Emissions controls
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Junior User
Joined: Aug 2003
Posts: 50
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From: New Jersey
Emissions controls
I recently bought an 87 Bronco. It is not my daily driver, just something to have fun with and drive on the weekends. Anyway, the previous owners I think changed a lot of things on the motor. It is a 351w with a 4bbl, not sure if it is the orig motor, but I think it might be because the VIN says it came stock with that motor and a 4bbl. My question is, there is a pipe that runs across the back of the motor from one head to the other, and in the middle there is a fitting that is capped off, what is this for? It has a holley carb and an edelbrock performer intake. And there is a plate that is bolted onto the intake to the left of the carb(looking at the front of the motor). Did these motors come stock with this intake and carb setup? What is the hole the plate is blocking off used for? I would like to firgure this out because I want it to beable to pass the emissions test at inspection here in NJ. I haven;'t taken it yet. Any help would be greatly appreciated.
Senior User
Joined: Aug 2003
Posts: 122
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From: kansas
Emissions controls
That pipe is where the air pump was supposed to blow air into the heads which is internally connected to the exhaust ports of the head. The plate is where the EGR valve mounts. Both of these pollution devices may have to be on there to pass emission test. But neither one will effect engine performance if left off or blocked off. EGR(exhaust gas recirculate) lets exhaust gas enter the intake to reduce emisions. But exhaust gas has very little oxygen in it. No oxygen means less of a bang when cylinder fires.Air pump blowing air into exhaust is only for the sake of the catalytic converter working right.
Senior User
Joined: Jul 2004
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From: Culpeper, VA
Yeah, the pipe on the back of the engine is called an air injection pipe and it is part of the thermactor system. It should be connected, in some way, to the thermactor pump (or "smog pump"), if your bronco is equipped with one. The way it works, it injects fresh air into the exhaust to further oxidize any remaining pollutants. I don't know the details of the system, but i remember reading about it in the Haynes manual. You will probably need it connected in order to pass the emissions test.
Last edited by PyroBandito; Jul 24, 2004 at 07:36 AM.
Posting Guru
Joined: Dec 2002
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From: Remsen, NY
Originally Posted by circledirt
That pipe is where the air pump was supposed to blow air into the heads which is internally connected to the exhaust ports of the head. The plate is where the EGR valve mounts. Both of these pollution devices may have to be on there to pass emission test. But neither one will effect engine performance if left off or blocked off. EGR(exhaust gas recirculate) lets exhaust gas enter the intake to reduce emisions. But exhaust gas has very little oxygen in it. No oxygen means less of a bang when cylinder fires.Air pump blowing air into exhaust is only for the sake of the catalytic converter working right.
I disabled the EGR on my '91 with the 300 and it pinged a little under load (the truck wasn't worth fixing it), and on my newer '95 351w the EGR was stuck, and it pinged badly. A replacement EGR valve fixed the pinging problem nicely.
Senior User
Joined: Jul 2004
Posts: 125
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From: Culpeper, VA
In order to disable to disable the EGR system without causing problems, you need to disable the EGR valve so that it doesn't open. Just remove the vacuum tube from the valve and plug it. The sensor must remain hooked up, so that the computer knows the EGR valve is closed and doesn't compensate. I did this on my 89 F-150 without problems. There may be a preventative measure in the newer trucks.
