ADU8479 ECU

[MatthewL]

It has really tried my patience and taken the shine off having the car. The thing that keeps me going is the nostalgia factor. It was always my dream car. Aged 17 I drove my mum’s 1987 white EFI in the very early 90s. This will be a simple fix. The engine is sound, mileage quite low, compression is good, car is almost rust free. It’s got a lot going for it. Apart from its ability to work!

[Jeff Turbo]

A turbo is very simple engineering but to make it work properly can be a bit of a faff when things go wrong and many look for the wrong things. Many have an opinion but it's basically fuel, air and spark. Most faults are quite easy to find if you eleviate one thing at a time

[MatthewL]

Agreed Jeff. Im convinced it’ll be a simple fix. My XR3 threw me as I’d diagnosed a duff coil and replaced it. Same issue. 6 months of replacing everything else later I changed my 6 month old coil. That was faulty!

Still my dream car. But I’d be lying if I said I wasn’t periodically heartily sick of it! One drive after it’s working and all will be forgiven.

[MatthewL]

Nice cool day today. Engine conked out before the fan kicked in so it’s not the draw from the fan. I can find no air leak. It’s runs beautifully until the temp gauge is nearly middle of the gauge when misfire starts and a little struggling to recover from a blip of the throttle

I had an Accuspark on throughout. Nice bright spark even as it died. And as I tried to restart the spark was strong. Swapped the coil to double check. Again, same strong spark but won’t start.

So I’m thinking something maybe fuel vapour related or timing. It’s quite a mystery!

[MatthewL]

How can I tell if the choke is stuck on? The stepper unit passes the tests in the workshop manual fir resistance and the little thing for settling the idle speed works, but I wonder if the choke isn’t coming off

[Jeff Turbo]

On starting the car from cold the little rod on the stepper motor pushes out to enrich and make the car rev a little higher on the arm, as the car warms up the rod gradually goes back to leave a gap to the arm. That's how you know it's working visually. Don't try to force it or you may damage the cogs in it. Have you tried altering the mixture screw to make it run a little richer if you have no air leaks? You could also check on the vent valve to see if that's working properly. When cold remove the vent valve pipe from the carb and using a bit of fuel pipe with a bolt on it replace it on the carb so no air will get into that part. Then start the car and and see when happens when warm. I would say air is getting into the system when warm somehow if it's running ok when cold or it's running too lean

[MatthewL]

I’ve checked the vent valve previous and also run it with it blocked off which hasn’t resolved the issue so I think that valve is ok.

Does the stepper motor only push that little pin? I had assumed it did a choke setting separately but that this was not visible. I’m not familiar with these units.

The little pin works in that the car starts at 1200 revs and then it drops in steps to about 800 as the car warms if it is in danger of stalling it seems to raise the tickover a little so that seems to be ok.

I’ve borrowed a colourtune so may see what that tells me and adjust the mixture accordingly. It seems set up right to start the engine from cold but from there on smells a lot richer than say my XR3 which after a few minutes is remarkably lean and unsmelly.

[Jeff Turbo]

Visually the stepper pushes out the rod and retracts, there is also a hole inside it to block out air to enrich the mixture and as it turns let's air in as it warms up. If you look under the bonnet when cold, turn the ignition on and the rod should move out, this might be when turning it over but from memory it just pushes out when cold. As the car warms up you should see it retract to leave a gap to the arm. If that happens it's working correctly. If the stepper seals were perished the car would be difficult to start from cold so I have to assume the seals are good.

[MatthewL]

Thanks Jeff. I’m comfortable the stepper is working as it should as I ran through that check using the workshop manual and it behaved as per the manual. I wonder if the hole to block out air is staying blocked shut? I wonder if it’s tied to the position of the pin or if it opens and shuts independently? Be interesting to remove the unit when the car has stalled to look if it’s possible to see this hole is open as it should be?

[Jeff Turbo]

Thanks Jeff. I’m comfortable the stepper is working as it should as I ran through that check using the workshop manual and it behaved as per the manual. I wonder if the hole to block out air is staying blocked shut? I wonder if it’s tied to the position of the pin or if it opens and shuts independently? Be interesting to remove the unit when the car has stalled to look if it’s possible to see this hole is open as it should be?

It could be blocked with something wedged in it as that has happened before but unusual. I would say as its moving the rod in and out it's working correctly, inside it are cogs that all connect to move the interior of it. Try your colourtune but if the car stalls when warm it possibly won't read correctly. Rule of thumb is screw the mixture screw all in and wind out about one and a half turns from memory. Have you also checked on the rotor arm as that can go faulty on getting warm as can the crank sensor. As you say you have a healthy spark it would only be fuel/air related. Have you also tried replacing all of the rubber tubes including the balance pipe as any tiny crack can cause your issues

[MatthewL]

I’ve replaced the crank sensor recently - an awful job! - and looking at the rotor arm and cap - they’re new and still look mint - I can’t see any issues.

I’ve replaced the oil breather hoses as these were cracking, but not the fuel hoses. I wasn’t convinced the 3 way valve connecting the oil cooler hoses was doing much.

Sorry Jeff - which pipe is the balance pipe?

Vinny set the carb to factory standard - I recall him talking about that backing-off a turn and a half or whatever it was.

I might look to inspect the stepper to see if it’s blocked.

Good point re Colourtune- I won’t have it running long enough when warm to tell.

[Jeff Turbo]

Balance pipe is the pipe from the back to the front of the carb. I didn't mean the fuels pipes but any pipe that have air going through it. Did you try removing the plenum and pouring a little fuel down the back of the carb? When warm after it's stopped Raise the piston an poor it in there, should only need a small amount to make sure fuel is getting to the plugs, don't spill it or use easy start as that also fires on plugs then turn it over, if it fires then fuel has stopped flowing.Are you still getting fuel into the carb when it conks out? Trying a few things as something is stopping working when it gets warm. If no fuel it could be the pump blocking or stopping fuel or earth lead behind the offside front light. I'm also assuming there's enough oil in the dash pot. It's a little difficult diagnosing things when not there btw but it'll get sorted eventually

[MatthewL]

Hi Jeff. Last time it conked out I pulled the fuel pipe off the carb and checked the pressure as I turned over the engine - 4psi. I’ll check that little pipe from the front to the back of the carb. Didn’t know what that did!

I wasn’t sure previously about adding the fuel so thanks for clarifying what to do- I’d not tried it.

I have sprayed carb cleaner around all air pipes and joins from filter through to plenum and all around the carb - it’s not raised revs so I don’t think there’s an air leak. It also runs great until it starts to get warm.

May be a few days before I get a chance to do any more but it’s good to have more checks to do. Thank you.

[Jeff Turbo]

I can send up a couple of fast checks, one for the ignition system and the other for carb if you need them. They're simple light up things but can help if needed to find issues

[MatthewL]

Thanks Jeff. Can I take you up on that kind offer in the New Year?

I’m going to see if I can get the car running by adjusting the choke manually by removing the stepper motor I think. See if when it conks out I can manually adjust the choke to be off and see if the car will start and run.