After doing a head gasket replacement this winter, the Z28 just failed emissions here in Toronto. Results were: At idle HC allowed: 200, Actual HC was 669 - CO% allowed: 1.00 and actual CO% was 1.97. At 2053 RPM the emissions were much better - HC allowed: 55 and actual HC was 18 while CO% allowed is .31 and CO% actual at that RPM was .02. NO ppm allowed is 408 and actual was 281. For some reason there was no entry of NO ppm at idle (?) - is that standard?

Please see the mods in the sig. Of note is that this exact configuration and programming passed last spring at the same inspection station. All I did through the winter was the head gasket replacement and related disassembly. No programming was changed.

The only other thing I did was replace the driver's side front O2 sensor because I was getting a code. This is the sensor that was screwed up by the leaking coolant which was coming from the leak in the head after the porting job.

Do these results point to a particularly likely culprit? I am going to have it scanned after checking with you folks and giving the vehicle a going over. Am I looking for a simple vacuum leak here? What else should I check? Your input is much appreciated.

 

Sounds like its running to rich at idle. The would explain excessive HC and CO.

 

Yeah too much hydrocarbons and co products are from a rich mixture. I would put a hotter t-stat in it, add timing at idle and widen the plug gaps. I would make sure I had fresh gas in it, honestly I would run low octane gas in it for the test only as its more volatile. Might even add a little acetone to the mix to lower surface tension and promote combustion. I'd also drive the car at higher rpm on the way there by purposefully selecting a lower gear to get the pistons hot and burn any excess buildup out of the exhaust.

If you still have your air pump maybe set it up to run all the time. They just check ppm or percents so adding more volume of o2 will make the ppm readings better.

Do they test anything else beside the idle?

 

I have failed then added a bottle of heat and drove a good 10 minutes on the freeway and went back and passed. I was told not to sit in line to long so finding out the slow time will help you to do this. I also did a few wot runs which could have helped.

 

I don't know why that specific rpm, but that's what the printout said. I saw that the thing was way rich at idle and pretty good at the higher rpm but it seems to me since this exact configuration passed just fine last spring that I must have a vacuum leak or something else simple that I screwed up. Any ideas what type of minor mistake on my re-assembly might cause a situation where idle is pig rich but 2K rpm looks perfectly fine? The injectors are brand new SVOs and the tune is designed for my LE1.1 emissions cam by PCMforless. I sort of doubt that the short term tricks would get me by the test since my HC levels were triple the allowed limit but even if the tricks worked, I still need to fix my problem since it was not running this way last spring.

THX very much.

 

You would be really suprised what the tricks will do for you, I have tested them on a dyno at a previous internship when I did engine R&D. Just making sure not to shut the car off will do wonders for you. You could have been in open loop for the test if it didnt run long enough before they began testing. That alone is enough to put you over the limit with most tunes because a cammed car needs leaned out here pretty substantially.

I really doubt you have a vacuum leak. Your pcm would just adjust for it unless it was rather large. The condition that will make it run rich besides faulty or fouled o2's is an exhuast leak around the o2 sensors, leaking injectors, or low fuel pressure, bad plugs or misfires. Or it could be you just have an excess of unburned hydrocarbons in your exhaust and they need burned out, thats why i said drive it at high rpm on the way there not really under high load. You need the engine to run as hot as possible in the exhaust and piston areas to burn the hydrocarbons. If you had enough time you could put it into pe mode at idle or mess with the individual cylinder fuel trims, or command full time open loop and lean the idle out there with a wideband.

I also want to say that a really lean idle will cause a rich reading on gas analysis. Unburned hydrocarbons looks parabolic against the range of useful gasoline a/f ratios. What typically happens with a cammed lt1 at idle is this, your short term fuel trims switch from rich to lean. When you are rich you get UHC and when you are a bit lean you get NOx, and you end up with a nasty soup that smells like gas AND burns your eyes and throat.

 

I have two PCMs, one for smog and the other for performance. The only real difference in the fan control. The smog PCM is set to higher temps which also really helps the HCs. I use OBDI in an OBDII car so I have to switch to OBDII for smog. Here is the post regarding my last test.

https://www.camaroz28.com/forums/sho...d.php?t=566069

 

Check for intake or exhaust leaks.

 

I haven't really checked closely while the engine is still cold (in open loop), but when the engine is warm (with the electirc w/P it never goes above the 1/4 temp mark - 160 thermo as well) - anywyay when the engine is warm you can see the droplets of excess fuel coming out the tail pipes.

I hope it is just that the passenger side front O2 is finished - as I mentioned the driver's side front O2 was just replaced with a GM unit - it was throwing a code. I am not sure if coolant contamination combined with age may have buggered the passenger side O2, but not enough yet to throw a code, just enough to screw up the readings and cause a rich condition at idle. If that is the case, I still wonder why the HC readings at 2K rpm are fine - if in fact it is that O2 sensor - wouldn't it bugger up the readings at all rpms?

I tried to get it scanned today but the local garage couldn't see me. I may try to see if there is a Toronto F-body guy who might be able to scan it for a fee. The snap-on scanner at the garage doesn't sound as useful as the laptop software that most guys have since the hand-held unit can't save or print the results (I am told).

THX boys.

 

I had the car scanned by a local performance shop. Unfortunately, they are fairly knowledgeable in LS1s, less so in LT1s.

In no particular order, the guy at the speed shop said that the idle was holding at 900, as per the PCMforless program, that the IAC counts at idle were 75 with the engine warm, that the manifold vacuum at idle was showing 16", that both front O2s were behaving normally, that the short term fuel trim was 10% and the long term was 14% (I don't really understand that part), that the MAF readings appeared normal but the EGR valve was showing full open (according to the scanner) and also that the injector pulse width (again at idle) was 2.1ms - which seems very high compared to some of the info I have read. No missfires were shown but the CPS was disabled in my tune to allow for the use of the double roller timing chain so that missfire info is meaningless, correct?

Not sure what to make of the EGR issue, it was supposed to be left alone for the re-tune for emissions purposes. It seems to me that if the EGR was actually open at idle that the car would not run at all or at least very poorly.

At this point I am going to check plugs and wires in the search for a missfire - not sure what you think the above information would lead me towards, but the speed shop guy seemed to be leaning toward missfire. If that were the case, wouldn't the car run worse when it got up above idle because of the additional load on the engine? As it stands now, it seems to be running quite well above idle (at least not hgh on exhaust HCs anyway) but it is running way rich at idle.

THX

 

The EGR valve never opens at idle, at least with a "stock" tune. And its very unlikely a programmer would revise the program to have it open at idle. And, there is no way for the PCM to know the position of the EGR. What a scanner reads is the pulse width modulation that the PCM is commanding for the EGR vacuum solenoid.... "0" = closed and "100" = fully open.

A 2.1mS pulse width at idle wouldn't be unusual with that setup. The long term fuel trim is telling you that the O2 sensors are reporting a lean A/F mixture, and the PCM has adjusted the fuel system to add 14% extra fuel. What you need to know is whether he gave you an average value for all the various long term correction Cells, or whether he gave you the value for Cell 16, the idle cell. Elevated long term corrections at idle aren't unusual with a big cam - at least if its a closed loop tune at idle - since the overlap blows unburned air into the exhaust, making the O2 sensor report a lean mixture. But you indicate its an "emissions" cam, so it may not have a lot of overlap. The elevated long term corrections have the effect of making the injector pulse widths longer.

Misfires and exhaust leaks before the O2 sensors will cause it to run rich, particularly at idle. Again, air reaches the O2 sensors, creating a "false lean" condition, and the PCM addes fuel, using the long term corrections, that the engine doesn't need.

 

Any luck yet? Sounds like you need to get an address up in North Bay. Have any family up there??

 

address in North bay??? is there no E-testing there?