Bucking broncos--Coupe GT

[quk@isham-research.demon.co.uk (Phil Payne)]

In message <35168EAE.EE70A5AD@ouray.cudenver.edu> Brian Link writes:

>     I have an 86 Coupe GT and I got the bucking bronco symptoms also.  I
> was going skiing and just filled up.  At first  I thought I bought bad
> Gas, but on the way home (night time) I noticed my digital dash would
> randomly get very bright then go back to  normal and the coupe had no
> power.  "This is going to be expensive".  Well the ground lug on the
> intake manifold had one wire hanging on by a thread, the other wire
> completely gone.  Well I fixed the wires and the car is back to normal.
> What is being grounded to the intake manifold, and how would that effect
> my digital dash brightness?  I understand the bucking from the ground
> going to mass air flow sensor, but do not understand the dash lights. No
> other gauges were effected.

The ground doesn't go to the air mass sensor - those connectors have their own 
returns. 

The problem is - although the engine is bonded to the chassis in (depending on 
the model) up to four places, it's still an area where relatively large stray 
voltages (compared with sensor voltages) can arise, both from the spark plugs 
and the alternator returns. For this reason, the instrumentation has its own 
return circuits. These can affect all sorts of weird things.  It's _always_ a 
good idea to check the grounds to the inlet manifold first when you see erratic 
electrical behaviour - not just because that's often the problem, but also 
because it's easy to do. In financial terms, the ROI is high.  

-- 
 Phil Payne
 UK Audi [ur-]quattro Owners Club