[T2] ECU and larger displacement

[Sami Dakhlia]

Hi,

Fellow list member Chris Dreike offered more than a helping hand
today. He pulled his wideband O2 sender and gauge from his magnificent
DD bus and clamped the sender on my bus's '75 exhaust pipe; then sat
in the backseat, holding the gauge, while I cruised up and down I-405.

The readings' range was between 11.5 and 12.5, even at WOT,
invalidating my hypothesis that the engine might be running lean. On
the contrary, it might be running a tad rich.

This also means that there is no pressing need to replace the ECU for
an early '76 one. The '75 FI system designed for a 1.8-liter engine
appears to adequately cope with a 2-liter engine, i.e., not cause a
lean-running condition at WOT.

It appears that I was misled by a poorly installed CHT sender.

Thank you, Chris! Many thanks also to Bob, who offered to send me a
later-model ECU from his stash. And to Jon, Syd, and Dennis for
offline conversations and advice. I shall henceforth strive to worry
less and just enjoy the ride!

Cheers,
Sami

On Wed, Aug 3, 2016 at 2:15 PM, Sami Dakhlia <sami.dakhlia at gmail.com> wrote:
> 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
>>> _______________________________________________
>>> type2 mailing list
>>> type2 at type2.com
>>> https://www.type2.com/lists/type2/listinfo
>>
>>