My short term 75

[festy]

I brought this home today, on loan for a couple of weeks.
It was the first time I've driven an Alfa on the road since 1998 


And most importantly, it's a twinspark!


I did a lot of R&D work on the Motronic ECU system a couple of years ago, adding new features etc but I couldn't go any further without a car to test on, so I was a little bit excited to finally get my hands on one.

First job - find the ECU and diagnostic port. It's a '91 model so has the later 3 pin fiat style port.


After following the wires, I found the ECU hiding behind a metal cover panel so popped it open and installed my custom firmware chip, then started the engine. I've been waiting a long time for this 


It's got all the normal issues  - the VVT solenoid is stuck advanced (I think), it's only running on one coil, there's an ARC disco etc but that's all part of the TS experience 

[Divano Veloce]

Thats brilliant news, whatever you do don't give it back!

[Paul Gulliver]

Festy , that great news. What you achieved with your ECU thread on Alfa BB was unbelievable considering you didn't have a car . I hope you are now in a position to maybe revived that thread.

[lombardi]

Once you drive it, you will realise what all us owner's of 75s, you will not give it back !

[Bulli75]

  CORRECT!!!

[pasey25]

I stupidly sold mine. Now I look for it everywhere.

just looking at that pic of the diag connector gave me a serious pang of saddness/regret

[festy]

A few screenshots of the live data progress - I think there might be a bug in the coolant and air temp sensor code because there's intermittent faults in the logs, but no fault codes on the ECU.
The load of 100 at idle makes me think the AFM needs cleaning, so for now I just lowered the ignition advance at 900-1600 rpm / load point 100 so it doesn't bog down when you crack the throttle off idle.
I sat in the driveway blipping the throttle while tweaking the ignition map a little at a time until it responded better

The first two pics show advance of about 17* at idle, but the third pic (after the map changes) show about 14* at idle and 16* at 2200 rpm.

I stupidly sold mine. Now I look for it everywhere.

just looking at that pic of the diag connector gave me a serious pang of saddness/regret

This one is for sale, $1200 ono

[festy]

Fixed the temp sensor bug - it was in the datalogging software, not the ECU code which explains why there was no faults logged.

I spent ages yesterday trying to sort out the ignition issues, both distributor caps and rotors were pretty sad and they were firing in different orders.
I thought I was going mad because it would only run if cylinder 3 was firing when cylinder 1 should have been according to my timing light, until I eventually recalled being told that this engine has an alfetta water pump fitted... and I'm guessing the Alfetta's TDC pointer must be in a different spot to the TS?
   

[Duk]

I spent ages yesterday trying to sort out the ignition issues, both distributor caps and rotors were pretty sad and they were firing in different orders.
I thought I was going mad because it would only run if cylinder 3 was firing when cylinder 1 should have been according to my timing light, until I eventually recalled being told that this engine has an alfetta water pump fitted... and I'm guessing the Alfetta's TDC pointer must be in a different spot to the TS?

How do you mean they were firing in different orders? The leads were done incorrectly?

[festy]

How do you mean they were firing in different orders? The leads were done incorrectly?

Leads mixed up, or distributor rotated a *long* way out of position. The cam distributor was already lined up with it's reference mark, but couldn't find any reference marks on the other one so I'll pop the cam cover off when I get a chance and line it all up properly.

[festy]

Cleaned all the plugs and reset the gaps, cleanes the distributor caps again, and got it running on the cam distributor nicely so then set the other to match and now it will run with either coil disconnected (but not both)
Next job, test the cam variator...

[festy]

Cam variator is working just fine, the hesitation off idle must just be the overzealous AFM.
So, do I pop the top off it to clean the tracks and tighten the spring one notch, or just fix it in software? 

My logs so far show it idling with a 'load' of 85-100, which translates into about 5 millisecond injector pulse width.
I would have expected maybe 1-2ms?
The factory fuel maps have a load axis covering loads from 25 to 120 (1.25ms to 6.25ms) so it's almost off the end of the map just idling 

When I first pulled out the ECU I noticed signs that I wasn't the first to open it up (scratches around the folded tabs, one of the mounting nuts missing etc) and once I looked inside that was confirmed.
It had the original '191 chip which is correct for late model AU twinsparks, but someone had broken a leg off the chip and soldered it into a carrier socket so I'm guessing it had an aftermarket chip installed at some point in it's life and later removed - so I wouldn't be surprised if the AFM flap has been fiddled with. I should probably check to make sure there's no "instant +10hp" resistors connected to the coolant sensor too

[festy]

I just went for a quick drive, first time out running my firmware
It went a fair bit better than when I drove it home the other day, but I think that has more to do with sorting out the ignition issues than any improvements in the chip.
 


Then I pulled over and made a few tweaks to the ignition map with the engine idling, before heading back home.
And I only indicated with the wipers once 

I think next job might be to finish writing the wideband ECU code which will help if I need to adjust the AFM spring.
 

[festy]

I just noticed that I got a fault code logged when I returned from my drive.
It was DTC# 34, which is an idle switch circuit fault.

I looked up the parameters set for code 34:


What that means is that DTC 34 will be recorded if the following 4 conditions are met:
1) the coolant temp is at least 83* (i.e. engine is up to normal operating temp)
2) Engine speed is < 1000 RPM
3) Injector pulse width is > 2.5ms (which is a load of 50)
4) the idle throttle witch is closed

So that pretty much confirms that the AFM is lazy, it's delivering twice the maximum acceptable amount of fuel at idle if max is 2.5ms and my logs show 5ms.   

The only reason I noticed the fault was that it turned on my newly-wired-in "check engine" lamp, if these cars had one from the factory it probably would have been on for a very long time...

[festy]

Hey, that doesn't look like factory silicone on the AFM cover 


Surprise! this AFM has been interfered with, but at least they were kind enough to mark the original setting (well I assume that's what the white paint is marking...)


So I set the spring tension back to the mark and started it up - and like magic the throttle crack stumble has completely gone, who would have thought....
Then I went for a quick lap around the neighborhood, it's a completely different beast now

The owner wasn't real impressed with the TS, he told me it had nothing down low compared to an Alfetta and was a dog off the line. I'll have to see what he thinks of it now it's working properly