samwise Samba Member
Joined: May 04, 2010 Posts: 611 Location: North Salt Lake, Utah
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Posted: Sat Jul 27, 2019 1:42 pm Post subject: Another CHT thread... |
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Back story:
1979 CA Spec engine rebuilt in 2012 - engine builder removed and did not re-install the flap system. Business no longer in operation.
Catalytic converter still in place
Changed from Hall Effect distributor to 205P
California ECU still in place
Compression test: #1 120, #2 130, #3 120, #4 130
Last emissions test in Feb:
Idle HC 355ppm, CO 0.20%
High Speed (2500rpm) HC 53ppm, CO 2.04%
Engine runs nicely in itself (idle is lovely, pulls well in any gear, etc), but the DD CHT gauge shows very high temperatures (sender under #3 spark plug).
With Colin (Amskeptic) here, we changed plugs, changed out the DD sender, cleaned up the wires to avoid them being offended by the spark plug wrench. Driving around, the CHT gauge quickly showed temps in the low 400s (ambient shade temp was showing as around 100), and we could get it to get to nearly 450 with Colin driving with his foot on the brake and flooring the gas to simulate load. Sitting idling on the driveway, I could watch the head temps slowly crawl up to over 400 - Colin hit the engine area with his infrared thermometer to see if the gauge was working properly (if I remember correctly, cat was at just under 500, exhaust manifolds at around 750, valve covers, everything seemed to show that the gauge was working correctly).
We tried running with the O2 sensor both connected and disconnected, tried adjusting the spring and the wiper to both lean and rich, tested with the vacuum line between #1 and 2 inlet manifolds attached, part obscured, and fully open.
I know that I need to get the flap assembly and fit it, but does anyone else have any ideas - maybe Colin can jump in, too, with what he remembers.
Could the CA-spec ECU be a cause of the high temps? The missing flaps for the oil cooler etc? Looks to be standard CA exhaust in place, no dump tubes attached to elbows, though. _________________ Ben
1979 7-passenger bus
Harvee the Wonder Bus' pics |
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Gregg in the 603 Samba Member
Joined: April 13, 2013 Posts: 404 Location: New Hampshire, USA
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Posted: Sat Jul 27, 2019 7:38 pm Post subject: Re: Another CHT thread... |
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How many miles on the rebuild? A tight build makes more heat. Your temps are exactly what I saw on my 79 rebuild before I put in the potentiometer. Now I cruise at 65 with 385 degrees on the DD CHT guage. Never going back. _________________ 1979 Mexico Beige Westy auto
Dirty Dover, NH |
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SGKent Samba Member
Joined: October 30, 2007 Posts: 41031 Location: Citrus Heights CA (Near Sacramento)
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Posted: Sat Jul 27, 2019 7:53 pm Post subject: Re: Another CHT thread... |
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until you have the flaps in place you don't have a reliable test. Your high HC at idle then dropping at 2500 might imply a lean misfire at idle which is another issue unrelated to the high temp. High HC at idle could also be a leaky EGR or a weak / cold catalytic when it was tested.
my 1977 has about 4000 miles on the engine. The numbers were about the same when newly built and tuned.
15 MPH
HC 23
CO 0%
CO2 14.29%
O2 1.6%
25 MPH
HC 20
CO 0.01%
CO2 14.2%
O2 1.65% _________________ “Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin |
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