sonomacrew01

Out on a limb here. I've posted numerous times in the c4 tech and scan& tune. I've also posted in the northeast section seeking anyone rather local to help. ZR1 member "tomtom72" suggested I ask some of the ZR1 group to see if you can help.

car: 1993 LT1, LT4 hotcam kit, SW headers, RT cats, 3" B&B, e-waterpump, MSD setup

Problem: failed RI emissions by more than twice the legal limit
http://forums.corvetteforum.com/show....php?t=1804821

Since the test, I've replaced injectors,spark plugs and wired up new heated O2's. I've had a leakdown test done on the car and through Datamaster, the car is still running rich. Local tuner claims its not the tune but I've become frustrated with him for not helping or returning my calls so I turned to PCMforless and currently, awaiting a new chip.

Tomtom72 said LT5 motors tend to run rich? Any furhter mechanical suggestions or "experienced" suggestions would greatly be appreciated.

Justin

Crabs

Justin:

Tom is right, our LT5's tend to run rich, it's the nature of the beast. The normal things that go haywire causing a rich condition are, fuel injectors, spark plugs, pcv, rings, or tune, but it sounds like you've already explored these options.
Are you sure that your cats aren't fouled or hogged out?
From what I've read and seen, LT5's will not pass smog here in California without the cats doing their job.

Good luck!

Barbara_S

My Z failed emissions in Ma. last year and changing the O2 sensors helped - there were no codes thrown for the sensors being bad, but the emissions guy I went to thought they were a contributer to my failure - he was right. That may be the cheapest thing to check first.

Aurora40

You might want to get a datalog on the car. What are the O2's saying, are they saying it's rich? What are the block learns, do they show it being rich?

If that seems normal, it may be that the cats just aren't doing the last bit of cleanup that needs to be done.

FWIW, I don't believe our cars run "rich" when in proper tune/repair and in low throttle driving. I'm sure there are cleaner cars out there, but it passed the legal requirements for new cars in 1990, which should be more stringent than any state emissions test.

Generally speaking aftermarket cats are not as "clean" as OEM ones, though they flow more. Plus you've got a cam, and a tune. Datalogging should give you some idea though. Is your AIR system enabled in the tune? It helps warm the cats up faster. Though it probably wouldn't hurt to flog the car hard before you show up for the test, to ensure the cats are up to temp. They don't work without heat.

94ZR1

Cooler air will make it run cleaner
If you tried during the heat it might do better now

Jeffvette

The ZR-1, just as well as every other vehicle does run rich. being fat is better than lean. It just protects the motor from people being stupid.

Federal emissions is a broad scope. Several states have been reducing the amounts that are legally passable for years. Oregon and California being two of them. So a good running car from 1990 may pass one year and fail the next even though nothing has changed or gone bad.

I was able to get my 368 with cams through emissions with no cats. But i had to play around on the dyno for a few hours to get it dialed in, and run a little toulene through the gas. I put cats on later and it passed with flying colors.

Aurora40

In low-throttle driving? With a normal tune in open loop driving, I believe the car tries to be as close to 14.7:1 as possible for the cleanest burn.

I was curious about the standards. I was under the impression that states couldn't impose standards tougher than the vehicle had to meet when new, but I'm not sure if that's true or not?

The EPA's clean air act isn't directly comparable:
http://www.epa.gov/oar/caa/title2.html#iia
http://www.epa.gov/otaq/consumer/11-vehs.pdf

They set limits based on grams per mile, and most states test based on parts per million.

glass slipper

You're correct, except I think you meant closed loop driving. I think Jeff missed the "low-throttle" part of your post, he's clearly talking about full throttle open loop conditions.

Aurora40

Yes, damn it, I do that every single time. I don't know why I say open for closed and vice versa. I think because in my head I think of the circuit closing when the O2's come online, so I think of it as closed loop, when in fact it's an open loop system at that point. I have a feeling I will always say the wrong one...

sonomacrew01

I'm beginning to suspect that the ecm is toast.

ECM through datamaster reads TPS% and Voltage at idle at 0% and .55
-at 3000 rpm, 6.7% and .67

I checked the voltage at the sensor and its reading accurately.

MAP at idle is 50 KPA and at 3000, 31 KPA

I'm assuming the only way to monitor fuel ratio is through tuning software?

cv67

You want a shocker, check out VA.'s standards, I was blown away when I did a comparison with someone I know out there. We got it easy compared to them. Absolutely no way Id even come close to passing out there.

glass slipper

You did it again!
When the O2 sensors come online, it IS closed loop.


...at least you were right about doing it every single time.

Rkreigh

yes the VA standards got cut in HALF since the last time I tested.

the LSV is still not able to pass, but I'm working on it. the exemption criteria got stupid too. thing that bugs me most, is the later vehicles (OBD II) with way more of them, just "plug in" no code, no problem regardless of emissions. so they are in a way easier to mod and get by emissions.

not sure of the logic there. the zr1 factory cal is pretty rich also to protect the cats. when the car runs leaner for best power, the cats can overheat. the addition fuel makes the cats react properly without overheating and breaking down.

the newer metal substrate cats I believe can survive much higher temps.

get a wide band 02 sensor on your vette, you can log it all all RPMs and throttle settings and see what is going on. a dyno with the wideband is a good idea too. I don't like trusting the narrow band 02s, they really aren't very accurate outside their operating range.

gbrtng

Some history needed here:
1. has the car ever passed RI emissions and when?
2. what were the pass/fail emission levels for the car? on earlier link
3. what were/are the p/f emissions levels for RI? on earlier link
4. what has changed on the car since the last test?
5. summarize the RI test - is it an IM240 test or some variation?

sonomacrew01

1) last time the car passed emissions was in 05', just after I bought the car and it was bone stock
2) not sure
3)HC PPM at idle = 623, limit was 220
HC PPM at 2500 = 128, limit was 220
CO % at idle = 2.97%, limit was 1.20%
CO % at 2500 = 2.94%, limit was 1.20%
4) changes since 05.. Pulled the motor, new LT4 hotcam kit, SW longtube headers, RT cats and 3" B&B, complete MSD ignition setup, Electric waterpump, PCMforless tune.
Changes since test fail in August 07.... New 24# injectors, new plugs, new HEATED O2 sensors, new PCM tune on the way. I've also been testing several sensors (see above post)
5) not quite sure what an IM240 is but if it helps, it was a sniffer and gas cap OBD test.

Aurora40

Those aren't inherently wrong. If you gassed the car to 3,000 rpm and let off the throttle, it could have 6.7% throttle at 3k rpm. Same with the MAP, though 50kPa seems high to me for a car at idle. But then again your car is cammed, so I've no idea what is "normal". At 3k if you let off the gas, I'd expect the pressure would drop as the engine is trying to suck air down pretty hard.

I'm not saying your numbers mean things are normal, just that they don't necessarily mean things are not normal.

Edit: oh and you can monitor fuel ratio with a wideband sensor.

gbrtng

This (2500 rpm) is well within "pass" but no pass at idle probably means the cats are not up to temperature. Get a Raytek temperature gadget and measure the temps of the cats at idle and at 2500 rpms and I think you'll find the cats aren't hot enough - they should be above 600 degrees F (I think this is the range but please confirm with an emissions specialist). With the long headers getting 'em hot is a problem. Also, the hotter you can get the engine, the better.

IM240 is a 240 second test where the car is run on a dyno over a specified speed range and the exhaust is sampled from both pipes.
RI is just doing idle and 2500 rpm with no load on the engine which is an easier test to pass. Yours is running a bit rich at those revs.
Do you get a CO2 reading even though that's not a pass/fail gas?

Aurora40

God damn it... The other way I think about it is "open" meaning open to feedback. Which is wrong. But then I can never remember which way was the wrong way to think about it. What I don't get is why I don't get it right 50% of the time?

I thought the opposite was true? I thought running rich can melt the cats. They take the unburned fuel and convert it into non harmful things and heat. The heat causes the cat to get hotter.

At low throttle (not talking WOT here, talking regular driving) I thought a rich car with cats could be hazardous as they can get so hot as to catch other things around them on fire.

I'm pretty sure that in low-throttle closed loop driving, the PCM strives for as close to 14.7:1 as it can get. It doesn't intentionally run richer than this to my knowledge.

nickzvette

Iam new at using a computer I sent a message to LT 1 guy yesterday dont know if it went through so Ill try again 11 7 o7 I also had a lot of work done on my ZR 1 after failing Emissions test in Illinois since moving to Tennessee 2 yrs ago and failing here 2 times but good news each time I failed I went to WalMart and for about $7.50 bought a bottle of Guaranted To Pass I put a half bottle into about 3 fourths tank of gas drove about 10 miles took the test and passed each time I was so supprised because my emissions were also very high P.S. Ididnt follow directions on the box I hope this helps you to pass and anyone else who needs it nickzvette