Failed Air Care; Valves too tight?

[Hendog]

In the seven years I've owned my 911 it has never failed an Air Care inspection. I wasn't entirely surprised it failed. The car passed while at road speed of 40KMh (25 MPh) but did not pass at idle. The last valve adjustment i did I set them slightly on the tight side. This has stuck in the back of my mind ever since, and I believe is the cause for the high Hydrocarbon count at idle. Is this possibly the cause?

BTW it has SSI into B&B 2in/1out, Oxygen sens, no cat (always been this way).

[jwasbury]

When was the last time you replaced spark plugs? What about the distributor cap and rotor? Age and condition of plug wires?

I've found that simply putting fresh plugs has often made a big difference in many an old machine.

[ivangene]

wow - no kidding...my 1.5 year old plugs were SPENT!! changed them last week and OMG!!!

get the idle and CO reset too....

[Hendog]

Car currently has 103,470 Km
Could be plugs; they were changed at 82,143 Km along with new cap, rotor, Magnecor wires.

Injectors rebuilt at 83,462 Km
New O2 sensor at 87,406 Km

It passed Air Care after those items.

So, could too tight valve adjust cause a high hydrocarbon reading at idle?

[HawgRyder]

Some of the tricks to pass air care....
New plugs (sometimes hotter ones than normal)
Highest octane fuel available
Hot Engine (temperature)
New or very good plug wires
New Air Filter
Clean fuel system (gas modifiers..filters...decarbon intakes)
One of the most difficult cars to pass is the Mustang 5.0L ...I have to change the timing (retard) to get it to pass.
In that condition...the car is almost undriveable...but it does pass..and after the test...put the timing back where it belongs.
Hope this helps
Bob

[Hendog]

Thanks Hawg.

What I think I'll do is: Check/redo valve adjust. Change plugs. Lean out the AFR. Fill with 93 octane. Air filter is new so that's good.

[Jeff Alton]

I am not advocating this, but...... You can unplug one of the injectors (wire harness). I know it has been done before on a 3.2 to pass AirCare....

Cheers

[john walker's workshop]

yep, turns one cylinder into an air pump. works good.

[Canada Kev]

Originally Posted by Hendog

Thanks Hawg.

What I think I'll do is: Check/redo valve adjust. Change plugs. Lean out the AFR. Fill with 93 octane. Air filter is new so that's good.

In BC, Chevron's got 94 octane. How does one lean out the AFR in a motronic car for this purpose?

[db_cooper]

What were the numbers for HC and CO? Do they check NOx? You may need a new Cat. Convt. depending on the numbers. Some thing cannot be adjusted out..like Nox.

[Hendog]

Originally Posted by syzygy

In BC, Chevron's got 94 octane. How does one lean out the AFR in a motronic car for this purpose?

Whatever the highest Chevron octane available; 94 if that's what you say.

The Volume Air Flow sensor (some call it the Mass Air Flow sensor) has an adjustment screw underneath which allows you to set some bypass air flow. If you turn it out (CC wise) you allow more air through thus leaning out the fuel mixture.

I had to adjust the VAF when Chevron switched their 92 octane fuel to 91 because I sent my Steve Wong chip in to be recallibrated for 91. I had a shop check my emissions readings and they found them to be within specs at that time.

[Hendog]

Originally Posted by db_cooper

What were the numbers for HC and CO? Do they check NOx? You may need a new Cat. Convt. depending on the numbers. Some thing cannot be adjusted out..like Nox.

Here's the readings.

[Quicksilver]

Originally Posted by db_cooper

What were the numbers for HC and CO? Do they check NOx? You may need a new Cat. Convt. depending on the numbers. Some thing cannot be adjusted out..like Nox.

I you connect the brown wire (the California emissions option) it will retard the ignition which reduces NOx.

[m110]

Originally Posted by Jeff Alton

I am not advocating this, but...... You can unplug one of the injectors (wire harness). I know it has been done before on a 3.2 to pass AirCare....

Cheers

have done this too on Mercedes EFI cars with much success

[john walker's workshop]

that's a lot of HC to blame on an idle adjustment. you have something else wrong. do a leakdown and compression first. ohm all the plug connectors. when it's hot and idling, unplug an injector, one at a time and see if the idle drops off. 3.2s often suck in the lower intake gasket, killing that cylinder at idle. anything that causes incomplete combustion will cause high HC.

[Hendog]

Just removed the plug wires. #5 was not "clicked" onto the plug. May have been the culprit.

Oh well, I don't mind going through and checking the valve clearances and putting in new plugs; I'll sleep better. Previous HC readings were anywhere from 53 to high as 99 once, usually in the 50's though.

[db_cooper]

High HC is unburnt fuel..A loose spark plug connector would allow this to happen at idle..the spark may have been jumping the loose connector at higher RPMs.

High HC can be from too lean a mixture too..too lean and the fuel will not completely burn..and out the tail pipe it goes.

If you do a retest and it fails..do like Johnnie suggests. He is spot on as usual.

The good news..It is not likely your valve adjustment.

[Hendog]

Originally Posted by db_cooper

High HC is unburnt fuel..A loose spark plug connector would allow this to happen at idle..the spark may have been jumping the loose connector at higher RPMs.

High HC can be from too lean a mixture too..too lean and the fuel will not completely burn..and out the tail pipe it goes.

If you do a retest and it fails..do like Johnnie suggests. He is spot on as usual.

The good news..It is not likely your valve adjustment.

Yep, I know John's word is one to heed! Unfortunately I don't have a compression tester (s'pose I could pick one up), and I certainly don't have a means to check for leak-down.

Intake gaskets and spacers were changed at 95,374 Km

I know my car pretty good; it did smell like it was burning rich and it idled differently. I'll check the valves since I'm going in that direction and install the plugs. I think I'll know after if it's back to normal. It can't be to much wrong; look at the previous Air Care results about 4000 Km ago.