Reflashing the trucks computer after Cat/ Emission Delete

[IRQVET]

So I went ahead a removed both cats from my exhaust system and installed the Jegs Y pipe. I used the stacked spark plug arresters between the exhaust and the O2 sensors to fool the computer into thinking my cats were still there. However, my Tahoe is a California truck, so it has not 3 but 4 O2 sensors. My Y pipe only had 3 bungholes to plug in 3 O2 sensors. So now I have my 4th O2 sensor unplugged, and of course, the check engine light is on.

So has anyone ever “reflashed” your computer so you can delete the emmissions stuff? I live in a state with no smog requirements, but I have zero experience in this.

Talk to me Goose!

BTW, if anyone is looking to do this mod, its a pain in the a$$ and not as easy and straightforward as this video implies it is. Drilling out those 18mm spark plug arresters so they accept the O2 sensors took me several hours, as there is not alot of real estate (metal) left once you start boring/ hallowing them out, so its a painstakingly slow and tedious process.

 

[east302]

My 98 (49-state or non-CARB) has dual cats as stock so four oxygen sensors. On mine, one bank’s oxygen sensor is downstream of the flange after the converters (and wouldn’t be included with the y-pipe if your setup included the converters).

Edit: sorry, completely misread your original post. I’d delete my post but can’t quite figure out how to do it

 

[iamdub]

So I went ahead a removed both cats from my exhaust system and installed the Jegs Y pipe. I used the stacked spark plug arresters between the exhaust and the O2 sensors to fool the computer into thinking my cats were still there. However, my Tahoe is a California truck, so it has not 3 but 4 O2 sensors. My Y pipe only had 3 bungholes to plug in 3 O2 sensors. So now I have my 4th O2 sensor unplugged, and of course, the check engine light is on.

So has anyone ever “reflashed” your computer so you can delete the emmissions stuff? I live in a state with no smog requirements, but I have zero experience in this.

Talk to me Goose!

BTW, if anyone is looking to do this mod, its a pain in the a$$ and not as easy and straightforward as this video implies it is. Drilling out those 18mm spark plug arresters so they accept the O2 sensors took me several hours, as there is not alot of real estate (metal) left once you start boring/ hallowing them out, so its a painstakingly slow and tedious process.

I believe you can get those non-foulers on ebay already modded. Also, I think they have 90° ones for the tighter areas such as in your pic. Probably not as cheap as buying the non-foulers and drilling them yourself. But, what's your time and labor worth? I've seen small wads of stainless pot scrubber added between the two non-foulers to further filter the exhaust from the sensor. Keep this in mind if you get a catalyst inefficiency code.

Your '98 is OBD2, so it can be tuned by any shop worth their salt. Or, you can have someone (or a shop) weld another bung in the pipe for you to add that other sensor in. If you still have your original exhaust, you can cut the bung from it and weld that in. Adding that bung might be cheaper than getting it tuned, or maybe not. If you get it tuned, you could have some other items modified if you want such as top speed limiter raised or "removed", speedometer adjusted if you're running (and keeping) a non-original tire size, shift points and firmness altered, etc.

 

[IRQVET]

What type of shop can do this kind of a “tune.” Seems like it wouldn’t be your average Joe Blow achanic shop, but maybe I’m wrong?

 

[iamdub]

What type of shop can do this kind of a “tune.” Seems like it wouldn’t be your average Joe Blow achanic shop, but maybe I’m wrong?

Any speed shop worth visiting can tune. They all can turn off codes and adjust speed limiters, speedometers, etc. since all that entails is checking/unchecking boxes and typing in numbers. But, if you wanna tweak engine and trans parameters for power or improved drivability, that's gonna require knowledge and experience. Ask around or read up for reviews on facebook. There are people that can flash your ECM for you if they have the stuff (likely HP Tuners or EFI Live). Doesn't necessarily have to be a shop.

For kicks, I Googled "speed shop tallahassee fl" and the first hit is "Tallahassee Speed Shop". They look to be an import or more high-end place, but I'm sure they can point you to a handful of people and/or places to tune a GM.

 

[east302]

I’ve never used them, but Black Bear Performance is commonly used by a lot of GMT400 owners.
HP Tuners is another one…

Blackbear tune to disable security, rear O2s...anything else???

Had my cats cut out since they were plugged solid and may have also installed a magnaflo muffler at the same time. Then as of late, my security system kicks in everytime I start my truck. Enough is enough so I ordered a tune from Blackbear to get rid of the rear O2 sensors and disable the...

www.gmt400.com

 

[iamdub]

^^^ Yup. If you're on facebook, you could ask on a couple local car pages if anyone has HP Tuners. For just an engine tuning credit, it'd probably be $50. Maybe see if someone would do it for $50 and a case of beer.

Or, I bet you could find a welder that'd put those bungs in your exhaust pipe for a case.

 

[east302]

That’s a good idea.

Quick aside, your avatar makes my eyes hurt

 

[iamdub]

That’s a good idea.

Quick aside, your avatar makes my eyes hurt

That's the second comment on my avatar today! What's cool is that it's not the pic doing it. It's your brain and mind trying to process what it's not accustomed to. Which is the true antagonist? Which is more convenient to blame?






















...Okay, so it's just an annoying avatar.

 

[swathdiver]

Which is more convenient to blame?

You!

 

[Eman85]

I don't know why you'd have pipes with no bung for the 4th O2 sensor. I have a 97 Tahoe, 99 Yukon and 98 K2500 and they all have 4 sensors. My K2500 had the cats removed and the PCM was never reflashed and never sets any codes. I would just have the bung welded in and see what happens. I question how the spark plug antifoulers are any type of real fix, need to see the theory.
If I were you and did pull the PCM to eliminate the downstream O2 sensor setting codes I'd also have the security system disabled.

 

[east302]

I don't know why you'd have pipes with no bung for the 4th O2 sensor. I have a 97 Tahoe, 99 Yukon and 98 K2500 and they all have 4 sensors. My K2500 had the cats removed and the PCM was never reflashed and never sets any codes. I would just have the bung welded in and see what happens. I question how the spark plug antifoulers are any type of real fix, need to see the theory.
If I were you and did pull the PCM to eliminate the downstream O2 sensor setting codes I'd also have the security system disabled.

On mine, the fourth sensor is on the muffler-side of the flange and not on the y-pipe. Seems like it should still be there is that part is still stock?

 

[IRQVET]

This is what I ended up with. 3 bungs

JEGS 31006: Y-Pipe for GM - JEGS High Performance

SS409 Y-PIPE 99 GM

www.jegs.com

 

[east302]

Did you keep the section downstream of the flange (what I posted) that goes to the muffler? On the stock part, the fourth sensor bung is in that section and not in the y-pipe section.

Your part looks to be correct.

An aftermarket exhaust is pictured below, but it matches stock. The converters with y-pipe are to the left, fourth O2 sensor is on the right of the flange:

 

[IRQVET]

So the issue I’m having is the 4th o2 sensor is right below the drivers side door, and the lead/wire is maybe 10 inches. Minewhile, the left side of that pipe listed above drops down and cuts steeply toward the passenger side. So the pipe is literally 2 feet from the o2 sensor that is 14 inches short of being able to stretch that far.

For a crude visual, my o2 sensor is about where the left page arrow is on the screenshot. My o2 sensor is nowhere near the flange like yours is . . .

 

[east302]

The y-pipe is dropped down for a head replacement, but the driver upstream sensor is shown below. It looks to be in about the same place as the upper left one in your catalog photo. Is that the one you cannot get the wiring to?

I meant to ask, are you doing true duals on it? I’ve done my 98 trucks since there’s room, but can’t quite figure out the routing to make it work on my two-door.

 

[IRQVET]

No not true duals, two into one. I wanted to keep my exhaust as stock (looking) as possible. I’ll take some better pics this week so you have a better idea what I’m looking at. Appreciate it East302 with all the pics your providing, its nice to see what other folks sets up look like.

 

[east302]

Not a problem. Those pictures are of my son’s truck (98 ex-cab) with a Walker setup, but it’s the same as my Tahoe.

Your Jegs pipes look correct in the catalog, so it seems like it should bolt right on.

Catch up later, maybe it’s something simple or they sent you the wrong part