Greetings all!

I have a 79 F150 4x4 with a smoged 351m and most of the smog stuff is either disconnected or plugged. I live in an area where emissions testing is NOT required and I'd like to get all that crap off the engine.

Since most of this stuff seems to be connected the the vacuum system, I'm afraid that it won't run if I just rip it all out. I'm thinking that all I need to keep is the vacuum advance to the dist., the line for the choke, and the resevoir canister (although my 460 doesn't have a resevoir, so maybe I don't need that)

Is that right or even close?

Any thoughts would be appreciated.

Kevin K.

 

I removed it all from my 81 F-250. Just make sure you hook the dist up to the ported vacuum on the carb, not constant vacuum. I would keep the canister there, it's not hurting anything.

I took off the air pump and put a plug in the manifold. I also took out the temperature controled vacuum switches in the t-stat housing just to make it look better. I left the EGR spacer on, but pulled the vacuum lines off. driving 55-60 I get 15.5-16 MPG running the timing at 8 BTDC. With out the EGR you might have to go up a couple jet sizes to keep it from running lean, but so far I have been ok with the stock jetting.

Hope that helps,
Jerry

 

That helps a great deal! And, it's just what I wanted to hear.

What about the choke? This may sound dumb, but is that run off of a vacuum from the carb or is it electronic? I'm not sure what I have but I want to put a manual one on.

Thanks for the info!

Kevin K.

 

Here's some info about the choke:

http://home.earthlink.net/~bubbaf250...b/carb02a.html

 

Leave the choke alone. It's electric, has nothing to do with smog, and runs off an auxiliary feed from the alternator.

Leave the EGR. It hurts nothing. Most of them are non operative or plugged up, anyway.

Removing the air pump can cause the catayltic converter to get cherry red. Don't do it unless you are going to remove the converter too.

The rest of the stuff is easy. All you need are the vacuum lines to the distributor advance and the PCV valve. All the rest can be removed and capped off.

Be sure you don't remove vacuum lines that control heater valves, or other accessories.

I find that the best way is to remove things one at a time, and check the results. That makes it easier to restore if you take off something you needed.

 

I don't want to start a argument, but removing the air pump will not hurt the cat. The air pump is supplying the oxygen to burn the fuel in the cat. so with out it the unburnt fuel just goes out of the tail pipe. Also, the diverter valve on the air pump is controlled by vacuum, so once you pull the lines it just venting to atmosphere anyway.

I agree, most EGR systems on older vehicles don't work, but if your going to pull part of the system off, you might as well pull it all off.

 

Pulling or disabling the EGR will cause EGR ping. You can read about it in at least a hundred posts here.

Remove the air pump. The air pump was set up to heat up the cats faster with a rich mixture in the engine. Sometimes the rich mix will plug the cats after a while.

 

The AIR pump does more than just heat the cat up faster. It supplies the free oxygen (O2) that the cat needs to do its cat thing (i.e., catalyze CO and HCs into CO2 and H2O). Without an AIR pump, the cat will do very little.

Some Thermactor diverter valves send air into the system constantly when you disconnect their vacuum signal(s). That will cause massive backfiring under closed throttle deceleration.

You can avoid the increased tendency to ping without EGR by enriching the carb's mixture. EGR was invented to compensate for over-lean mixtures, which were used to reduce CO and HC emissions before catalytic converters were developed.

My preference for power with decent emissions is to keep the Thermactor AIR system (smog pump, diverter valve) and catalyst, get rid of (or just disable) the EGR, and retune the carb to get more power and avoid pinging.

Even if you live in an area with emissions testing, a good smog pump and cat will hide a multitude of sins.

 

I will agree with the premise that emissions tuning is hurting the performance of the 351m. But I don't see any advantages to removing any of the emissions or so-called 'smog' equipment.

A guy can on this forum a while back and explained the strategy of the tuning of 351m and 400 engines. There are two important things that have a big impact on performance of these engines. The biggest factor is the retarded timing of the camshaft. You can do youself a lot more good by fixing the cam timing than by trying to remove anything. The other big factor in performance is the jetting of the carb; it's too rich. Strange as it sounds the rich jetting was part of the Ford factory tuning intended to reduce emissions!

Here's how it was supposed to work.

By retarding the cam timing (a lot!) the engine's intake charge gets diluted. The exhaust valve is still open when the piston is on the intake stroke and some exhaust gas is sucked back into the cylinder. Thiis dilution of the intake charge with inert exhaust gas causes the air/fuel mixture to burn more slowly and to have less temperature when it's burned (the heat from the combustion is spread out over a larger volume of air). The lower combustion temperature results in reduced Nitrous Oxide emissions.

Obviously, any amount of the combustion gasses that is exhaust cannot be used to create power, so the retarded cam is causing a loss of power. From what another person who posted information on this web site said, the 351m cam is a pretty decent performance part. It would have to be, it has to overcome the loss of power caused by being retarded.

The other technique that Ford used to reduce Nitrous Oxide emissions is to jet the carb rich. As you know, a lean mixture burns hot. A rich mixture burns cooler. They cleaned up the HydroCarbon emissions with the air pump and the cats.

So, obviously, if you take the 'smog pump' off you will be trying to push a lot of unburned HydroCarbons through the cat. It will get plugged up.

By the way, this rich mixture and the sooty exhaust has the ironic side effect of gumming up the EGR valve.

Also, by the way, if you remove the EGR, you will have to get the distributor fixed to correct the timing. If you don't, it will ping at part throttle and if you try to turn the distributor back to 'cure' the ping, you'll kill the performance. Now you're back to square one.

So what do you do? Glad you asked. Put a new timing chain on there and set the cam back to a straight-up setting. Change the carburetor or re-jet the carb to lean it out. Clean the EGR valve. Leave all the other stuff on there. It really doesn't hurt performance, it will improve gas mileage, and it will make your engine last longer.

I really hope you do this. It's a little complicated, but it will give you the performance you wanted, and the gas mileage you didn't know you could get.

 

Well, I did it anyway.

I agree that a functioning smog setup is better left alone. However, as I stated in the original post, the PO had plugged most of the hoses with screws, and disconnected almost everything else. The air pump doesn't have a belt on it and the pulley won't turn for anything.

I left the EGR as it was plugged anyway. I also left the big hose going from the front of the carb to the resevoir, and connected the VA to the carb.

The choke had a wire going to it and a vacuum hose coming out the bottom. The vac hose is not connected to anything though. Anyone know where that's supposed to go? Manifold heat exchanger, maybe?

Anyway. The truck starts and runs better that it ever has. Thanks for all the help!

BTW Bubba, great article on the choke and throttle positioner!

Kevin K.

 

I've worked on late 70's and early 80's engines before. They're a nightmare of hoses, vacuum switches, check valves and vacuum motors. I completely understand why someone would take that mess off. It's unreliable and hard to troubleshoot.

 

At which point it will turn cherry red, as I correctly stated above.

 

I've been doing this for a long time, trust me, no air pump, no fire in the cat. we used to play with a Mk VIII at the ford training center. if you ran it with one coil pack unplugged (it was part of a training test. they actually run pretty well on 4 cylinders), the cats would start to glow and burn the paint on the floor. to avoid the damage to the floor, the instructor pulled the fuse for the air Injection, they would stop glowing and cool off, you need oxygen if you want a fire. Thats what the air pump is there for. I you could get the cat to light off with out the air pump, ford wouln't have spent millions of dollars installing them.

On a side note. I ran a 78 LTD II with a 302 in it that had 2 cats right off the manifolds for 5 years with the air injection tube removed from the back of the heads, 2 bolts plugging the holes and no pump. I never plugged or melted a cat.

I also have not experianced any "egr ping" on any of my 70's or 80's cars and trucks. I have removed it from almost everyone I own. Yes you "might" have to rejet for it but most of the time they are fine the way they are. I have actually been able to advance my timing with no EGR and no problems. that included a 500 mile trip pulling a trailer. EGR gived the carburator the false sense of a smaller engine by filling the cylinder with exhaust gasses instead of air. less displacement means less air thru the carburator. That means it will pull less fuel. If everything is working properly you have no EGR at WOT, that means the carb has to deliver enough fuel at WOT to feed the whole engine. and since that is when most pinging problems happen. I would have to say that you will be just fine with the stock jetting.

 

KJ Kozak2,

If I am hearing you correctly, you have a vacuum line from the choke that goes nowhere? If the choke has a "thermal" dressed tube going to one side, the vacuum line should go to the carburetor at the top on the air horn. If it is not a thermal tube type, it will probably go to a multi-ported vacuum device/switch hooked into the heater hoses or near the water pump.

 

Gearhead,

Yes, there's a metal tube that comes out of the bottom back side of the choke. It has a short rubber hose on the end as if it was connecting two metal tubes, but I'm sure it's not original.

I'm not sure what a "thermal" dressed tube is, but I don't think that's what I have. And, since the vac port on the air horn has a large (3/8") hose going to the resevoir, I think the choke tube goes to one of the 6 ports on the thermostat housing, or to the resevoir.

However, I pulled all the hoses off the thermostat ports so hooking that one up probably won't do much. I could hook it up to the resevoir, though, and see if it does anything.

Thanks for the info!

Kevin K.