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Returning after a few years... need help passing emissions....

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fattom

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Joined
Dec 25, 2003
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arizona
Hey guys! Sold my old 80 k5 about 8 years ago. But finally was able to buy another. Now I have an 87 k5 350 700r4 208... problem is I can't seem to pass emissions. Fails on hydro carbons (4.06 passing is 4.00) and fails the nox kinda bad. Cooling system flush new water pump and thermostat, and a pcv valve with a fresh oil change.
P.O. put true duals with no cats so I'm thinking that could be the problem. With the hydrocarbons....
I bought a new egr valve but haven't installed yet... the one on there looks kinda new ish... but will change anyways...
If I can avoid buying cats that would be great... but any ideas on what else to try?
P.O. I think mentioned something about an after market computer chip and a throttle body spacer...
I'm really not to familiar with any of this tbi stuff. So any help would be appreciated.
Thanks
Tom
 
Ignition. HC is from poor ignition - partial or incomplete burn. NOX can be from too much timing. You should have failed visual for not having cats.
 
fattom said:
Hey guys! Sold my old 80 k5 about 8 years ago. But finally was able to buy another. Now I have an 87 k5 350 700r4 208... problem is I can't seem to pass emissions. Fails on hydro carbons (4.06 passing is 4.00) and fails the nox kinda bad. Cooling system flush new water pump and thermostat, and a pcv valve with a fresh oil change.
P.O. put true duals with no cats so I'm thinking that could be the problem. With the hydrocarbons....
I bought a new egr valve but haven't installed yet... the one on there looks kinda new ish... but will change anyways...
If I can avoid buying cats that would be great... but any ideas on what else to try?
P.O. I think mentioned something about an after market computer chip and a throttle body spacer...
I'm really not to familiar with any of this tbi stuff. So any help would be appreciated.
Thanks
Tom
Click to expand...

What temp thermostat?

The aftermarket mass-production chips (Hypertech, etc) are utter garbage, and because they were so terrible, generally required a colder thermostat to not knock. A colder thermostat could have the thing dumping extra fuel all the time to try and warm the engine up (no idea at what temp it's programmed to stop that) but the extra timing probably doesn't help either if it's in the range they are testing. Nor would a colder chamber.

Advice would be to check the chip (usually they have a sticker on them if a big name) and if it's something like a hypertech, yank it. Replace with stock. Replace thermostat with a 195* if it's not.

Don't toss the old EGR in the trash, especially if Delco. There is a problem with aftermarket EGR's. Most are very generic, and GM was not generic with their EGR applications. It can cause problems.

Have you verified the ignition system is good? Cap/rotor are in good shape, terminals are tight, contacts aren't corroded? Plugs/wires are in good shape? Is the check engine light on? Does the light work right? The O2 sensor is there?

I'd try again after those changes/verifications.

If it fails, yank the duals off and put a converter back on it. A converter alone would solve the HC problem in your case, but I don't know much about how well, if at all, NOx is handled by the various converters.

I'm very biased on duals, I hate them. In your case, if you care, the exhaust is federally illegal, it would be illegal with dual converters too. But regardless of legality, as a single exhaust, you'd only need one converter. There are other benefits of properly done singles, but cost is one, especially when talking converters. I understand the cost and hassle of having to go back to a stock style exhaust setup, so I'd certainly do that as the last option.
 
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I've got duals on my 80, but I have a cat on each pipe. The emissions monkeys aren't really all that into their jobs here. Many of them are 1 step above McDonalds workers. Went in the other day and because he didn't feel like climbing up on a step stool to look at my air/pvc he just put inaccessible on it and passed it.
 
JoshHefnerX said:
Ignition. HC is from poor ignition - partial or incomplete burn. NOX can be from too much timing. You should have failed visual for not having cats.
Click to expand...
Yeah I thought I would have failed on the visual too but the guy didn't even care enough to notice there was duals until his boss walked over half way through the first test and stopped it to put the sniffer on both pipes lol
But I will grab the timing light and check that. Along with pulling all the plugs and wires.
 
Lucky your not in Calif. It would not have passed the visible inspection. They check every after market item for a CARB number. Duels would be a failure. no cats failure. TBI spacer questionable. My last test failed the evap test on the gas tank. allowed .05 vacuum lost, had a .06.
 
dyeager535 said:
What temp thermostat?

The aftermarket mass-production chips (Hypertech, etc) are utter garbage, and because they were so terrible, generally required a colder thermostat to not knock. A colder thermostat could have the thing dumping extra fuel all the time to try and warm the engine up (no idea at what temp it's programmed to stop that) but the extra timing probably doesn't help either if it's in the range they are testing. Nor would a colder chamber.

Advice would be to check the chip (usually they have a sticker on them if a big name) and if it's something like a hypertech, yank it. Replace with stock. Replace thermostat with a 195* if it's not.

Don't toss the old EGR in the trash, especially if Delco. There is a problem with aftermarket EGR's. Most are very generic, and GM was not generic with their EGR applications. It can cause problems.

Have you verified the ignition system is good? Cap/rotor are in good shape, terminals are tight, contacts aren't corroded? Plugs/wires are in good shape? Is the check engine light on? Does the light work right? The O2 sensor is there?

I'd try again after those changes/verifications.

If it fails, yank the duals off and put a converter back on it. A converter alone would solve the HC problem in your case, but I don't know much about how well, if at all, NOx is handled by the various converters.

I'm very biased on duals, I hate them. In your case, if you care, the exhaust is federally illegal, it would be illegal with dual converters too. But regardless of legality, as a single exhaust, you'd only need one converter. There are other benefits of properly done singles, but cost is one, especially when talking converters. I understand the cost and hassle of having to go back to a stock style exhaust setup, so I'd certainly do that as the last option.
Click to expand...
Well I just threw a 160deg thermostat in as it was running pretty warm when I got it but I also replaced the water pump at the same time... was running between 210 and that hash mark above. Will be checking ignition today.
 
dyeager535 said:
What temp thermostat?

The aftermarket mass-production chips (Hypertech, etc) are utter garbage, and because they were so terrible, generally required a colder thermostat to not knock. A colder thermostat could have the thing dumping extra fuel all the time to try and warm the engine up (no idea at what temp it's programmed to stop that) but the extra timing probably doesn't help either if it's in the range they are testing. Nor would a colder chamber.

Advice would be to check the chip (usually they have a sticker on them if a big name) and if it's something like a hypertech, yank it. Replace with stock. Replace thermostat with a 195* if it's not.

Don't toss the old EGR in the trash, especially if Delco. There is a problem with aftermarket EGR's. Most are very generic, and GM was not generic with their EGR applications. It can cause problems.

Have you verified the ignition system is good? Cap/rotor are in good shape, terminals are tight, contacts aren't corroded? Plugs/wires are in good shape? Is the check engine light on? Does the light work right? The O2 sensor is there?

I'd try again after those changes/verifications.

If it fails, yank the duals off and put a converter back on it. A converter alone would solve the HC problem in your case, but I don't know much about how well, if at all, NOx is handled by the various converters.

I'm very biased on duals, I hate them. In your case, if you care, the exhaust is federally illegal, it would be illegal with dual converters too. But regardless of legality, as a single exhaust, you'd only need one converter. There are other benefits of properly done singles, but cost is one, especially when talking converters. I understand the cost and hassle of having to go back to a stock style exhaust setup, so I'd certainly do that as the last option.
Click to expand...
Oh and again not familiar with tbi where is the computer in these???
 
Cold thermostats do nothing to cure an overheating engine. Thermostat sets the minimum engine temp, not the maximum.

Put a 195* in there, if it's overheating, fix that problem. The position you describe on the gauge may just be tolerance, and not really as warm as it indicates. You'd have to either hook another gauge up to test accuracy, or use a scantool to see what the coolant temp sensor is telling the engine to get an idea of how accurate the gauge is. My experiences have been good, but it's possible it's off by a bit. If you get fairly decent temperature swings under different engine load conditions, you've got a cooling issue, not gauge.
 
UPDATE***
Bit the bullet and paid to have new cats put on. completely took care of the hydrocarbons problem and got the nox cut in half but I barely failed the nox again... reading was 6.84 passing is 5.5. Any more ideas?
Cats was the only thing changed today.
But I did check plugs wires cap and rotor. All looked almost new.
 
fattom said:
UPDATE***
Bit the bullet and paid to have new cats put on. completely took care of the hydrocarbons problem and got the nox cut in half but I barely failed the nox again... reading was 6.84 passing is 5.5. Any more ideas?
Cats was the only thing changed today.
But I did check plugs wires cap and rotor. All looked almost new.
Click to expand...
How much do you have to spend before that give you a waiver?
 
causes of NOx being high in engine.
1 Lean fuel mixtures cause high NOx. Do you have an O2 Sensor. 2 The Exhaust Gas Recirculation system is designed to reduce NO. Is it in good working order. 3 Inadequate engine cooling can will high NOx. If your vehicle's cooling system is not working efficiently, (i.e. bad radiator, thermostat, hoses) high NOx will be created. 4 Carbon build-up decreases the available space for the air/fuel mixture to combust, and causes higher cylinder compression. High compression results in high temperatures and high NOx more in a high mileage engine.. Did you set timing with the brown wire disconnected at the firewall.
 
frankin5 said:
causes of NOx being high in engine.
1 Lean fuel mixtures cause high NOx. Do you have an O2 Sensor. 2 The Exhaust Gas Recirculation system is designed to reduce NO. Is it in good working order. 3 Inadequate engine cooling can will high NOx. If your vehicle's cooling system is not working efficiently, (i.e. bad radiator, thermostat, hoses) high NOx will be created. 4 Carbon build-up decreases the available space for the air/fuel mixture to combust, and causes higher cylinder compression. High compression results in high temperatures and high NOx more in a high mileage engine.. Did you set timing with the brown wire disconnected at the firewall.
Click to expand...
Already got the cooling system. But I do have a new egr valve just need to put it on. Hopefully that and a new o2 sensor will do it. If not I think it may be the chip that p.o. put in the ecm. But it's nice to get these maintenance things out of the way anyways... can I just buy a new ecm at oriellys? Or would that be a junkyard trip?
 
fattom said:
Already got the cooling system. But I do have a new egr valve just need to put it on. Hopefully that and a new o2 sensor will do it. If not I think it may be the chip that p.o. put in the ecm. But it's nice to get these maintenance things out of the way anyways... can I just buy a new ecm at oriellys? Or would that be a junkyard trip?
Click to expand...

Hell, they could have turned the EGR off in the PROM.
 
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