1990 Trooper 2.6 Failing NOx

Howdy Everyone,
I've a problem here maybe someone with a similar thing can help fix:
My 1990 2.6 Trooper (air, 5sp) has failed the test-only here in CA a
couple of times. HC passes at 53/48 ppm. CO passes at 0.19/0.20, but
NOx is 1189/1096. The Cat conv has less than 1000k, the head gasket
was replaced just before the smog test and I cleaned all the EGR tubes
and ports and sensors. Timing is right on.

I took it in for repairs and the smog check guy couldn't figure it
out. But here's what he said: The EGR valve, though good, doesn't seem
to be staying open long enough. The vacuum is quickly dropping off,
closing the valve too soon. I've checked all the hoses, etc, and it's
all good. Thermal valve seems to be good, though I haven't removed it
to test it. His suggestion was to replace the EGR valve and Cat... I
think he's just shooting in the dark...

I have a concurrent problem that may or may not be related: Idle is
too low on warm up... Cold start enrichment is fine, truck idles fine
for a minute, but once it's slightly warm, until it is fully warm, it
idles too low, stumbling. Warm idle is perfect. Smog guy said vacuum
to the pressure reg is also dropping off, but the VSV is good. I don't
see where the EGR and fuel pressure reg vacuums are connected, except
at the throtle valve vacuum ports...

Any suggestions or more information?

Pulling my thin hair out, slowly

Alf.

I have a 1994 Isuzu Pickup 2.3L manual.

As what I read from Haynes Manual, the emission control subsystem you
also want to check is Air Injection Reactor System which provides
favorable condition to burn the emissions by providing oxygens.



Spike Strip wrote:

> Howdy Everyone,
> I've a problem here maybe someone with a similar thing can help fix:
> My 1990 2.6 Trooper (air, 5sp) has failed the test-only here in CA a
> couple of times. HC passes at 53/48 ppm. CO passes at 0.19/0.20, but
> NOx is 1189/1096. The Cat conv has less than 1000k, the head gasket
> was replaced just before the smog test and I cleaned all the EGR tubes
> and ports and sensors. Timing is right on.
>
> I took it in for repairs and the smog check guy couldn't figure it
> out. But here's what he said: The EGR valve, though good, doesn't seem
> to be staying open long enough. The vacuum is quickly dropping off,
> closing the valve too soon. I've checked all the hoses, etc, and it's
> all good. Thermal valve seems to be good, though I haven't removed it
> to test it. His suggestion was to replace the EGR valve and Cat... I
> think he's just shooting in the dark...
>
> I have a concurrent problem that may or may not be related: Idle is
> too low on warm up... Cold start enrichment is fine, truck idles fine
> for a minute, but once it's slightly warm, until it is fully warm, it
> idles too low, stumbling. Warm idle is perfect. Smog guy said vacuum
> to the pressure reg is also dropping off, but the VSV is good. I don't
> see where the EGR and fuel pressure reg vacuums are connected, except
> at the throtle valve vacuum ports...
>
> Any suggestions or more information?
>
> Pulling my thin hair out, slowly
>
> Alf.
>

I have a 1994 Isuzu Pickup 2.3L manual.

As what I read from Haynes Manual, the emission control subsystem you
also want to check is Air Injection Reactor System which provides
favorable condition to burn the emissions by providing oxygens.



Spike Strip wrote:

> Howdy Everyone,
> I've a problem here maybe someone with a similar thing can help fix:
> My 1990 2.6 Trooper (air, 5sp) has failed the test-only here in CA a
> couple of times. HC passes at 53/48 ppm. CO passes at 0.19/0.20, but
> NOx is 1189/1096. The Cat conv has less than 1000k, the head gasket
> was replaced just before the smog test and I cleaned all the EGR tubes
> and ports and sensors. Timing is right on.
>
> I took it in for repairs and the smog check guy couldn't figure it
> out. But here's what he said: The EGR valve, though good, doesn't seem
> to be staying open long enough. The vacuum is quickly dropping off,
> closing the valve too soon. I've checked all the hoses, etc, and it's
> all good. Thermal valve seems to be good, though I haven't removed it
> to test it. His suggestion was to replace the EGR valve and Cat... I
> think he's just shooting in the dark...
>
> I have a concurrent problem that may or may not be related: Idle is
> too low on warm up... Cold start enrichment is fine, truck idles fine
> for a minute, but once it's slightly warm, until it is fully warm, it
> idles too low, stumbling. Warm idle is perfect. Smog guy said vacuum
> to the pressure reg is also dropping off, but the VSV is good. I don't
> see where the EGR and fuel pressure reg vacuums are connected, except
> at the throtle valve vacuum ports...
>
> Any suggestions or more information?
>
> Pulling my thin hair out, slowly
>
> Alf.
>