would be far simpler. I had just assumed that it wouldn't be. When installing it, I found that dropping the rear sub frame a bit helped a lot. I attached it with several heavy duty zip ties. The new line I made became the supply line and the existing CS line became the return line. Because you'll be making cuts on the line to trim it to final length and you'll then have to ream the ends to get rid of the inward flange the tubing cutter creates, you're bound to get some metal filings in the line after the filter. Because of this, you must flush the fuel line once it's all hooked up by directing the fuel supply line into a bucket just before the hook up to the fuel rail running the fuel pump directly from the battery.

 

Injector Rail and Fuel Pressure Regulator

The usual set up is injectors attached to the rail with rubber injector tubing and the pressure regulator by intake runner #1. The person I got the EFI from had changed this to a Motronic rail in which the injectors are inserted into cups on a square profile rail and held there with clips. This makes it much easier to disassemble the system particularly if you need to replace just one injector. My regulator is between the firewall and intake runner #6. This is the ideal time to replace the 22-year-old probably cracking and soon to be if not already leaking injector hoses if you stick with the original rail. Refer to the FAQ on the First Fives site. Remember to be very careful when removing the hoses from the injectors so as not to scratch or otherwise damage the hose barbs on the injectors.

 

Injectors

Take all the injectors, including the cold start injector to an injector service place to have them cleaned, rebuilt, tested, and, if necessary, replaced. This costs about $20 per injector and is money well spent. Believe me, you don't want to be disconnecting injectors after the system is fully assembled. The injectors are 22 years old and even if well cared for (mine were) can be dirty, can leak, or fail. My local mechanic will not use rebuilt injectors after having to replace them with new injectors too many times. This may be sound advice but on the other hand, new injectors run at least $70 each. You can do the math. I had one stuck injector after the servicing. The place that did it, recommends installing them less than 1 wk after the servicing. Why this is necessary for cleaned and/or rebuilt injectors and not for new ones, I don't know. I had to remove the injector, thinking it had to go back to the service place. Then I figured gently tapping it on the garage floor might free it up and it did. Probably could have done this with a 12" socket extension and a hammer without removing it but, oh well.

For peace of mind, you can check the continuity of the injector plugs to the ECU plug (refer to the ECU and combo relay pinout FAQ on the First Fives site) and the plug that goes into the combo relay (terms 88b & 88e). There is approx 16.2kohm internal resistance at the injectors. Once the injector plugs are on, they can be difficult if not impossible to remove without some intake disassembly. Incidentally, you can buy new injector and sensor connectors at an auto electric place if the connectors on your system are really trashed. They're about $12 each. They can be purchased with or without the wires and there is apparently a tool available to remove the metal tabs from the plastic connectors.

 

Intake

I had all the pieces (plus the t-stat housing & valve cover) except the AFM and throttle body bead blasted for about $50. Use all new gaskets. Check all air hoses and be liberal with replacement if damage is found, especially the accordion boot between the AFM and throttle body. I used intake runners from a 320i, which are supposed to provide a noticeable increase in low-end torque. Check out the FAQ on the First Fives site. In order to hang wiring and fuel lines from the intake runners, I had two of them (cyls 2 & 4) drilled and tapped to hold a bracket, which then holds a cable clamp. I found the cable clamps by chance at a random auto parts store I was in looking for something else. The maker of the cable clamps is Umpco but that wasn't listed on the package. Refer to the pictures.

 

Exhaust

You will need to have a boss mounted for the O2 sensor. A mechanic friend of mine who has experimented with its position, says that it's best placed on the down tube near the firewall 12-18" distal to the connection to the manifold. While Motronic systems are apparently sensitive enough to require a bridging tube between the down tubes with the sensor mounted there, the L-Jet system is not. I mounted mine on the front down tube in a vertical plane with the top of the sensor angled about 20 degrees to the right side of the car. It was done at an exhaust shop for $25 while I waited. Pointing straight up may be best from an ease of replacement standpoint but there are other options with regard to this as well. You'll have to decide what works best for you. Just keep in mind that its position dictates how the wire is routed. Close proximity to exhaust, suspension, and steering components is bad and the wire should not run too close to plug wires due to electrical noise. For just that reason, the O2 sensor wire is shielded once it enters the ECU cable. I used new down tubes and sent them along with the manifolds and heat shields to Jet Hot after the boss was mounted. The O2 sensor (single wire) connects to the green wire coming from the main cable to the ECU.

 

Wire & Fuel Line Routing

Working on the 1000 words theory, refer to the labeled pictures. Do what you like. These just show how I did it.

 

Troubleshooting

There will definitely be some of this after you're done. Count on it so that you're not too disappointed when you make that last connection and it doesn't turn out to be plug and play. The problems I ran into were: distributor inserted incorrectly, AFM door spring tension way too tight giving lean mixture appropriate for Denver but not sea level where I am, bad AAV that was always open, a bad O2 sensor, and finally the female connector inside the combo relay plug for one of the two power leads to the injectors (one for injectors 1-3 and the other for 4-6) would slip down and fail to engage its male pin from the combo relay.

One thing I've gradually discovered is that virtually everything can be tested and diagnosed without disassembling a thing by observing starting and running behavior and by having a multi-meter, the wiring diagrams, and the ECU and combo relay pinouts from the First Fives site. The most you'll have to do is unplug a few things to gain access to the pins for continuity, resistance, or voltage checking.

I'm not going to go into much detail here but I will give a few quick checks.

1. Fuel pump: when the AFM door is slightly opened with the ignition switch on, the combo relay should click and the fuel pump should run. If it doesn't, the relay is probably bad. It can be repaired. Check First Fives FAQ. Alternately, the contact inside the AFM could be bad but that is highly unlikely.
2. Combo relay: as mentioned above it has relays for the fuel pump and injectors. With the ignition on, you can do test #1 above or test #5 below checking power to the injectors.
3. Fuel pressure: should be in about 28psi at idle. The easiest place to check it is at the fuel hose to the cold start injector. Also, once the system is pressurized it shouldn't drop much below 24 or so after you shut it off. If it does drop off rapidly, it may be a bad check valve in the main fuel pump.
4. Individual injectors: ECU unplugged, ignition on, fuel system pressurized by opening AFM door briefly, fuel pressure gauge connected. Briefly (less than 1sec) bridge each ECU injector pin to one of the ground pins. If the injector is working, you'll see a drop in the remaining fuel pressure.
5. Power getting to injectors? This is sort of a trick question because when the ignition is on, there is +12V to both pins of each injector plug. That can be checked with the ignition on by running each pin of the #1 injector plug to ground with a test light or volt meter. Use the #1 cyl because you can unplug it without taking anything else apart. The ECU works by allowing a shaped partial-to- complete ground to a given injector pin when it is its turn to fire. Check this by putting a test light across pins and crank it over. The light should flash. If it doesn't and there was initially 12V at each side, the only thing left is a bad ECU.
6. AFM door tension: air filter off, car warmed up and running, O2 sensor unplugged, holding throttle at 2-3k rpm, advance the AFM door. If speed picks up quite a bit before it starts to stumble, it is set too lean. The stumbling occurs as it becomes too rich. This assumes no vacuum leaks and accurately set timing. Spring tension needs to be loosened which I won't be going into here.
7. Aux air valve: put it in the freezer for a bit. When it comes out it should be at least 2/3 open. Hook it up to its plug and turn the ignition to on for a few minutes. It should now be completely closed and difficult to blow any air through. Although they can sometimes be loosened up with WD40, be prepared to replace it if there is no movement.

   NOTE: If you are using an 80-81 system from the start where one pin for the AAV goes to pin 34 on the ECU, I don't know if this is always at 12V when the ignition is on or if 12V is supplied after a certain temp threshold is reached. Since I have a converted 79 system with 80-81 AAV, my power lead does not go to the ECU but instead to term 50 of the starter and is therefore always at 12V with the ignition on. Potentially, you may have to simply supply a 12V jumper to the AAV from the battery to test it.

8. Coolant and AFM air temp sensors: car cold (whatever ambient temp is) then warm (about 80 degC), ECU unplugged. Check resistance at ECU plug between the appropriate and ground pins. Reference ranges (same for both): 68 degF (20 degC) 2-3kohm, 104 degF (40 degC) 900-1300ohms, 176 degF (80 degC) 250-400ohms. Bad coolant temp sensor $15, bad AFM temp sensor $270 at alloembmwparts.com (cause you're buying a whole new AFM).

   ECU function note: as the AFM door opens further supplying more fuel, the resistance on the AFM wiper track is increasing. This means that the more resistance the ECU sees from whatever source, the more fuel squirts out of the injectors. Just a little tid bit for you. Example of practical application: you want to enrich the mixture for whatever testing reason - unplug (infinite resistance) the coolant temp sensor.