'86 Vette...failed Maryland Emissions

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Jun 21, 2006 | 06:59 PM

UDLUV12

Thread Starter

Racer

Joined: Jul 2000

Posts: 421

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From: Glen Burnie Md

'86 Vette...failed Maryland Emissions

Original owner...for the past 16 years since adding mods, my car has failed miserably every year.

This year no different...here are my first fail readings:
HC (State Standards) = 1.8000 GPM
Inspection Reading = 10.3055 GPM (Failed)

CO (State Standards) = 30.0000 GPM
Inspection Reading = 35.4521 GPM (Failed)

NOx (State Standards = 2.8000 GPM
Inspection Reading = 3.0588 GPM (Failed)

However, after changing just the plugs, and increasing the timing to 12º...I drove the car for a full hour...just to heat the engine up real good...to see if this might really make a difference...and I have to tell you, it made a hell of a difference.

I still failed, but here are the results:
HC Inspection Reading = 7.1551 GPM (Failed)
CO Inspection Reading = 25.1969 GPM (Pass)
NOx Inspection Reading = 1.7255 GPM ( Pass)

I was told by the technician that my failed HC reading was due to "too much air, and not enough fuel."

This is really hard for me to accept, because I know
my engine runs rich...I mean just take a glance at my mods.

I would appreciate your thoughts?

Jun 21, 2006 | 07:51 PM

warpmine

Instructor

Joined: Feb 1999

Posts: 136

Likes: 0

From: baltimore, maryland

Being that the fuel your using is hydrocarbon I would think that it is running to rich as well. Try backing down the fuel pressure a couple of pounds. Can you do that? Hows that Cat converter. Is it older than dirt?
It should burn off excess fuel if it's fully functionable.

Jun 21, 2006 | 08:04 PM

doc's toy

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Joined: Apr 2002

Posts: 62

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From: Hopkinsville Ky

failed?

What are your mods?

Jun 21, 2006 | 08:24 PM

CFI-EFI

Race Director

Joined: Sep 2000

Posts: 17,298

Likes: 33

From: The Top of Utah

Quote:

Originally Posted by UDLUV12

This year no different...here are my first fail readings:
HC (State Standards) = 1.8000 GPM
Inspection Reading = 10.3055 GPM (Failed)

CO (State Standards) = 30.0000 GPM
Inspection Reading = 35.4521 GPM (Failed)

NOx (State Standards = 2.8000 GPM
Inspection Reading = 3.0588 GPM (Failed)

I still failed, but here are the results:
HC Inspection Reading = 7.1551 GPM (Failed)
CO Inspection Reading = 25.1969 GPM (Pass)
NOx Inspection Reading = 1.7255 GPM ( Pass)

I was told by the technician that my failed HC reading was due to "too much air, and not enough fuel."

Too little fuel IS a possibility. High COs result (are a byproduct) from the combustion of a richer than ideal mixture. HCs are unburned fuel. That can be caused by an overly rich mixture, where all the gasoline isn't consumed, OR by an overly lean mixture that doesn't "light off", a lean misfire. Either way you end up with raw gasoline (HCs) in the exhaust. With the CO in check, I suspect the technican is correct.

RACE ON!!!

Jun 21, 2006 | 08:45 PM

JrRifleCoach

Team Owner

Joined: Sep 2003

Posts: 20,179

Likes: 673

From: Freedom is never more than one generation away from extinction.

St. Jude '03 thru '24

Quote:

Originally Posted by UDLUV12

However, after changing just the plugs, and increasing the timing to 12º...I drove the car for a full hour...just to heat the engine up real good...to see if this might really make a difference...and I have to tell you, it made a hell of a difference.

I still failed

Thats cause you advanced the timing. You need to retard the timing back to 3-4 degrees BTDC.

Here are my proven results:

-------HC Max----Measured-------CO Max----Measured
Idle.......120............410........... .....1.00............2.31.......FAILED
2500.....150.............39............. .....1.20...........0.06.......PASSED

Next day I backed the timing off 3 degrees and added a pint of denatured alcohol.
Delivered it to the test center HOT!

-------HC Max----Measured-------CO Max----Measured
Idle.......120.............25........... .....1.00............0.03.......PASSED
2500.....150.............10............. .....1.20...........0.07.......PASSED

Try it.

Jun 21, 2006 | 11:57 PM

SunCr

Le Mans Master

Joined: Dec 2000

Posts: 7,839

Likes: 22

From: San Diego, Ca

I'll go along with the Tech assuming he took a look at the O2 readings. If it senses more air than is being reported by the MAF, it's going to tell the ECM to add fuel; ie, it's lean - Only it doesn't need the fuel - so the mix ends up too rich and you fail your test. Look for a vacuum or exhaust leak and if you have a scanner (you might consider investing a 100 Bucks to get one), pinch off the air pump hose to the left header. If the lean condition goes away, the pump solenoid is bad or the check valve is busted on the header - that's easy to check - remove the hose and unscrew the valve and then make sure air only flows in the direction of the header.

Jun 22, 2006 | 10:29 AM

UDLUV12

Thread Starter

Racer

Joined: Jul 2000

Posts: 421

Likes: 0

From: Glen Burnie Md

'86 Failed Emmissions...some Mods now shown

Certainly appreciate everyone's thoughts.
It sure has me confused.
I would think with all the mods I have, I would be running very rich?
Trick Flow Heads (9.5 Compression Ratio)
TPiS ZZ9 Cam and Lifters
TPiS Mini Ram II
TPiS Long Tube Headers
TPiS Prom VI Chip
Cut Open Lid
Air Pump Eliminator
The Cat Converter is original, but the inside packing has been removed.

Now that you see some of the MODs I've done...might you have any other contributions?

Thanks for your help!!

Last edited by UDLUV12; Jun 22, 2006 at 03:28 PM.

Jun 22, 2006 | 01:21 PM

JBB

Instructor

Joined: May 2006

Posts: 202

Likes: 16

Quote:

Originally Posted by UDLUV12

I still failed, but here are the results:
HC Inspection Reading = 7.1551 GPM (Failed)
CO Inspection Reading = 25.1969 GPM (Pass)
NOx Inspection Reading = 1.7255 GPM ( Pass)

I was told by the technician that my failed HC reading was due to "too much air, and not enough fuel."

I would appreciate your thoughts?

No, I disagree. If you richen it up, the CO will increace. Retard your timing a bit as was suggested.

Real Rich = High CO + High HC (Low NOx)
Leaning it out drops both HC +CO (unchecked, NOx will peak around stioch)
Leaning it too far still lowers the CO, but causes the HC to begin to climb sharply (lean misfire)

(I am a registered emissions repair tech with apx 20 yrs exp)

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Jun 22, 2006 | 02:47 PM

CFI-EFI

Race Director

Joined: Sep 2000

Posts: 17,298

Likes: 33

From: The Top of Utah

Quote:

Originally Posted by UDLUV12

Certainly appreciate everyone's thoughts.
It sure has me confused.
I would think with all the mods I have, I would be running very rich?
Trick Flow Heads (9.5 Compression Ratio)
TPiS ZZ9 Cam and Lifters
TPiS Mini Ram II
TPiS Long Tube Headers
TPiS Prom VI Chip
Cut Open Lid
Air Pump Eliminator

Now that you see some of the MODs I've done...might you have any other contributions?

Thanks for your help!!

The only items on that list of modifications that could cause the mixture to be rich, is the cam, depending in the overlap and the chip, depending on the tune. If anything, most of the items on that list REQUIRE the addition of fuel, because they tend to LEAN the mixture due to greater air flow.

The CO says the mixture is not rich. The HC says there is unconsumed fuel leaving the cylinders. Be careful of retarding the timing too much below spec, because it can raise the NOx numbers.

RACE ON!!!

Jun 22, 2006 | 03:31 PM

#10

UDLUV12

Thread Starter

Racer

Joined: Jul 2000

Posts: 421

Likes: 0

From: Glen Burnie Md

Gentlemen,

I forgot to mention that my Cat Converter is original, but the insides have been gutted.

Thanks again for any and all contributions.

Jun 22, 2006 | 06:43 PM

#11

CFI-EFI

Race Director

Joined: Sep 2000

Posts: 17,298

Likes: 33

From: The Top of Utah

My cat is in my storage shed and the car just passed the sniff test last week. That said, a fresh cat will improve your test results by as much as the new plugs, timing(?), and thorough warm up did.

RACE ON!!!

Jun 22, 2006 | 09:39 PM

#12

JBB

Instructor

Joined: May 2006

Posts: 202

Likes: 16

Quote:

Originally Posted by CFI-EFI

Be careful of retarding the timing too much below spec, because it can raise the NOx numbers.

RACE ON!!!

Sorry, No. Retarding the timing from 12 to 3-4 base timing will lower the NOx. If the combustion temp is lower, the NOx will drop.

The gutted cat is NOT helping you (emissions wise). Not saying you won't be able to pass, just going to be tough w/o the 3 way cat.

Jun 24, 2006 | 10:55 AM

#13

doc's toy

Advanced

Joined: Apr 2002

Posts: 62

Likes: 0

From: Hopkinsville Ky

failed emissions

Anytime you increase or improve the breathing capability of an engine,
it is going to lean your fuel mixture.But since you have a fuel injected
car then your MAF & O2 should be helping to correct this.Have you
ck'd ignition,it could be hot enough to run car but not hot enough to
give you a complete burn of fuel mixture.

Jun 24, 2006 | 01:17 PM

#14

CFI-EFI

Race Director

Joined: Sep 2000

Posts: 17,298

Likes: 33

From: The Top of Utah

Quote:

Originally Posted by doc's toy

Have you ck'd ignition,it could be hot enough to run car but not hot enough to give you a complete burn of fuel mixture.

Of course, I agree that the ignition system should be well maintained. However, if the ignition system has the energy to jump the plug gap, increasing the reserve or capacity of the ignition system isn't going to make the spark any hotter.

Quote:

Originally Posted by JBB

Sorry, No. Retarding the timing from 12 to 3-4 base timing will lower the NOx. If the combustion temp is lower, the NOx will drop.

I realize cooler combustion temps lower NOx. That is why the EGR dilutes the A/F mixture with inert gases, to cool the heat of combustion. When I retard the timing on my car it runs hotter. I admit I have no way of knowing what it does to the combustion temps. I ***-U-MEd...

RACE ON!!!

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