I have a 1975 F150 with a 360 that the PO did some major vacuum line reduction renovation. There is a line from the front left of the carb to the distributor. A trunk at the rear of the manifold that goes to the egr, transmission module, and brake booster. Last is the PCV line off the carb. The temperature conrolled PVS is capped. When I look at diagrams it lists several check valves and modules none of which are on the truck now. I have also read conflicting reports of where the distributor advance should be fed from manifold, PVS, and card. What is your opinions on how I can best set this up given what little I have left to work with?

 

I don't know much about the smog stuff, but a stock engine will like ported vacuum better than manifold vacuum. Do a search for "ported vs manifold vacuum". There are more detailed explanations than I can give.

 

I am pretty sure you want manifold vacuum, not ported vacuum.

Is the truck running poorly as is? Do you need to rehook everything for emission reasons? Has any other emission parts been removed? My experience in the 73-79 forum and my experience with a 1979 F250 smog truck, it seems like you need ALL of the emissions parts working properly, or deleting everything completely. Some people thought plugging things here and there were fine.

 

Actually it can vary. One would do well to have a vacuum gauge in the truck and then experiment running ported vs. manifold to see what happens. Mileage, coolant temperature to name a few.

 

The truck was running awful. Replaced timing chain and it was better for a while. Then the dizzy went bad. I replaced it and did the duraspark conversion. Also replaced plugs and checked resistance of plug wires. Its running better but still idles rough and shakes on and off. I do have a vacuum gauge and was preparing to check for leaks when I realized how haved up the vacuum system is.

I dont need the smog equipment but the egr does open and close with vacuum. The distributor advance is currently fed by a port on the carb but it has constant vacuum at idle so I guess that is not the ported vac then? I did read the argument for manifold vs ported vac and didnt reach an understandable conclusion. If it uses ported vac it should have no advance at idle correct? If I used manifold vac I would need to set the curb idle with the vacuum hooked up?

 

Well, if your vac lines are not hooked up, then your thermactor is not working, so your egr is not doing anything, and your cat is probably burning up because your engine is not running rich/or lean as it should. Your truck can run awesome with full emissions, or with zero emissions. It will not run right with 1 foot in and out.

 

For the OP:

The vacuum hose to the distributor should be off of one of the "ported" vacuum switches off of the carb's body. The PCV reads like it is plumbed correctly. Same goes for the brake booster and transmission, that should have manifold vacuum. These are basics.

Now, one major question to ask is where do you live and do you need the emissions components to pass CA SMOG or some other state inspection? Reason I ask is that in the 1970's most of the emission equipment was add on equipment that helped with emissions, didn't do much if anything positive for performance.

The temperature control switch that is threaded into the intake, in contact with coolant (the TVS), is usually plumbed in line with a ported vacuum source (PVS) off of the carb, going to both the "dump valve" for the air injection / SMOG / "thermactor" pump AND also to the EGR valve. The EGR valve is not meant to be open at idle or cold conditions. Same goes for the air injection system. These two mentioned systems are usually defeated by simply un-hooking the vacuum lines to them. You can search pros and cons to doing so.
Where it gets complicated is for high temperature setups- typically the TVS has three ports rather than two.
The check valves and resistors are to help smooth the operation of the vacuum circuits.

One last item I almost forgot about is the EVAP system, which depends on vintage. My '73 canister is very much different than my '79 I used to own. The later model 70's trucks had a canister valve that accepted gas tank and carb vapors with a what I remember was a PVS signal through the TVS, yet used manifold vacuum (with a restrictor) to purge the canister.

First things first, do you know the emissions calibration code? Should be on the valve cover label, if it's still there and legible. Using the code, you can track down the original diagram. I used to have all the diagrams for '73-7'9 trucks, but gave them to M1illion (Dennis) about 12 years ago- in other words, I still have access. Typically, the lighter the truck, more emissions components were originally installed. Do you need them operating? Well, that all depends.

 

Thank you for all of the info! I am in Ohio and not in an emissions check county. Sounds like the egr is definitely wrong and I will just cap it. There is no air pump and no canister either I believe. I think the distributor is also hooked wrong. The ported vacuum from thw carb body should have little to no vacuum at idle correct? I will have to check the valve cover sticker. Its there but I wasnt aware of the emmissions codes.

 

Yes, there should be a code if the old, original sticker is still there- typically it's a 3-5 digit code, if I recall correctly.

Yes, the ported vacuum switch off of the carb will not have a vacuum at idle. Your dizzy should not have the vacuum advanced at idle. If you have timed your motor with the dizzy hooked up to manifold vacuum, you need to re-time with it not hooked up AND it should be hooked up to the carb for normal running conditions. You also set the idle without vacuum to the dizzy.

 

Problem solved! Thank you to everyone for all the help! I disconnected and plugged the line to the egr off the manifold. It was an improvement. The ported outlet had vacuum at idle but after disconnecing the egr I was able to adjust the idle down where the vac went to zero. She runs great now! This old 360 runs better than any of the 351 and 400s I have had.

I did check whats left of the sticker and I think it reads 658. Does that sound right? Sticker also said 6BTDC. I am runnng 10 now and the new timing set is from a 60s model to eliminatet the 4deg retardation. Any reason for me to set back the timing to 6?

 

Glad to read she is running better. You can Google a vacuum diagram for a 1975 F250 with a 360. I didn't find much that is specific to the 360 (doing a quick glance), but I did find some of the old diagrams do come up for 351's and you can see what the code (and diagram) looks like. I'd think your code would be something like "65-B-0." Seems pointless to dig to hard on this now that you have her running fine.

Shouldn't be a problem running at 10*, you'll see better performance with a little more advance, but it might ping a little when you get on it if you're running lower octane gas- but who knows what sort of compression your motor has. In the '70s, the automakers tended to reduce compression, retard the ignition timing, cam timing, and add components like the air injection and EGR to improve what they could on emissions, yet engine performance just suffered. Believe it or not, things just got worse in the '80s until advances came in sensor technology and computer control in the late '80s.

You have to realize that Ford simply came out with a heavier truck, the F-150, to help skirt emissions requirements. By the early 80's the F-100's were being phased out.

 

Good info is this thread, thanks to decaruby

One thing I will interject, but it's just a piece of info, not that you should change anything at this point if it's running great.

The EGR can help with mid-range pinging on motors that actually have enough compression and spark advance to ping It can also help with highway gas mileage, but with a 360, you're never going to notice the difference.

You could probably advance the timing even more, but there will come a point where it won't start when hot because the ignition will actually push back against the starter. If I remember correctly, I ran 12-14 on my stock 360 in my highboy. But, on the other hand, it can make it harder to get rolling from a dead-stop with a stick (especially a 435NP tranny that you start in 2nd gear) but since yours is an automatic, you could try going up another 2 degrees or so.

Either way, glad to hear that you got it running right, and hopefully it gives you lots of miles in the future

 

Thank you again for all of the help! I absolutely love this site. Truck is still running good and passed the test this weekend. Drove around 150 miles and hauled 1300 pounds of old carpet and padding to the junk.

I think the spec sticker is too far gone to find that emissions code. But I am so happy with her now that I will probably leave her be for now.