[T2] ECU and larger displacement

[Sami Dakhlia]

Hi Dennis,
I had removed the crush washer to adjust for the presence of the
sensor ring. Did not hear any unusual noises and did not see tell-tale
marks around the hole. :-( Too bad, because I really wanted to believe
in the escaping hot gases story...

The injectors are the same for the various years. So I'm still
thinking it could be the ECU. I wonder if with a 1976 ECU (only the
displacement changed between '75 and '76, the AFM did not -- and in
particular was of the 6-prong type without air temp sensor, so
compatibility with the rest of FI system is more likely), the
injectors would fire more often for a given AFM position?

With a ECU swap, the AFM would then need to be re-adjusted (adjust
spring to make it stiffer), effectively increasing the air flow rate
at which the AFM reaches the full open position. In other words, just
swapping the ECU would not be enough. And together with the stiffer
AFM, the ECU would get meaningful information as the AFM reacts to
WOT.

Good idea to do a dyno test, perhaps I'll be able to do that on my
next trip. A proper diagnostic would make a lot of sense before I
concoct more hypotheses!

Thanks again,
Sami

On Wed, Aug 3, 2016 at 1:46 PM, Dennis Gentry <dennis.gentry at gmail.com> wrote:
> Did you use a crush washer plus the sensor ring, or just the sensor ring?
> If you left off the crush washer, the plug might extend into the cylinder a
> tiny bit more, making it run hotter?  If hot gases were escaping, you should
> have been able to hear it, plus it would leave tell-tale marks around the
> hole.  (Try running with a spark plug only screwed in a couple of turns to
> see what I mean. :)
>
> I like your hypothesis about it running lean, since too lean will definitely
> cause high CHT.  Are you thinking that the injectors meant for a 1.8 L
> engine are failing to keep up with 2 liters of displacement at high RPMs?  I
> don't think that's the cause, since (I think) the injectors were the same
> from 1975 through 1979, when the stock engines became 2.0 L in 1978 or so.
> You could check for too-lean and for reasonable vs. too-low power output by
> putting it on a dyno and measuring the CO/O2 levels in the exhaust, but I
> imagine there is an easier way to do it that I'm not thinking of right now.
>
> Good Luck!
> Dennis
>
>
>
> On Wed, Aug 3, 2016 at 11:46 AM, Sami Dakhlia <sami.dakhlia at gmail.com>
> wrote:
>>
>> Hi,
>>
>> I'm back in California for the month, my annual pilgrimage to the US
>> to work on my '75 bus (and see family, too :)
>>
>> I must admit that I'm just not enjoying the bus as much as I used to;
>> it's just a big headache. Too much time spent on fixing things, not
>> enough time spent traveling. Last year I installed a Dakota Digital
>> head temperature gauge and the temp readings went through the roof!
>>
>> We suspected that the O-ring crimped on the thermo-couple didn't allow
>> for a proper seal of the sparkplug, allowing hot gases to escape and
>> cause the high temp readings. I've now relocated the sender, wedging
>> it between the fins, not under the sparkplug. Not perfect, but a
>> better solution will have to wait until the day I have to pull the
>> engine.
>>
>> While the temp readings are no longer outrageous, they're still north
>> of what's acceptable, sometimes above 380 F. And the engine is lacking
>> power, even by vw bus standards.
>>
>> Which brings me to a new hypothesis: the engine is running lean when
>> pushed to the limit (highway driving at 60mph, or climbing hills).
>> It's a '75 model and came stock with a 1.8 liter engine. I have since
>> "upgraded" to a 2 liter engine. I have so far assumed that the AFM
>> would properly compensate for the extra displacement, but now I'm
>> wondering.
>>
>> BTW, I also adjusted the AFM following the instructions at
>>
>> http://www.itinerant-air-cooled.com/viewtopic.php?f=50&t=7761&sid=26d79b8f4581a7c3219fbb1581ad5523
>>
>> Thoughts?
>>
>> Sami
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>