MBE ECU failure how to check ? Help needed please!

[marcos59]

Sorry for my bad technical english

 

On a 1.8 Zetec on carbs with MBE ECU 956 Model

 

Engine do not start: No spark on plugs

Rev cut light is bright when ignition is on (Was not in my memory when car running OK but I(m unsure now )

Is that a symptom of problem on ECU?

Everything else have been checked (coil,crank sensor,buterfly sensor, water temp sensor and loom)without result.

 

Any avice about how to check it warmly welcome !

 

I will prefer to be sure that problem come from ECU before send it back in UK

 

Thanks for your help

 

[Steve Cornford]

Does your car have an Inertia Switch, if so try resetting by pressing down in the middle of its top.

 

It is a rubber covered switch like these

 

Sigma SteVe

[Paul Deslandes]

Are the injectors delivering fuel when the engine is cranking? Remove the airfilter and look down the throttle body with the throttle open. You should see and smell the fuel (defense de fumer 😬)

 

The 956 ECU can be programmed using EasiMap 4 so that pin 14 either controls the fuel pump or the gear shift light. The light will remain on for a short time every time you turn on the ignition, as you have described, if its been programmed to control the fuel pump rather than the shift light. Is it possible that this has been changed by mistake?

 

Can you hear the fuel pump run when the ignition is switched on?

 

If you have no spark and no injectors working I would suspect the crank sensor. Did you try a new one?

 

Paul

 

 

[andy_h]

Do you have a battery master switch? If so the ignition circuit from the MBE passes through this via spade connectors and if the switch is broken internally (I mine was) then the ignition circuits is not made and hence no spark.

 

I learnt this the hard way.

 

Try by passing the master switch to check.

 

Cheers,

Andy

 

White road legal 2.0 HPC VX race car - stolen with trailer 27/03/09... found 11/06/09 😬... now under repair

[marcos59]

Thanks for all replies

 

@ andy_h: I do not have master switch

@ Steve: No inertia switch

no solution there !

 

@ Paul:

- I heard fuel pump

- Carbs are full of fuel

- Sparks smell fuel

- I have fitted exchange crank sensor with a friend zetec caterham: Friend car started with my sensor..my car didn't start with his sensor. So not a crank sensor issue

 

However my shift light is now bright all time when ignition is on and even when starter motor is running.

I think (As I'm now a bit confused with all my tests ) shift light brighted briefly as you described when car running sweetly few days ago.

Does it mean that ignition is cut by ecu itself ? (It seem to be what shift light say)

If it is I have no chance to see engine start

 

I have check another time full loom: Nothing special

 

Nothing have been modify just before problem happen. Car have been parked in my garage with no problem..and didn't start on next WE

 

What could I test further more before send it back in UK? (SBD seem to not answer emails 😔 are they recognise to have a good service 🤔)

 

Thanks

 

 

 

 

 

Edited by - marcos59 on 17 Sep 2009 20:30:44

[Paul Deslandes]

I'm sorry Marcos, I didn't read your original posting properly before replying the first time and didn't notice that you are running on carbs, not injection.

 

Have you checked the voltage at the throttle potentiometer? You say you have checked the pot and maybe swapped it with your friend's. The voltage on the pot red wire (pin 5 on the ECU) should be +5Volts, pot yellow wire (ECU pin 15) should vary between about 0.38Volts at tick-over and 4 Volts as you press the throttle pedal to fully open.

 

Does your wiring loom have either one or two relays built in or separately connected? If so, one of them switches the gear shift light and the other switches power to the coil when the ignition is switched on. There may be a clue here as a short circuit or other fault in that area could cause your shift light to come on permanently and also stop power going to the coil. If you need a circuit diagram please blatmail me and I'll see if I can find one so you can make your own tests. Try changing the relays in case one has gone faulty and is causing the problem. Also check that the relay wiring loom pins are fully pushed home and are making a good connection. Check the voltage on the ECU pin 14. It should be approximately +12V and not 0V. If it is 0V then the shift light will be on as you describe as this ECU output controls the shift light by switching to ground. If its not 0V and the light is on, you definitely have a relay or wiring fault.

 

The only other suggestion is to find someone with a laptop with Easimap software loaded and the proper MBE serial cable (do not use a standard serial cable or you will damage the ECU or laptop or both) so you can test some of the ECU functions.

 

Otherwise it seems you must either have a wiring loom fault or a faulty ECU.

 

SBD are the official agents for MBE but the 956 is considered a very old unit now and its probably cheaper to buy a more modern one than get the 956 repaired. The trouble is that you will have to fit a new connector to your loom for any of the newer ECUs as the 956 was the last ECU to use that connector. If you advertise here on Blatchat 'Wanted' you may find that someone has an old 956 for sale. You will need to transfer your ignition map.

 

SBD can be a bit slow responding to emails but you may do better if you telephone them.

 

Sorry this is a bit rambling but I would certainly check the relays and loom before doing anything else.

 

Good luck.

 

Paul

 

 

[EFA]

Monsieur Marcos, A bunch of us are travelling through Calais on October 6th at 12.00. I'd be happy to have a quick look over it for you. Do you have a laptop? I can bring the cable.

 

Blatmail me your reply as I don't get on here often

 

Arnie

[marcos59]

More investigation this WE without result ☹️

 

@ Arnie:

Many thanks: YHM regarding checking ECU on a laptop

 

@ Paul :

Pin 5 checked: 5V: Perfect

Pin 15 checked: 4.8V all time

You said it should vary between 0.4V and 4V depending throttle pedal position: Electronic problem? or perhaps just mechanical issue (wrong ajustment on butterfly: say open when close).

But anyway could it do not start just because throttle potentiometer do not work or badly adjusted? (It may cause a bad advance curve but not nill spark isn't it?)

Pin 14 checked: 0V (Not 12V) so at least explain why rev lmiter light is always on.

 

So question is why I do not have 12V on pin 14 ?!

 

I have check coil connector: Pin 3 and 10 have +-12V with ignition ON and when starter motor is running. Last one (not connected to ECU?) have permanent 12V. Is that correct ?

 

I do not find any relay

Nothing separatly

Nothing "build in" I assume you mean build into the loom ???

Are these relay in ECU ? (Can send a pic of ECU interior if needed.

I assume they can't be on original caterham fuse box

 

Many thanks for your help !!

 

Still not answer from SBD an my technical english is not good enough to give them a call an explain/understand what happen.

[marcos59]

In fact question is where pin 14 come from ?

From key ignition switch ?

Is something could be simply disconected there ?!

[Paul Deslandes]

Marcos

 

MBE 956 ECU pin connections as follows. If this is too difficult to read, blatmail me your email address and I'll send you the same info in Excel.

 

ECU CONNECTOR PIN OUT FOR MBE 912 V3/956 E (Injection)

 

PIN NO SIGNAL DESCRIPTION REMARKS

 

1 ELECTRONICS GROUND To sensors and car chassis (BLACK)

 

2 ECU SUPPLY +12V To Battery +ve relay controlled (PINK)

 

3 IGNITION COIL DRIVE 1 To coil pin 1 (BLACK/WHITE)

 

4 LAMBDA If not use, GROUND to pin 1

 

5 LOAD (THROTTLE POT) REFERENCE To throttle Pot supply (RED)

 

6 CRANK SENSOR SPEED SIGNAL To Crankshaft Signal (Sensor Pin 02) (BLACK/WHITE)

 

7 AIR TEMP SENSOR SIGNAL To Air Temp Sensor 1 (Sensor Ground to ECU 01) (GREEN)

 

8 COOLANT TEMP SIGNAL To Coolant Temp Sensor 1 (Sensor Ground to ECU 01) (BLUE)

 

9 POWER GROUND 1) To ECU Loom Braid (BRAID)

 

10 IGNITION COIL DRIVE 2 To coil pin 2 (GREEN/WHITE)

 

11 INJECTOR DRIVE (GROUPED INJECTORS) To all injectors Pin 1 (Pin 2’s to be connected to separate +12V

 

12 CRANK SENSOR SPEED RETURN To Crankshaft Return Sensor Pin 01 (BLACK)

 

13 TACHOMETER SIGNAL To Tacho (GREEN/WHITE)

 

14 GEARSHIFT LIGHT To –VE side of gearchange lamp (GREY)

 

15 LOAD (THROTTLE POT) SIGNAL To Throttle Pot Signal (Throttle pot return to ECU 01) (YELLOW)

 

As your setup is ignition only, not injection, you should ignore any of the connections to injectors etc. Also the loom wiring colours may be different.

 

Pin 14 is connected to either one side of the shift light (the other side is connected to +12Volts) or to a relay that will also have its other coil terminal to +12V. Pin 14 switches to ground when the shift light is activated. So if its permanently at 0 volts the light will stay on.

 

Is the shift light an LED or normal bulb? If its a normal bulb it should definitely have a relay in the circuit. Otherwise the bulb current through the transistor in the ECU will be too high.

 

Pin 15 should definitely swing between 0.38 and about 4.5 Volts as you press the throttle. If its stuck at 4.8 volts then either the throttle pot has come off the spindle, has a poor connection or is faulty. The ignition timing when cranking the engine will depend on the ignition map but I suspect that it won't be very much advanced, even with 4.8V, until it starts. So I agree, it should not prevent a spark but it may be a symptom of your problem as its definitely not correct.

 

The coil voltages sound ok. The pulses to the coil from the ECU on pins 3 and 10 will be too short to see on a meter and you will need an oscilloscope to see them.

 

The relays can be built into the loom but are easily seen. If you go the the SBD website there's a picture of a typical loom with built in relays so you can see what they look like. If they're not in the loom they will be connected to it somehow and, as I said above, one of them should be connected to the shift light. The other one will be switching the +12V supply to the ECU and coil. But as you have 12V at the coil and +5V at pin 5 if there is a relay its obviously working.

 

I suspect a wiring fault somewhere because of the throttle pot voltage not changing correctly and the shift light being permanently on. Even a faulty ECU shouldn't be able cause the throttle voltage not to change. Did you measure the pin 14 voltage at the pin on the ECU or at the potentiometer connector? They should be the same but if they're different you may have found your problem.

 

I wonder if the throttle pot ground, and maybe some other connections, has come off pin 1 ? This is one of two ground connections so it may have more than just the potentiometer connected.

 

I know SBD very well and I'll give Steve a call on the phone tomorrow in case he knows if a particular fault can cause pin 14 to stay at 0 Volts. I'll post back after I've spoken to him.

 

If its not fixed by the time Arnie comes over he'll almost certainly be able to determine where the problem is. He's been playing with these things even longer than I have.

 

Paul

 

 

[marcos59]

Many thanks for your help it is very appreciated ! *thumbup*

 

I will check further more tonight but I can already say:

- Shift light = normal bulb (not LED)

- Pin 5 tested from loom

- Pin 14 tested from ECU

- Pin 15 tested from ECU

 

I will remove throttle pot from crabs tonight to see if it is a setting problem or if it is still allways say 4.8V

 

Regards

 

[Paul Deslandes]

Hi Marcos

 

I phoned SBD this morning but Steve is away after having surgery on his back, so I will not be able to talk to him for a few weeks. No one else there has the detailed knowledge of the MBE systems.

 

If the throttle pot centre connection is not connected to the ECU, pin 15 will stay at a fixed voltage. I suggest that you measure the voltages on the red (5 Volts) and yellow wires (0.38 - idle to 4.5V - full throttle) on the throttle pot. I assume that there is a connector that you can temporarily get a piece of wire onto each pin, one at a time, particularly to see that the voltage on the yellow wire (centre/wiper) changes when you operate the throttle. If the centre voltage doesn't change when you operate the throttle and you are sure that the pot is rotating, I suspect that the pot is either faulty or the ground connection has come off. Check that the third wire is at zero volts first. I can't remember the colour (green?) but its the third wire so easy to find.

 

My concern about the shift light is that unless your main problem is affecting the shift light output, the high current required to power the standard light bulb might have damaged the output transistor. Hopefully, although you haven't found it, there is a relay in the circuit and there's something simpler wrong.

 

Let us know how you get on tonight.

 

Paul

 

 

 

 

[marcos59]

Back from garage.....

 

Paul many thanks for your call to SBD.

 

This is where I am tonight:

 

1 ELECTRONICS GROUND To sensors and car chassis (BLACK) Loom tested OK and 0V OK

 

2 ECU SUPPLY +12V To Battery +ve relay controlled (PINK) Loom tested OK and 12V OK

 

3 IGNITION COIL DRIVE 1 To coil pin 1 (BLACK/WHITE) Loom tested OK and 12V ok with ignition on

 

4 LAMBDA If not use, GROUND to pin 1 Not used (injection)

 

5 LOAD (THROTTLE POT) REFERENCE To throttle Pot supply (RED) Loom tested OK and 5V OK

 

6 CRANK SENSOR SPEED SIGNAL To Crankshaft Signal (Sensor Pin 02) (BLACK/WHITE)Loom tested OK

 

7 AIR TEMP SENSOR SIGNAL To Air Temp Sensor 1 (Sensor Ground to ECU 01) (GREEN) Not used (Injection)

 

8 COOLANT TEMP SIGNAL To Coolant Temp Sensor 1 (Sensor Ground to ECU 01) (BLUE) Not used (injection)

 

9 POWER GROUND 1) To ECU Loom Braid (BRAID) I do not understand what it is and what difference is with Pin1

 

10 IGNITION COIL DRIVE 2 To coil pin 2 (GREEN/WHITE) Loom tested OK and 12V ok when ignition on

 

11 INJECTOR DRIVE (GROUPED INJECTORS) To all injectors Pin 1 (Pin 2’s to be connected to separate +12V Not used (Injection)

 

12 CRANK SENSOR SPEED RETURN To Crankshaft Return Sensor Pin 01 (BLACK) Loom tested OK

 

13 TACHOMETER SIGNAL To Tacho (GREEN/WHITE) Loom tested OK

 

14 GEARSHIFT LIGHT To –VE side of gearchange lamp (GREY) Still 0V so explain why shift light light is on. I just need 12V here but do not understand how to do or what problem couls be if there is no faulty relay and in fact no relay at all !

 

15 LOAD (THROTTLE POT) SIGNAL To Throttle Pot Signal (Throttle pot return to ECU 01) (YELLOW) (Green on my car) Loom tested OK and Dismantled from carbs value change from 0V to 5V: Perfect !

In fact the spindle was unscrewed..so no modification of value even carbs butterfly was open or closed

 

- Crank sensor swap OK

- Throttle pot test OK

- Coil swap OK

 

Any relay found....will remove full loom from car if necessary but I'm 99% sure there is no relay.

 

So last question is why I do not have 12V on pin 14 when ignition is on if there is no faulty relay ?

[Paul Deslandes]

Hi Marcos

its sounds as though you have found the reason that the throttle pot voltage was not changing and have fixed that. As a matter of interest, after you fixed the throttle pot, did you try to start the engine?

 

The ECU has two ground connections and they are connected internally. One is described as 'power ground' and the other 'electronic ground' but they are the same connection and I don't think it matters which one you use for any ground connection, although its better for the power connection to the car chassis to be on the power ground and things like the throttle pot and crank sensor grounds/braids to be connected to the electronic or signal ground..

 

Pin 14 is called an 'open collector' output. Inside the ECU this is connected to the collector of a transistor which switches 'on' when engine revs reach the gear change speed, e.g. 7500rpm or what ever it has been set to. The shift light is connected between +12V and this pin, preferably via a relay as described before to limit the transistor current to stop it being overloaded. So when the light should be off, pin 14 should be at about +12V when measured with a meter. Its dragged there by the internal resistance of the bulb or relay. When the light should be on, the transistor turns on, connecting that side of the light or relay to ground. If the transistor is faulty, i.e. short circuit, the light will be on permanently regardless of the engine revs. Don't connect the pin directly to +12V as this will definitely damage it.

 

I hope you don't have to remove the engine loom. You should be able to trace any faults without that drastic action!

 

All of your loom/connector tests now look ok, apart from the shift light, pin 14. Maybe the engine will start now but if not I think the next step is to have someone look at it with Easimap software on a laptop. Unfortunately I don't have a similar setup to test it on, otherwise I'd say send it over to me to look at. You really need it tested in your car or on a similar setup. Hopefully Arnie will be able to come and see you when he comes to France in October.

 

Paul

 

 

 

 

[marcos59]

Paul,

 

At least pot throttle problem is solved...thanks for your help

 

I have removed loom: No relay anywhere.

 

SBD (Steve Broughton) answered me today: Rev limit light always on is not a good news and it seem that ECU is damaged.

 

I think we have done together all possible tests on loom and sensors.

 

I will try to go to Croix en Ternois track day with car and trailer. Perhaps Arnie will find something with laptop and easimap.

 

Your help have been very appreciated many thanks Paul

 

Regards

 

Huggy/Nicolas

 

[Paul Deslandes]

Hi Nicolas

 

I'm sorry we haven't found a simple answer to your problem. Maybe Arnie will have more luck.

 

If you do find out the problem I shall be very interested to hear what it is.

 

I would certainly try to get a second hand 956 as this will be much cheaper and simpler than having to buy a brand new ECU. If Arnie is able to read the maps in your ECU it would be worth trying to save them to a disk so that they can be uploaded to your new ECU, whichever type you get.

 

Paul