I have been busily trying to get to know my new old 1987 F250 and as it turns out the previous owner has removed a lot of stuff. So, here I am, trying to figure out where to find a few of those things..

The truck has a vacuum leak or six so I started out by following the vacuum hose diagram printed on the air cleaner box. I've located all the components listed except two:

Air Bypass Valve (not the Throttle Bypass Valve)
Air Check Valve

I would assume that they should normally be on the passenger side, pretty close to the firewall, but alas there is nothing that resembles either of these there on my truck.

In addition I can't seem to find the air purge solenoid valve that (I believe) should be located between the throttle body and the charcoal canister. On my truck, the charcoal canister has a line coming in from the fuel tank and one going straight to the throttle body, where it splits in two and connects on the upper and lower parts. Is it possible that a purge valve wasn't used on the 1987?

Any help would be greatly appreciated

 

The air bypass and diverter valves were usually mounted to a bracket to the side of the ignition coil.

My '87 does not have a canister purge valve either. I think early 302s did not use a valve here, so I wouldn't worry about that.

 

Were the HD trucks(anything bigger than a 1/2 ton) always that way? I know the later HD trucks were and I know they were setup different than the 1/2 ton trucks but wasn't sure about the early versions.

My '90 doesn't have a can purge valve either.

 

Weird... My 90 has it.
What's it called, evap purge solenoid valve or something.

 

Canister purge isn't it?

 

Thanks.

I had a quick look next to the coil and there is a thingy mounted next to the TAB and TAD solenoids, on the same bracket. Would the ABV and ACV be in one unit? It appears to have two ports on first glance...

 

The third solenoid is the EVR which controls the EGR valve. The diverter and bypass valves were combined in later years, but the diverter and bypass valves are separate on my '87.

 

Ah, yes, that makes sense. I thought i had the EVR one under control but I guess not. Well, I suspect that the previous owner has removed those two components then.

I will have a closer look to make sure though

 

So on your truck you have a diverter valve, a bypass valve and a check valve? Are they all supposed to be located close to the ignition coil? I can't find the bypass valve and check valve and it also seems that the vacuum lines going to those two items have been cut behind the engine. The diverter valve is also missing though I'm not entirely sure where to look for it as it's not listed on the vacuum hose routing diagram.

That said, there are a few other things missing from the vacuum hose diagram. The diagram shows four connections to the vacuum tree on top of the manifold but mine has seven connections of which one is like a tee piece that's blocked off. This might have something to do with the fact that I have A/C on my truck though.

Another vacuum related question... there is a hose, made of that flimsy aluminium looking stuff, coming out of the air intake, just before the air cleaner box. As far as I can tell this is a pre-warming hose. Is this supposed to connect to anywhere? Mine is not hooked up to anything, it's basically just a shoddy looking piece of flimsy aluminium looking hose that's just laying there facing the driver side exhaust manifold.

Phew

 

I might be telling you things you already know, but just so that we are on the same page, there is a check valve at the top of the crossover tube between the heads, and another on the line going to the catalytic converter. These are just mechanical devices to keep exhaust from pumping backwards through the air injection system. The bypass valve is controlled by the TAB solenoid and on my truck it is located just behind the smog pump. The diverter valve is just behind the intake plenum and is controlled by the TAD solenoid. The TAD and TAB solenoids and the EVR solenoid are the only things mounted near the coil, but I don't know if being an F250 changed any of that for component location on your truck.

It's been so long since I looked at the vacuum diagram I can't remember how many it shows on the vacuum tree.

You are right about the aluminum tube being the heat riser hose. There should be a sheet metal piece hose clamped to the exhaust manifold on the driver side with a connection point for the hose. I think '87 was the last year this was used and was one of only a few years where a heat riser was used with EFI.

 

Thanks again, EPNCSU2006, for lots of helpful information.

Well, the smog pump is still there and connected to the drivebelt. On my truck it's on the passenger side, pretty much the leftmost pulley when facing the front of the truck. As far as I can see it has two vacuum connections. Is that correct? On my truck one hose goes to a black canister (next to the charcoal canister), while there is no hose attached to the other connection (which is an elbow type connection facing backwards). I assume that the diverter valve should be somewhere in that line as it looks like it's supposed to go back to the catalytic converter. Which by the way is also missing.

With this in mind I have a couple of new questions:

1) Is there any point in spending money on getting hold of the diverter/bypass/check valves and cat. w/air tube in order to get the smog pump system back up an running? From what I've read, removing the smog pump and associated components shouldn't affect engine performance much at all and since AR doesn't bother to check anything related to cars...well, it just seems silly to spend money on it.

2) If I decide to completely remove the smog pump, would installing a new cat witout the air tube work as it should? I know I don't have to install one, but it would make me feel slightly better plus it might do the O2 sensor some good?

3) As it is right now, the smog pump just pumps air straight into atmosphere but it doesn't seem to be a vacuum leak as such since it seems to pull the air through that black canister and right back out again. Correct?

4) With the smog pump out of order, will it be okay to remove the TAB and TAD solenoids? They don't seem to do much at the moment but will the PCM "miss" them?

When it comes to the heat riser hose I'm at a bit of a loss as I can't seem to find that sheet metal piece anywhere. Nor a place where it would connect to. God knows what happened to that thing.

 

Solenoids need to stay. Computer needs them hooked up, but vacuum lines don't need to be there.
Smog pump can go, or just pump it into whatever connection is left when you get rid of the diverter valve thing. A few of mine pump air into the head connection. Some are vented, some are unhooked with shorter belt. Your choice. If you have emissions testing, here's my thoughts, pump it into the cat, or head, it will burn more, but if it fails, pump it after the cat... That way it dilutes the exhaust some.
The solution to pollution is dilution. More air in exhaust means less ppm.

 

Hmm. Then my guess is that the solenoids are normally closed, so with their vacuum hoses cut they simply never change position because the input never changes. Basically they will forever stay closed and that is a value that the computer needs in order to not throw fault codes. Am I on the right track?

The diverter valve and check valve is already gone and it will probably stay that way. I've considered removing the smog pump and canister in order to make the engine compartment a little more tidy and accessible, but if I get a new cat (because I'm a bit of a tree hugger deep down) I'd probably go for one that has an air tube connection based on your comments. Is there any chance that adding a cat will fail though? On my model it would be installed at the very back of the headers, after the O2 sensor. Well, if I re-modify the original headers to include a cat that is. Can I then assume that the smog pump doesn't affect the O2 sensor at all?

 

The solenoids stay hooked up to ecu because it knows when they are unhooked (different current) and will throw a code. Leaving them plugged in, but non functional, the ecu will be happy.
Air pump into the heads will effect o2 sensor. Air pump after the o2 sensor is better.
How can adding a cat fail... Not sure what you mean. If the cat gets super hot from you injecting extra air, you have an excessive rich problem. So really, I don't see an issue.
Cats won't effect the o2 sensor, because it's before the cat.