[T3] Two Tests

[Jim Adney]

On 16 Sep 2019 at 16:58, William Jahn wrote:

>  Since you tested these 048 ECU's and the one in your car makes it rich
> perhaps that's why yours works well with TS1 . 

I removed the brain that ran rich 3 years ago. Yesterday, when I ran that 
batch test, I included the "rich" one, just to see if it still gave the same 
impression. It did. I could smell MUCH more gas when that one ran.

> If you ever find what goes wrong in this version that can make it run
> rich/lean let me know. I'm still confused what the real difference is
> between the 028 and 048. All I could find was the 028 worked with the
> 72 dual vacuum can yet both 72 

We'll never know, because Bosch has never released data on their ECUs. 
All we know is that they figured out a way to get around the complicated 
tuneup proceedure that the dual vac can required, which was a really good 
thing, if only because those cans have a much higher failure rate and they 
are VERY expensive.

> and 73 distributors had the trigger point cam advanced.

As did the '72 distributors.

I don't think this is related to any of the other changes. You can swap '68 
and '73 distributors into either year car and not notice much of a change. 
What I've read, and believed, is that the change was made so that the gas 
would sit behind the intake valve for a bit of time for all 4 cylinders. Earlier 
cars, up thru '71, gas got sprayed behind closed intake valves on 2 cylinders 
and behind open intake valves on the other 2. They thought that making 
both "the same" might even out the idle. At speed, where the times are much 
smaller, I don't see this as having any effect.

Once the engine is hot, there's no longer any question of how quickly gas 
will get vaporized, so the timing of the injection pulse no longer matters.

We don't know if Type 4s ever got this change.

> I also read that on the 72 they had the adjustment pot for the CO Mine
> does not. 

No, Type 3s never got the adjustment pot. That was strictly Type 4s, 914s, 
and Volvos, perhaps others.

> For all I know since the tag is missing both ECU's I have could be 048. 

Without the tag, I don't know how to tell the difference. It's possible that you 
could see something different inside, but you'd have to have them side by 
side to look closely.

> if I see 1000 RPM idle and push the pedal down it will raise up to 1200
> so I think my cable is sticking . 

By far, the most common cause of the pedal sticking is that the "ramp" on the 
back of the pedal is catching on the carpet. This is easy to see, once you get 
down there and look, and feel. Do this with the engine off. It's easy to fix, by 
just readjusting the carpet position: Slide it upwards a fraction of an inch.

If that's not it, check that the throttle cable is not "bare" between the body 
and the engine. There should be a flexible housing there, and that housing 
should slip into a pocket in the breast plate of the engine. Careless engine 
installation often leaves that housing misaligned and not dropped into its 
pocket. That can make things stick, and the misrouted cable will slowly saw 
thru the sheet metal of the breast plate and pocket.

That housing also has a sort of sleeve fitting at its front end, which must 
slide over the cable tube where it exits the body. Make sure that connection 
is also properly done.


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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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