Hello and a question

[Peter Vieth]

Hello everyone... my name is Peter Vieth and I'm a 3rd year Computer 
Science and Engineering student at UC Davis.  I have a 1986 Acura Legend 
2.5L that has had constant fuel problems since I got it in February.  About 
a month ago I finally got all the mechanical issues ironed out and went 
ahead on tackling the Honda PGM-FI (programmed fuel injection) ECU.  I 
didn't have much luck until I came across several Rover websites and 
diy-efi.org.  Since then I've been observing the workings of the ECU and 
have some good information that I hope to post at a later date...

I have run into one problem that I could use some help with.  I keep 
getting a solid yellow light on the ECU (The light means turn idle speed 
adjustment 1/4 turn counter clockwise which I think means lower the idle 
speed) whenever I rev the car at a steady rpm for a long time, like 30 
seconds.  ~30 seconds keeps coming up again and again with the ECU by the 
way (seems to be the amount of time before the computer will switch into 
open loop after a sensor is disconnected).  If I let it idle without 
revving it at all the light will not go on. Some sensor must be broken I 
think... My guess would be that the car thinks it's idling at whatever rpm 
I hold it at.  Of course I have the throttle halfway to the floor. When the 
car stays at 4000rpm for like 30 seconds it must think that 4000rpm is the 
current idle speed. So my question is, what does the ECU use to determine 
that the idle speed is incorrect? Or rather, how does it know that the 
engine is idling? I am assuming that the ECU determines that the car is 
idling indirectly from several sensors.

Incidentally, I noticed this when I was watching the o2sensor voltages with 
a DMM.  At idle the o2 sensors swing between .35v and 0.70v in closed loop. 
In open loop they are 0.75v +/- 0.08v usually. When I rev the engine the o2 
sensors read a steady 0.7v in what I believe is closed loop (I take the 
rpms up slowly since I realize the ECU will go into open loop if I floor it).

Also, I believe this idle speed weirdness is the reason why I am able to 
pass the idle test for smog but not the 2500rpm test.

----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org