88 5kq - Intermittant Hard Starting

[SJ]

I am reposting because I got no replies to my Labor Day weekend post. I
forgot that you were all down on the beach drinking beer and chasing women
this entire weekend.

Update on the Problem:
Original post 21 July 06

> Symptoms:
> 88 5kq - no turbo - NF engine
> Symptom: Intermittant Hard Starting under cold and hot conditions.
> Majority of the time, the car starts up fine . .cold or hot.

Once started, Engine runs fine 100% of the time. It will start fine 99% of
the time. Sometimes, it will stumble on start up when cold.
Problem isolated to a fuel issue. Tested for spark when engine would not
start.
When engine would not start, using starter fluid got it started.

Newest detected symptom:
Oxygen sensor wont work if revs are under 2500 RPMS. Same problem with a new
sensor.
---------------------------------------------

Parts swapped out with my 90 100Q
Coolant temp switch
ISV valve - idle valve
DPR - Differential fuel pressure regulator

Parts tested:
Cold start valve works
idle switch works . .was rebuilt before

Systems tested:
Fuel delivery system tested - all test fuel pressure test points agree with
factory specs

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

The oxygen sensor issue and intermittant no start/stumbling might be an
excessive air symptom (vacuum leak). I didnt find anything obvious, nothing
cracked or defective.
I set up a propane leak test. Used my barbecue tank with adapted regulators
and feed lines.
My first test was to see how far off my idle speed mixture was. I connected
the propane to the fuel vapor carbon filter port in the boot.
I wanted to see if I could compensate for any leak, and get the oxygen
sensor to work.
I disconnected the O2 sensor lead from harness, and connected it to a DVM.
Engine started, ISV valve disconnected, DPR disconnected.
I turned on the propane and slowly increased the flow.
DVM started out as a low negative number(very lean) and started going up as
I increased the propane flow. With fine tuning of the valve and propane
pressure regulator, I could get the O2 sensor to float at around + 0.5volts,
which is Stoich Air Fuel mix. OK, theory works so far.

I then did the same experiment on the 100q audi. Hmmmm, starts off the same
. .O2 reading as negative number.
Increasing the propane level changes DVM reading . . .I got it to settle at
+ 0.5 volts.
I was hoping that the O2 reading would be close to 0.5 volts with the DPR
disconnected. But, I think the injection system is set up to run on the lean
side if the electronics fail (limp home mode).
What I did notice though, was that on the 100q, I need less propane to get
the DVM to
read 0.5 volts. This confirmed that I had an air leak on the 5kq audi.

I then switched to "propane leak detector mode" -- long hose and thin copper
tube probe at the end.
DPR and ISV disconnected.
O2 sensor disconnected and hooked up to DVM.
I found the air leak, a small one at the #3 fuel injector. No other leaks
found.

Note: Using the DVM and the O2 sensor is a very effective method of finding
a vacuum leak. The DVM reacts to the smallest changes in A/F mixture
changes. This is much easier than listening for RPM changes.
I probed all over the engine and only found that one leak at the #3 fuel
injector.

Questions:
Maybe its possible that the #3 fuel injector seals shift and develop a
larger leak under different temperature conditions?
Maybe another injector also leaks under "ideal" conditions and this makes
the A/F too lean for engine to start?

I want to take out all the injectors, check them out, and replace all the
seals. Car has 170k on it. Original injectors.
I also want to remove the fuel injector inserts as these have seals also.
Is the job easier if I remove the intake manifold?
Can the intake manifold(old rounded style) be removed without taking off the
head? Bentley does not help here.
Is it simpler to just remove the head and do the work on the bench?
Is there a kit for all the seals and O rings?

I've read horror stories about dropping the insert plastic parts inside the
head.
I need some BTDT advice and tricks for this R&R job.

SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q




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