High HC levels at Idle! Failed emissions (long)
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From: Irwin, PA
High HC levels at Idle! Failed emissions (long)
This sucks. Just got the 1990 20vQ insured and paid for plates. My wife took it to my trusted PA Inspection station. It failed for HC at idle. CO is good and HC is good at speed. Before I put this car on the road, I put new Bosch plugs along with cap, rotor, and air filter, fresh oil change w/Mobil 1. I have also disassembled the Idle Valve and cleaned it. The car idles and runs great.
Well, here's the question: is anything really adjustable that would remedy the high HC at idle? Am I correct in assuming the O2 sensor doesn't contribute at idle speed?
I remember reading something about if you use the CO adjusting screw to raise the CO, the HC level will go down. Can anyone confirm that?
I'm suggesting to the tech that he just raise the idle to 1000 rpm to try and get it to pass. He knows the CIS system, but not Motronic. He's a good guy and will work with me here, so I would really appreciate some suggestions.
Also, do I understand correctly that we really can't change the ignition timing? He tells me thats the quickest way to get a car to pass the HC part.
Any suggestions appreciated.
Dave
Well, here's the question: is anything really adjustable that would remedy the high HC at idle? Am I correct in assuming the O2 sensor doesn't contribute at idle speed?
I remember reading something about if you use the CO adjusting screw to raise the CO, the HC level will go down. Can anyone confirm that?
I'm suggesting to the tech that he just raise the idle to 1000 rpm to try and get it to pass. He knows the CIS system, but not Motronic. He's a good guy and will work with me here, so I would really appreciate some suggestions.
Also, do I understand correctly that we really can't change the ignition timing? He tells me thats the quickest way to get a car to pass the HC part.
Any suggestions appreciated.
Dave
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did it fail on HC's by alot?
sometimes you can throw in some 93 octane gas and that will get it to pass, also with that tank of 93 octane gas some gas line anti freeze will help out a little bit too. If that doesn't get your car to pass the cat might need to be replaced.
Thread Starter
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From: Irwin, PA
Yes, on retry the machine requires the car be run for 3 minutes...
at 2500 rpm. We are leaning away from the cat, since the CO, HC (at 2500), and oxides passed. I agree with you about it being hot and I will suggest he take the car to lunch and maybe test immediately after.
keep the ideas coming.
keep the ideas coming.
Thread Starter
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From: Irwin, PA
Re: did it fail on HC's by alot?
I did put 93 octane Sunoco in it on Saturday. So you are thinking cat also? I must do some research now.
The printout is in the car now, at the garage, but it didn't fail by much. I remember that.
The printout is in the car now, at the garage, but it didn't fail by much. I remember that.
Thread Starter
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From: Irwin, PA
From the Bosch O2 sensor document:
<snip>Variations from this optimum ratio result in various levels of emissions. Excess fuel results in the formation of hydrocarbons (HC) and carbon monoxide (CO). Excess air can cause increased levels of nitrogen oxides (NOx). The oxygen sensor or sensors can identify any variations from the ideal air/fuel ratio and send a signal to the engine management system to adjust the ignition and injection processes.
<end snip>
So it looks like I could lean it out until the NOx levels approach failure.
What really hurts here is that 10 miles down the road in the next county, people don't have to get tested. No Fair!
<end snip>
So it looks like I could lean it out until the NOx levels approach failure.
What really hurts here is that 10 miles down the road in the next county, people don't have to get tested. No Fair!
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Re: Have you checked the air sensor plate? Look in my pic poster.
On my car, the nut holding the sensor plate was loose. Also, I agree, you are running rich at idle. It could mean your ISV isn't allowing a little more air, OR, it could be that the mix was turned up (richer) before you got it to cover for an ISV leaking air.
I'd try leaning out the mix at the air sensor/potentiometer (T-handle hex adjustment). Your mechanic should know how to do that.
I'd try leaning out the mix at the air sensor/potentiometer (T-handle hex adjustment). Your mechanic should know how to do that.
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ya that isn't too fair
now my situation sucks as much or more than yours. I live in Los Angeles county which yields me a insurance rate of $2200 where as 2 1/2 miles away from my house it goes into two other counties which get their rate cut in half.
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Thread Starter
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From: Irwin, PA
The 20v has a different setup. No CIS
You made a good point regarding prev owner. It used to stall before I cleaned the ISV, so maybe adjustments were made. There's a plug covering the adjustment screw that can't be replaced, so if its uncovered, somebody already touched.
thx
Dave
thx
Dave
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Dave, this is a long time problem with the 20V's. You are letting a lot...
of unburnt fuel go thru your cat. at idle. Ususally it's the injectors at fault. Look at your plugs, I'll bet they show alot of black on them..unburnt fuel. Stand behind your car while it's idling. Does it have a certain acrid smell that may sting your eyes a little. Same thing. Download the blink codes and see if it gives you any numbers. Check the Bentley or 20V.org. on how to do it