EGR Conversion?
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EGR Conversion?
So, my 81 4.9 came with the EGR that relies on backpressure from the exhaust to operate. Someone a long time ago removed the cat, and now I believe its whats preventing me from using vac advance on the dizzy. The way I understand it, the EGR flow reduces combustion temps, allowing for additional timing and performance. My question is, is it possible to just change the EGR out with one of the non-backpressure reliant ones? Right now I have to run with the EGR and vac advance capped off to prevent knock under acceleration on the highway. I also discovered that the check valve for the smog pump that enters under the egr adapter has apparently failed, and lets exhaust flow out (can't be helping).
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the EGR is a diaphram that controls the amount of exhaust gas that is allowed back into the combustion chamber by engine vacuum. The tube that comes from the exhaust manifold is the source of the exhaust gas. There's a vacuum line that goes to the EGR that actuates the EGR.
There's is a specific port on your carb labeled "SPARK" that the vacuum advance goes on to.
i removed my smog pump and egr and had the same issues you're having until i put the vacuum advance on the spark port and reset base timing to 10*.
hope this helps.
There's is a specific port on your carb labeled "SPARK" that the vacuum advance goes on to.
i removed my smog pump and egr and had the same issues you're having until i put the vacuum advance on the spark port and reset base timing to 10*.
hope this helps.
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Interesting, my carter doesn't have any labeling on the ports (I looked while I was rebuilding it). Mine has three ports on the passanger side, and a WOT one on the driverside. The three on the passangerside are arranged like this: * . * and my dizzy is connected to the one in the middle. Does yours pass through the VCV "tree", or just go directly to the dizzy? Any delay valves, check valves, or other gizmos in the line, or just a straight vacuum connection to the carb? Heres an old pic before I replaced all the lines and rebuilt the carb.
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Its hard to figure out how all these vac lines are supposed to go, with all the check valves and stuff in there. Mine had 2 lines going to the dizzy which seemed to be stock, but the vac diagram under the hood only shows 1. I'm pretty sure that if I get the EGR working, that the vac advance will work better.
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From: Virginia
With the engine warmed up, rev the engine and see if you feel vacuum at the hose that feeds the egr.
Then with the engine idling, see if you can get your fingers up through the slots in the egr valve and push up on it. The engine should run rough and may stall.
If it passes the above tests, I would leave the egr alone. It is not working as good as it should with less backpressure, but it will still work some.
The biggest change I did on a 351w I had which was in the same boat, was put a 180 degree thermostat in it. That really helped the pinging alot. You can also play with the timing a little bit, and you can decide if you want to turn it way back and hook the vacuum on the dist back up, or set the initial timing high and leave it disconnected and or get an adjustable vacuum advance unit.
Then with the engine idling, see if you can get your fingers up through the slots in the egr valve and push up on it. The engine should run rough and may stall.
If it passes the above tests, I would leave the egr alone. It is not working as good as it should with less backpressure, but it will still work some.
The biggest change I did on a 351w I had which was in the same boat, was put a 180 degree thermostat in it. That really helped the pinging alot. You can also play with the timing a little bit, and you can decide if you want to turn it way back and hook the vacuum on the dist back up, or set the initial timing high and leave it disconnected and or get an adjustable vacuum advance unit.
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I think I allready have a 180 thermostat in there, I told them I wanted the factory one at the parts store, and they said it was a 180. If I push the EGR, it will very nearlly stall the engine. My understanding of these particulair EGRs though, is that even with vacuum applied, it will not open on its own without backpressure (mine has the felt filter on the bottom). I allready have the timing set lower than I'd like (kinda sluggish taking off) when I raise it, it knocks when accelerating on the highway. I'm wondering if the springs in the dizzy are worn out, and instead of the vac advance raising the timing slightly, it is raising it waaay too much?
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From: Virginia
Pushing up on the egr and the engine wanting to stall confirms your exhaust passages for the egr are open. I would still get it warmed up though, and make sure you have vacuum at the hose when the engine is revved. It probably has a water temp vacuum switch in the line that could be bad, so it's good to confirm you have vacuum.
You still will have some backpressure, and the valve will still crack open some. But it won't open at all with no vacuum on the hose.
You still will have some backpressure, and the valve will still crack open some. But it won't open at all with no vacuum on the hose.
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you have a dual vacuum advance, one pulls more advance the other retards the timing.
as for all hte check valves and vacuum spider web, i pulled it all off when i pulled the smog pump and stock air cleaner.
the only vacuum i have hooked up are
dizzy advance
brake booster
PCV
line going to the "T" on the firewall
as for all hte check valves and vacuum spider web, i pulled it all off when i pulled the smog pump and stock air cleaner.
the only vacuum i have hooked up are
dizzy advance
brake booster
PCV
line going to the "T" on the firewall
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I was wondering if the truck had a two stage advance dizzy, but the one thats in there now is not. The vacuum diagram on the truck only shows one connection going to the dizzy from "S" on the carb. I have not been able to locate a calibration code that conforms to anything. This truck is smog exempt in my area, but I think they are supposed to visually check that the equipment is still in place. I have also heard that the EVAP system, EGR, and VAC advance working properly increases mpg, so i'd prefer to keep it functioning. I may need to take a few pics of some of the wierd check valves I found (mainly one) and see if ya'll can identify them. There is one that is the diameter of a quater, gray on one side, black on the other, and says "carb" on one side "dist" on the other. There is no mention of this anywhere on my diagram between the carb and dizzy.
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