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Maybe you need to go thru your EBL again.
Look under Scalers ( π ) then EGR - SA Added
That affects the entire Spark Advance ( SA ) slew of tables when active. Would you want to go add 4.22 to every single SA table cell?
As you can see it's "only" 4.22 degrees of spark advance, but depending on your fuel octane for a particular gas station fill up that could be enough to run into spark knock, which should be picked up by the knock sensor and adjusted/retarded accordingly. Can you feel spark knock when you drive vs looking back over your data logs? I sure can't. But like I said earlier, what if it's just enough to not knock, it's enough spark advance you won't be getting full engine potential.
If you don't believe me, slide that scaler adjustment up, let's say 10, maybe 20 degrees if you are braver than me to try and prove me wrong, load it and try it. You should be able to feel the difference then. The engine won't feel more powerful at that point. At 4.22 you'd probably need a dyno to see how much power you're giving up
Originally Posted by GregMartin
People can believe what they want its the internet after all, but I only comment in things I’ve done and know about.
That's why I tell people on here if they don't have the ability to do their own tuning, to keep the EGR functional.
Since you have EBL Flash 2 you should be able to go look, the EGR has TPS and MAP setpoints. A functional EGR WILL NOT rob you of engine performance when the engine is under load from acceleration or on hills or a dragstrip, when you want more/max power
Last edited by flannel_man; Feb 8, 2025 at 04:27 PM.
Also Greg, since you have the EBL and the EGR blocked off I'd recommend you change the Coolant Temp Sensor ( CTS ) setpoint for the EGR activation to the max. I want to say it's like 340⁰F
That way the EGR and it's tuning will never activate and you'll bypass the whole EGR SA changes, plus not activate the expensive to replace solenoid unnecessarily
Last edited by flannel_man; Feb 7, 2025 at 07:56 AM.
The honeycomb in my factory cat collapsed and clogged up the cat back around 2011. Some rebar fixed it
We don't have any emissions testing here. But I could smell that exhaust pretty bad on a cold day and with no mufflers it was a tad obnoxious. I redid the exhaust and put a high flow 2.5" on each bank before the factory cat position, no smog pump needed. Can't smell it at all now, just the cats made the sound level much more bearable on longer drives but went ahead and added a resonator where the factory cat was
Hahah! Rebar...
Do you happen to have pictures of this? I.E. ... the high-flow 2.5s on each bank? I'd really like to see that if you don't mind. I think I'd like to do what you've done.
Originally Posted by GregMartin
Yep correct. The AIR pump was needed on the old catalytic converters but not on modern ones. You can remove the AIR and use an 85” belt, no idler pulley required on an 84. If you have no emission laws to worry about why replace the cat at all. I replaced my exhaust and put an x pipe where the cat use to be. I was worried about funny smells etc but that’s all BS. Also you can remove your egr valve and block the hole off with a plate. None of this affects how the car runs, in fact it just runs better. The old ecm doesn’t care and it doesn’t set any codes.
Man, I bought so much stuff while reading through this thread. I'm way too impulsive. I bought the bypass kit from Ecklers, and then also bought the 50" belt, and then a 50.5" belt I think it was, and then saw what someone else did up above, where they kept the pump in there, cut the wheel off, and replaced the belt... and it even provides better coverage on the alternator (not that it's bad). Well, at least I have options... and things I can sell on eBay when I decide which way I want to go. I'm wondering what kind of performance gains you felt / saw from removing the pump? More than anything... to me... the biggest take away will be to clean up the engine bay and help the engine run a bit more efficiently.
Originally Posted by GregMartin
Pretty sure that is completely incorrect. There is not a egr timing table in an 84 ecm and tbh I haven’t seen one on later ecms either. There also isn’t a timing correction table for egr so I have no idea where you got that idea from. There is however a narrow band O2 sensor and that is how the feedback works on these cars. They are very simple. The only inputs that mater are TPS, CTS, O2 and MAP. Oh and knock. Removed my EGR no change in engine function or mpg. Later did a whole lot of mods (see my bio) still used the factory ecm and the power was strong but I figured there was more to be had. So then about a year late I swapped in an EBL Flash II and tuned it. BTW the EBL Flash two is just a flash tunable 90s GM ecu and has all the factory tables and compensation tables but no egr table??? Imagine that. People can believe what they want its the internet after all, but I only comment in things I’ve done and know about.
@flannel_man is correct about the EGR. I do a lot of stuff on the Pontiac Fiero, and it's the same deal. The engine's fuel map is designed to compensate (and expects) the EGR. You have to disable it in the code, and re-adjust the fuel mapping. Don't get me wrong, there's a lot of benefit to eliminating the EGR. Like on the CFI motors... all that black soot and carbon buildup in the intake is horrendous. My daughter just rebuilt her 2.5 Iron Duke, and we had to use a Dremel with a metal deburring bit to chisel out the 180k miles of EGR "cake" that was effectively sealed to the EGR passage.
A much longer thought about this... modern motors (I'm thinking about the 2.4 VVT ECOTEC I had in my Pontiac Solstice back in ~2006. It had no EGR system. The engine was pretty modern of course, high compression, VVT, direct injection, etc.. but it was extremely efficient... and therefore didn't need the vast majority of the nonsense that our Corvettes have:
It was such a great motor for what it is (also... you guys will notice the clamshell design is a lot like our C4s!).
I installed a cold air intake (which made it sound like *** because it was a 4 cyl), but I also installed a shorty header, and a high-flow catalytic converter... it ran mid 14s naturally aspirated. But just look at that engine bay. There's only a couple of vaccum lines there. One big one for the brake booster, one other big one for the PCV valve to intake tube, and one to power the vacuum controlled HVAC system. There was NOTHING else... it was amazing (all the other black snakes you see in there are wiring harnesses).
Now... don't get me started on Throttle By Wire... but otherwise, so insanely efficient, it was a fantastic motor.
Sorry, I'm going off on a tangent. My point though is... we're working off 80s tech. It's still pretty impressive... but last I remember, the baud rate is like 300 bps. Back in the day, I used to call BBSes with my computer... I didn't tell anyone in high school because it would have been emberassing, so I was really quiet about my secret nerd life. But I called BBSes at 2400bps, and then eventually 9600, etc. But 300 was... you could see the characters show up on the screen. This is old tech.
There are much newer aftermarket ECMs that have a type of self-learning, which allows you to eliminate the EGR. The EGR can be used to help cool the pistons, and you do see some slight fuel economy savings from it (under cruise)... but the carbon flowing through the intake... ugh... that's hard to like when you open that lid and see black everywhere. I haven't opened the intake on this car yet, but I had an 82 TransAm back in the day (hence my name, haha), and I have a huge love/hate relationship with EGR.
I used these cause they are small enough to fit and most importantly at the time they have o2 bungs so I could add a wide band and data log without having to pay extra for bungs to be added. Plus they were cheap
Now I will stress, the ones I linked will not fit and just clamp up to stock 84 exhaust. These are 2.5" vs the 2.25" double wall that came from the factory. Your exhaust shop should be able to bend you new 2.5" pipe if you go 2.5" Or they can even make some ugly welds filling in the 2.25" to 2.5" gap
I don't seem to have any pics of mine on my phone. But, right after the downpipes turns about 90⁰ from the collectors and start to run straight, right about beside your feet, is where I had them install these.
When I got home I wrapped them from the collectors to about 4" after the cats. The cats get hot and since they don't have a heat shield like the OEM one I didn't want to heat up my foot wells/transmission tunnel.
If you ever use an exhaust wrap, wear disposable gloves, a dust mask, and before install drop the roll of wrap into a 5 gallon bucket of water for 5 minutes or more. The water will keep the wrap from releasing it's nasty fiberglass and powdered lava rock dust into the air. When that crap goes airborne any exposed skin will itch for 2 days, and your nasal passages, throat, and lungs will feel the same horrible itch. Get em soaking wet and they won't go airborne. Then once it's installed and dry you can spray the wrap with the exhaust wrap silicone encapsulating spray and they won't go airborne every time the wind blows and you are working in the area around it.
Just put stuff in your cart for later, it'll stay there till you actually need it or decide against it
Last edited by flannel_man; Feb 7, 2025 at 09:57 AM.
I know that this is an old post, but for those that still have these older cars and are trying to keep them alive, I'm working on an 84 C4 and keeping the AC but removing the smog pump. It does leave an ugly gap between the power steering reservoir and The idler, Pat removing the pump and getting a K060845 13/16" 6 rib X 85¼" Gates belt from O'Reilly also works like a charm.
Now to take off all the ridiculous overcomplicated pump goodies 😜 A photo of the belt number and the gap the pump removal leaves
Last edited by Cynical Poptart; Oct 9, 2025 at 01:53 PM.
Reason: Adding a photo
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Slideshow: A Jaguar designer's personal project imagines what a modern front-engined Corvette might look like if Chevrolet revisited the golden age of the Stingray.
