Re. Narrowing down my start issue (84 4kq)

[Ben Swann]

It is about a 50/50 chance that the problem is fuel pressure related.  If you suspect
fuel pressure leakdown due to faulty check valve or accumulator, then you can rule that
out fairly easily.  Unless you are the mechanic being paid by the hour, You don't want
to start cracking these fuel components open to troubleshoot.  Not right away anyway.

Instead, run the fuel pump before starting.  To do this, either use a jumper in place of
the Fuel Pump Relay, or use a non-triggered relay.  The Orange Fan relay is perfect for
this.  Borrow one of these from the fan position if need be for testing ( or your
buddies car).  These are good to keep on hand as this lets you turn fuel pump on with
the key, so get a few from the boneyard when you go.

Using the substitute relay will run pump continuously allowing max. fuel pressure to be
reached before cranking.  There may still be a fuel pressure problem, but this will rule
in/out a bad check valve or accumulator and/or a general problem with pressure leakdown
somewhere in the system.  The accumlator is mostly for damping fuel pressure spikes,
although it also serves to keep pressure in the system overnight when things are tight.

Fuel pressure regulator could be a problem.  So can injectors and odds are this is more
likely than any of the other components you mentioned so far.  You may want to do some
system and regulated pressure tests.  I'm sceptical,  since any problem with flow or
pressure that is not a leakdown issue would be apparent not just at startup.  Anyway,
once again do the easy convenient tests before resorting to more difficult or expensive
ones.

Is the only issue you have right now a starting problem and happens both warm and cold?
Is there a driveability issue, hesitation, power loss under load???

Anyway, for purposes of trouble-shooting in the indefinate future you probably should
just keep a fan relay installed in place of the normal FP relay. These are typically
orange or gray rated at 40 AMP and large terminals for the power supply bridge.  That
way every time you go to start the car, you can turn ignition on for a couple seconds
and let fuel system pressure "normalize".  Keep the relay there until you solve the
problem - you just don't want to leave the key on and walk away

Tommorrow you will be one step closer to knowing where the problem is or isn't.

Ben

[Date: Sat, 14 Aug 2010 10:59:57 -0700
From: Johnny B <pre95 at live.com>
Subject: Narrowing down my start issue (84 4kq)
To: <quattro at audifans.com>
Message-ID: <BLU142-W26BB9483B20CBFF6B50E83C8990 at phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"

Well, I got some work accomplished on the 84 Friday and have some more specific start
symptoms now on the car. Definitely narrowing things down!

First I'll say I noticed the starting issue is not just when cold, but always when
starting (Even after sitting for say 30 seconds after the engine is hot). When the
engine is warmed up, it SEEMS like the start issue isnt there (as it starts easily) but
in reality, if you try to give it any throttle for the first 10 seconds it bogs. After
the 8-10 seconds, all symptoms are gone and it drives as it should. During all of it the
idle is rock solid. 

I started by doing a very thorough vac leak check with chemtool at idle, checked all
essential bits including all formed vacuum tubing (X, ISV, Intake boot) and all the vac
lines, all connectors, injectors, seals, intake manifold, TB, all vacuum related systems
and found zero vacuum leaks. I installed the "X" & ISV silicone tubes from 034 and
replaced all vacuum tubing under the hood clamping all connections. I re-checked the
system with chemtool after the install and again, no vacuum leaks. 

I tested the idle & WOT switch at idle, both respond as they should. I pulled the DPR
off the side of the fuel distributor to check for clogs, screens are clear. I then
adjusted the metering plate screw by 1/8th of a turn towards the rich side. I restarted
and same bog symptoms within the first 8-10 seconds (as the engine was still warm). I
did notice after the adjustment the car feels a lot better while WOT, smoother idle, and
was told by the PO it was 1/8th of a turn on the lean side of "11ma" for smog purposes,
so a proper tune is definitely in order here (getting the harness bits from the yard
tomorrow). I dont believe this is my starting issue as the symptoms remain the same this
morning when cold and when warm. 

At this point I think Steve nailed it with a lack of residual fuel pressure after shut
down. The fuel pump check valve is in the mail and will be arriving on Tuesday. Other
then that I believe the only possible culprit would be the accumulator? Visually the
fuel pump & accumulator look to be factory units, the filter looks new. Could it
possibly be the fuel pressure regulator mounted in front of the fuel distributor causing
this? My buddies 4kq is down for the next few months and he has no start issues, so I
can swap the expensive bits from his for testing before spending any more money (or
strike gold in the yard tomorrow). 

Thanks for the help everyone! 
Johnny
]