Carb black box people..look inside please.

**russiankid** · 08-13-2009, 12:48 PM

My 89' LX passes emissions but NOx is extremely high. It is at 3592 with a limit of 3600. I did some searching and read that the EGR valve is most likely the cause. So I checked the valve and it holds vacuum. I put vacuum onto the line for the EGR valve, which is line 16, it does not hold vacuum. Looking at the diagram of the black box, lines 16,19, and 3 are all connected together. Line 19 holds vacuum, but it is also connected to a one way valve so the one way valve in the black box works. I then put vacuum onto number 3 and it does not hold vacuum. Line number 16 and 3 are T offed into the main valve and that one way valve(line number 19). I checked the main valve for the EGR system for line number 16 and it holds vacuum. I cannot find any area's in the hoses where they could leak.

I also checked the vacuum at the EGR valve when the car is running and its at zero. Revving the engine does not make any difference.

Any ideas on whats going on here? Car idles nearly perfect, but it does have a small pop noise in the exhaust which leads me to believe there is a vacuum leak. On a good note, the car does pass emissions basically without an EGR.

***2oodoor*** · 08-13-2009, 01:16 PM

without looking at the diagrams in the service manual, I believe ultimately the vacuum source for egr comes from one of the thermowax valves. Where and when from there Iam not positive.
When is the nox too high? at idle or cruise rpm?

EGR is only supposed to be on at open throttle then backs off at cruise somewhat, depending on the model vehicle.
Never on during idle. EGR driveability issues are funky idle or stalling and "tugging or surging" at cruise speed.
Other than those, EGR problems are usually the cause of CEL on for EGR position sensor or similar things that the ECM sees of it.

**russiankid** · 08-13-2009, 01:20 PM

NOx is high at 1500rpm. I checked the thermowax valve that is T into the EGR valve line and it holds vacuum.

**ecogabriel** · 08-15-2009, 11:24 AM

EGR system has a problem otherwise the NOx numbers should be A LOT lower. I failed emissions in GA with NOx @ 2200 or so (EGR valve dead; pintle control mechanism had failed... EFI engine)

Normally, the EGR valve only has vacuum when it is working. At idle speed it does not work; idle would be rough otherwise. That may sound dumb, but the EGR valve might not be receiving exhaust gas (clogged). If you draw vacuum from the EGR valve with engine at idle, it should become rough or stop it.