Question about 1990 Suburban & emissions

[Slooptin]

I'm moving to Denver/picking up a new-to-me 90 burb in the next week and I had a question about emissions. I'm buying the truck from a friend there who has it registered in a county that doesn't require emissions testing, but I'll be in the Denver metro area so I'll have to bite the bullet. I know he doesn't have cats on it so I'm assuming I'll have to add them back on, but I'm mainly wondering where in the exhaust to the cats need to be (i.e before or after the O2 sensors)? And will the aftermarket cats from rockauto be good enough?

As far as I know it's a mostly stock drivetrain with the stock efi, long tubes, a 4l60/700r4 and regeared axles

I'm also seeing on the air care Colorado website that they do a dyno test for the emissions; This burb has 5.38 gears in it (6" lift on 35's) and I'm wondering if I need to get it regeared to maybe a 4.11 or 4.56 prior to getting it emissions tested to bring down the RPM since I'm assuming they have a set vehicle speed they're testing at?

I've never had to deal with emissions testing before so any guidance will help. Also pics of the burb in case anyone was curious

 

[Vbb199]

Primaries go into a y pipe which is 3" OD or whatever.
Single wire o2 goes on drivers bank collector.

After the y pipe, you have about 1 foot of pipe until the pellet converter, following that you have about 2 feet of pipe which then leads to the muffler which is similar to a Flowmaster 40 series in size and chamber


After that is the bendy pipe that loops over the axle and out the back of the truck

Look under the cab. You'll see heat shields where the muffler and cat was approximately . Nobody that deletes the cats ever removed the heat shields, which you really can't unless you unbolt the body and lift it up to get to the bolts.

In the pic I attached, arrow points where the cat would be.

You must be registered for see images attach

My muffler is close to oem location.


Second pic I have attached is o2 location.

You must be registered for see images attach

If you have more questions regarding your tbi suburban, I'll be glad to answer them, as well as @gmbellew

He may know more regarding emissions requirements.
I don't have emissions here, I can saw the exhaust off completely and still pass.

 

[Vbb199]

If you know how to measure your output AFR by reading the ECM (I can point you in the direction to be able to read the ecm's live data)

You can play with resistances on both the CTS and o2 to read the afr they want to see on the output, I won't tell you how, because I might go go jail, but it's just something to think on.

 

[Slooptin]

@Vbb199 Awesome, that's just what I'm looking for. I know the truck also has long tunes and true duals so I may be looking at a whole new exhaust system....

And I'm definitely interested in being able to read ecm live data so any help there would be great. I think I still have to do a sniffer test so idk if changing AFR output readings is going to do much for me. I'm used to newer stuff (i.e. HPTuners and OBD2 ports) so carbs and early tbi is new territory for me

 

[Vbb199]

Or if you have a means to just measure millivolts...... you don't need to monitor the ecm.

The 1 wire o2 reads in Mv and ideal schociometric range is 450mV or .450v


I don't know what those people like to see with their sniffer, but there's a process to outsmart them, unless they know what they're looking a t


Probably should check if the EGR valve to the left of the tbi and behind it (if you open the hood up) hasn't been blocked off.



I'm going to tell you right now if it's long tube headers, no cat, no egr, and they are running a 1 wire sensor for o2........


It'll never get hot enough to measure accurately


You must have a heated 3 wire o2 in conjunction with open free flowing exhaust on a tbi.

Common mistake

 

[Vbb199]

@Vbb199 Awesome, that's just what I'm looking for. I know the truck also has long tunes and true duals so I may be looking at a whole new exhaust system....

And I'm definitely interested in being able to read ecm live data so any help there would be great. I think I still have to do a sniffer test so idk if changing AFR output readings is going to do much for me. I'm used to newer stuff (i.e. HPTuners and OBD2 ports) so carbs and early tbi is new territory for me

If you add or subtract resistance from "certain sensors"

It will change what "a certain AFR reads"

I cannot and will not say anymore.


The device I use to observe my ECMs live data is from 1320 electronics.

The app is ALDLDroid from Google play.

The total cost of the rig islike, <200$


GmBellow also uses it as well.


I can send links if and when you cross that bridge.

 

[Vbb199]

There's no downstream o2 on the system so you can fudge the numbers , without a cat.

I can "even" show you a "less restrictive" cat that's for

"offroad use only"

 

[DoubleDingo]

Get a post office box there in the town you buy it from, and have your suburban keep the registration there. You will need to check the mailbox once in a while, but you won't have to do emissions testing.

 

[adamj]

Colorado is now following the same California catalytic converter standards (only CARB certified cats) so be aware of that because you can no longer purchase federal converters in state. The price difference is significant: $300 for a good Magnaflow regular federal emissions cat and $1200 for a california cat. If you have a dual cat system, that is going to get expensive.

Check the emissions sticker under the hood and follow that to the T. You need all the original emissions equipment like EGR valve, AIR pump(s) + associate lines/proper exhaust manifold, and evap canister and lines. Air Car Colorado will check for the presence of all that stuff, and then do the gas cap test first, all before even putting your wheels on the dyno. If you fail that, they will not do the dyno test. You can fix those things and then come back for a free retest.

Hard to tell from the photo if you have a 1/2 or 3/4 ton burb, but if your GVWR is over 8500 lbs then they will give you a small break and you get to do the 2-speed idle test (no dyno, less strict) opposed to the full dyno test.

Measure your 35s. If they are taller than 34" then you need to check that the emission test location dyno is one of the few in the state that can accommodate the larger tire sizes, those that can are by the major cities.

They will clamp a tachometer over the #1 spark plug wire and get RPM from that, no other sensors are read, no OBII port hookup (which you don't have anyway). Then they hook up a tailpipe emissions sensor to read CO2, NOx, and total hydrocarbon, while idling and at different dyno loads.

Good luck!

 

[DoubleDingo]

Registering it in the same town you buy it from is looking better and better

 

[Frankenchevy]

A lot of places here do a two speed emmisions test. It’s based on engine speed(2500 rpm iirc), rather than wheel speed. I don’t remember exactly, it’s been a long time since I’ve had to smog anything (too new, too old, too diesel or too electric). My 3rd gen ram will need a smog in 18 months or so, but diesels are different. That’ll be the first smog check in a long while and it’ll likely get moved to my place in Idaho.

 

[idahovette]

@Frankenchevy good to hear about the Idaho move.......we got water here...you can WASH your truck..s............lol

 

[Frankenchevy]

@Frankenchevy good to hear about the Idaho move.......we got water here...you can WASH your truck..s............lol

I still have at least a decade of work out in lala land.

 

[Grit dog]

@Slooptin
I would 100% take the easy route and register it at the friends place or any other option to keep it out of the aircare system.

 

[idahovette]

@Frankenchevy OK, I might not be around, but I'm sure the water will still be available.....?