W124 goes in to "Limp Mode" I think.

[lester]

I have a 1994 w124 Cabriolet with a 2.2 4 cylinder engine, every now and then it runs bad like on 3 cylinders which I think is the limp mode, when I stop and turn ignition off and then restart it runs ok for a while until it does it again. Iv'e pulled the fault codes and on pin 8 get 13 blinks and 21 blinks can anyone help?

Thanks, Les

 

[grober]

On that age of car there is no limp home mode. You have the HFM combined injection and ignition ECU. The ignition consists of a lost spark system of two coils each firing two plugs. What you are experiencing is a breakdown of the HT system causing a cylinder/s to misfire. This can be due to the following ---Faulty coil or coil extender or plug lead [ HT] -- faulty low voltage side of the coil wiring insulation [LT]--- or faulty ignition transistors in the ECU. the ECU can be repaired or its a do-able DIY for someone good with a soldering iron. I posted a how to on this some time ago.
for fault codes see
http://www.diakom.ru/CARS2/pribor/cs1000/manual/cs1000_mb.pdf

 

[lester]

Thank you Graeme for your prompt educated reply, I understand all of what you said. Today I fitted new plugs and checked the condition of the 2 coil wiring insulation which look OK no insulation degrading, I know about the Eco wiring problem. Is it possible to check/test the coil packs or would I only know after fitting new ones. One last thing, the transistors in the ECU, Iv'e never heard of that before is it a common problem?
Thanks again,
Les.

 

[grober]

Quite frequently these ECU ignition out transistors overheat due to problems with the ignition coils or their low tension supply wiring from the ECU to the coils themselves. This is often due to thermal stress causing wiring insulation breakdown or bad connections in the ECU plug. After you repair the ECU it would be a pity if that work was wasted by the original fault causing a second failure. Have a good look at the wiring and check the coils since they are a very common failure on that engine. One coil fires 1 and 4 and the other 2 and 3 plugs. If there is evidence of coil failure replace it. The coils [ primaries] are " powered up" on ignition switch on- the ECU power transistors "earth" the primary coils at the appropriate time causing their field to collapse inducing current in the HT secondaries- thus firing the plugs IN PAIRS the so called lost spark system. Simplest approach is 1 check the low tension wiring and ECU plug. 2 buy a new coil and substitute it for the faulty one. You can just swap em to see if the the misfire relocates but you run the risk of blowing the remaining good ECU transistor if the other one is gone. If 2 good coils don't do it -its likely to be the ECU power transistors

Cheers Graeme

http://forums.mbclub.co.uk/threads/how-to-repair-your-ecu-ignition-part-1.144774/

http://forums.mbclub.co.uk/threads/how-to-repair-your-ecu-ignition-part-2.144776/

 

[lester]

Hi grober,
I know it's quite some time ago since you gave me advice regarding the fault on my W124 E220 cabriolet but I hope you can help further. I changed the 2 coils and the HT leads this hasn't cured the problem, I attached a timing light and found that it's the number 1 and 4 that suddenly stops firing. So I then ordered the transistors from Farnells, I removed the ECU and dismantled the cover. I found that it wasn't like the one that was repaired in the photo's, what looks to me like the output transistors are different they have 5 pins and not like the ones I got which are 3 pins, can you shed any light, any help would be much appreciated. ive tried to send photos of it but the file is to big.
many thanks,
Les.

 

[grober]

It would appear you have the later ECU which is also used in the W202 with the same engine.
Details are discussed in this thread
HFM Ignition Coil Driver Transistors
It would appear you require two VB027 units altho you may get away with using the 3pin transistor package and ignore the logic circuits compare the two packages from their spec sheets -----never got any feedback on that? If ordering make sure you get the right package
see SGS Thomson Microelectronics - datasheet pdf

the old BU931 spec sheet
ST Microelectronics - datasheet pdf

 

[lester]

It would appear you have the later ECU which is also used in the W202 with the same engine.
Details are discussed in this thread
HFM Ignition Coil Driver Transistors
It would appear you require two VB027 units altho you may get away with using the 3pin transistor package and ignore the logic circuits compare the two packages from their spec sheets -----never got any feedback on that? If ordering make sure you get the right package
see SGS Thomson Microelectronics - datasheet pdf

the old BU931 spec sheet
ST Microelectronics - datasheet pdf

Hi Grober,
Thank you for your reply, what do you mean when you say make sure you get the right package?

Thanks,
Les.

 

[grober]

Hi Grober,
Thank you for your reply, what do you mean when you say make sure you get the right package?

Thanks,
Les.

If you look on the spec sheet you will see that there are three packages pictured with different pin arranagements -they have different parts nos VB027, VB027[011Y] , VB027[012Y] you need the right one to fit on the PCB

 

[lester]

Thank you I understand what you mean, will get two and fit them.
Les.

 

[grober]

You could try these guys if you have supply difficulty- Their Mbe 956 ecu appears to use the VB027- if indeed that's what MB used in their ECU-which remains unconfirmed
Oddified - world class tuning services..

 

[lester]

Hi Graeme,

Thanks for your help, Iv'e managed to find some on ebay, the pins aren't exact but I'm hoping to be able to gently bend them to suit, I will let you know if it works, shame I didn't know which one effects the no 1 and 4 coil, if i did then I could just fit that one.

Les.

VB027 STMICROELECTRONICS SEMICONDUCTOR TO-220-5 VB027 | eBay

 

[grober]

This might give some clues?
the connection plug.
https://www.benzworld.org/forums/at...71213679-ecu-shematics-pinouts-needed-hfm.pdf
and circuit diagram
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1995/C220/SYSTEM WIRING DIAGRAMS/5301.pdf

pins B9 and B10 might be worth a look?? you would then have to determine which coil the signal pins relate to then try to work out which transistor is involved with which pin using a DVM. [ I have yet to find a internal circuit diagram for these HFM ECU's]
The circuit works thus- the coils are powered up on ignition switch on and their fields collapsed by being momentarily earthed via the power transistors thus inducing a HT pulse firing two plugs.

 

[lester]

This might give some clues?
the connection plug.
https://www.benzworld.org/forums/at...71213679-ecu-shematics-pinouts-needed-hfm.pdf
and circuit diagram
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1995/C220/SYSTEM WIRING DIAGRAMS/5301.pdf

pins B9 and B10 might be worth a look?? you would then have to determine which coil the signal pins relate to then try to work out which transistor is involved with which pin using a DVM. [ I have yet to find a internal circuit diagram for these HFM ECU's]
The circuit works thus- the coils are powered up on ignition switch on and their fields collapsed by being momentarily earthed via the power transistors thus inducing a HT pulse firing two plugs.

Hi Graeme,

I received the VB027 transistors today, I figured out which transistor effects number 1 and 4 cylinder and de soldered and re soldered the new one in, put it all back and started the car, it now only runs on 2 cylinders from start up, if you remember before it ran perfectly for around 8 to 10 miles before it started to not fire on number 1 and 4. I thought that I had made a decent job of it, I used the sucker to remove the old solder, bent the pins to suit, and soldered it ok. What I'm now thinking, is it possible that the 5 pins can be 180 degrees out in other words the opposite way around, but I replaced it just like the original with the heat-sink in the same orientation, or have I made a mess up? Do I fit the old one back or try again with the other new one that I have?

Many Thanks,

Les

 

[grober]

Without knowing the exact pin designations of the original package and the new one its difficult to say for sure. the applications note isn't helpfull. The OLD 3 pin BU 426 Pinouts are clear = 1,2,3 emitter base collector in that order. The VB027 5pin package is less clear the pin out diagram is not what I would expect- sorry I can't give you a definitive answer

 

[lester]

Hi Graeme,

Thanks for your speedy reply, do you think it's worth me fitting one of the BU931T type that I bought in error and just solder in the 3 pins, or try the other VB027 just in case the first one was a duffer, Iv'e nothing to lose?

Thanks,
Les