[T2] ECU and larger displacement

[Sami Dakhlia]

Quick update:
I relocated the thermocouple, wedging it quite firmly between two
fins. See photo:
https://drive.google.com/open?id=0B3JXI3RTjfDCamQybXVXTHA3anM
(ring-shaped connector is cut off)
I think it's close enough to the spark plug hole and it will have to do.

Took the bus on a 25-mile test drive from Topanga to Malibu and back.
Here is an elevation map for the outbound journey:
https://drive.google.com/open?id=0B3JXI3RTjfDCN3hKb2lLdjhoM0k
[Start altitude: 420 metres, End altitude: 71 metres, Maximum
altitude: 420 metres, Minimum altitude: 1 metres, Distance: 31.3 km,
Total ascent: 236 metres, Total descent: 585 metres]
(BTW, the elevation map was created at
https://www.doogal.co.uk/RouteElevation.php)

Pleasant 75 F ocean breeze.
Idle CHT: 365 F
Easy cruising at 45 mph CHT: 370-380 F
Slight 7 deg. incline at 40 mph, 4th gear: 395 F
Same in 3rd gear: 380 F
Return trip, climbing up Topanga: 410 at 30-35 mph, 3rd gear 3-5 deg incline.
390-414 F in 1st and 2nd gear at 5-15 mph on 10-20 deg incline.
Throughout, oil temp gauge showed 210-220 F, went up to 240 during the
last half mile up the steep hill.

So it's still running hot. That's all for now. Leaving California in a
couple of days, so further troubleshooting will have to wait until
next year.

Cheers,
Sami

On Tue, Aug 9, 2016 at 12:15 AM, Sami Dakhlia <sami.dakhlia at gmail.com> wrote:
> 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
>>>> _______________________________________________
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>>>
>>>