BMW 750iL
Current To-Do List:
- Air/Fuel Related
- Replace a cracking fuel hose (part has arrived)
- Check Engine Light at idle – I need to determine whether the car is running rich or lean, and on which sides, then figure out why and how to fix it.(Q1 2012)
- Front Suspension
- Misc. wear items ($35)(Q2 2012)
- Shocks ($320)(Q2 2012)
- Replace passenger distributor cap and rotor ($50)(Q2 2012)
- Replace driver’s seat memory switch (burned-out bulb) ($60)(Later)
- Fix sticky driver’s-door handle ($)(Later)
13 Feb 2012: Making progress on custom transmission control module…
It’s been a while since I’ve discussed this, so I’ll briefly touch on what I’m working on, how it could improve the car, and where I’m at on this project.
I’ll ultimately write my own software, and design hardware to interface with the car to replace both the EML and transmission control modules. The EML is the module that controls the throttle bodies, and is also closely tied to the cruise control system. The TCM controls the transmission solenoids. In the ’92 750iL, there are 4 solenoids – earlier model years had 5.
By making my own TCM, I can control when the car shifts gears. I’ve run some mileage tests over about 1,000 miles, and have determined that accelerating quickly in lower gears, then shifting to the highest gear is the same mileage overall as leaving it in Economy mode, where it up-shifts quickly, which hurts acceleration. By making my own TCM, I anticipate not only improving the overall acceleration of the car under typical driving conditions, but I could also improve mileage – particularly from 40MPH to 65MPH. In any case, my 1,000 mile test shows that regardless of how I program my TCM, I should expect the mileage to stay the same or increase.
I noticed that the mileage increases dramatically when the torque converter (TC) locks – which happens around 60-65MPH. Where I live, the highways are all 55-60MPH, so the TC is always unlocked. The difference is ~14MPG at 60MPH with it unlocked, and ~17MPG at 65 with it locked on level ground, warmed up. That is over a 20% increase in mileage!
I’ve purchased a used TCM to tear apart – that way I can use the real connector and metal enclosure for my TCM, while leaving the original one alone since it works fine. This also means I won’t have to splice into any wiring. I am designing 2 separate circuit boards for the TCM: One that converts the OEM connector to a ribbon cable, and the TCM itself. By using a ribbon cable, I can easily modify the hardware later on to add more features such as paddle shifters. Below is an image generated from my design of the connector circuit board:
Top
Bottom
These are images of the actual TCM I’ve designed:
Top
Bottom
Done so far:
- Purchased another TCM to use the OEM connector and enclosure from
- Designed a circuit board to connect a ribbon cable to the OEM connector
- Designed the TCM hardware *
- Tested a minimal version with the engine running to ensure proper display in the instrument cluster, with no errors of any kind
- Written fault-tolerant serial communication to use between the 2 CPUs in my TCM design. This means that if the CPUs ever can’t communicate or the transmissions have corrupted bits, the receiving CPU will trigger the hardware line to the Check Control Module for the TCM. This means a “Trans Prog Error // Owner’s Manual” message will appear on the instrument cluster, and the transmission will go into fail-safe mode.
Left to do:
- *I still need to determine the format, amplitude, and frequency of the transmission speed, RPM, and throttle position signals. Everything else in hardware is done.
- Still need to write the software for both CPUs
- Order the circuit boards, install the parts and software, and test, test, test outside the car before using it!
By making my own EML module, I can dramatically improve the throttle response, and un-limit top-speed (not that I would ever take a 20 year old car to top speed). My goal is to have the EML emulate the current smoothness of the throttle response when the transmission is in “E” / Economy mode. When the transmission is in “S” / Sport mode, I’ll push the response time way down to make it more like a drive-by-wire system. I still have not decided whether “M” / Manual mode should have “stock” response or not. I’ll probably wait until it’s ready and try it both ways. For now, my focus (and most progress) has been on making my own TCM.
15 Jan 2012: Look how much leg-room there is!
I bought a used transmission for my Z3 with about half the miles. I estimate that (if I didn’t care about the car) I could have fit SIX Z3 transmissions in the car, without even using a seat! At least three could fit in the trunk – maybe four; another one could fit in front of each of the rear seats, and one in front of the passenger’s seat.
I didn’t want it rolling around in the trunk destroying everything in its path, so I kept it where I could see it. As it turns out, it didn’t move at all – of course, I was driving carefully. It’s not shown, but I put another piece of heavy cardboard to the side of it to protect the door panel.
If you can fit a transmission in front of your seat, you probably have enough leg-room.
05 Dec 2011: New Suspension Pressure Accumulators
This has made the vehicle into a whole new car! When I replaced the accumulator in the brake system, the brakes were a lot better; now, the suspension is a LOT better!
For example, I can no longer really feel the change in grade when backing out of my driveway slowly. Going over bumps actually feels good, you barely feel anything. I notice that the seats don’t have to take nearly as much of a beating since people aren’t bouncing around. If these had been replaced sooner, I bet the seats would be in better shape. $600 for the 3 pressure accumulators – parts only – and it was worth it.
One problem I had was that the hose was VERY hard to remove without damaging the fitting, and I didn’t have a vice. So I made my own using partial-weight of the car:
04 Dec 2011: Images of Speaker Repair
This first picture shows the new mid-range speakers in the rear. They are a slight upgrade from stock. One of them was blown so I replaced the pair. I had to drill out the old rivets and use new ones – luckily I already have a rivet gun.
This shows the speaker as it was being repaired. The outside edge of the foam was held on first by rubber cement, then I used hot-glue to hold the outer plastic frame over it. For the inner edge, I used rubber cement first, then sealed the connection with wood glue (visible yellowish glue seen below).
Here, all the glue has dried, and the speaker is properly sealed. The cone was centered correctly, so there aren’t any scratching noises when using the speakers.
They sound great now!
04 Dec 2011: Images, Video of Power Headrest Cable Repair
Below, you can see the beginning of the power headrest cable fix. I’ve cut the sheath open, removed the cable, and removed about 1/2″ of the sheath. The cable is now ready to go back in, and then have everything secured.
Here, the work is done. You can see the shortened cable sheath, with heat-shrink holding everything in place.
Video
26 Nov 2011: Slightly Positive Crankcase Pressure
This is usually caused by one of two things: bad valve-stem seals, or a bad PCV or PCV check-valve. I’m lucky because it is really, really low positive pressure, and the oil filler cap is a little loose to help relieve that pressure, so I don’t think any damage was done, but I’ll stop driving it until it’s fixed.
When I did all the engine work earlier this summer, there were 2 areas where I didn’t replace parts, to try and save money:
- Distributor caps / rotors / spark-plug wires
- PCV valves and PCV check-valves
Coincidence? I’ll know when I replace the PCV and check-valves. The reason I looked into this was because the check-engine light is back on at idle. It goes away whenever I give it gas, but it’s very annoying. The DME code is 201, “O2 Sensor Control”, meaning the car is either so rich or so lean it can’t compensate. since the throttle bodies are virtually closed at idle, I’m assuming it has to correct by giving it fuel, and can’t give enough. If it had to correct the mixture by adding air, it would just open the throttle body a little more.
Causes for this could be: bad O2 sensor (it’s new so that’s not likely), bad DME (unlikely but not unheard of), vacuum leak, exhaust system leak (but it looked REALLY solid when I took it off to replace the O2 sensors), plugged injector(s). Could positive crankcase pressure emulate a vacuum leak?
If nothing else, I hope replacing the PCV valves and check valves helps the crankcase pressure to become negative again. This way the engine is running like it was designed, if it’s burning oil now, it will burn a lot less, and it should help with emissions. The oil cap has a bad seal, maybe due to the positive pressure. Once it’s negative again, I’ll need to replace that, otherwise there will be a vacuum leak from that cap.
I guess all this shows is that if you’re going to the trouble of replacing almost everything, you might as well just spend a bit more and be done with it.
11 Nov 2011: Matching Side Mirrors
I got the side mirror I ordered, so both match now. Both are heated with the “split” view. I did solder extensions onto the mirror heater wires so I could install them both “backwards”. I think it’s a lot more natural to have the distorted side of the split-view be the side closer to the car.
I guess this could be an issue if I let someone else drive, and they’re bad at parking. I doubt anyone else will be driving, and they could always move the mirrors to be able to see more clearly.
28 Oct 2011: Fixed Driver’s Seat Power Headrest
I noticed a couple days back that the driver’s power headrest stopped working. I was originally going to replace the cable for $12, but soon realized that dis-assembly would be very difficult, and I might end up breaking something along the way.
The cable stops working when the internal cable shrinks, but the outer sleeve stays the same length. I ended up fixing the cable by slicing the outer sleeve of the cable, pulling the internal cable out, cutting off about 1/2″ of sleeve, and putting the cable back together. I used some heat-shrink to hold the cable together and keep the grease in. The total cost ended up being next to nothing (for less than 25 cents). The driver’s power headrest works again.
21 Oct 2011: New and Repaired Speakers
I replaced both rear mid-range speakers since one of them was blown. Since I have a riveting tool and a grinding wheel, it was very easy. They sound better than stock. There was also a blown 6.5″ in the rear, and a 5.25″ in the front. I started repairing the 6.5″ speaker, and so far, it sounds perfect! It might last forever, it might only last a few days, we’ll see. Same goes for the 5.25″ speaker.
I kind of guessed when I was repairing them, and ended up using 3 different kinds of glue on each speaker: rubber cement at first, followed by hot glue to seal the outer edge, and wood glue to seal the inner edge. They look pretty good, and sound fine. Lets hope it stays that way.
20 Oct 2011: NO MORE LEAKS! Brake lights work correctly now
Earlier this week, I was able to adjust the brake-pedal switch so the brake lights come on a little later. It was to the point where moving the pedal less than 1mm would trigger the brake lights, and sometimes they would stay on with my foot off the pedal, at least when it was parked.
All I had to do was bend the metal piece that contacted the switch so that the pedal now has to be moved ~10mm before the lights come on, which is perfect since braking starts around that point. The metal piece was exactly at a 90-degree angle after I “bent” it, so I think I just bent it back to where it should be. Amazing how many little things can be off in a 20-year-old car.
As an added bonus, the transmission does not leak any more, which means there are NO leaks! Maybe 5-10 drops of oil per week now, but that’s hardly worth putting money towards to fix. What did I do? Nothing. I was so busy in school I just ignored it. It turns out that I slightly over-filled it because the dipstick-marks were misleading. When checking the level, the correct fluid level was exactly at the point that I thought meant “low”. I checked the level and it’s perfect. The car drives great, as always.
04 Oct 2011: Brakes work better! Suspension is next…
I just replaced the brake pressure accumulator (aka “brake bomb”). The part was rather expensive at about $300 shipped. Basically, it’s a metal ball with hydraulic line attachments, and a bladder with a charge of nitrogen gas inside. The gas helps keep pressure in the brake and steering systems so the pump can work less. It also serves as the only source of appreciable brake pressure if your main belt breaks!
When I removed it, it was full of pentosin fluid – not gas – which meant it was completely shot. The good news is that the brakes now work 100% when I slam on the brakes. Previously, the brakes worked fine when lightly adding pressure, but when slamming on the brakes, there would be a 1-1.5 second delay!
Seeing how this pressure accumulator was bad, I figure I should replace the other two pressure accumulators on the car. They are both in the rear suspension system. Currently, the rear suspension bounces all over when you go over a bump. When I replace the suspension pressure accumulators, I hope the results will be as noticeable as they were for the brakes.
06 Sep 2011: Finished Tapping into the Phone Keypad
I always make a bunch of piggy-back circuits that let me add features to my cars (adding one-touch up windows in the back, for example). Since the phone was of no use, and it has a nice keypad, I am hoping to use it as an input center for all the circuits I eventually add. It would be an alternative to plugging in a USB cable (that I haven’t installed the port for yet), and running custom software that I have only partially written, to alter settings in the various control modules I’ll be adding to the car.
I tapped into the buttons 0-9, “Send”, “Clear”, and “Power”. “Send” and “Clear” are pretty straightforward; I have not figured out what I’ll do with the “Power” button yet, but I’m sure it will be good.
*This video is probably best not watched in full-screen. I was moving the camera around a lot.
05 Sep 2011: Ambient Lighting on the Center Console
The E38 7-series (the generation after this car) has ambient lighting. It uses two LEDs in the dome light that shine down on the center console area where you might keep drinks, a cell phone or a credit card.
I’ve added this feature to my car – in one day! I use two LEDs in the rear-view mirror.
05 Sep 2011: Improving the Trunk Lighting
A HUGE IMPROVEMENT!
04 Sep 2011: Adding an Illuminated Gear Shift Indicator
Fairly useless since the cluster already displays the gear lever position, but I think it adds a touch of completion to the area.
02 Sep 2011: Old video of engine disassembling
I had already planned on replacing all the fuel hoses, so I was just having a bit of fun.
01 Sep 2011: Fixed the vacuum leak – and the Check Engine Light at idle!
I fixed the vacuum leak, and didn’t even have to remove any fuel hoses. I had to remove a throttle body and an air intake tube, tightened 3 bolts (they were already torqued to spec. I just just tightened them more), and no more vacuum leak or Check Engine Light.
Unfortunately, this means I wasted the $110 I spent on oxygen sensors, since they were most likely good. The real problem is that I was fixing and replacing too many things at once, so I lost the obvious cause-effect relationships since I was adding so many variables by working on everything simultaneously.
The lesson: if you do a bunch of engine work, start it up and think “It shouldn’t be making that hissing noise, should it?”, you’re probably right.
30 Aug 2011: Plans for a more integrated Power Windows Controller
I’m planning on designing and building my own controller that will take as input the following:
- LOCK and UNLOCK signals, so that I can have all the windows and the sunroof roll up automatically when I lock the car, for example. Also I could have it so that if I unlock the car, say, 3 times in 30 seconds, all the windows could be rolled down all the way.
- Door switches (4), so I know when a door is open or not. Occasionally a door won’t close all the way if I’m gentle (and I usually am), so I could have the window of a particular door open 1/2″ or so whenever it’s opened, then go back up when it’s closed again.
- Ignition (ACC) signal, so I can automatically roll windows up, if they were previously rolled down 1/2″ to make door closing easier, for example.
- Window Position Micro-switches (8), so I know if a window is fully up, fully down, or in some unknown middle position. Then for example if I’m rolling windows up if I locked the car, it wouldn’t need to roll up windows that are already up, saving a little bit of power and wear on the motors.
- Temperature sensors (inside and outside). Say I leave the car with the windows down (I don’t lock it). This could: raise the windows if it gets too cold, or it could crack the windows an inch and tilt open the sunroof (to avoid things dropping into the car) if the temperature inside is too hot.
- Ambient Brightness sensor. As above, say I leave the car with the windows down but it’s warm enough that the windows don’t go up. The brightness sensor would sense that it’s getting dark and could roll up the windows.
- Rear Windows Enable Switch input, so the controller can know whether the rear windows should be disabled. In this case, the controller will do nothing with the rear windows, and will continue working with the other windows as normal.
The controller will give as output the following:
- Sunroof Switch Outputs (3). The sunroof has 3 outputs on the switch: close, slide open, and tilt open. Tapping into these will allow control of the sunroof. I’ve not yet looked into the intricacies of how I’d work this.
- Power Window Switch Outputs (8). Again, I’ve not yet looked into the intricacies of how I’d work this. I believe that each window is controlled by two wires, but I don’t know if I can control more than one window at once in this car. This is how I propose to control the four power windows.
Possible issues: I’ve done something similar on my Z3, but it requires far fewer input and outputs (no sunroof, only two windows) so it fits on a 28-pin controller. The programming will require more space than my larger, 40-pin controller can fit.
My options include using 2+ controllers that are networked together, or searching for an even more capable controller. Either way the cost will be higher, so I’ll probably search for a larger micro-controller.
I’m thinking the ATMEGA1284P. It is pin-compatible with the 40-pin chip I already have, but has two UART controllers (easier to network), and it has 16 times as much programming space! The down side is that in low quantities, it costs about $12 per chip, compared to $3! Maybe once I test things and get a working prototype, I’ll submit my circuit board design to be professionally made so it’s more reliable and looks cleaner. This would be a Dec-Jan project at the earliest.
27 Aug 2011: Need to re-tighten intake manifolds
I noticed after all the work I did that there was a whistling noise like a vacuum leak. Today I had my dad look at it, and as he leaned in he pushed down on the RH intake manifold, and no more vacuum leak! I was close, but had never pushed down on the intake manifold, so I never quite located the noise.
So, I’ll have to remove a LOT of parts just to re-tighten those manifolds. Then the only real issue is the Check Engine Light coming on at an idle (running either rich or lean), but that was there before any of the work I did, so who knows what’s causing it.
Fuse box light (LED, timed)
The fuses in the fuse box are too hard to see at night without a flashlight. I figured it would be nice to put a strip of LEDs over the fuse box, design a timer circuit for it, and wire in a switch so that the light is only on when the fuse box lid is taken off. I decided on a 3-minute timer; if the light goes out and you need it back on, all you have to do is tap the switch with your finger and it comes back on for another 3 minutes.