CDI Engine Does NOT Start! :(

Purpose: Assist debugging a non-starting Smart Car CDI

The information presented below has been collected and organized from posting by many people who have put considerable time and effort into understanding the inner workings of this quite amazing OM 660 engine and the quirks of its integration in the Smart Car 450. This page is an exercise is to pull the information together for ease of access.

This page is structured in a sequence of blocks. Each block is a functional prerequisite for the next. Or more simply put, check the blocks in the order presented on this page.

Immobilizer Anti-theft

The immobilizer is a very secure system. It is a horribly expensive thing to replace. Some functions, like programming a key fob can only be done by a Mercedes dealer who still needs access to folks in Germany.

I was told that the process and security to unlock the car is separated from that to start the car (from Mercedes mechanic who tested my dysfunctional key fob). The fob has at least 1 rolling secret key code that needs to be synchronized with the control unit. When you get a replacement key, there is some process where a functional key together with the control unit generates a seed code that gets sent to Germany. This generates a NEW set of codes to program into both the keys (this implies that a used key fob might be re-programmable but no evidence to this being possible).

It is very important to have two key fobs. If you lose your only key you are totally hosed and apparently have to junk the control unit and replace. And it is expensive.

1. Does the car unlock properly? [unlock symbol in dash is NOT present]
   

• Does the car lock with the 3 flashing signal lights? (check that all door are properly closed)
  
• When it tries to unlock ... does it flash multiple times? (bad key fob circuit, likely fatal to fob)
  
• Does it work with your backup fob?
  

1. If NO - bad fob or battery (buy new from dealer or online, must be programmed by dealer and requires backup key fob)
   
2. If NO - bad immobilizer (need complete package with keys if buying used)
   
3. If NO - is the car battery totally drained? (do the headlights seem bright when turned on? Radio? Fan?)
   

The ignition switch itself is purely mechanical and you can use and leave a mechanical key in the slot (not sure why this is a good idea). That said, a mechanical key can open the rear hatch and you can gain entrance if you are otherwise locked out.

1. If you key fob battery totally dies ... some say you need to resynchronize.
   • Process to do the synchronization?
     
   • Keep spare batteries for the fob in the car as a good luck omen.
     

[*]Some evidence that early variants where the key can get out of synch if not used.

ONLY if you can get past "lock" symbol when in ignition position 1 go to next section

Engine starter functionality

1. Ignition Position 1:
   • Transmission gets to N (neutral) - did you hear the clunk?
     
   • Foot on brake?
     
   • Did you hear the sound of fuel pump over the safety belt beeping?
     

[*]If NO - any sound of transmission actuator grinding? (check battery, transmission actuator failure, stuck in gear)

[*]If NO - brake pedal switch bad?

1. Ignition Position 2:
   
2. Glow plug activation (don't think there is a go/no go blocking function)
   

1. Ignition to start position 3? Does starter engage? Intermittent problem?
   
2. Any clicking of starter solenoid?
   
3. Any grunt from the starter?
   

1. Check for bad or low battery (how old? how cold? test under load)
   
2. Check connections at battery terminal. Clean and tighten.
   
3. Check ground strap to engine block.
   
4. Check signal circuit to starter solenoid (check spade connector on solenoid; on backside and hard to get to)
   
5. Check for bad high current wire from solenoid to starter (braided copper cable that gets corroded)
   

ONLY if the starter spins the engine at a good cranking speed go to next section

Fuel delivery

​Ignition start position 1 - electric low pressure fuel pump should run for 5 seconds or so.

Ignition start position 3 - starter should spin engine at a good rate.

1. Check low pressure fuel pump
   • Low pressure pump has cut out for accident safety feature (engine crank sensor?)
     • Believe there is an over-ride for at least 5 seconds when you initiate a start sequence.
       

[*]Low pressure fuel pump electric circuit (relay modification, SAM connector problem)

• Should hear it turn on at position 1 (in tank electric pump. need to drop tank to access).
  

[*]Low pressure fuel pump is it pumping?

• Crack one of the fuel fittings on the rail ... fuel should come out when the key is turned to position 1.
  

[*]Gelled fuel (do you use fuel conditioner in winter?)

• ​If it is less than -10C, beware if you still have summer diesel in place.
  
• Fuel filter and separator should be not overdue for replacement. It can get frozen in winter.
  

[*]Check high pressure fuel pump

• High pressure pump is mechanical. Powered by camshaft.
  
• High pressure pump has a solenoid actuator that reduces output at under low load conditions by disabling 1 of 3 elements of the pump.
  
• Any leaking? (there are o-rings in pump area that fail. Much cheaper than a new pump)
  
• See pump timing in next major section.
  

[*]Check common rail fuel pressure

• Is the rail coming up to pressure?
  
• Check by measuring the output of the pressure sensor on the far end of the rail.
  • Pressure sensor is active and must be powered.
    
  • If you have a surplus 3 pin socket of the correct pitch it makes this much easier. The sensor connections are in a deep well that you can't easily see due to the orientation.
    
  • Should be 1.5V when cranking. O.32V when quiescent.
    

  [*]Pressure is dumped out of rail by modulator with PWM signal.

  • Not sure if it is normally open or closed without power.
    
  • Check signal by pulling connector (spec is? )
    

1. Low pressure fuel sensor and cutoff
   

• Is there a cutoff?
  
• Does an independent fuel pressure sensor exist?
  

ONLY if you have good fuel delivery to the common rail go to next section

Fuel Injection

There may be multiple factors could prevent the ECU from triggering the injectors (electrical). The timing is set by the crankshaft sensor so this must be one. The phase of the engine (4 stroke and we need to trigger on the power phase and not the exhaust phase) is determined by the virtual crankshaft sensor.

1. Crankshaft sensor
   1. 
      
   2. Reads notches in flywheel.
      
   3. Lack of crankshaft signal will block injector signals.
      
   4. To test without pulling sensor TBD.
      
   5. It is very inaccessible and often frozen in place.
      
   6. Soft or hard failure modes? What is the engine code?
      
   7. Sensor gets contaminated and may need periodic cleaning.
      

[*]Virtual crankshaft sensor

1. Uses angular velocity variance due to compression cycle as an alternative to a real crankshaft sensor for injection phase timing (4 cycle engine).
   
2. If the compression is compromised, this signal may become muddled.
   
3. Lack of a virtual crankshaft signal blocks injection signal (need reference).
   
4. To compensate for poor compression (or to somehow bootstrap this process), inject light oil into intake manifold (through hose in boost sensor or by removing rubber hose from EGR to inlet manifold). Torsen suggests WD-40. I used spray penetrating oil (it was handy).
   

[*]Diesel fuel injectors

1. Piezoelectric actuated (apparently same p.n. as that in 2.7L 2002 Sprinter Van)
   
2. Reported to be 70V differential across pins when firing?
   • PWM to modulate volume
     
   • May need to be connected to get signal.
     
   • Pulse may not show up on digital meter.
     

[*]Period is 4X of engine cycle during cranking (~100 rpm). Lower rate than you might first guess (100/60/4 = 0.4Hz. or 2.5s period)

[*]Reported that failure of virtual crankshaft sensor (and therefore crank sensor) prevents any injector signal.

[*]Alternator stuck

• Notorious for corrosion and a tight tolerance between rotor and stator
  
• Is this an input to ECU to block starting? TBD.
  
• There is signal to SAM though, on diesel only
  
• N11-8 (7) Alternator to SAM [no fuse as input]
  

[*]Air in fuel lines

• There is a clear section of the fuel line return that you can look for bubbles.
  
• If a mild case of air in system .. apparently should work its way out with enough cranking cycles.
  • Don't burn out the tiny starter motor. Cycle it. Let it cool off. It is a pain to replace.
    

  [*]If a heavy case of air in system ...

  • Purge by cracking open (14mm wrench) the high pressure connections to the injectors and rails.
    
  • Do one at a time. Just turn key to position 1 and watch the flood.
    

  [*]If the air is in the low pressure section, may be easier to disconnect the fuel return line at the rail pressure modulator.

  • Press the white U clip in to expand the black plastic C clip beyond the flange.
    
  • Looks quite fragile and a hassle to replace if you bust it.
    

Almost starting or poor running at idle

1. Glow plug functionality

   [*]Fuel delivery

• Check above
  

[*]Bad or worn injectors

• Unlikely all three would die at the same time. Uneven or lumpy idle?
  
• Expensive to replace. Can be rebuilt with new nozzle. Good luck finding a place. Otherwise, mail in and wait.
  
• Pull and clean may help.
  

[*]Bad compression

• Measure through glow plug holes.
  

[*]EGR stuck open? Usually gets plugged shut. Usually will throw a code if stuck.

[*]Leak in intercooler? Would expect to affect top end performance vs. idle. There is a design flaw that can wear a hole in the intercooler where the plastic support rubs.

[*]Leak in rubber pipe to intake manifold? Should not affect idle. A hole makes a mess in the engine area. And reduces boost (performance hit). There is a spot where an overlying hose can rub a hole right through.

Related Signals on SAM (ref: fq101.co.uk sam wiring)

where N11-x is the connector number

where (y) is the pin

1. N11-1 (3) Glow plug signal from SAM [fuse 8; 20A]
   
2. N11-1 (8) Starter motor relay from? SAM [fuse 1; 15A]
   
3. N11-2 (1) ECU also known as EDG from SAM [no fuse?]
   
4. N11-3 (10) Fuel pump and fuel level sensor from SAM [fuse 16; 10A]
   
5. N11-4 (1) Ignition in position 1 to SAM [no fuse as input]
   
6. N11-5 (11) Fuel pump instruction ECU signal from SAM [fuse 10; 15A]
   
7. N11-5 (12) Engine run ECU signal from SAM [fuse 10; 15A; how can this be the same fuse as above?]
   
8. N11-6 (1) Starter motor from SAM [fuse 1; 25A]
   
9. N11-7 (3) Ignition starter switch from SAM (constant live) [fuse 33; 50A]
   
10. N11-8 (7) Alternator to SAM [no fuse as input]
    
11. N11-8 (38) Ignition in position 2 to Sam [no fuse as input]