[urq] stumbling under boost

[fdekat]

> From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf
> Of Gary Brown
> Sent: Friday, June 06, 2008 6:29 PM
> To: urq at audifans.com
> Subject: [urq] stumbling under boost
> 
> 
> Hey guys-
> 
>  Having an issue...
> 
> My 85 urq runs great, except it has developed a nasty
> stumble at full throttle and full boost.
> 
> Can't find a vacuum leak and duty cycle readings seem
> to be correct.
> 
> While crusing at 4k RPM, part throttle, I see around 
> 66%. Full throttle is 77-79%.
> 
> Rotor was a little crisp, but I sanded it back to its
> shiny self.
> 
> No difference.
> 
> Thoughts?
> 
> Gary
> 


I have been having a similar problem. Only in my case it's more 'stumbling
under any acceleration at all'.

Following Craig Cook's suggestion, I put a voltmeter on the o2 sensor output,
which told me that mixture was going lean whenever motor was stumbling

That leads to two possible situations: Lack of fuel delivery, or ignition
missfire (A missed ignition event makes the o2 sensor think 'lean' as all the
oxygen is still in the unburnt mixture).

(In your case though, I'd think the duty cycle would go to 'full rich' if the
o2 sensor though mixture was lean. Maybe?)

After messing around measuring fuel pump voltage (and relacing some
'overheated fuel pump wiring'), and doing a 'fuel delivery test', concluded
problem wasn't fuel.

Measureing spark plug wine continuity (two wires measured 'open'), and
looking at sparks (kind of lame), I'm concluding I have an ignition problem.
Further testing with some new wires and different coil are in order, but I'm
thinking that's where *my* problem may lay.

Of course, CIS is involved, so the quantity of variables that *could* be the
cause of your problem is still quite large...  :-)

Regards,

=Frank=