FAQ - Frequently Asked Questions about BMW 745i Engine and Self leveling System

We have just started to build this page. Right now here are more questions than answers, but we try to fill it in as soon as possible. We are working also on other Q's and A's of general interest. If you have good questions (and answers) to add here please send us email.

1. How do I know which Motronic box is in my car? 2. Do I have L-Jetronic or Motronic ECU?

3. What is the most common engine problem?

4. 745 Motronic and manual transmission?
5. Can I use other ECU wire harnesses with 745 engine? 6. Should I replace SLS with normal shocks?
7. Can I have higher RPM limit? 8. How steep cam is possible in street use?
9. Can I install 745 turbo into a 735? 10. How do I install Turbo and other gauges?
11. What is the most economical and easiest way to get started with 745 tuning?
12. How do I convert PSI to bar, Nm to lbf-ft, etc...? 13. Can I modify the KKK-27 turbo for even higher power?
14. I live in UK. Can I install 745 engine in RHD car? 15. Which are correct Fuel Injectors for 745?
16. Why should I spend money and time on a 16-23 year old BMW 745? It's not a classic car; not even a sports car.
17. Do you have chip upgrades for other BMW models? 18. Which repair manuals are available?
19. Can I turbocharge my 5/6/7 Series 2.8/3.2/3.3/3.5 L M30 standard engine?
20. Math formula for road speed: How to check your speedometer 21. Should I use bigger fuel injectors to increase power?

 

 

 

 

 

 

 

 

 

 

 

1. How do I know which Motronic box is in my car?
Open the front right loudspeaker cover. The Motronic box is behind it. The type code is on the Motronic box cover. You do not have to take out the box. The right 745i Motronic unit is 0 261 200 013 or 0 261 200 024. For more information go to My Motronic?. Note that some 745i owners have also installed 0 261 200 018, 0 261 200 019 and 0261 200 025 Motronic boxes "successfully". Those boxes are from other models of BMW engines and DO NOT operate correctly in an 745 engine! However, at least Motronic version 0261 200 025 could be modified by changing few components and reprogramming those to fit 745i.
Note that 745i Engine Control System includes two computer boxes in the cockpit:
1. Motronic 0 261 200 013 (024) behind the loudspeaker
2. Knock sensor unit 0 261 201 003 in the glove department
You can see here the picture of the wire harness

2. Do I have L-Jetronic or Motronic ECU?
See question 1 for fool proof identification.

3. What is the most common engine problem?
Air/pressure leaks. The 745i engine has a lot of pressurized hoses and tubes in the intake chain. Leak in any of those will cause engine malfunction or full stop because of computerized mixture analysis. If you have a problem always check first for a leak. A good practical way to monitor leaks is with turbo gauge. Drive at reasonable speed (100 km/h at 3rd gear) and take your foot off the gas pedal. The turbo gauge should go down below -0.5 bar. Anything less than that and you have a leak. Good way to locate leaks is spraying "start pilot" fuel (or CRC) around hoses at idle RPM. If RPM's increase suddenly, then that is where you have a leak.

Another common problem is that engine cuts off around 3000-3500rpm. While accelerating, all the sudden the engine loses all the power and it comes back after rpm goes down and will be lost again after same rpm value have been achieved. This we have called "kangaroo gasoline effect". In most of the cases it is caused by stuck wastegate. In some cases the wastegate can be repaired, in some a replacement is needed.

4. 745 Motronic and manual transmission?
See wire harness information in More.../Motronic section.

5. Can I use other BMW ECU wire harnesses with 745 engine?
This question has come up many times when people want to install 745 engine into some other BMW model.
The answer is I don't really know how easy or difficult it would be. I do not know all the different wire harness versions, but I know the 745 wire harness. You can judge this question yourselves by comparing your system with the information I have put together of the 745 Motronic system in Motronic section of these web pages.

6. Should I replace SLS (Self Leveling System) with normal shocks?
Your SLS system can be repaired to last as long as your super car. Don't throw away that excellent system with first problems! The SLS system is essential part of the 745i car (it was available also for other models). Considering the classic car status it is important to keep these kind of parts of the car as original as possible. That will add considerable value to the car. The vast majority of the problems is in the SLS Pump. It is very expensive (some 2000$ in the USA), but can be totally rebuilt to last next 15 years or so.

7. Can I have higher RPM limit?
That will be possible. RPM limit is one thing. Shifting points is other consideration. If we increase the max. RPM limit we also have to increase the shifting points at least in the "S" mode accordingly. We do not usually recommend to increase the RPM limit because of safety and reliability reasons. Standard 745 pistons are good for piston speeds of approx. 15.7 m/s. To increase RPM limit one should change the pistons to higher quality. Also, with standard cam shaft the max. power and torque are well below the standard rev. limit.

8. How steep cam is possible in street use (M30/M102 Motronic engines)?
Keep it below 290.Anything above that will affect idle and low R.P.M. characteristics too much for meaningful street use.The standard duration is 264. Always buy complete cam assemblies when you change the cam duration. At least following versions are available: 276, 280, 282, 288, 290, 300, 308 and 328.

9. Can I install 745 turbo into a 735?
This is one of the most frequently asked questions. We will address this question later on with better detailed information. Right now see answer no: 18 for some more info.

10. How do I install Turbo and other gauges?
You will find example installation instructions in Gauges section in our web pages.

11. What is the most economical and easiest way to get started with 745 tuning?
The most economical and easiest way to get started is the Motronic Chip Upgrade. In addition you only need a turbo pressure gauge and a simple valve to restrict air flow to the wastegate control hose (do not bleed the hose for higher boost!!!). Total cost is about 300$. This is a good way to start and to get the feeling of considerably higher power and torque. In this set up you should limit the boost to about 0.7-0.8 bar (about 300 hp/450-500 Nm). You can install the valve close to the wastegate or into the cockpit (this is recommended as that same valve can then be used with the adjustable wastegate, if you decide to upgrade). This is very useful to start with. The max. full throttle boost in this set up is about 0.6-0.7 bar giving 0-100 km/h acceleration of approx. 6.3-6.5 s., which is already an exellent figure for any automatic sports car. More importantly, the middle range boost is about 0.7-0.9 bar giving tremendous acceleration in the 60-160 km/h speed range. More detailed instructions in the Start-up Kit and Wastegate sections of these web pages.

12. How do I convert PSI to bar, Nm to lbf-ft, etc...?
Download this exellent convert.zip program made by Josh Madison. It has everything.

13. Can I modify the KKK-27 turbo for even higher power?
Yes you can. You have two main possibilities:
1. Go to your local turbo specialist and ask them to custom modify the wheel. This is what Juha Tuoma did.
2. Increase the turbo compression wheel and housing from 52 mm to 56 mm inlet side. This version of the turbo is used in Porsche 959 so you can buy it from them.Important note: This concerns only the 3.2 L engine! The 3.4 L engine already has a bigger turbo.

14. I live in UK. Can I install 745 engine in RHD car?
No. There is no room on the right hand side of the engine for both the turbo assembly and steering mechanism without major redesign.

15. Which are correct Fuel Injectors for 745?
We have learned that surprisingly many 745's have been equipped with wrong injectors. Here is the list of injectors, that were used in different BMW's during the 1980's. Injector coding is as follows ( numbers are stamped on injector body):
0280 150 126........167 cm3/min
0280 150 130........185 cm3/min
0280 150 200........271 cm3/min = 745i
0280 150 201........236 cm3/min = M6, 735
0280 150 203........185 cm3/min
0280 150 208........133 cm3/min
0280 150 209........176 cm3/min
0280 150 211........146 cm3/min
0280 150 715........149 cm3/min
0280 150 716........134 cm3/min

2.5 bar nominal operation pressure: 0280 150 126/200/208/209/716
3.0 bar nominal operation pressure: 0280 150 130/201/203/211/715

The extra injector is for cold start only and is located underneath
the intake pipe. Its capacity is only 93 cm3/min. It is controlled by the DME.

16. Why should I spend money and time on a 16-23 year old BMW 745? It's not a classic car; not even a sports car.
You are dead wrong on this one! In many parts of the world it is already considered as a classic car. Many consider it also a sports car and some drive it in tracks. To me it is one of the best ever combinations of ageless body design, luxury comfort, top reliability and high performance. It is still today an eye turner and I've seen more and more articles of the restored 745's in top car magazines. The 745 is still today fairly economical "hobby" in comparison to many other classic cars, but the situation is changing fast. All 745's were manufactured on order only and it was the most expensive model available from BMW at that time (Over 100.000 DM in 1985). If you spend few thousand dollars to restore your 745, it is not much compared to many other hobbies, but with the 745 you have concrete, permanent results. How much one can spend e.g. on golf a year? You can still buy "project cars" at reasonable prices especially from Germany, where there are still some 500-700 745's on the road, but not for long. Prices for restored 745's have gone up already to 15.000-22.000 euros (approx. 17.000-25.000$) in Europe. When I have time I will make own web section of this interesting subject including e.g. history and manufacturing statistics of the car.

17. Do you have chip upgrades for other BMW models?
NO! We only work on 745i Motronic code. However, some of the other products listed in Related products section of our web pages may be of use in other BMW models.

18. Which repair manuals are available?
The newest one is E23 CD from BMW. Order no 01 560 030 284. You can buy also from BMW their "ETK" CD, which has pictures and spare part numbers of all BMW models. There are no schematic diagrams or repair instruction. Chilton has a book covering Models from 70 to 88. Order no 18300(8789). Factory Repair Manual is available at approx. 135$.
If you know of any other publication pls send us email and we add the information here.

19. Can I turbocharge my 5/6/7 Series 2.8/3.2/3.3/3.5 L M30 standard engine?
Yes you can. You can buy complete turbo kits from e.g. Mosselman or Korman (go to our Links-page for further info). These are low boost kits, which do not require any changes inside the engine. Typical power increase is +30% and torque increase +50%. Price level is 5000 €. Many times a good idea is to ask your local turbo specialist for a quote for their solution. Many have asked if they could install the turbo parts from a 745 engine into their engine. It is possible, but requires good knowledgement of the 745i engine as there are quite a lot of differences, and you can never reach the full 745i performance in this kind of "hybrid". We have only worked on M102 engines, so we do not have any practical experience on these questions and therefore can not really help you in these kind of projects. However, you may find some of the technical information in these pages useful in such projects.

20. Math formula for road speed: How to check your speedometer
Here is an example how to calculate real road speed. It does not necessarily refer to any particular car.
The engine Revs Per Minute is 2500
The transmission output ratio is .73 = 1.37 revolutions per revolution of input
The differential ratio is 2.93 for one revolution of the tire axle
The tires are 195/60/14 inch : Circumference of the tire in feet= 2TT(3.14159)x Radius (11.75 inches in this case) divided by 12 inches in a foot = 6.14 ft per revolution of the tire
Road speed formula = 2500rpm x1.37 transmission output ratio divided by 2.93 differential output ratio x 6.14 feet
per revolution at the tire x 60 minutes in an hour divided by 5280 feet in a mile= 81.5MPH

21. Should I use bigger fuel injectors to increase power?
Here are some ideas about the fuel supply and over-sized injectors.
I personally would try to avoid using over-sized injectors as long as possible. In non-turbo conditions those would just inject more fuel meaning that the engine would run richer with poorer mpg. The same happens when one replaces the 3.4 L Motronic standard 2.5 bar fuel regulator with the 3.2 L L-Jetronic 3.0 bar fuel regulator (some people have done it).

I prefer following approach:
1. Replace air filter with a free flow air filter like the K&N 33-2005
2. Replace standard exhaust with either 2*2.5" or 1*3"

With this basic set-up one can expect following basic performance with modified chip and adjustable boost:
At 0.7 bar boost 350 hp
at 0.9 bar boost 400 hp
At 1.1 bar boost 450 hp

The mixture would start to go lean somewhere above 0.7 bar.
3. Add Rising Rate Fuel Regulator ( Like the BEGI; photos available)
This will kick in as soon as needed and keep the mixture correct upto somewhere 1.5-1.7 bar with standard fuel injectors.
So now you would have
At 1.3 bar 500 hp
At 1.5 bar 550 hp
At 1.7 bar 600 hp

If even more fuel/hp is needed then I would ADD two fuel injectors into the intake manifold (some photos of such set-up are available). Those are boost pressure controlled. One can buy a specific injector controller box for these kind of injectors. You can preset the injector on-point to desired boost level (e.g. at 1.5 bar). With this system you can probably add about 0.5 bar usable boost, so now you would have
At 1.9 bar 650 hp
At 2.1 bar 700 hp

As a summary here we have a "chain" of power levels from 252 hp to 700 hp with standard injectors and ideal fuel maps for also for non-turbo driving conditions.

Some other comments:
- a steeper camshaft would increase the starting power level by some 25 hp thus increasing the power with same amount throughout the "chain". I personally would not make this kind of change immediately .
- I have seen in the discussion forums that people claim that the standard Motronic 3.4 L 745 injector size is this or that ( 300 cc, 320 cc, etc...) . The correct injector is 0280 150 200 = 271 cm3/min . You can see the version number on the injectors. The Motronic program is based on that fuel flow volume. If you use a lot bigger injectors the mixture will not be ideal anymore and the Motronic box should be reprogrammed. Of course there is some tolerance built in to the system, so I guess +10- +15% higher flow is not so bad. Plus 10% higher basic flow of the injectors would give you in theory plus 10% in max. power.

I hope this gives to you some ideas how to proceed with your project. Don't kill me if you will not get same power levels as I predict above. These are just guidelines.

Happy New Year,

Jarmo