1986 Austin Montego EFi with cold start issues

[Jeff Turbo]

Fuel ECU wiring details

[Wild Bill]

Thanks Jeff. Here's another update from the mechanic. Sounds like it could be the ECU?


I have had some more time on the car, a bit at the end of last week and some today. What I did and what I found out:

1. The cold start on Friday morning, whilst initially making me think it was better, once warm it seemed to be worse.
2. I found the ballast resistor that is in the coil to ECU wire, removed it, cleaned the contacts, made sure it wasn’t
open circuit, hooked it back up
3. I refitted the black stepper this morning & fired the engine up with my stethoscope on the stepper:
Ignition on - stepper operated
Fire up, Initial idle was low (600RPM), slowly climbed 700, after about 2 minutes the stepper
operated and idle dropped back to 600, after around 3 minutes more the revs were again
around 700 and the stepper operated again dropping the idle to 650 (approx)
Now warm I followed instructions to close stepper, disconnected it & tried to fire up but it
wouldn’t until I’d screwed in the throttle stop screw - when running set base idle to 650,
reconnected the stepper but it did nothing at all
4. I found an article online about ECU issues with dry solder joints so I removed it, took it out of
it’s case and examined it under a my magnifying lamp - no apparent dry joints or blown components

I have these questions regarding the operation:

1. When the stepper operates on ignition on how does it decide where to position the pintle? I am assuming this is just a basic setting unrelated to anything on the input as you can close the stepper by disconnecting it and reconnecting it with ignition turned on and off.
2. Once the engine is running how does the ECU set the position of the stepper? The stepper only has an effect on the idle speed, I am guessing the main source of this would be the input from the coil, fine tuning would then be done using the inputs from the temperature sensor & air flow sensor. This detail information is hard to find so I can't confirm.

In an ideal world I’d like to swap the ECU, I spent a bit of time looking and came up with this:

https://www.johnrichardssurplus.co.u...u-auu1051.html

The only issue with this is the part number, it’s listed as AUU1051, yours is AUU1051E, I have no way of finding out what the difference is.

I will have time to talk this through tomorrow if you want to give me a call when you are free.

Best regards,

Chris

[Jeff Turbo]

Will, E means exchange on the part number. That ECU isn't available on his link
You would be better buying these manuals to help Chris your mechanic as the bottom one covers everything for you car Chris is asking information on. It's available on Facebook selling pages. Just look up Austin montego
I'm away ATM enjoying London but will look up what Chris has asked for on my return as I've forgotten and need to look it up

[Wild Bill]

Cheers Jeff. I will see if I can find on FB. Any pointers appreciated

[Wild Bill]

The mechanic has now fitted a new ECU and seems to think he's got the car running as well as he can and said it drove well from cold today. Starts without throttle at about 850rpm and idles down to about 750-800rpm when hot. Says you can here the stepper motor now working, which you couldn't hear before. Sounds like he's had enough now, so guess I just have to go and collect it and see how it drives.

[Wild Bill]

Collected the car. Started OK from cold but needed a few seconds to fire. Sounded a little bit spluttery for a minute and idled about 850rpm. Drove well. When hot it probably idled about 750rpm. Stepper is doing something but not convinced its working properly and may even be the incorrect one as its like its not operating to its full range. I think I need to get with someone who's runs bang on and see if they will let me borrow their stepper to test

[Jeff Turbo]

Collected the car. Started OK from cold but needed a few seconds to fire. Sounded a little bit spluttery for a minute and idled about 850rpm. Drove well. When hot it probably idled about 750rpm. Stepper is doing something but not convinced its working properly and may even be the incorrect one as its like its not operating to its full range. I think I need to get with someone who's runs bang on and see if they will let me borrow their stepper to test

I'm a bit far behind due to work. holiday, working on my MGZT V8, diesel and Chris etc but seems you're about 90 percent there then. you could try changing it? https://www.ebay.co.uk/itm/321450124...2FHYT4HCVN6MZJ

[Wild Bill]

Cheers Jeff. I think I will look at getting one but want to be 100 it's the correct one. From experience, are there different types or all pretty much the same?

[Wild Bill]

Decided to change the stepper again. Unfortunately no improvement. It appears that it doesn't do anything beyond initial instructions at ignition. I plugged the old one in and held it in a bottle whilst my Mrs to started the car. With ignition on the stepper pushed out. When starter engaged it moved very slightly outwards. With the engine running it didn't move, including when revved. Stepper contracted when engine switched off

[Wild Bill]

As the car smells quite strongly of petrol when started, I am thinking the mixture screw isn't quite right. I am going to see if a local garage can test the CO2 and adjust to 2.5% and see if this improves things

[Jeff Turbo]

You either have a leak or it's running very rich. On early cars there is a mixture adjustment screw but that was discontinued

[Wild Bill]

[Jeff Turbo]

As I said, it was on early cars only and was discontinued in later models. You maybe lucky in that yours has the mixture screw

[Wild Bill]

I got an email from the mechanic today and he seems to think the speed sensor could be playing a part in the low idle:

Hi Will,


Sorry for taking so long to reply, have had a few things in the workshop to sort.

There is a chance that the mixture adjust is incorrect but I don’t think it is that which is causing the low idle. I do not have a CO analyser but my pal runs a garage with an MoT station, he sometimes will let me check and set this if I pay him for the time.

Today I called Roger Bywater at AJ6 Engineering, he’s written a book on fuel injection so the main reason for speaking to him was to buy this but it also allowed me to make a contact and start a discussion about the issue. One thing he mentioned, other than that he hadn’t done much with the Lucas system for many years, was that the vehicle speed sensor can cause idle problems if the ECU thinks the car is moving when it is not. I’ve downloaded the book this evening and will be reading through it over the next few days, I will see if anything comes to light that will point me in the right direction and be in touch after the weekend.

Best regards,