[mdlug-discuss] [TECH SUPPORT REQ] OBD-II typical readings

[Peter Bart]

On Wed, 26 Sep 2007 12:36:20 -0400 (EDT)
Robert Meier <eaglecoach at wwnet.com> wrote:

> Aaron,
> 
> > Bigger question... what exactly is the car doing that is
> > driving (heh!) you to monitor its behavior so obsessively?
> 
> The car is a Saturn SL2 2001 with 75Kmi.
> 
> In late July, I had new tires put on the car.
> The prior tires were Firestones with 75Kmi on them.
> The new tires are same radius Cooper tires.
> 
> As always, I kept track of gas mileage,
> and expected to lose a percent or two simply
> due to widing of tire with new tread.
> 
> The actual gas mileage dropped from about 30mpg to 25mpg (~20%).
> The car also seemed to be struggling up some hills I remember
> having no trouble climbing and otherwise appearing slightly
> "sluggish". After a second tank of gas confirmed the mileage drop,
> 
> I tried pressurizing the tires to 4psi over the door plate figure,
> as the old tires had been.  There was no noticeable change.
> 
> I was too busy trying to satisfy a long-hours job, and so couldn't
> readily take the car to the mechanic until about 1month had passed.
> I confirmed the presence of adequage oil, transmission fluid, coolant,
> and my inexpert eye could not find any disconnected/broken
> hoses/clamps/...
> 
> Taking a coworker to lunch on M-59, the speed topped out at 45mph
> and the tach was ~4000rpm.  I scheduled to take it to the mechanic
> the next day.  On the return trip, the speed topped out at 15mph,
> with everything I could think of to reduce engine load.
> A few days before, on the weekend, I'd used it with only slight
> sluggishness compared to pre-July performance at Detroit highway
> speeds.
> 
> I dropped my coworker off and took it directly to the mechanic.
> Enroute to the mechanic, I tried pushing the accelerator to the
> floor (when traffic permitted) to engage the "flood mode" switch
> that leaned the fuel injection (to permit starting when flooded).
> After three such operations, the cars top speed climbed to 45mph
> at which I made it to the mechanic.
> 
> The mechanic originally said the computer reported multiple
> trouble codes (the MEL was NOT lit), and that the transaxle output
> speed sensor was not reporting.  The mechanic assumed that
> most drivers would not have noticed that the speedometer was
> reporting 0mph.  I would have noticed a speedometer reporting 0
> and did not at anytime see such.
> 
> The next day, the mechanic said that the speed sensor was working
> and the misdiagnosis was due to misuse of the monitoring equipment.
> They did change the fuel filter (which was already reported to
> need replacement (50% blocked) when next convenient).  The
> mechanic reported that the car behaved fine in multiple test drives
> and they could find nothing wrong.  The mechanic recommended that
> I merely watch the car until I could learn something deterministic.
> 
> The mechanic did suggest watching the transmission change points
> and said the torque converter should be bypassed at 47mph.
> 
> Since then, despite the time limits of the above-mentioned job,
> I stepped up my long-planned efforts to install a modem (already
> assembled) in the car and begin monitoring (planned for baseline
> measures, now unfortunately for diagnostics).
> 
> I have found that its misbehavior is intermittent,
> usually but not always when the outside air temperature (not the
> engine) is hot.  (Driving the car in the cool morning, cool evening,
> on a cloudy day, or after sitting in the shade, it seldom misbehaves.
> After sitting on a hot parking lot on a sunny day, it frequently
> but not always misbehaves.)
> 
> When it misbehaves, the tach rises above 3000rpm without downshifting.
> When it is not misbehaving, it seems less peppy than I remember,
> and it takes several times as long to accelerate to I-75 speed,
> as I remember when I was commuting daily to/from downtown.
> 
> At no time have I seen the MEL lit, nor have I found any trouble
> codes in the queue.  I've been unable to identify conditions
> under which it reliably misbehaves.
> 
> I've verified accurate dashboard speedometer reading with a
> gps receiver on several occasions.  On two occasions, when
> I had neither palm nor gps, I observed my dashboard speedometer
> reporting less than posted speed while keeping up with traffic
> (once on M-59 and once on I-75).
> 
> The monitoring tool is OBD-Gauge running on a salvage (for 5$,
> suffers total amnesia every few days) Palm.  It reports and graphs
> (not uploadable) throttle position, tachometer, vehicle speed,
> calculated load, ignition advance, coolant temperature,
> manifold air pressure, short term fuel trim, long term fuel trim,
> manifold air temperature, oxygen sensor (pre-catalytic),
> oxygen sensor (post catalytic).  I understand 0 fuel trim
> indicates stoich burning; negative readings like I see,
> indicate rich mixture.
> 
> 		    normal observation		misbehaving
> tachometer:	    2000-3000			2500-3500
> vehicle speed:	    (matches speedometer)	(matches
> speedometer) calculated load:    ~33 in drive with brake	
> 		    ~25 in park
> coolant temp:	    ambient->95<->105oC		same
> manifold aid press: ~100KPa engine off
> 		    ~40KPa idling
> 		    ~20KPa under load
> oxygen sensors:	    250-750mV (almost white noise) same
> short fuel trim:    ~0 to -40/99 averages -13	same
> long fuel trim:	    ~0 to -23/99 averages -9    same
> 
> On one occasion, I observed an OBD vehicle speed of 0, while the
> car was in motion, and the dashboard speedometer was apparently
> reading correctly.  (This may have been loss of data cable
> connection.)
> 
> Reporting,

Dr. Meier,
	My suggestion to you is to find a mechanic/shop you can trust;
either by recommendations or good means; that is familiar with your
vehicle. That may or may not be a dealer shop, you get what you pay for.

Best Regards,

-- 
Peter The Plumber sm on the Road