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ReSaabin' (Read 2,623 times)
Lance
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I love YaBB 1G - SP1!

Posts: 1

ReSaabin'
Nov 14th, 2004 at 6:13pm
 
Hello again, forum. I have some posts on the old archive - am going at a Saab 900 once again! Any comments or suggestions most welcome

Driveability problem: initially (20K miles ago), slight bucking @ 2800 RPM when going down hills in 5th gear. Now car bucks, variable intensity (but almost always present to some degree), between 2200 RPM and 4200 RPM, going down hills, on level ground/steady-state throttle, or under light-to-moderate throttle. Occurs with both cold or hot engine. Sometimes transition from less than full power to full power is abrupt, when accelerating thru 4K RPM.  Is difficult to hold RPM static @ 2800 RPM, where engine sounds thready and can rock in its mounts. Subtle intermittent miss at idle.  Essentially stable vacuum manifold pressure.

Car has been to 3 Master Saab Techs, to no avail.

Much has been done, but, alas, not enuf as yet. In brief (?!) - more can be offerred - no evidence of a single-cylinder problem. Parade peak KV even. Fuel pressure steady, measured from inside the cabin, while bucking occurs.  Fuel pump volume output tests good. TPS tests good. Hall-Effect/crank sensor square/tests good. Air Mass Meter tests good. All ignition and fuel system grounds clean/secure/good. Vital ignition and fuel system wiring load-tested, when possible, and also piggy-backed/paralleled (including grounding circuit directly to negative battery terminal): no change in driveability. Knock sensor input removed; load signal input removed: no change in driveability. Fuel mixtured intentionally enriched: little to no change in bucking/power loss. HCs reported normal per exhaust gas analyzer. Alternator AC ripple current nominal/tests good. Timing chain tensior at upper end of wear spec: valve/camshaft timing properly aligned. Charcoal cannister wiring disconnected, and/or vacuum plugged at intake manifold: no change. No engine codes. Highway gas mileage has dropped over last several weeks by 6 - 8 MPG.

O2 sensor switching or rise/fall time very fast. Enough rambling for now, and on to some captures from a Fluke 97

http://pg.photos.yahoo.com/ph/alancemor/album?.dir=/8eec


2dary: burn time seems a bit on long side, but doesn't appear to shorten. "Nose" height varies noticeably.

Interesting O2 sensor waveforms....

I thought ISCV/AIC (same AIC as used on circa 85-92 VW Golfs and Jettas) waveform abnormal (was puzzled at seeing such high voltage, but perhaps similar to a saturation fuel injector spike?) until seeing this

http://www.picotech.com/auto/waveforms/graphics/bmw325-iscv.gif

NTC/CTS shows same negative drops @ 2ms/Div (just able to catch it easier at faster sweep)


With thanks,

Lance Morgan
CA

91 Saab 900S non-turbo 4 cyl 5spd, 138K miles, Bosch EZK ignition system with Hall Sensor, single induction coil, "shell" distributor (advance/retard controlled by EZK computer), no EGR

LH 2.4.2, very similar to LH.2.4 (URL floats)

http://68.155.225.199/electrical_system_folder/lh24wiringnfmp.htm

component 200 = fuel computer / ECU

176 = EZK ignition computer

205 = AMM
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« Last Edit: Dec 19th, 2004 at 3:43pm by Lance »  
 
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