MG Turbo

[MatthewL]

My 87 MG Turbo is a New Zealand car and I’m just wanting to see if the ECUs are the ones which should be fitted. I ask as I’m working through a lot of checks in the workshop manual to see why it runs beautifully for around 10 minutes idling until about the time the thermostat opens at which point it’s got too rich and conks out if you so much as touch the throttle. The fuel ECU in the glovebox is ADU8499 and the timing ECU in the engine bay is ADU9335. Does anyone else with a Turbo of this vintage have different ECUs? I’m sure I’ve seen Maestro Turbos with an ADU9475 ignition module but that may have been newer. It’s the fuel one though I’m most interested in Cheers, Matthew

[Jeff Turbo]

My 87 MG Turbo is a New Zealand car and I’m just wanting to see if the ECUs are the ones which should be fitted. I ask as I’m working through a lot of checks in the workshop manual to see why it runs beautifully for around 10 minutes idling until about the time the thermostat opens at which point it’s got too rich and conks out if you so much as touch the throttle. The fuel ECU in the glovebox is ADU8499 and the timing ECU in the engine bay is ADU9335. Does anyone else with a Turbo of this vintage have different ECUs? I’m sure I’ve seen Maestro Turbos with an ADU9475 ignition module but that may have been newer. It’s the fuel one though I’m most interested in Cheers, Matthew

Hi Matt
You say it runs rich?
I'm guessing you can't drive the car when warm but can when cold? Carb runs richer when cold so I can't see that would be the issue. The part numbers you put up are not correct. ADU8499 and ADU8479. Does it conk out when revving it when not moving? When it conks out does it re-start and idle? Is the auto choke working, does the small rod push out when cold and retract when warm?
What adjustments have you done from the workshop manual and was it running better before you started working on it? Is the carb set up correctly, is it clean inside, do you have any air leaks. I also think the head gasket blew when you bought it? Was is running ok before that happened?
Sorry for the questions but it will need going through to find your issue as it does sound like a fuel/carb/air leak issue

You could also have a look at this as it might help https://sucarb.co.uk/technical/techn...ault-diagnosis

[Jeff Turbo]

https://maestro.org.uk/forums/forum/...rting-problems
This was a previous issue with I think the same car

[MatthewL]

Hi Matt
You say it runs rich?
I'm guessing you can't drive the car when warm but can when cold? Carb runs richer when cold so I can't see that would be the issue. The part numbers you put up are not correct. ADU8499 and ADU8479. Does it conk out when revving it when not moving? When it conks out does it re-start and idle? Is the auto choke working, does the small rod push out when cold and retract when warm?
What adjustments have you done from the workshop manual and was it running better before you started working on it? Is the carb set up correctly, is it clean inside, do you have any air leaks. I also think the head gasket blew when you bought it? Was is running ok before that happened?
Sorry for the questions but it will need going through to find your issue as it does sound like a fuel/carb/air leak issue

You could also have a look at this as it might help https://sucarb.co.uk/technical/techn...ault-diagnosis

Hi Jeff, thanks ever so much for your interest.




The car ran for a brief period of time after I had the head skimmed and pressure tested. What I found was that it would start and drive absolutely beautifully when cold but once it got warm, I would get some jerking as I accelerated unless I teased the engine speed up slow slowly with the throttle. It was then a race to get home as it would not idle. It felt like at that point it was either to lean, or too rich because the fuel wasn’t burning right. As the fuel gauge plummeted I suspected the latter. Looking now at the spark plugs having run it on the drive for as long as it will run before conking out the spark plugs are black and smell of fuel implying it’s too rich.




I’ve not made any changes from the workshop manual except to run through the tests for the symptoms of fuel issues




I’ll do a separate post to include the list of all of the changes I’ve made and things I’ve checked. The car exhaust smells rich on first starting it but it runs really smoothly as time goes on. It doesn’t smell much less rich at the exhaust after 10 minutes, but then it starts to splutter a little and one press of the accelerator and it conks out. I can restart it but it runs appallingly and then conks out.




The reason I was interested in the ECU was in case these were reacting correctly to the inputs, particularly from the air and coolant temperatures sensors. I figured that if the ECU didn’t know to ease off the choke, this might be the reason for experiencing these problems.




There are no air leaks - I have tested this with car cleaner with the engine running.




Vinny kindly help me out with the correct head gasket set and helped me with re-fitting so I’m confident that is all spot-on. Similarly, Vinny helped me with a carb rebuild (full kit) and ultrasonic clean and the stepper motor fitted works well - the car starts at about 1200 revs and then gently drops the revs to about 800 over the first couple of minutes so that seems to be working as expected.




What ECUs should it be running? I’d like to see if this is the issue. As you’ll see in the next post, the many changes and checks have not identified anything that has changed the symptom.

[MatthewL]

Attempted to check timing (proved to not be possible with our timing light) but it runs super smooth at start up and Vinny checked belt fitted correctly.

Removed split section of wire on low tension side of coil

Used spark tester to check each cylinder was firing

Gapped new spark plugs

New distributor cap and rotor arm
looked at health of battery - was ok but a candidate fir a future change just in case

Swapped battery for known good one

Checked and cleaned up all earth and positive battery terminal contacts

Replaced oil breather pipes (still have. concern about 3-way valve) and checked with engine running that air was being pushed out of the sump

Cleaned contact on both ECUs
Cleaned contact and re-seated plug to stepper motor on carburettor

Carried out tests based on voltage and resistance on ignition timing ECU

Checked all pipes for air leaks and joins around carb

Fitted fuel filter

Blew air down return fuel line to make sure it was not blocked

Tested voltage at fuel pump (seemed low at 11.6v with engine running where car battery was at 14.2v)

Checked fuel cut off emergency switch (does not appear to be working - car will run with plug removed from the switch)

New cylinder head gasket fitted and head skimmed, new valve sales fitted
Compression tested engine all cylinders around 125 psi

Checked for float on turbo charger impeller very little movement

Replaced temperature sender in the thermostat block - tested resistance with hot/cold water - meets spec
Ran engine with oil pressure switch earthed

Checked (and refitted) vacuum pipe from carburettor to ECU

Replaced pressure regulator diaphragm, which was split in fuel pressure regulator

Tested fuel pressure with engine cranking into carburettor showed a reasonable roughly 3.5 psi

Swapped ignition coil

Swapped fuel pump relay

Bypassed wiring to fuel pump - pump ran smoothly before and after engine stalled - so pump healthy

Swapped out ECU for ignition timing- same issue after 10 mins of running

Disconnected and bridged air temp sensor contacts. Car stalled within 2 minutes of starting - reinstating sensor and it ran ok, if rich.

Plugs checked - sooty and black, smell of fuel - running rich

Resistance across pin 6 and 7-10 is roughly 15ohms on the stepper motor as per manual

On fuel ECU Pins 2 and 5 show near battery voltage but manual suggests it should drop to 6 when starting - only stops to 10v - not sure if that’s an issue

On fuel ECU resistance across pins is as per manual

Replaced ignition switch which showed high resistance as o searched fir the “lost bolts” - no change

Checked resistance on auxiliary ignition 1 and 2 relays which get warm - seem fine

[Jeff Turbo]

Have you looked at the vent solenoid and checked that as that allows air into the system.
Also the float height maybe incorrect or float can stick in the bowl as that would cause over fueling. Have you also done an emissions test ?

[MatthewL]

Have you looked at the vent solenoid and checked that as that allows air into the system.
Also the float height maybe incorrect or float can stick in the bowl as that would cause over fueling. Have you also done an emissions test ?

Hi Jeff. I tried blocking off the carb vent valve to check there was an air leak - is this what you are referring to? I’m not sure where there is a solenoid - where would I be looking please?

I’m hoping the float height will be ok as set by Vinny to factory setting (I planned to take to a rolling road/emission check to fine tune but it’s never worked enough to get to the place!), I wonder if the float could be sticking. Is there a best way to check? The carb piston moves freely.

[Jeff Turbo]

Vinny knows what he is doing so I assume the float height is ok. The ignition ECU you have on the car is a normal carb one I think and not a turbo one. The vent valve is the solenoid, have you tested the valve? Disconnect from the carb, turn ignition on and blow down the pipe, then turn off and blow down the pipe. If on it should be blocked If off you can blow through. If you have a colour tune you can also set the emissions via that. You could try altering the mixture screw a quarter turn a time while it's not running then restart it, if you adjust while it's running the ECU compensates so won't set correctly. Does the car restart once it conks out ?

[MatthewL]

Hi Jeff - not tested it beyond blocking it off and seeing if it ran any different (engine and fuel cold) and there was no difference but I’m not sure how I should test that valve - is there a technique?

Interesting I seem to have the wrong ignition ECU - should it be an ADU 9475? Think I saw one on someone’s Maestro. What about the fuelling one please? Is that also wrong? Looked undisturbed fur 40 years when I took it out!

I’ll order a colour tune and look to trial weakening. Be interesting to see if it starts and runs ok set up weaker. Be great if it was as simple as this to fix!

[Jeff Turbo]

Hi Jeff - not tested it beyond blocking it off and seeing if it ran any different (engine and fuel cold) and there was no difference but I’m not sure how I should test that valve - is there a technique?

Interesting I seem to have the wrong ignition ECU - should it be an ADU 9475? Think I saw one on someone’s Maestro. What about the fuelling one please? Is that also wrong? Looked undisturbed fur 40 years when I took it out!

I’ll order a colour tune and look to trial weakening. Be interesting to see if it starts and runs ok set up weaker. Be great if it was as simple as this to fix!

Ignition is adu 8479, I have also edited how to test the vent valve on the previous post. Running the incorrect ECU adjusts the timing and this may also be your issue, turbo ecu has a boost retard program in it, normal ECU doesn't. Your fuel ECU is correct

[MatthewL]

Thanks Jeff. I’ll carry out the vent valve test. Also will keep an eye out for an ADU8479. Is the fuel ecu the right one? that’s an ADU8499 on my car.

Appreciate the help! Thank you

[Jeff Turbo]

Thanks Jeff. I’ll carry out the vent valve test. Also will keep an eye out for an ADU8479. Is the fuel ecu the right one? that’s an ADU8499 on my car.

Appreciate the help! Thank you

Yes the fuel ECU is correct, you should also change the crank sensor as that might be getting hot and shorting out. Something is failing when it gets warm so try the vent test, ignition ECU change to correct one, emissions testing

[MatthewL]

Right - I’ll try to find a new crank sensor Jeff - don’t suppose anyone in the club has a stock of spare ECUs for sale do they? If not I’ll set an eBay alert. Thank you

[Jeff Turbo]

Have a read of this https://maestro.org.uk/forums/forum/...-warm-problems
You should also recheck the rotor arm, you should be able to search how to do that on the search button, it's quite easy.