Misfire, wont smog test. Need some advice

[Rham243]

Hello all, i have a misfire on my 85" f250 with the 460 and it wont smog. Yes, I am in California and still have to smog this thing. What's worse is that it cant even be tested because of the misfire so I don't have any failed test numbers to work off of. I tried a couple different smog stations and they are all saying it is giving a diluted sample and that they cant even run the test. At first i thought I had an exhaust leak but i had everything checked out by a muffler shop, and there were no leaks. The exhaust system looks good. The engine does run really rough at idle and misfires so the smog shops said the misfire is most likely the cause. I replaced the carb and adjusted the idle but this didn't seem to change anything.

Really just looking for some advice on some things I can try at home to diagnose and maybe figure out what is causing the misfire. I am not a mechanic so some simple (break it down like I'm 5) explanations/steps to try would be much appreciated.

I have done online research on misfires but every thing i can find just says to hook up a scanner and see what codes its throwing and obviously i can't do that with this so that's why I am turning here for help.

Some pics attached. Thanks!

[Gary Lewis]

Welcome to the forum.

But in the email I just sent you I specifically said "Please go to the New Members Start Here folder, read the guidelines, and then start a new thread/topic in that folder about yourself and your truck." That is because I need to you read the guidelines, which are posted on the New Members Start Here folder. We hold everyone to those, so need you to read them.

Once you've done that I'll come back to respond to this post. In the interim I'll be thinking about your problem.

[Rham243]

Welcome to the forum.

But in the email I just sent you I specifically said "Please go to the New Members Start Here folder, read the guidelines, and then start a new thread/topic in that folder about yourself and your truck." That is because I need to you read the guidelines, which are posted on the New Members Start Here folder. We hold everyone to those, so need you to read them.

Once you've done that I'll come back to respond to this post. In the interim I'll be thinking about your problem.

Thanks Gary, sorry about that. I read the guidelines and posted an intro post.

[85lebaront2]

Ok, first thing to look at are all the vacuum lines, especially the large canister purge hose, for some reason Ford thought having a soft 3/8" hose make a sharper than 90° bend into a fitting with manifold vacuum on it was a good idea. Second, disconnect the vacuum to the EGR valve, if the engine smooths out, then you have an issue in the vacuum lines (Lord help you on that). Distributor will have vacuum at all times, except the primary is through a restrictor, the cold and overheat different thermal vacuum switches bypass the restrictor. Also check that the PCV valve hasn't come apart.

If you find nothing obvious, start the engine cold and carefully check the EGR valve area for getting hot quickly with no vacuum connected. If you know a shop or a friend with one of the older ignition scopes check the plug patterns, a lean cylinder will show up as a high spike. Everything sounds like a vacuum leak causing one of more cylinders to be lean. An unlit propane torch can be used to find vacuum leaks by passing it near gaskets. I will ask one question, when you replaced the carb, did you pull up the spacer and replace the lower spacer to intake gasket?

If you need it, I do have access to the emission diagrams, all I need is the code number from the label either on the left valve cover or radiator support.

Very nice looking truck! From the engine picture yours isn't as cluttered as mine was, dual air pumps and enough piping on top of the intake for two engines and the "spiders" on each exhaust manifold.

[Gary Lewis]

Yes, there are no codes to pull 'cause the system has no computer.

Things I can think of that would cause a miss at idle include:

• Blown power valve: There's an enrichment valve in that carb that can blow if there's been a backfire, and it'll leak gas into the intake. If it does that the idle will be very rich and could cause it to run very roughly. Go to Documentation/Fuel Systems/Carbs Chokes & EFI/Holley 4180C to see documentation on that carb which should show the power valve.

• Bad plug or plug wire(s). I think I'd start here and replace these.

• Bad cam: This is more difficult to determine, so we should think of the other things first.

I'm sure others will come along with more/better ideas soon.

[Gary Lewis]

Thanks Gary, sorry about that. I read the guidelines and posted an intro post.

No prob. And I see Bill beat me to responding to the problem. Trust him. He ran a carb/ignition shop for decades and has forgotten more than I know about these trucks.

[Rham243]

Ok, first thing to look at are all the vacuum lines, especially the large canister purge hose, for some reason Ford thought having a soft 3/8" hose make a sharper than 90° bend into a fitting with manifold vacuum on it was a good idea. Second, disconnect the vacuum to the EGR valve, if the engine smooths out, then you have an issue in the vacuum lines (Lord help you on that). Distributor will have vacuum at all times, except the primary is through a restrictor, the cold and overheat different thermal vacuum switches bypass the restrictor. Also check that the PCV valve hasn't come apart.

If you find nothing obvious, start the engine cold and carefully check the EGR valve area for getting hot quickly with no vacuum connected. If you know a shop or a friend with one of the older ignition scopes check the plug patterns, a lean cylinder will show up as a high spike. Everything sounds like a vacuum leak causing one of more cylinders to be lean. An unlit propane torch can be used to find vacuum leaks by passing it near gaskets. I will ask one question, when you replaced the carb, did you pull up the spacer and replace the lower spacer to intake gasket?

If you need it, I do have access to the emission diagrams, all I need is the code number from the label either on the left valve cover or radiator support.

Very nice looking truck! From the engine picture yours isn't as cluttered as mine was, dual air pumps and enough piping on top of the intake for two engines and the "spiders" on each exhaust manifold.

Thanks for this! Where can i find the large canister purge hose, will this be on the emission diagram? Also, to answer your question, i did replace the spacer when i replaced the carb. I bought the carb from National Carburetor and it came with a new spacer.

I just ran it and pulled the vacuum from the EGR valve (or what i thought was the EGR, not sure) and no change.

Here is the label for the emission diagram:

 

[85lebaront2]

Ok, first thing to look at are all the vacuum lines, especially the large canister purge hose, for some reason Ford thought having a soft 3/8" hose make a sharper than 90° bend into a fitting with manifold vacuum on it was a good idea. Second, disconnect the vacuum to the EGR valve, if the engine smooths out, then you have an issue in the vacuum lines (Lord help you on that). Distributor will have vacuum at all times, except the primary is through a restrictor, the cold and overheat different thermal vacuum switches bypass the restrictor. Also check that the PCV valve hasn't come apart.

If you find nothing obvious, start the engine cold and carefully check the EGR valve area for getting hot quickly with no vacuum connected. If you know a shop or a friend with one of the older ignition scopes check the plug patterns, a lean cylinder will show up as a high spike. Everything sounds like a vacuum leak causing one of more cylinders to be lean. An unlit propane torch can be used to find vacuum leaks by passing it near gaskets. I will ask one question, when you replaced the carb, did you pull up the spacer and replace the lower spacer to intake gasket?

If you need it, I do have access to the emission diagrams, all I need is the code number from the label either on the left valve cover or radiator support.

Very nice looking truck! From the engine picture yours isn't as cluttered as mine was, dual air pumps and enough piping on top of the intake for two engines and the "spiders" on each exhaust manifold.

Thanks for this! Where can i find the large canister purge hose, will this be on the emission diagram? Also, to answer your question, i did replace the spacer when i replaced the carb. I bought the carb from National Carburetor and it came with a new spacer.

I just ran it and pulled the vacuum from the EGR valve (or what i thought was the EGR, not sure) and no change.

Here is the label for the emission diagram:

Ok, on your vacuum diagram, the two connected purge C/V (Purge Control Valve) devices, the black line that doglegs part way through and has a Tee going to the carburetor portion, that is the canister purge vacuum. The lines that connect to the bowl vents and canisters are the vapor lines, both of those will be decent size hoses 1/4" or bigger on the cannister side, the other larger one to both valves should be manifold vacuum.

The small line in the middle is the control and is teed to the EGR valve, it appears white in the picture, and comes from a port on the carburetor to a 2 port thermal vacuum valve then through a vacuum delay valve and tees to the EGR and purge control. One item, if the purge valves are bad, they can leak air into the intake. There may be a quick connect on the right front of the engine where they run toward the control valves and cannisters. If needed I can take my diagram for the 1984 CA spec and mark the different areas and functions.

Now I know why yours doesn't look as bad as mine did, it's a 1984.

Here is what mine had before going MAF/SEFI

[85lebaront2]

Ok, on your vacuum diagram, the two connected purge C/V (Purge Control Valve) devices, the black line that doglegs part way through and has a Tee going to the carburetor portion, that is the canister purge vacuum. The lines that connect to the bowl vents and canisters are the vapor lines, both of those will be decent size hoses 1/4" or bigger on the cannister side, the other larger one to both valves should be manifold vacuum.

The small line in the middle is the control and is teed to the EGR valve, it appears white in the picture, and comes from a port on the carburetor to a 2 port thermal vacuum valve then through a vacuum delay valve and tees to the EGR and purge control. One item, if the purge valves are bad, they can leak air into the intake. There may be a quick connect on the right front of the engine where they run toward the control valves and cannisters. If needed I can take my diagram for the 1984 CA spec and mark the different areas and functions.

Now I know why yours doesn't look as bad as mine did, it's a 1984.

Here is what mine had before going MAF/SEFI

See if this helps in tracing things out. The blue is the one I would temporarily disconnect and plug.

[Rham243]

Ok, on your vacuum diagram, the two connected purge C/V (Purge Control Valve) devices, the black line that doglegs part way through and has a Tee going to the carburetor portion, that is the canister purge vacuum. The lines that connect to the bowl vents and canisters are the vapor lines, both of those will be decent size hoses 1/4" or bigger on the cannister side, the other larger one to both valves should be manifold vacuum.

The small line in the middle is the control and is teed to the EGR valve, it appears white in the picture, and comes from a port on the carburetor to a 2 port thermal vacuum valve then through a vacuum delay valve and tees to the EGR and purge control. One item, if the purge valves are bad, they can leak air into the intake. There may be a quick connect on the right front of the engine where they run toward the control valves and cannisters. If needed I can take my diagram for the 1984 CA spec and mark the different areas and functions.

Now I know why yours doesn't look as bad as mine did, it's a 1984.

Its an 85' sorry had a typo in my signature. (fixed)

So is this the EGR then, the silver canister behind the carb? see picture.