88 5kq - Intermittant Hard Starting

SJ syljay at optonline.net
Fri Jul 28 19:55:07 EDT 2006

Here is the latest on my non-start-sometimes problem.

My last diagnosis showed the oxygen sensor not working. Although, I dont
think this is related to my no-start problem as the O2 sensor does not come
into play until about 3 minutes after engine start.

I put in a new Denso oxygen sensor. I tested it first to make sure it
worked. Also tested the oxygen sensor heater.
One change though, I used an old catalytic converter, which was gutted out.
I even cleaned the cat mounting flanges and put in a grounding strap between
cat and tranny. Just to make sure the O2 sensor had a good ground.

Tried starting the engine . . it coughed a bit . .and then just cranked.

I checked spark. Pulled the cap center wire and connected it to a spark
tester (old plug). Cranked over engine - Plenty of spark - firing like mad -
can see the sparks in daylight.
I cracked the cold start valve fuel feed - fuel is under pressure - so pump
works. Will check fuel pressure tomorrow.

I pulled a vacuum line and sprayed starter fluid while wife cranked engine
over. It started . .a bit rough at first . .then it caught.

DPR current was as before . .starts around 90 ma with ignition on, then
finally settles down to around 12 ma.
The oxygen sensor was not doing much. Started at 0.6 Volts . .then went down
some . .. but it wasnt fluctuating.

I increased throttle to above 2000 RPM, and finally the oxygen sensor
started going high . .and and then started fluctuatiing.
The DPR was keeping pace with the O2 sensor - DPR current was fluctuating
between 4 and 10, or thereabouts.

However, the O2 sensor stopped working when RPM's were low or at idle.
I unplugged the idle stop switch and jumped the connector contacts - - I can
hear the RPM's change. Plugged connector back in, and RPM's again
changed - - -so idle switch is ok.

Tomorrow, I'll put in the working cat (not gutted out). I will also put in a
spare Bosch O2 sensor (tested).
Maybe the extra heat produced by the Cat Converter is required to keep the
O2 sensor hot and functioning?

When checking the O2 sensor heaters, I noticed that the Bosch unit drew
about 1.5 amps when cold and tapered off to little less than 1.0 amp when
The Denso Oxygen sensor started off at 0.5 amps and stayed at that level.

Maybe the Bosch unit heater is hotter and the sensor works even at idle

Has anyone tested the Oxygen sensor output with a gutted Cat Converter?

So, I'm still stuck with an intermittant no start condition:
- which appears to be fuel related
- no start with engine computers in open loop mode.
- temperature sensor was swapped with one from my 100q
- spark ok
- will check fuel pressure tomorrow, and will check cold start fuel injector
tomorrow also.
- can fuel injectors be leaking and cause a rich condition or flooding
problem at start??

Any other ideas?

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

From: "SJ" <syljay at optonline.net>
To: <audi at humanspeakers.com>
Subject: Re: 88 5kq - Intermittant Hard Starting

> From: "Huw Powell" <audi at humanspeakers.com>
> > > 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.
> >
> > > I'm suspecting the MFS temperature sensor, thats the bottom sender
> > I think the MFTS only runs the temp gauge and feeds info to the AC
> > system - the top, two pin black bodied sender is for the CISE3 warm up
> > control (and ignition, too).
> **** Yup, my bad. I had to de-confuse myself.
> The bottom sensor is the MFS (Multi-function) sensor. It contains 2
> and 1 temperature resistor. Switch #1 grounds out when temp gets hot
> to warrant shutting off the A/C compressor. Switch #2 grounds out and
> up alarms when the engine is really hot. The resistor changes value
> according to temp and this runs your Instrument Cluster coolant gauge.
> When checking the sensors, I noticed a broken wire in the rubber cover for
> the MFS sensor. This was the B+ wire. I cut out the sensor connector,
> brought it to the workbench, found another connector with similar contacts
> and put in another contact with wire attached. I added about 4" of
> additional wire to each contact wire so things wouldnt be so tight at the
> sensor where the connector gets plugged in.
> Back at the car, I somehow got the wires screwed up. I reversed the B+ and
> temperature resistor wires. Started engine, and instrument gauges went
> Checked the fuse, blown. Chit!
> I figured out what I did wrong. Turns out that the MFS is the newer 3 wire
> type and not 4 wire type. B+ is not needed. Started up engine . . .temp
> gauge dont work. I swapped in a spare MFS, and that worked.
> After having 3 beers to calm myself, I took apart the MFS sensor to see
> made it tick. As outlined above, its pretty simple inside - 2 switches,
> 1 temp reisistor which was nicely fried . . just carbon remaining.
> While examining the guts, I think that I found the failure mode for these
> MFS sensors. The temp resistor is grounded by spring pressure only. Maybe
> they use a conductive grease or something during assembly. Also, the
> return for the 2 switches and resistor is a little brass tab on the
> connector plastic that makes contact with the brass threaded body. This
> corrode over time and will stop conducting, and the first indication is a
> non-reading temp gauge.
> I took a bunch of close-up pix of the gizmo and will post them when I get
> the roll finished.
> > NTC temp sender (top one) - each terminal, resistance to ground should
> > be around 500 ohms cold, drops to about 70 when hot, even lower at, say
> > boiling.
> **** The resistances checked out both cold and hot. I swapped this sensor
> with the one from my 100Q. The 100Q has been riding around fine for couple
> of days now.
> > Resistance (open/closed) of idle and wot switches.
> **** Yup, I checked resistance . . .its a solid Zero when closed. I
> the idle switch a couple of years ago.
> > Resistance (should be about 16-22 ohms) of control pressure reg. (DFR)
> **** I got 19 ohms
> > Cleanliness of fuel path through DFR.
> **** I took out the gray DPR (Differential Pressure Regulator). You cant
> take this one apart. I didnt see any dirt in the in/out holes.
> > Air leaks anywhere... can be hidden.
> **** I took out all the rubber stuff and checked it. Its all airtight. No
> cracks. The major items were replaced about 3 years ago. I cant do the
> "dipstick stall test" as crankcase air going to the intake manifold is
> controlled by a .070 orifice.
> I did find a leak in the vaccum line going to the A/C controller. I
> disconnected the line and plugged it with a golf ball "T".
> > Cleanliness, function of ISV.
> **** It works. Unplug it and RPMs increase. I gave it a good cleaning
> 4 years ago . . .and cleaned it again lightly about a year ago.
> > Spark quality - wire resistance, plug quality, cap-rotor age, hall
> > sender problems.
> **** I replaced plugs, cap/rotor when I first detected this problem. Wires
> are couple years old.
> I dont think problem is the hall sender - there is no abrupt stop like
> cutting out ignition, or misfiring. When the problem appears, the RPMs
> dropping . .playing with gas pedal brings them back up.
> > Grounds to intake manifold & all other electrical connections.
> **** Grounds are tight. I redid them couple years back  . . .removed,
> cleaned, new hardware, put back. I loosened and tightened them again.
> > Ignition switch intermittence in "run" position...
> **** Dont think so . .no sudden stop to engine. Playing with gas will
> maintain RPM.s. Jiggling the switch wont stop the engine.
> > There is more, but only maybe a dozen things to check all together.
> **** Yeah, I decided to do a DPR current and Oxygen sensor voltage check
> when starting up.
> DPR starts out at about 90 ma, and drops to about 13 ma in 3 minutes. The
> voltage starts at 0.5 volts and drops pretty fast to almost zero. And
> a 5 minute warmup, the O2 voltage is still at zero.
> I did the same test on the 100Q. DPR started at about 90, dropped to about
> 10, then started swinging between 7 and 12 ma. The O2 sensor started at .5
> and in about 1.5 minutes started swinging between .2 and .9 volts.
> I ordered a new O2 sensor. Will try and put it in tomorrow. Then I'll
> DPR current, and O2 voltages.
> Still, I dont think the O2 sensor causes the hard starting symptoms as the
> problem occurs right at startup when engine is running in open-loop mode.
> I'll do some more testing after I put in the new O2 sensor.
> I'll also check the fuel system pressure as soon as I make an adapter to
> connect to the cold start injector line.
> Maybe that leaky A/C vacuum line is the culprit. This line terminates
> the A/C controller head. It connects to other lines and valves via a 'cone
> and socket' rubber contact connector. Just a bit of pressure is what holds
> the connector together. I can see temperature affecting the rubber and
> making/stopping air leaks.
> I'll do some testing after the O2 sensor gets installed. Will try starting
> the engine with this vacuum line open and see what happens.
> SJ

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