[urq] hesitation, bucking on takeoff

fdekat fdekat at sentex.net
Wed Oct 19 14:33:22 EDT 2005

HEllo Ben:

Looks like you are testing things that can 'be tested'. But what if it's
something else?

For example:  A friends 4kq ran great, except for when he pounded on it
(especially in low gears). It would then buck like crazy, if he gave it loads
of throttle.

Problem turned out to be a broken wire to the  'differential pressure' thing
on the front of the fuel distributor. As the motor moved under load (And more
so in the lower gears, as more torque), the bad connection would unload, and
the motor would cack. Back off, connection would be good again, and all was
well.  Even when testing under the hood..

My point is that most of the things you have dealt with would affect
drivability and economy, but probably not create bucking.

I'm wondering if you may have an intermittent connection of some sort (or air
leak?), related to motor position, brought on  by high torque situations, in
the lower gears.

Perhaps a ground coming loose, a connector being affected, a vacuum hose
leaking or even a 'mildly broken' wire somwhere? Perhaps just push and pull
things under the hood, and see if you can get something to happen!

Good luck!


> ------------------------------
> Message: 4
> Date: Wed, 19 Oct 2005 12:53:00 -0400
> From: "Ben Swann" <benswann at comcast.net>
> Subject: Re: [urq] hesitation, bucking on takeoff - not resolved yet!
> To: <DGraber460 at aol.com>, <urq at audifans.com>
> Cc: Ben Swann <benswann at comcast.net>
> Message-ID: <028a01c5d4cd$90c59820$6601a8c0 at Swansong>
> Content-Type: text/plain;	charset="iso-8859-1"
> I am still chasing this problem - '83 UrQ bucking/violent hesitation and no
> power when accelerating in first and second gear/from a standstill.  Since
> the problem began here is what I have done to no avail:
> 1.  Checked airfow plate level and adjusted as it appeared a little high -
> nope.  Then compared the plate movement to others and noticed it seemed to
> be binding a little, and did not bounce when dropped.  I replaced with
> another that moved freely.  Still no improvement to my surprise.
> 2.  Ran fuel pressure tests as I had been suspecting control pressure too
> high.  Tried 3 different WUR/CPR units and am using the one which most
> closely matches desired pressure range and operation according to IST doc. 
> Pressure when cool 65degF is about 23 PSI and warms up within 5 min to 55
> PSI where it levels off.  This seems to correspond with the IST range of
> 1.5 Bar - 4 Bar. The diagram in IST document.however does not map temp and
> may not be right.  I noticed the pressure range to be somewhat higher than
> for CIS in NA coupe.  The problem occured in the same way regardless -
> other regulator range was 22-45 PSI ( WUR from 2.2l NA Coupe) is the one
> that was in the car when problem began.  The engine had been running fine
> for awhile with this regulator, and the problem occured due to no equipment
> changes.
> 3.  At this point I pulled the injectors.  All seemed to have a marginal or
> bad spray pattern, so I broke down and replaced them.  I was sure this
> would be it, since when I tested them, the injectors came on
> abruptly/sporadically and dribbled. peed sideways or a stright stream.  Yet
> after installing them - new injectors and seals, the engine bucks as bad as
> ever.  The spray pattern was much better and looked like it should.  At
> this point I am getting rather frustrated.
> 4. Adjusted duty cycle - have been doing this whenever changing something. 
> Duty cycle can be adjusted to near 50%, but does not always ocillate around
> 50%.  Duty cycle does range from 5%-95% under varying conditions, or if I
> enrich or enlean by adjustment.  Still I decided to swap out the ECU. 
> Still no improvement.
> This problem occurs when the car is warmed up, mostly after having driven,
> shutdown and restarted, but will happen when driven then hitting traffic. 
> Car just bucks like crazy when put in gear and given throttle.  Once the
> car get going, it drives fine, but in lower gears just does not want to go
> without major hesitation.
> 5.  Other things replaced in last 6 months/6000 miles:
> Distributor Cap, rotor,  spark plugs and wires, new coil(done after problem
> began). O2 sensor new.  All grounds are clean and good connections to
> battery.  I continually check for leaks and most of the vacuum lines have
> been replaced.
> 6. Fuel pump and filters were new about 2 years ago when I brought the car
> back from the dead.  Recently changed pre filter and continue to not some
> accumulation of residue getting caught by pre-filter.  Pressure is good and
> if anything on the high side - pegs my fuel gauge which stops at 60.  Id
> guess system pressure is around 90 - using NG pump.  Did not test flow, but
> nothing to indicate there is a fuel delivey problem - perhaps I need to
> double check.  Does not make sense that the car seems to have full power at
> speed, yet not enough to get out of it own way when starting from a
> standstill.
> So presently I'm at a loss as to what is going on - everything I check or
> change seems to make no difference.
> Ben

More information about the urq mailing list