Fellow Volvoers,

Today my -89 760T passed CA smog with the result given below.

Is there anything that can be done about the somewhat crappy HC and NO values at 15 mph? I've been unwise enough to mess with the idle screw without really knowing what I was doing. Can this be a contributing factor?

Car starts and runs fine with a somewhat bad 17 MPH, which I blame the non-engaging overdrive for.

This is more fine tuning from my point, but any help is greatly appreciated.

Thanks!

/Magnus F.

The verdict:

HC(PPM) 15 mph: MAX: 112 -- MEASURED: 102
HC(PPM) 25 mph: MAX: 086 -- MEASURED: 055


CO (%) 15 mph: MAX: 0.72 -- MEASURED: 0.40
CO (%) 25 mph: MAX: 0.60 -- MEASURED: 0.14

NO(PPM) 15 mph: MAX: 778 -- MEASURED: 768
NO(PPM) 25 mph: MAX: 717 -- MEASURED: 250

CO2 (%) 15 mph: MEASURED: 14.5
CO2 (%) 25 mph: MEASURED: 14.7

O2 (%) 15 mph: MEASURED: 0.30
O2 (%) 25 mph: MEASURED: 0.10

15 mph = 1772 rpm
25 mph = 2117 rpm

I've been unwise enough to mess with the idle screw without really knowing what I was doing.

You need to ground the pigtail on rt fender well to set the IAC correctly.

Since you have the idle adj knob you probably have the 007 AMM that has an adjustment screw and has probably benn screwed around with(literaly)

Set this screw per FAQ (analog dwell meter works great) right turn is rich and turns led on or dwell meter peged to right.

This is an input to the ECU and needs to be set correctly. Not by what is coming out of your exhaust. This works in combination with the oxygen sensor for the engine ECU to correctly set the fuel mixture.

I will definetly try this.

Thanks!

/Magnus F.

Try takeing her on the freeway and punching it. A mechinic told me to try that before pouring too much $$$ on fixing it, and sure enough, that did the trick. "honestly, officer, i was just fixing the emissions..."

The 15 mph numbers, from combustion viewpoint, indicate too lean a mixture, except that if it was that simple the HC would be much lower. Since everything straightens right out when you pick up a little speed, I'd have to wonder if the injectors have a poor pattern at low flow. The high NO and O2 would indicate that there is enough oxygen getting in, combustion is taking place at a high enough temperature (maybe higher than it ought to be) to create NO, but that much of the fuel is not being burned. Poor fuel atomization will produce this result. Just a wild-ass guess, but a bottle of Techron might not be a bad idea. Unless you have done it already.

Hmmm.

About two weeks ago, I removed the injectors and cleaned them out with compressed air and injector cleaner. They atomized the fuel quite well when I tried them.

Can it be low fuel pressure hindering the injectors from working correctly? My guess would be no since the car has a nice, even power.

More wild speculations are welcome!

/Magnus F.

What about deposits on the intake valve stems? Seems like that could disrupt both air flow and injector spray patterns?

The combustion chamber should be clean.

I've subjected it to the steam clean procedure described in the 700-FAQ. The spark plugs went from standard brown/black to sparkling white. I believe the rest of the engine got cleared out as well.

I will give it a full throttle treatment suggested by COSilverBullet above.

/Magnus F.

Hello, high NOX is caused by the ff: overheated engine/lean air fuel ratio/vacuum leak/overadvance ignition timing & finally a defective egr. high HC is usually caused by the ff:ignition misfire/improper ignition timing/excessive lean or rich fuel ratio/low cylinder compression/defective valve guide,piston or lifter/defectivepiston ring,piston,cylinder/vacuum leak/plugged flame trap/engine oil diluted w/ gasoline.I guide you in diagnosing your problem.