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Discussion Starter · #1 ·
Failing smog due to NOx being about 2X the limit

Cleaned out the EGR passageways, wasn't very dirty. Function check via TRSM on the EGR valve is good, stumbles at idle when vacuum is applied.

Checked the VSV with battery voltage, it clicks like it should.

Down to transducer / modulator as being the primary suspect. I've tried cleaning it out, but I think it was busted already and there's no helping it.

On the '84 I've got the transducer type that has one port in, and one port out. This part seems to be unobtainable, and any listing I see for it it's around $80 and not available anyway.

The P-Q-R port style is very common, and can be had for $20.

So, here's my question: How do I update to the newer, readily available part? I think it's a matter of correctly routing vacuum lines. Studying the TRSM, one diagram shows the "R" port being pre-throttle plate and "P" port being post throttle plate. Another diagram shows all the vacuum ports as pre-throttle plate.

Hopefully someone can explain it to me?

Thanks!
 

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Discussion Starter · #2 · (Edited)
Some images may help

Here's what my car looks like:



Vs later style that seems common all the way through the 90's and early 2000's



What it looks like, the vac ports on the throttle body are aligned so that only one port gets vacuum when throttle is closed, but both get vacuum when throttle is partly open

 

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Matches what were your other numbers O2, CO, HC etc??

Fully warmed up??
 

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Post your pictures again??
 

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I have had and owned numerous vehicles that Smog Check II hasnt been really easy to pass smog...

Here's some tips to assist passing SMOG

Recent oil change, yes dirty oil does effect tailpipe emissions...

Recent tune-up plugs, cap and rotor.

Fresh gas...

Fully warmed up 10-15 mins at freeway speeds...

Some have used CRC guaranteed to pass additive with good results
 

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Discussion Starter · #7 ·
Matches what were your other numbers O2, CO, HC etc??

Fully warmed up??
Tried the test four times, three fully warmed up once cold. Old timer smog guy said let's try it cold just to see. Yeah it failed.

Everything passing except NOX at 15mph and 25mph. High combustion chamber temps. That normally indicates the EGR isn't working, right? Numbers are like 1400, when passing max is 700.

I cleaned out the manifold passage and EGR tube. Tested the EGR valve via TRSM method, and it works. VSV works. I'm thinking the modulator diaphragm is busted or leaking
 

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See post #4 here


You can buy the later 3 port modulator aftermarket pretty cheap to try. You have to find a smog guy to look the other way though since its non stock.
 
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I might have a spare on an intake plenum I have, have to get off duty first...

PM me tomorrow to remind me pls...

You live in the West or East end of the island??
 
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Discussion Starter · #10 ·
That's brilliant, thank you. I'm thinking I could attach a hose to the R port then run it down under the intake manifold and have it just kinda "vanish" into the rats' nest of vac hoses and whatnot in there. If this fixes my problem, then the car should pass tailpipe and hopefully the smog tech doesn't look too closely


See post #4 here

You have to find a smog guy to look the other way though since its non stock.
 

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Discussion Starter · #11 ·
I might have a spare on an intake plenum I have, have to get off duty first...

PM me tomorrow to remind me pls...

You live in the West or East end of the island??

East end, in the neighborhood just off the High St bridge
 

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AKA Fernside District...my sis lives on High St.

I lived on Fernside before moving to San Ramon Valley a long time ago...grew up in Woodstock

My Pops worked for AFD...
 
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Well, test the modulator according to manual, it may be perfectly functional. A lot of times, it may be a single vacuum-hose in entire system that’s cracked. If modulator tests Ok and vacuum hoses are OK, replacing perfectly-working modulator with another perfectly-working modulator will change nothing.

Also failed cat will also cause high NOX.
 
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