[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: 4kq Cruise Problems (Still)

> The second car that started to not work happened right after I changed the
> speedo in it so I figure that the new unit is not sending the brain the
> right info. As I just posted to list, I wonder how to check this.  Do I
> check the pins at the back of speedo.  IF so, what should they read or
> what range do I measure.  Resistance or Voltage or Amps?  I guess the
> faster the little wheel spins the more speed it registers so it must be a
> voltage or amperage thing???  Faster it spins more power it gives brain?

could be measuring a generated voltage but I suspect it's more likely to
be frequency.  That little coil is probably being driven by a magnet
spinning on the speedo cable or whatever it attaches to, so the raw
output would be a sine wave with freq. dependent on speed.  faster might
not make more voltage, just a higher frequency.

>         Anyhow, I suspect that is the problem on at least one of the cars.
> Huw, you say there is a section in Bently that covers Cruise Control?  I
> cant find mutch other than a hard to understand diagram.  What page.  I
> have the 4kq/tqc Bently.

My coupe/4k bentley has it under Engine/Fuel Injection Controls, section
22.  Starts with a pretty good skecth of all the bits and some bad
photos of their locations, then comes the troubleshooting sequence.

I suspect a bad ground may affect the cc functioning too but I haven't
dug into that.

btw, since cleaning my switches, my cruise has worked like clockwork,
except for one strange anomaly - especially when cold, it will keep a
speed *lower* than I set it for.  I did toss in the servo from another
year and model so maybe that is screwing it up but I'm not sure.  That
is where my ground theory comes in, it may be messing up the read on the
inductive pickup signal.  swapped control units, same result.  I'm gonna
swap pumps, too, just for fun.

Huw Powell


82 Audi Coupe; 85 Coupe GT