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Question: LT1 Emissions Questions.

WillC4

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'94 LT1 Green Coupe. 6-spd. All Bolt-ons.
Hey, I have a '94 LT1 w/ 6-speed manual. And i just recently ordered an exhaust system for my car from headers to mufflers. The headers are being made, so they have not been sent out yet. For potential resale reasons, i wanted to keep as much emmisions stuff as possible. That goes without saying that there is no cat with this system, it is straight pipe, but should there be need for a cat, then there is a removable section i can utilize to place one.

Getting to my point, as i was ordering the system i learned that there are several questions that i wanted to ask, they said that they do not provide an LT1 EGR tube, well so i asked for block off plates, but they do offer the headers with the air pump holes, so i told them to put that on. Well upon inspecting my engine during my routine winter maintenence, i wanted to see where the EGR tube was, apparently it is connected with the air pump hoses, i could not trace an individual pipe from the EGR inlet, next to the EGR valve, going directly from header to intake (like my last car, a LT1 Camaro). So, is my hypothesis correct, i will not require any special block off tubes as i thought and that the EGR system is interconnected with the air pump system?

In addition, i knoticed that my car has a after cat O2 sensor on the passenger side, are there any O2 simulators out there to rectify any issues since i am not utilizing it? The last thing i want is my computer reading that something is missing and risk the potential of it "detuning" the engine? Or will i simply need to tune out the aftercat O2 sensor?

Note that where i live, there are no emissions laws, so tests are not of any concern.

Thank You,
Will
 

boomdriver

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87 z-51
one thing ata time...

first, EGR has no connection to the A>I>R> system. AIR just injects fresh air into the header tube to keep the exhaust gas burning and hot. thats all.

EGR is MORE important. EGR is waste gas thats already been burned so its hot but not nearly as hot as gas thats igniting in combustion. The purpose of EGR is to give a small shot of EGR to the intake when the engine is under a high load, hi-stress, or when it senses severe knock. The cooler EGR gas enters the combustion, chills the raging explosion, stops the knocking, saves your piston, allows the ECM to return to max timing advance and life goes on...all that in .023 seconds....

It all happens incredibly quick. Having NO EGR means complete detune or serious spark retard so knock and pri-ign cannot destroy the engine./ with no cool exhaust gas from EGR to lower temps inside the heads, the combustion can runaway and cause terrible things.
When EGR works, you hardly even notice. IF EGR were not to work, you;d notice alright..on the flatbed tow truck. EGR hurts so little bit, if anything, but it does so much more to save the engine from temp, pre-ign, knock and low back-pressures. You can get a stock EGR tube and get someone to braze it into the header manifold down low and the top mounting at the intake should be there. all you''ll need them is the working EGR solenoid and a couple vac lines and you're ready to race AND probably get past any under hood inspection.The ONLY issue with brazing the EGR tube in would be in the headers were already ceramic coated, which I bet they are...opppps

yes on O2 stimulators. That or get the ECM reprogrammed to take O2 data at a set amount from prom or new uplink. The ECM will be searching for this input, so you have to give it something. There ARE performance shops (off road, of course) that can burn you in easily.
Actually, you could run the O2 sensors as normal. They don't hurt anything.They will keep the ECM open to tuning instead of having to run off a program that won;t fit all.
 

stang-etr96

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Messages
95
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michigan
Corvette
1996 Yellow LT4 1991 WHT conv. Blue top & int.
I thought 94's where OBD1's and had no rear O2 sensors????? And if they did, wouldn't there be one for the left and right?
 

WillC4

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Messages
94
Location
Colorado
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'94 LT1 Green Coupe. 6-spd. All Bolt-ons.
one thing ata time...

first, EGR has no connection to the A>I>R> system. AIR just injects fresh air into the header tube to keep the exhaust gas burning and hot. thats all.

My apologies for cramming it all. I want to keep EGR. But, when i inspected my engine, i followed the air pump hose from the pump itself, it connects to a T splice next to the driver side manifold. One direct of the T splice plugs into the driver side manifold, and the other heads towards the back of the engine. When i followed it to the back of the engine, the hose connects to a metal pipe. This pipe is located next to the EGR valve, the pipe then splits in two directions, one of which is connected to the EGR inlet port on the back of the intake manifold, and the other attached to the passenger side exhaust manifold on the top of it. I am assuming that the LT1 A.I.R. system and the EGR utilize at least the same hosing/piping on the Vette at least, as i cannot find any other tubing connected to the back of the intake manifold.

I thought 94's where OBD1's and had no rear O2 sensors????? And if they did, wouldn't there be one for the left and right?

In '94 and '95, GM was experimenting with OBDII, i dont think i have a true OBDII, but it isnt OBDI only. I did some researching and i know it is odd, but the passenger side pipe has two O2 sensors, one before and one after the cat converter. The driver side only has one O2 sensor, and thats before cat. Again i find it strange as well.
 

toptechx6

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404
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1993 Coupe, Bright Aqua
You are correct that the plumbing for EGR and AIR is the same between the EGR valve and manifolds or headers. The 94 and 95 PCM can set codes for the single downstream O2 sensor but I do not believe those codes will illuminate the MIL and since they are 4 digit codes similar to OBDII codes retrieval using the paper clip method may not work, they may only be accessible using a Tech 1.
 
S

surfer93

Guest
You are correct that the plumbing for EGR and AIR is the same between the EGR valve and manifolds or headers. The 94 and 95 PCM can set codes for the single downstream O2 sensor but I do not believe those codes will illuminate the MIL and since they are 4 digit codes similar to OBDII codes retrieval using the paper clip method may not work, they may only be accessible using a Tech 1.

95's I know are inbetween OBDI and OBDII, but 94's are strictly OBDI's.
But to answer your question, O2 bungs are a couple of dollars and have someone weld them is pretty cheap and your car will run much better than w/simulators. Do not think sims are a good idea, if one injector starts leaking or something similar, how is the PCM going to know and compensate.
 

roger longman

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1977 c3 orange ! 1988 c4 kinda purple 1991 'race
Hi all, boomdriver has me worried, I've blocked off my EGR to cure a miss at low revs in a high gear. Am I facing a catastrophe ? Any advice would be appreciated. I reconnected it to pass emissions,it squeezed through. Roger.
 

WillC4

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Aug 7, 2009
Messages
94
Location
Colorado
Corvette
'94 LT1 Green Coupe. 6-spd. All Bolt-ons.
You are correct that the plumbing for EGR and AIR is the same between the EGR valve and manifolds or headers.
Thanks for clarifying, I will give the company a call and tell them not to worry about the block off plates, and to be sure to keep the emission ports on top of the headers.

But to answer your question, O2 bungs are a couple of dollars and have someone weld them is pretty cheap and your car will run much better than w/simulators. Do not think sims are a good idea, if one injector starts leaking or something similar, how is the PCM going to know and compensate.

I am keeping the upstream O2 sensors, not very smart to remove those haha. Its that 3rd one that was originally behind the passenger side cat is what i want tune out. My exhaust is a 2-1-2 setup (Long tube headers, 3.5 inch Y-pipe, split again to two flowmaster mufflers) with no cat converter. I have a service manual for my specific year car, and the Check engine light will not illuminate. However, it does log a code, now does this affect the engine performance or not is still unsure to me. I dont want to risk any potential unknown damage this code is logging into the computer, so thats where the O2 simulator came to mind. I will look to see who can just delete the aftercat O2 sensor alltogether locally.
 

WillC4

Well-known member
Joined
Aug 7, 2009
Messages
94
Location
Colorado
Corvette
'94 LT1 Green Coupe. 6-spd. All Bolt-ons.
Hi all, boomdriver has me worried, I've blocked off my EGR to cure a miss at low revs in a high gear. Am I facing a catastrophe ? Any advice would be appreciated. I reconnected it to pass emissions,it squeezed through. Roger.


Boomdriver does have a valid point, but i think if you retune the car properly for it without the EGR, i wouldnt see much issue from my perspective.

In addition, and probably off topic slightly. But my friend has an 88 Vette vert as well, and he just recently carbed it, there are no emmisions on the car at all, but thats all mechanical tuning now, no computers to worry about it.
 

roger longman

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southern california
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1977 c3 orange ! 1988 c4 kinda purple 1991 'race
Boomdriver does have a valid point, but i think if you retune the car properly for it without the EGR, i wouldnt see much issue from my perspective.

In addition, and probably off topic slightly. But my friend has an 88 Vette vert as well, and he just recently carbed it, there are no emmisions on the car at all, but thats all mechanical tuning now, no computers to worry about it.
Whoa, I've just blocked off the EGR nothing else. I have a thread called...."why the miss" but nobody could answer the cause of my problem, maybe because I don't know enough. Roger. ;shrug
 

boomdriver

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87 z-51
Roger, sorry, I missed out on this somehow. Not to cause a bunch of worry about the EGR, but I think Will is right in saying that you can tune the system to do without it. For the OBD-1 on the L98 thats a custom prom as far as I know. Not really that big of a deal.
As for the "mis"...
I've had problem 'misfires' that were anything from the ign pickup module to new plug wires that caused it.
I wish that I could remember exactly where and how the EGR gases are introduced to the intake. Best guess is that there is the one cyl running rich from an injector. The smog report supports that. Blocking off EGR CAN alter the fuel/air ratio and maybe work to your advantage. When (trying) to think this thru, I see the EGR as cooling combustion (when its there) which could possibly result in a slightly richer mix and under a high load that will cause a misfire.Thats why EGR is only applied to certain conditions and not all the time.
Nows a good time to note that the OD is way to tall a gear to kick in under 55 mph. I'd reset the trans throttle cable so it does not grab OD until 55+ mph.
Blocking off the EGR could have leaned it out a bit, by forcing higher combustion temps that also mean a hotter burn.
The EGR valve MIGHT have been leaking a little causing your mis...

Best guess, I'd look at injectors or a leaking EGR as the true source of the misfiring. Loading up at low rpm in high gear just compounds the problem. Is it more like one stumble when throttle is applied while cruising in OD at 50 mph? or more of a steady mis until it gets to a higher rpm? A stumble is expected with the load at low rpm.

More often than not, a complete tune-up with cap, rotor, dist connection cleaning, wires and plugs solves the problem. Sometimes its the collection of things and not any single thing. I do know that mine hates aftermarket electonics and just loves Delco.

Did'nt mean to alarm you with the EGR. Blocking it off just means that its going to burn at the normal combustion temps all the time and IF you were doing any damage to it, you'd have a distinct knocking that would eventually damage a piston skirt. You'd hear something....
EGR helps to manage the combustion temps which in turn helps to keep the balance for proper emissions.
 

Kenny

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Nov 29, 2009
Messages
86
Location
Imperial,Mo
Corvette
93 Coupe Torch Red Daily driver
R

EGR helps to manage the combustion temps which in turn helps to keep the balance for proper emissions.

EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. In a gasoline engine, this inert exhaust displaces the amount of combustible matter in the cylinder. This means the heat of combustion is less, and the combustion generates the same pressure against the piston at a lower temperature

EGR is typically not employed at high loads because it would reduce peak power output. This is because it reduces the intake charge density. EGR is also omitted at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle. The EGR valve also cools the exhaust valves and makes them last far longer (a very important benefit under light cruise conditions)
 

roger longman

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southern california
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1977 c3 orange ! 1988 c4 kinda purple 1991 'race
Thanks boom and Kenny, The missfire/stumble occurs at low revs under any sort of load, in OD. I need to change down in order to accelerate at all, or even to keep going. Blocking off the line to the EGR enables me to just select OD,if I feel so inclined, leaving it there she drives fine,as she used to. If it is at all retarded it is not noticable (by me).Reconnecting the EGR for the smog test, went through at MAX on HC's at 15 mph, measuring 112, at 25 mph the reading was 74 with an allowable 86. What should that be telling me? Thanks for your help. Roger.
 

Hib Halverson

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95's I know are inbetween OBDI and OBDII, but 94's are strictly OBDI's.

Both 1994 and 1995 VIN P engines had partial OBD II capabillity. Both had the 16-pin DLC. Different levels of OBD II capability are present in those two model years. The ECMs set both 2 and 4 digit codes. Only the two-digit codes turn on the MIL. You need a scan tester to see the four-digit codes.

Be careful is you disable EGR without changing the calibration. Running and engine originally equipped with EGR without EGR usually may have the engine into detonation at part throttle.
 

WillC4

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Messages
94
Location
Colorado
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'94 LT1 Green Coupe. 6-spd. All Bolt-ons.
Both 1994 and 1995 VIN P engines had partial OBD II capabillity. Both had the 16-pin DLC. Different levels of OBD II capability are present in those two model years. The ECMs set both 2 and 4 digit codes. Only the two-digit codes turn on the MIL. You need a scan tester to see the four-digit codes.

Be careful is you disable EGR without changing the calibration. Running and engine originally equipped with EGR without EGR usually may have the engine into detonation at part throttle.

Thanks for the info on the "OBD 1.5" as i have come to call it now haha.

As far as egr, i am keeping it because i learned that the A.I.R system and the EGR system utilize the same plumbing. therefor my only primary concern at the moment is researching into O2 sensor delete or simulators for the single aftercat O2 sensor on the 94/95 vettes.
 
S

Steve40th

Guest
Thanks for the info on the "OBD 1.5" as i have come to call it now haha.

As far as egr, i am keeping it because i learned that the A.I.R system and the EGR system utilize the same plumbing. therefor my only primary concern at the moment is researching into O2 sensor delete or simulators for the single aftercat O2 sensor on the 94/95 vettes.
The 96 LT4 has no EGR, but uses the AIR system. Maybe a picture from someone can show the "difference" Also, tuning out the EGR is a simple click on any program for re-flashing your ecm year.
If you tune the "code" out and block off the EGR you wont have a major loss of power.
 

roger longman

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1977 c3 orange ! 1988 c4 kinda purple 1991 'race
The 96 LT4 has no EGR, but uses the AIR system. Maybe a picture from someone can show the "difference" Also, tuning out the EGR is a simple click on any program for re-flashing your ecm year.
If you tune the "code" out and block off the EGR you wont have a major loss of power.
Hi, How do I do that on my '88 Vette ?.....Roger.
 
S

Steve40th

Guest
Hi, How do I do that on my '88 Vette ?.....Roger.
Ask any chip tuner to send you a chip, deleting EGR code. Then you block off the egr with a plate. I amsure L98 EGRs are the same as LT1's physical design, so blocking it off shoudnt be difficult. But it isnt as easy to get to the EGR on an L98.
 

roger longman

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1977 c3 orange ! 1988 c4 kinda purple 1991 'race
Ask any chip tuner to send you a chip, deleting EGR code. Then you block off the egr with a plate. I amsure L98 EGRs are the same as LT1's physical design, so blocking it off shoudnt be difficult. But it isnt as easy to get to the EGR on an L98.
Hi Steve, I've blocked off the line going to the EGR but some of the guys say I will get problems and a friend who had done the same needed to replace the EGR to get through emissions......Roger.
 

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