B230ET Motronic Testing v B23ET - Haynes
 

The purpose of this thread is to share experience testing the Motronic system (electrical side, not fuel side) on a B230ET using the Haynes instructions for the B23ET which is 'believed to be similar'.
All according to my Haynes Volvo 740 and 760 (petrol) 1982-1989 Owners Workshop Manual dated 1993 ISBN 1 85010540 5. The spine of the book is numbered 1258.

Testing Procedure Electrical side (page 155)

See www.autoelectric.ru/auto/volvo/740/1989/740-89.htm for the correct wiring diagram and location of all the components and connectors etc.

Item 4, No earth continuity on pin 16 or 17. There is however earth continuity on pin 6, but only when the ECU is plugged in to the harness.

Item 15 does not apply. No Air Conditioning Advance Relay on B230ET.

Items 16 and 17 do not apply as there is a separate 'Power Stage, Motronic' which is specifically for the Fuel injectors.
This is NOT to be confused with the separate 'Ignition amplifier' on the B230FT and mentioned liberally in the FAQ. On the B230ET this amplifier is integrated in to the ECU itself so don't go looking for it.

I have not tested the Fuel injector resistances but it appears straightforward from the web site information above.

There is additionally the ' Radio Interference Supression Relay'

Still no spark
 

Hi, thank you for the comments on the differences between the 230ET and 230FT control boxes - I was looking for the Ignition Control Box! I've been working outwards from the non-sparking plugs and am happy with the coil - the distributor and rotor arm - and the TDC/rotation output. But there my knowledge and testing have hit a brick wall. I have run all the 'Haynes' tests (from page 157/158) and they seem OK. What I can't resolve is which of those tests actually prove the ignition amplification that pushes a decent VAC through to the coil primary wiring - which clearly I am not getting. One flow chart I have followed says that the Power Stage is the culprit. But the Power Stage in our cars seems only to cover the fuel injectors? Just wondered if you had any thoughts?

You say nothing about the LV side.
The Radio Suppression relay on the 760 Turbo is also in circuit for the ignition although not shown on the Haynes diagram as that is for the 740. It is under the bonnet on nearside on my car and identical to the electic fan relay if you have air conditioning so they can be swapped for testing.

In addition the Motronic relay is in circuit, on the main relay board inside the car.
Then there is the ECU itself which contains a built in power amplification stage. I bought a second hand one to test with on a swap out basis.

If those are all working ok and there is no wiring problem, you should be getting the corect LV feed to the coil as far as I know.

Hot days!
 

I realise that this is the resurrection of ancient history but maybe somebody can help me with an intermittent fault on my Motronic B230ET 760T. On very hot days, when slow moving (sticky traffic) she will splutter and die. She also worryingly did it on a not very hot day recently just as emerging (slowly) from the Rotherhithe tunnel. Leave her 20 minutes and she will run perfectly - and if kept above 35 mph continue to run perfectly.

I had a similar fault on one of my B230FT 940 Sports, and that turned out to be the crank position sensor. New despite some experts saying that the Motronics did NOT have a CPS, my garage changed the CPS and it has not effected a cure.

Others said "ignition amplifier, needs fresh thermal paste" - which is why Mr Google led me here - but from this thread it seems that I have not got an ignition amplifier - save for the power stage for the injectors. Can anybody pls post a picture of the power stage so I can find it, and check that it has proper heat dissipation?

Another possibility might be overheating of the coil - possibly to be cured by new coil and thermal paste in the securing strap.

A third possibility could be fuel vaporisation, but what could have changed to affect that?

I do NOT want to have to replace the ECU, so I hope it will not be that. And it's one of the parts I have not got a spare for!

Of course a fault that only crops up once or twice a year is a real bathmat to find.

What does the team think?

Isn't the powerstage the black box in the engine bay in front of the N/S strut tower? Been a few years since I looked at Motronic as I'm yet to fit the ET in to my 360.

Fuel vapourisation could be caused because fuel has gone to a 15% ethanol content.

Ethanol
 

Ah, interesting. Which has more ethanol, super or ordinary? And how to treat that if it were to be the problem? Try to wiggle a further heatshield in by the fuel rail?

I'm not sure which has more, I don't think they would have a different Ethanol content to be honest as it would be the petrol part that is different and I think it is law now that petrol has 15% ethanol.

I know the cars at work old 1950's and 60's Bentleys have an overflow pipe in the fuel system, once it has got to temp and you turn the car off the ethanol carries on bubbling away as it has a lower boiling point and drips out of the overflow pipe. So yeah I have ethanol dripping on me daily haha.

Found the power stage
 

I've found the power stage. But I can't get it out to see how it is heatsinked and how to remove old thermal paste and insert new paste. 10mm headed bolt on top easily removed - but it's still solid. It mounts to a bracket with a bolt to the inner wing and a nut onto a stud on the wheel tub - I MIGHT be able to get at them if I took the battery out. There is a big plug on one edge and that looks as if it should spin out upwards - but with the amount of force I have used so far it does not budge...

From your description of the location, it sounds suspiciously liek the injector resistor pack on the inside wing. Should be able to check it with a multimeter on resistance to see if it's failed.

Any pics so i can say yes, it is the resistor pack or no, not seen one those before?

It looks the same as on a 940 Dave, it has some wires going in to cylindrical looking objects all joined together in a small metal cage.

https://www.ebay.co.uk/itm/Volvo-940...-/401642493511