[urq] hesitation, bucking on takeoff - RESOLVED!

[Ben Swann]

Well John Larson gets the lucky cigar!  As his post encouraged me to redouble my efforts to find an intake leak...
"----- Original Message ----- Too much to quote ..............  I often see this problem on CIS and CIS-e Golf/Jetta cars.  Almost invariably a cracked intake hose, which opens and closes during a loaded condition, particularly starting out from a stop.  I say "almost", because I have a 16v here that isn't that, and I'm hours into it and haven't a clue.  BTW, I've seen it on 5KTs, as well.  John"

That pretty much is what I found.  Under the clamp on the intake hose to the turbo the hose was coming apart.  I had checked for leaks earlier and this did not show up visually, nor when I pressure tested the intake by applying pressure into the manifold and intake.  I did hear some air coming out in the proximity of the air intake behind the light and this may have been what I heard, as they are very close together, so I originally mistook it as air going out where it should, although now I realize this would have been sealed largely by the airlow plate.  

Anyway I decided to take all the intake hoses and interooler off for further inspection and when I started pulling out the intercooler hose, I saw how the ripped part of the hose under the clamp at the front of the turbo would appear as I was pulling on the hoses.  It was as if the clamp had cut around the hose almost halfway around, yet it remained concealed normally.  While accelerating, this must have been pulling out, creating a massive vacuum leak.  In my last few test drives, I could hear it as the car accelerated and I shifted gears - sounded like a blowoff valve going hiss.

This was one of those very frustrating searches for a problem where I had to tell myself as I seemed to be running out of things to look for - it had to be something discrete, no magic, double check and look again for something obvious.

Anyway, now the car starts pretty much on a turn of the key, better than ever!  Even when I have the idle screw turned almost all the way in, it idles slow but nice and smooth without stalling.  No stumbling on startup, no backfiring or rough running on  warmup or need to give it the gas.  With the new injectors and seals as well as everything gone over, the car runs great and acceleration is well - Wow!

So thanks to all who replied even with some obvious things to check, these Q'lists continue to be a great support resource to turn to.  I'm glad I have an extra '83 UrQ to use for parts and troubleshooting while I build up an engine for it.

Ben
  From: Ben Swann 
  To: DGraber460 at aol.com ; urq at audifans.com 
  Cc: Ben Swann 
  Sent: Wednesday, October 19, 2005 12:53 PM
  Subject: Re: [urq] hesitation, bucking on takeoff - not resolved yet!


  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
  ----- Original Message ----- 
    From: DGraber460 at aol.com 
    To: benswann at comcast.net ; urq at audifans.com 
    Sent: Saturday, September 24, 2005 8:47 PM
    Subject: Re: [urq] hesitation, bucking on takeoff


    In a message dated 9/23/2005 8:05:25 P.M. Mountain Daylight Time, benswann at comcast.net writes:
      This problem has gotten progressively worse on my '83.  Earlier this summer she was running great with no problems except the occasional hard start. 
      Now, particualarly after warm and mostly after shutting down and starting after 15 min. or so, the car bucks and hesitates like crazy on takoff, mostly in first gear, if I double clutch it enough to get some momentum going and shift into a higher gear it'll pull fine and then seems fine at higher speed or cruising.  It has gotten really annoying as often won't get out of 
      its own way when taking off at a stoplight.

      I know it is not the fuel pump cutting out.  O2 sensor has been replaced and attempt at adjusting the mixture make no difference.  The ignition components are new, incl. coil.

      I suspect control pressure, as this happens after it is good and warm. Sometimes is hard to start and stalls out after starting fine and then want stay running without giving the particular magic footwork to the throttle. 
      I had recently cleaned airflow sensor and filter, and all was right and it ran good until it started doing this.

      Really strange as it seems to have full power once going over about 7 MPH but off the line bucks like crazy.

      Any ideas or BTDT.

      Thanks,

      Ben 


    Check and see what your tach does during these episodes. If it drops and bounces, it is probably an ignition problem. If not, then fuel is the culprit. Do you have a fuel pressure gauge?

    Dennis
    Denver