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You can disconnect the oxy sensor to the LH and let the controller settle at idle with that. Then puff starting fluid around each injector base, watching for a change in your WB02 reading. If you prop the throttle open a bit so the idle speed switch is open, you'll see a slight increase in RPMs too when the starting fluid smothers an air leak.
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Who did the injectors? Rebuild/cleaned or new? My NOx was creeping up, but the ignition was still strong enough to get the slightly-lean mixture from a cylinder or few, so the after-cat HC numbers still looked good. NBO2 readings showed total CO still good ahead of the cats. New injectors as part of an intake refresh cleaned up the NOx readings completely. Now we live in a no-test area in Oregon. Kind of a mixed blessing. I don't have to have it tested, but I also don't get the diagnostic benefits of the test results.
Looking at your past results, it has been about .10 CO all along.....so that has not changed.
Excessive HC is a sign of a misfire...that's why they measure it. Start at the beginning. Compression good? Correct heat range plugs? Spark plug wires?
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
You can disconnect the oxy sensor to the LH and let the controller settle at idle with that. Then puff starting fluid around each injector base, watching for a change in your WB02 reading. If you prop the throttle open a bit so the idle speed switch is open, you'll see a slight increase in RPMs too when the starting fluid smothers an air leak.
----
Who did the injectors? Rebuild/cleaned or new? My NOx was creeping up, but the ignition was still strong enough to get the slightly-lean mixture from a cylinder or few, so the after-cat HC numbers still looked good. NBO2 readings showed total CO still good ahead of the cats. New injectors as part of an intake refresh cleaned up the NOx readings completely. Now we live in a no-test area in Oregon. Kind of a mixed blessing. I don't have to have it tested, but I also don't get the diagnostic benefits of the test results.
Looking at your past results, it has been about .10 CO all along.....so that has not changed.
Excessive HC is a sign of a misfire...that's why they measure it. Start at the beginning. Compression good? Correct heat range plugs? Spark plug wires?
Ya..I think I saw a chafing of the drivers side coil wire about 8mo ago, I wasnt sure so I wrapped it with tape.
I suppose when I get back in October from Thailand...ill do all of that.
FWIW the coil wires should not touch any parts of their run,
if they do the voltage will begin leaking ,
best to buy two new coil wires and install them,
throw out the ones that were rubbing
FWIW the coil wires should not touch any parts of their run,
if they do the voltage will begin leaking ,
best to buy two new coil wires and install them,
throw out the ones that were rubbing
Agreed. This is also on the non WBO2 side of the car..
Agreed. This is also on the non WBO2 side of the car..
Coil wires feed 2 cyls on each side, but that could still be an issue. If there is a misfire of any sort-- ignition wires or one or more weak injectors-- then you have unburned fuel in the exhaust, and unused oxygen. The LH, using the O2 sensor, is going to see the excess O2 as "lean" and add fuel which adds to the excess HC.
However the high NOx-- as V2Rocket pointed out -- suggests a lean mixture, somewhere. An ignition misfire wouldn't leave those cylinders literally lean, just with excess O2 which looks lean to the LH but isn't. But weak injectors would result in cylinders which were literally lean, low HC and high NOx and excess O2 which would drive the non-weak cylinders rich but leave the high NOx from the weak cylinder(s).
Definitely fix the chafed wires, and when you get back I would consider checking the injectors again-- or at least trying a different set. And check the plugs, they sometimes tell a story.
09-17-2018, 12:54 AM
