4kq hard starting-stumbling-UPDATE

[William Perron]

Well-
Got a lot of input from listers: Huw, Jan P, Bob D.,
Ben S, Chris, Sam L, Bob M, Jim D.
The main suggestions were -- ECU temp sensor or
connector, CSV problems, O2 sensor, DPR problem and
finally basic mixture setting.
1.  ECU temp sensor--double checked this sensor at a
few different temps-- reistance was correct according
to Bentley.  Also I checked the function by
disconnecting the sensor, and shorting it to simulate
extreme cold(disconnected), or normal operating
temp(shorted)--ECU responded correctly so the
wiring/connector appeared to be OK as well.
2.  Cold Start Valve- CSV/thermotime switch is working
properly-- sprays when cold, and you are cranking
starter.
3.  DPR clogged/dirty-- took it off and cleaned it out
w/ brake cleaner--no change
4. O2 sensor - Sensor is 6 months old-- working
properly as mixture bounces around the set DPR
current--although I don't think this should have any
affect on my symptoms as the ECU is not reading the O2
sensor signal right after startup.
5. Static mixture--This seems to be my problem.  I had
been setting the current with a harness on the DPR--
but apparently I wa setting it to lean to keep the
engine running after startup.  SO I decided to set it
the old fashioned way--Disconnected the O2 sensor and
started the car.  I kept richening the mixture via the
3mm hex until the idle speed started to slow, then
leaned it out a bit from there--basically tried to get
the highest idle.  I then drove it a few times, had a
bit of a stumble off idle so I leaned it out another
1/8th of a turn.  Car seems to be starting good now,
no stumbling or stalling and drives very well.  I
still need to check the DPR current to make sure I am
not so rich that the ECU can't adjust the mixture
properlyduring normal running.

Thanks for everyone's input--especially Jim Dupree for
suggesting the static miture adjustment.

-Bill
'85 4kq

 
> On 6/22/05, William Perron <w_perron at yahoo.com>
> wrote:
> > I've been having a problem w/ my '85 4kq lately
> that I
> > can't seem to figure out.
> > 
> > Problem:  Hard starting when "cold"-- cold varying
> > from 50F to 95F.  Car will sometimes catch when
> key is
> > first turned, but then stalls.  After a few
> attempts
> > the car will eventually start, but will have
> trouble
> > idling for about 30 seconds- usually need to keep
> the
> > revs above 1500RPM during this time - then the
> idle
> > evens out and I can drive away.  Once car is warm,
> I
> > can turn off and restart easily.  AFter it sits
> for a
> > few hours, the hard starting begins again.
> > 
> > Diagnostics/Changes so far:
> > -Checked Idle switch- it is working properly
> > -Swapped ECU temp sensor with known good--no
> change
> > -Cleaned all grounds, connections including intake
> > manifold grounds for ECU
> > -Swapped in known good plugs/wires distributor cap
> -
> > no change
> > -Swapped large intake manifold boot - no change
> > -Attached hose clamps to all ISV hoses - no change
> > -Swapped ISVs - no change
> > -Checked all hoses for vacuum leaks - nothing
> found
> > -Re-did all small vacuum hoses in engine
> compartment
> > w/ new ones- no change
> > - Installed new injector seals - no change
> > -Centered air plate in fuel dist. - no change
> > -Checked that Cold start valve is receiving
> voltage
> > when cranking - it does receive voltage
> > -Checked after start enrichment function--ECU does
> > enrich mixture after starting
> > -adjusted idle speed (w/ duty cycle meter),
> mixture
> > and timing- no change
> > - installed known good fuel pump relay no change
> > -installed a normal relay so fuel pump runs
> whenever
> > ignition is on--waited at least 30 sec to "prime
> > system" ---no change
> > 
> > I'm really not sure what else to check at this
> point.
> > ONe interesting thing I noticed is that the car
> seems
> > to start pretty well if I leave the ISV
> unplugged??  I
> > though the ISV might be a problem so I swapped in
> a
> > differnt one--no change...
> > 
> > Any thoughts or comments appreciated
> > 
> > 
> > -Bill
> > Burlington CT
> > '85 4kq
> > 
> > 
> > 
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> 
> 
> -- 
> Chris Hall
> badcomrade at gmail.com
> "making girls cry since 1974"
> 



		
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