- Location
- SLC UT, USA
Background: Swapping 1991 GM 350 TBI w/ TH700-R4 into 1990 YJ 4.2l w/ AX-15 & NP231. Must pass Davis County emissions standards.
I know the topic is tired, but I've tried to do my homework before asking for help. From what I've gathered, in order for a vehicle with a transplanted engine to pass emissions, you have to demonstrate that the emissions output of the vehicle does not exceed the original engine's emissions output. I've taken this to mean that if the original engine has EGR, PCV, catalytic converter, and air injection, that the replacement engine must have the same (assuming the engine is equally or more efficient than the original). Please correct me if i'm misinterpreting this.
If my interpretation is correct, then I assume a TBI 350 GM is more efficient than the 4.2l because I've read and heard that the design of the intake, exhaust, and head on the 4.2 is a model for inefficiency while the SBC with various heads is a fairly efficient design. Although I've heard/read this repeatedly, it's too weak for me to base a deci$ion on and would appreciate some help/guidance from somebody who is more knowledgeable and experienced than I.
Thinking ahead under the above assumptions, I plan on using the EGR, PCV, and catalytic converter spec'd for the donor engine. Air injection is apparently handled differently on the GM than it is on the Jeep. Correct me if I'm wrong about any of the following (I'm emissions-ignorant, but trying to learn fast, so I may have misunderstood what i've read). The GM uses a garden-variety belt-driven air pump to force air drawn from the air cleaner into the catalytic converter. Other than a check valve and a ECM-controlled solenoid valve, it's pretty simple compared to the system on the Jeep. The Jeep does not have an air pump and instead uses vacuum (I'm guessing here on the actual mechanism that draws air into the system) to inject air into the exhaust system at two points. The first point (upstream) is somewhere in the exhaust manifold and the second is in the cat itself. A computer-controlled solenoid bypass valve delivers air to the exhaust manifold at cold startup and once the engine has warmed, switches the delivery to the catalytic converter. I realize I don't have a great understanding of this, so please have mercy on me -- I'm trying. A few hours ago I couldn't tell you what any of the emissions components do and couldn't tell an EGR valve from a charcoal canister.
Now, what I'm trying to figure out, before I really dig in and figure out all the details about the Jeep air injection system, is if I can use the simpler air-pump system from the GM and pass emissions.
Although I want to give it a good shot and am willing to spend a few bjucks to do it right, I'm getting kinda PO'd at how difficult the unclear/vague laws are to interpret and am tempted to pick up and move to some county where I can just run headers out the fenders in spite.
Any help is appreciated.
Cheers
PS: Is anybody aware of any governmental resources that can help me with this? I mean is there a referee station ro something where I can ask for official advice/guidance on what I need to do to pass?
I know the topic is tired, but I've tried to do my homework before asking for help. From what I've gathered, in order for a vehicle with a transplanted engine to pass emissions, you have to demonstrate that the emissions output of the vehicle does not exceed the original engine's emissions output. I've taken this to mean that if the original engine has EGR, PCV, catalytic converter, and air injection, that the replacement engine must have the same (assuming the engine is equally or more efficient than the original). Please correct me if i'm misinterpreting this.If my interpretation is correct, then I assume a TBI 350 GM is more efficient than the 4.2l because I've read and heard that the design of the intake, exhaust, and head on the 4.2 is a model for inefficiency while the SBC with various heads is a fairly efficient design. Although I've heard/read this repeatedly, it's too weak for me to base a deci$ion on and would appreciate some help/guidance from somebody who is more knowledgeable and experienced than I.
Thinking ahead under the above assumptions, I plan on using the EGR, PCV, and catalytic converter spec'd for the donor engine. Air injection is apparently handled differently on the GM than it is on the Jeep. Correct me if I'm wrong about any of the following (I'm emissions-ignorant, but trying to learn fast, so I may have misunderstood what i've read). The GM uses a garden-variety belt-driven air pump to force air drawn from the air cleaner into the catalytic converter. Other than a check valve and a ECM-controlled solenoid valve, it's pretty simple compared to the system on the Jeep. The Jeep does not have an air pump and instead uses vacuum (I'm guessing here on the actual mechanism that draws air into the system) to inject air into the exhaust system at two points. The first point (upstream) is somewhere in the exhaust manifold and the second is in the cat itself. A computer-controlled solenoid bypass valve delivers air to the exhaust manifold at cold startup and once the engine has warmed, switches the delivery to the catalytic converter. I realize I don't have a great understanding of this, so please have mercy on me -- I'm trying. A few hours ago I couldn't tell you what any of the emissions components do and couldn't tell an EGR valve from a charcoal canister.
Now, what I'm trying to figure out, before I really dig in and figure out all the details about the Jeep air injection system, is if I can use the simpler air-pump system from the GM and pass emissions.
Although I want to give it a good shot and am willing to spend a few bjucks to do it right, I'm getting kinda PO'd at how difficult the unclear/vague laws are to interpret and am tempted to pick up and move to some county where I can just run headers out the fenders in spite.
Any help is appreciated.
Cheers
PS: Is anybody aware of any governmental resources that can help me with this? I mean is there a referee station ro something where I can ask for official advice/guidance on what I need to do to pass?
