[urq] hesitation, bucking on takeoff - not resolved yet!

[Pasqualoni, James E]

On Wednesday, October 19, 2005 12:53 PM, Ben Swanndered:

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

----------------------------------------------

Ben,

Have you tested the throttle position sensor and WOT switch?  Try unplugging
it and running closed loop for a while to see if this makes a difference?
Strange symptoms...

HTH,
Jim