OldS10

We have a 98 LS1 from a 98 Vette in our 89 S10 pickup. Overall conversion has gone well. One issue that we have found is that NOX level is a bit high. It is 2.33 VS 1.55 (where it should be). This engine did not come with EGR. Does anyone out there have any suggestions as to how to lower the NOX levels? The only suggestion that we have is that the cats may be on the edge & going bad.
Your input IS appreciated.

imma_stocker

iTrader: (19)

Single exit exhaust? Can you see the difference between each bank o2 sensors? If a cat(s) is going bad you should be able to see one bank burning hotter.

Did you swap the evap can? You might also be running a too lean. Leaner conditions tend to produce more NOX.

jimmyblue

iTrader: (11)

Retard timing, colder water jacket temps, richer idle
mixture all help. So does fresh O2 sensors which will
not swing as wide, for as long, about stoich keeping
the mixture out of super-lean excursions.

Look for elevated misfires on one or a couple of cylinders
which can indicate one lean injector, making that hole
a NOx "superstar".

OldS10

Thanks for your time...We're running duals, using the original C5 cats & O2s. We monitored the O2s and the 2 front ones & the 2 back ones seem to be fluctuating about the same. We did NOT swap the evap canister and are using the Vette unit there as well. I will check all of the lines though.
This is my first experience with LS technology and I figured that the PCM would throw a code if mixture wasn't right.

OldS10

Thanks for your time as well.
The PCM was programmed with stock operating parameters (to the best of my knowledge). The O2s came over from the Vette with the engine, so they aren't new, but the voltage readings seem to be about the same when we monitor them. Are you suggesting that we could modify the operating parameters to bring the NOX down?
Also, not sure what you mean by "elevated misfires" or how to check for them. The engine seems to run very smoothly with no misses or power loss (which may not be noticeable in an S10 body). We DID run a can of BG 44K through the fuel system prior to emissions testing. As far as running temperature, I don't think that the fans have come on all winter and we set them about 5 degrees cooler than stock (I am not sure how that translates to combustion temperatures).

jimmyblue

iTrader: (11)

You could modify O2 sensor switchpoints to make
closed loop richer. This will tamp down NOx but raise
CO, we don't know how close you are to some other
bind. F-bodies use 350mV and my wideband says
this is 14.5:1 or so on a truck I mess with; truck
had 500mV settings originally and this made it idle
fat at 13.5:1.

I'd set fans to run low at 175F ECT and high at 185F
if you have a stock 'stat. Those pivot about 184F
on F-bodies. Stock fans on F-bodies are much higher
ECT settings, dunno about 'vettes. If you figure the
air charge coming in is at ECT temp, and you then
put a 10:1 squeeze on it, that's some real hot gas
and what NOx needs to be created is high temps and
excess oxygen. Every degree you take out of the
water jacket, takes ten degrees off the pre-ignition
charge temp at 10:1 CR.

Misfires you observe with a scan tool, in HPTuners
it's Misfire Current Cylinder (mode) 1... 8. Look at
them all, for any that stand way above the rest
especially when the motor is tuned toward the lean
side; this can flag a short-injector-delivery type
issue.

Going the other way, a single "drooler" will push the
fuel trims lean, and the other 3 in the bank will be
leaner than desired to make the net exhaust oxygen
content come out right by the sensors. This would
probably not show as a misfire on the fat boy but
might raise the other three.

OldS10

Thanks again for your reply...
Our readings are as follows...Co is 9.211 with a limit of 15, HC is .8110 with a limit of 1.2, so it doesn't look like we have a lot of room to work with.
The stock thermostat is 210 degrees and we have the fans set to 215 & 225. I'm not sure that GM has a lower thermostat with the same housing, but will check.
The engine sat for 1 1/2 years before we got it installed & fired up, so a gummed up injector may be a possibility. We DID run a can of 44K and a bottle of Lucas fuel system cleaner through the system seperately to try and make sure that things were cleaned up (no guaranty on that).
Our lap top diagnostics don't show misfires, but our "tune guy" uses EFI Live, so we may need to call him.
How can you isolate a drooler to identify?

Anyway, we have some things to look at.
Thanks again!

OldS10

Found something interesting......we hooked up a fuel pressure gauge to the fuel rail and turn the key on. It pumps up to 55-60 lb., but immediately drops to around 20 lb upon the pump shutting off. It then bleeds slowly down to about 15-16 lb. over about a minute. Upon startup (while graphing the front O2s), bank 1, sensor 1 oscillates several times and then settles down and tracks closely to bank 2, sensor 1. Upon shutoff, bank 1 sensor 1 viltage drops slowly, but bank 2, sensor 1 drops more quickly. My interpretation is that one of the injectors on bank 1 may be drooling. Is that a fair guess?
We are also getting rigid tubing installed in the "collector to cat" part of the system this week. We'll see if that changes anything.

FiredUpZ28

How bout a 00-02 cam?