re. 4kq Fuel distributor/pressure?

[Ben Swann]

[(edited for clarity-brs).. '85 4000 Quattro...wont start, but ..the only way to start it is to jump the fuel pump and let it run ..getting spark, and fuel, dont think it was getting the right amount of fuel.  

<snip> It would stutter and act like it was gonna die if you touched the gas for the first few minutes after it started, but once it got going it was okay. <snip> Ran kinda weak with hesitation and such but i was glad it would run at all.  If i drove to work then shut it off it would start right back up easy, and would start easy all day as long as i didnt wait more than a few hours since it was last running.  If i waited more than 3 hours it was maybe a 5 minute job to get it running, often using only the relay and no paperclip. 
- I replaced the fuel filter , fuel pump check valve and fuel pump relay itself is good.  ]

OK - after reading this a few time I got the gist.   The mixture is obvioustly off.  Presuming no one tampered with anything prior to the poor starting and running, I would suspect in the following order:

1) Massive air leak is not letting air plate rise and consequently not enough metered fuel is getting to the injectors to start.  Check the air intake "waffle" boot and inspect all vaccum lines and especially the one that connect the ISV, to the valve cover etc.  this hose looks like it is a part of someones intestinal tract.

2) Fuel injector O-rings.  Pull the injectors and perform a spray test to be sure none are completely clogged and all are spraying.  If you don't get fuel to the injectors when plate is lifted w/fuel pump jompered on, then you are onto the problem, but I don't think you'll see this.  Replace your O-rings as a matter of course while doing this part of troubleshooting.

3)  As Huw mentioned, the thermo-sender is a common culprit, but rarely does it keep the engine form starting, but more likely the poor running and warm-up problems.

4)  Airflow plate may be misadjusted or jammed.

5) You are definately sure that the fuel pump kick on when the engine is cranked/starter bumped for a second.  Just turn the key for .5 sec and make sure you hear the pump run momentarily when key is released.

6) Dirty/clogged Differential Pressure Regulator(DPR) - related to (3).

7) Not likely the starting problem, as would cause poor running after engine running for a few miutes and O2 control running closed loop - your O2 sensor may need replacement.

OK after doing some methodical checks for above I think you will have resolved a few inter-related problems that have culminated in the problem and possibly stumbled upon something else.  You will likely have replaced many vacuum lines in doing so which will increase the reliability for some time to come.

Happy Hunting!

Ben