My Friends 89 IROC 350 TPI Failed Emissions 15 MPH HC 0048/39 Pass 25MPH HC 0088/43 Pass 15 MPH CO% 00.19/0.49 Fail 25MPH CO% 00.28/0.44 Fail 15 MPH NO 0632/129 pass 25MPH NO 0614/331 pass Everything else passed. It's pretty much got these mods before the test. IT's basiclly stock too. Base Timing 0* / ECM timing 0* TCC it unlocked till 70MPH Injector Constants is set to 26. Removed -10 from spark table Max timing 25* Coolant fans kick on and off 225-220* High flow cats no mufflers 2.5 gals of 87 and 2 gals of 93 and 1 qt of denatured Achohal. Good fuel filter, plugs,wires,air egr,air pump,blocked PVC. MAF is descreened should we put the screen back on??? when the test was run the oil temp and coolant temp was 225* What else should we try please anyone?? Thanks

You could try lowering the switch point of closed loop, say from 450 to 400 mV. There's a little room to go leaner. Other than that, I'd blame the cats, O2 sensor, or some setting in the calibration that's richening the switch point at high temperatures.

Ok I'll try bring it to 400mv, I'm burning his EPROMs for him.

Also told him to put his MAF screens back in I have a feeling it's casuing a rich mix.

Do you think more Denatured Achool will do the trick as well before the test?

Is he failing by that much, that this is going to be to hard to pass?
Thanks Again

Redngold86z,

Is this the table I need to change below? Should they all be at 400mv. It's a ARAP/165 EPROM. Thanks
Closed Loop Rich/Lean Threshold vs. Airflow

gm/sec mvolt
%
% 522.15
64 531.00
56 539.85
48 592.95
40 610.65
32 628.35
24 628.35
16 610.65
08 575.25

Anyone have any more good advice please? Or that can verify this

Thanks

The emissions numbers for CO% are close to passing. No major violations. A high CO% is usually from an incomplete/inefficient burn. Pulling 10 degrees of timing may have been a little too much.

The NOX is OK (real low at idle). HC a little high at idle. The cat-con eats a lot of that.

Try it with just pulling 6 degrees of timing. Most likely will trade off some additional NOX for lower CO numbers.

{edit: can try more denatured too.}

RBob.

Awesome Rbob,

Thanks very much. Sorry to bother you with this last question. It sounds like this is all you want me to do am I correct? 6 degrees and 1 qt denatured.

Should I include the advice in the replies from RedNgold 86z? My guess is no at this point?

Yes, instead of pulling 10 degrees of SA, only pull 6 degrees. Another quart of denatured won't hurt.

When you used ARAP in this car were the spark tables changed to what an iron headed L98 used?

Other items that always help with emissions is an oil change and new spark plugs.

RBob.

it's got vette heads on it, so the SA tables match up. So we'll give it a another shot. I do apreshate all the help.

It's got a clean tune up. It runs a little dirty I think becasue the cats worn maybe? Hopeful it passes the second time. Is it a problem if we add to much Denatared or will it help overall? Thanks Again

Using the long 3/4" reach flat gasket seat spark plugs?

RBob.

sorry for the delay - I couldn't open the site from here (China) yesterday for some reason. That table is the top of the switch point, i.e. 628-~300 = 328, so it switches lean at 328 and rich at 628. I think... It might also be only 53mV offset, I'd have to check the code, but no time at the moment.

Compared to the AUJM bin (mostly at 540mV), it's a bit richer. I'd try 540 mV.

There's also a Closed Loop Rich/Lean Offset vs Coolant table that when stock is 0 cold to 16mV warm to 0 hot. Not sure if that was tinkered with on yours.

Thanks for all your help guys. But I’m confessed as to what this mean Rbob “Using the long 3/4" reach flat gasket seat spark plugs?” You mean break loose the plugs ¾ turn?

Last night we add 1qt and set timing -6 on the SA and bumped my injector constatan to 27lb which should lean it out more it was at 26lb. I have 22lb injectors. It smells extremely clean. I think we’ll take it to the shop this week.

The Corvette aluminum heads use a different spark plug then the standard '89 5.7l IROC heads. Using the iron head spark plugs has the electrodes recessed back in the threaded portion of the plug opening of the head.

The aluminum head spark plugs have a 3/4" long threaded portion (the reach) and a flat gasket seat (instead of a tapered seat). Lot's of folks get this wrong, so I have to ask.

It would also account for a dirty burn (high CO).

RBob.

I'm sorry ok makes sense. It's got the correct plugs for the heads. Given the circumstances do you all think it's going to pass this time? Do you think more denatured will help it pass for sure? It still has about 2 gals of 87 and 2 gals of 93 with a total of 2qt of denatured. Only one free retest so hopefully it's passes this time. Again thanks for all the effort on this guys.

try some E 85 to pass