Ilovemountains

Ive been searching for a while but cant find any info or a write up on an exact procedure for removing all of the unnecessary vacuum lines and smog equipment. My new to me Trekker has a slight miss and I noticed that some of the lines are really old and cracked, or not tight any more. I found a copy of the diagram but if Im going to do this Id rather eliminate everything that I don't need, I would assume that the distributor is really the only thing that needs a vacuum line but Im not 100%. Does anyone sell block off plates for anything that can come out, OR should I just replace the lines and keep it stock since its a Trekker and under the hood has never been messed with, with the exception of tune up work. Im also going to replace the coolant lines while Im in there, the cooling system needs totally flushed so nows the time to do it! Thanks again! ~Matt

cdg

Well there are two schools of thought on this and there are various reasons why you should/shouldn't mess with the emissions on your truck. My experience is based on my dealings with 2 different 20R pickups.

On my desmogged 1980 there is an anti-backfire valve that seems to need to be hooked up for the truck to run right. The choke pulloff and dashpot plus the vacuum advance distributor sums up the vacuum system. That's about it - no other vacuum needed. It is much like the Canadian 1980 diagram...

As for what you can and can't block off on other models it would seem to depend a lot. I think some trucks have a vacuum switch on the fuel idle cut solenoid that would be needed for good driveability. I would think there may be an A/C idle up circuit if your truck is so equipped.

Make sure the vacuum fittings you leave behind are tightly capped. Leaving the evaporative canister disconnected is an option but you should use your judgment on how to let the gas tank vent.

Now physically blocking the EGR valve is the only one you really need to physically make sure is blocked off I think. I usually block 'em off by wadding up some ultra high temperature epoxy or muffler repair inside the valve on the exhaust feed side... Then you reinstall the valve but block off its vacuum supply. In this way you can be sure that the EGR system won't accidentally stick open, and you dont have to make any special block off plate.

Remember though that these systems were basically designed to work specifically together. For example the EGR system functions as an emissions control device, but it also lowers combustion temperature by decreasing the oxygen content in the combustion chamber. Blocking the EGR can cause pinging under severe duty. Every truck is a little different and I know that my 1980 could run on regular gas just fine and never ping. Just something to be aware of...

I would check very carefully for a vacuum leak first before desmogging your truck. If you choose to go that route, I would recommend buying about 6 feet of 1/8 vacuum hose and simply use all new hose. I have seen many instances where simply redoing all of the vacuum hose (if you can't find any obvious leaks) will fix your problems.

Off the top of my head I cannot think of any other profound tips.

Gov't Mule

On my 2WD 82 I completely desmogged it, only thing l need vac for is the distributor. I swapped over to a Weber 32/36, put an engnbldr cam in it, and a header and couldn't be happier with how well it runs. LC Engineering sells block-off plates.

83

Good advice (you've been through it cdg! i remember all my emissions, and especially egr research...). I'd almost say that if you want to run the most simple set up, get the weber. The stock carbs are meant to run, and run best, with everything hooked up. At least when it's working correctly...

ledzeppelin3270

Old thread, but I can't really find any more information about desmogging, I've done a Google search and looked on Pirate and this site but can't find a list of pros and cons about the desmog process. Could anyone help? Thanks

kawazx636

iTrader: (3)

Here's the trick...

JUST START YANKING OUT HOSES!

That's what I did. I pulled every single 7/64" vacuum hose out from under the hood. Took off anything attached to the EGR and got the block off plates from LC Engineering:

http://www.lceperformance.com/EGR-Bl...-p/1016009.htm
http://www.lceperformance.com/EGR-Bl...001.htmhttp://
http://www.lceperformance.com/Air-In...-p/1045014.htm

Slap on a Weber and Run your 2 vacuum advance lines from your distributor to your carb and intake manifold and you are done.

Pros:
1-No more jumbled mess of vacuum lines under the hood.
2-More power
3-Better fuel economy (mainly because the majority of Smog systems are clogged and don't work anyway - I gained 5 MPG after desmogging)
4-Smoother idle and acceleration
5-Less crap to fail
6-Easier adjustments

Cons:
1-Will not pass smog tests in some states
2-I can't think of a second one!