I just took the car to emissions with the new motor. Vital specs are a hotcam, no emissions equipment besides a new catco cat, and DIY PROM capibilities. I attached the graph so you have a visual on whats going on. Both HC and CO are high at idle and they also both shoot up upon decel. HC are JUST over the limit during crusie and accel while CO is very low. Is there anything I can change in the PROM to lower particularly the idle and decel emissions? I am running ARAP bin with a 129 idle BLM and cruise BLM from 124-130, which is decent for a MAF car. My temp will not go over 185 either because of the 180stat and the fact that my fan runs all the time, no matter if I set the A/C switch thing to N/O or N/C, but even if it was around 210, I don't think it will be enough. What do you guys think?

 

Oh yeah, the graph.

 

damn good numbers.. wish i was that close to passin

 

Modify the Prom for high rpm/ High Vacuum to 0ms injectors pulse.. and Zero or -4 degrees timing

 

Hmmm, I'm interested in this topic too. I may have to face a similar situation in the spring (but haven't had the problem yet).

FWIW, here are some (untested) suggestions:

If it were mine, I'd make sure the O2 sensor was up to spec - do you have/need a heated O2?

Then I'd look at the injector pulses/IAC steps @ low RPM to see if everything were stable.

Assuming the High HC readings are caused by some reversion from the LT4Hot, I'd try to get more heat out to the cat so it could do a better job of HC conversion:

Maybe take a degree or two out of the spark timing; possibly step up the idle RPMs to try and minimize the reversion component; set the fan temps high to keep as much heat on the engine as possible (for the test).

Let us know how you make out.

DrJ

 

Does anyone have insight on why my reading are so high at idle? Also, both HC and CO spike upon decel, which is normally caused by a rich condition, but how is that the case with DFCO? I read that TRAXION passed with flying colors by forcing the car into open loop and running it lean. I am going to try that first but by a different method, Im going to try to enable highway mode at 10mph or so and try running the stock timing tables instead of ARAP.

 

Having recently run into the same.....
At idle drop the timing back. I had to take the timing in the table down to 15 deg.-that dropped the #'s on mine to near the limits. I also took out another 4deg at 2500rpm at low load.
Also-you stated you have a new cat-is it designed for air injection????
My divertor valve was not functioning; it had been smacked too many times when taking off and on the serpintine belt. After I replaced the divertor valves my HC went from 120 and 150 to 30 and 50. (at idle and 2500rpm).
Do you have to pass the "dyno" test?

 

Yea, its the dyno test. I don't have any AIR on my car so I can't do anything there. Ill try lowering the timing at idle also. We got snow here so the car will be benched until the snow is off the roads but keep the suggestions coming.

 

HC and CO on decel is one thing we spent a long time tuning on a chassis dyno in order to get a 1980 MGB to pass the People's Republic of California old FTP 75 full test. One thing we learned is that Decel Fuel Cutoff is hard to do cleanly, mainly because the manifold gets wet with fuel, and when you shut off fuel, and close the throttle, all the fuel on the walls gets passed through the cylinders unburned because it isn't enough to support a rich enough air fuel ratio to burn normally. It also presents a problem when the fuel is turned back on. We ended up not using decel cutoff, and had better results, but the trick that really cleaned it all up was a "gulp valve." It basically allowed the air pump air to enter the intake manifold (albeit restricted), during low MAP conditions, and without decel cutoff, the MAP didn't drop quite as quickly or far. You might be able to enable more IAC opening upon Decel. I don't know where or what it's called by GM, but basically I think there is some function where the IAC is opened X steps above Y RPM, or maybe the Throttle follower multiplier can be increased.
As for Idle, CO is mainly associated with rich conditions. HC is from rich or missfire, which may be more common than you'd think at idle and with rumpity cam (internal EGR dillution). Are you running closed loop at idle? Air injection works miracles at cleaning up Open Loop Rich operation, such as warm up, or sometimes idle, depending on who's tuning it. Catalytic converters (3-ways) need a strict 14.7:1 Air Fuel ratio to be most efficient. It also must be HOT (enough), and to maintain a hot cat at idle can be hard, and same goes for keeping an unheated O2 sensor hot. I'd put in a heated one, especially since they are about as cheap, and easy, no super easy to install, just wire one of the whites to a switched +12 (fuel pump relay?) and ground the other. That'll enable sooner (if the O2 is not responding while other sensors are OK for CL), more accurate closed loop.
CO being LOW during cruise, while HC is High suggests an occasional misfire, or Lean misfire, but closed loop should eliminate Lean misfire (unless there's an out of spec injector). So, perhaps you have a small ignition misfire. Check your plugs. If you don't know what to look for, do a search or something, but mainly look to see if one plug is wet, black, white, or anything other than brown. Brown (tan) is good. That'll indicate a more frequent problem, i.e. injector, or really bad spark plug wire.
I hope you find the solution, and I hope anything I've said isn't totally wrong.
Good Luck,
Jeremy

 

The misfire idea is a possibility I hadn't thought about, but it's a good one to check.

Just for clarity, when I looked at a misfire (with a WB before the cat) it seemed to raise the O2 level more than the HC level in the exhaust. If the engine is running Closed Loop, the ECM would (I believe) see this as a 'lean' condition, and increase overall fueling - that would result in excess HC in the exhaust. The misfire I was looking at was illustrated here: http://temp.corvetteforum.net/c4/doc.../misfire_s.jpg

Another possibility is that the O2 sensor on the engine is working fine, but it is only reading one bank of the engine (common on some GM designs). A stuck or leaky injector on the other bank would be undetected, and hence not corrected by the ECM AFR adjustment. Those can be a bear to diagnose unless you put O2 bungs in both manifolds.

DrJ

 

Tons of good info guys! Im gunna try to go through tomorrow with the stock spark table, DFCO disabled, increased IAC at decel, and increased idle speed. How much would an incorrect minimum air setting effect the emission output? I noticed my IAC steps at idle were at 88 or so and I knew that wasn't right. The car would start and instantly die on the stock motor's minimum air setting so I set it for a lumpy 500rpm idle and am now seeing 11 steps at idle. Any thoughts on that? As for the misfire, plugs are brand new, wires are 6 months old and the cap, rotor, coil are all 18months old. I don't feel any miss, but it still may be there. The only part of the igniton system that would be suspect is the carbon traced cap, but that forms after a few hundred miles on my car. Injectors are 18 months old also. Ill try these things and any other suggestions before tomorrow and let you know the results.

 

Try an idle of 750 or 800rpm (in the prom). Then just adjust the throttle blades until you have iac counts of 20 or so. With mods you can't really use the "by the book" method of adjusting min. air. Does your smog police have a maximum idle speed?

 

Im pretty sure it is 1000rpm.

EDIT: I couldn't make it friday, I worked saturday, closed sunday, so tomorrow it is. I tested my 'emissions bin' today and it idles much nicer with the stock spark table that with ARAP. I also left DFCO enabled because that is the only way to limit decel, I did shut off decel enlean though.

 

You are running an engine that seems similar to GM's HO 350 (which has recently been discontinued). GM advertises that when that engine is installed exactly has called for in the instructions, it is smog legal in all fifty states (even including the People's Republic of California). The reason I mention it is because part of the package included a prom. So, if everything else checks out, you might want to try the factory prom. The online GM Performance Parts Catalog has the part numbers. Good luck.

 

PP,

I'm by no means an experienced EPROM tuner (at least for ECMs), but the advice you've been given seems to be logical.

Applying what little I do know from rudimentary vehicle operation, it seems that Dr. J's "leaking injector" theory has merit. It certainly would be easy to check/eliminate with a fuel pressure test.

Also, the minimum air advice is sound, since it's very much like the procedure for teaching the IAC on a V-6 PCM. Regardless of the programmed target idle RPM, provide enough air from the throttle stop adjustment so that the IAC doesn't have to race to the full open position on decel to try to make the mixture correct. Get the IAC counts as low as you can and still have it control idle RPM, and that's about all you can do with that function. That constant extra air from the throttle plates may dilute the fuel enough to make some real difference. You DON'T want a dashpot on your TPI. That would at least help the decel numbers, if not the idle.

The next thing that really thorws a wrench into this - do you have a gas analyzer at your disposal or do you have to hit the treadmill every time to test your adjustments? That could get to be a real nuisance.

Hrock probably knows a lot more about it than I do, but wouldn't retarded timing at idle tend to raise the HCs? Maybe I misunderstood. On decel his advice makes sense, but at idle?

If you really get in a pinch, you might try to temporarily rig an electric AIR pump from an LT1 into your cat to help light it off and maintain the conversion. Just make sure you get a check valve installed between the pump and aspirator fitting on the cat. It's not a cheap fix, and might not get used often, but it might help get you through the lane. If you have the ability to monitor the exhaust in your shop, even an air compressor (regulated way down, of course) you could test the theory easily to see if it is worth any gains. If the HC drops way low at idle with more CAT air, you may have found your solution.

And several suggestions have been made to raise the coolant temp to help burn off everything as best you can. If you think the NOx numbers can handle it, you could try higher fan temps without changing the thermostat.

Good luck. The answer is probably going to be in several areas, not just one big, glaring problem.

 

I just got back from the sniffer and I passed! Here are my readings:
HC - 1.21 GPM
CO - 1.6 GPM
NOx - 0.92 GPM

Here are the changes I made for reference, working cat with no AIR, reset minimum air for the cam, set idle speed to 800rpm, disable decel enlean, stock spark tables, and set highway fuel mode to enable at 15mph with an AF of 16:1. Thanks for all your help guys, I'm in the clear for two years!