Join Date: Apr 2013
Location: Columbia, Missouri, USA
I have an interesting situation to share:
About mid-day yesterday, I thought I'd go out and start the Alfa again. After all, the fact that my newly-reinstalled engine even ran at all could have been a dream, or a hallucination induced by a steady diet of Oreo cookies and Diet Mountain Dew.
Crap! Similar problem as the day before: starts, runs fine briefly, but won't idle without feathering the accelerator pedal. I had changed nothing since Sunday evening, when it was starting and idling fine. The fact that it starts indicates to me that the Cold Start Injector (CSI) was working, and since it continues to run (although with manual assistance), made it seem that the four main injectors were functioning. It was as if the 'choke' function of the fuel injection system was not functioning correctly, but what had changed since last evening?
Between my wife's '76 Super Beetle convertible, and my Alfa, I feel that I have a pretty good understanding of how Bosch L-Jetronic systems work. I felt like the Grinch staring down at Whoville when the singing starts. I puzzled and puzzed; how can this be?
And then it hit me.
The Alfa has been sitting in the driveway with the hood off. We've had hot, sunny days...and the temperature was already over 90°F outside. I took my IR thermometer, and measured the temperature of various parts of the engine. The AAV read 127°F; the area around the Coolant Temperature Sensor (CTS) and Thermo Time Switch (TTS) read 123°F and 125°F respectively.
I theorized that the thermal action of the sun shining directly on these engine components, had heated them to the point where they were sending signals to the ECU, indicating a warmed-up engine. Of course the engine core itself was not that hot, and would require 'cold start' functions in order to idle correctly.
I made a test of my theory last night. After working late, I got home about 10:30pm, outside air temp was still about 84°F (I didn't think to take a temp reading of the engine with the IR thermometer). The engine started right up, and although not idling as smooth as normal, sustained the idle. This morning, after having set overnight, it started and idled perfectly.
It would appear that vigorous solar soaking of particular FI components led to less than optimal operation. (I should mention that I verified proper AAV operation during Sunday's troubleshooting alternately using a hair-dryer and deep freeze.)
It is certainly possible that there is an actual heat-related failure in one of the components. I am going to once again defer to Occam's Razor, and go with 'too much sunshine' as the cause. I covered the engine today while I'm at work, so I'll test my theory again this afternoon.
I'm hoping that my experience will save someone else some butt-pain later on.
1988 Spider Veloce (with lots of 3D printed parts)