What Thread Pitch?

[AndrewKing]

HI,



I was trying to find an easy way to disable the AFC on the injection pump (to reduce power when helpers drive my truck)... . I found the easiest and fastest way was to remove the bolt (banjo??) that connects the manifold boost tube to the top of the top of the AFC Housing... . (it's a bolt that has a hollow core and 4 holes cross drilled to the hollowed out center to feed the boost signal to the innards of the afc housing)and replace the factory piece with a standard bolt but was wondering what thread pitch I needed ( I took the factory piece to the hardware store to try on various nuts to determine the thread pitch but have had no luck finding a substitute bolt (the closest nut that wold start to thread but not continue was a 5/16 24 pitch nut..... I tried the metric sized they had at the store but none would thread easily... . I do not want to mess up any threads inside the afc housing trying to force the wrong bolt in... .



Also, If I use a bolt that is threaded all the way to the cap would the treads leak enough to still allow the afc to work?... . I suppose I could use teflon tape but I don't want to risk having pieces lodge into the supply tube should I decide to reuse the factory piece and allow the AFC to function like stock.



Thanks in advance for any and all help.



Andrew

 

[dpuckett]

You could tape off the end of the AFC tube, remove the elbow on the head, and install a 1/8NPT plug. That way, you will maintain the integrity of the system, and can still have the AFC for when you want to drive.



The bolt is the same thread pitch as a 1/8 OD union coupler. I had a write up in the Discontinued Parts forum a few years back. Even got published in the magazine Oo. Girlfriend didnt believe it was *MY* engine in the photo at first.



Daniel

 

[Moab4x4]

I agree, remove the tube connecting the AFC to the head. plug the head with the 1/8 plug and then if you want to keep the AFC really clean, use a 1/8 NPT plug into a 1/8 NPT to 1/8 OD adapter like Daniel mentioned (like you would use for a mechanical oil pressure guage or boost guage). I bought a cheap repair kit designed to replace the tubing for an oil pressure guage and it had various brass adapters in it and they worked well. I put a touch of permatex #2 on the threads to seal them and keep them from coming unscrewed.



Daniel, I don't know what possessed you to try that fitting but I am glad you did. I was skeptical that the 1/8 tubing would work well for the AFC, but I can't tell any difference than with 1/4 hose.

Ken

 

[AndrewKing]

HI,

Thanks for the reply guys... . I think I will still try to leave the tube on the head and screw a short 1/8 NPT pipe into the AFC side then I will cap off the the other threaded end... . I was hoping to keep a stock looking setup while still blocking off the boost signal to the AFC housing... . Also, I was hoping not to have to remove the boost tube(?) because with my luck it would get damaged or worse lost after awhile...

Andrew



PS - In looking at Lowes, I noticed that if may be possible to use plumbing fittings and some compression fitted white PVC lines to substitute the factory steel lines (connecting the boosted intake manifold to the AFC housing), This was intriguing because Lowes also sold a needle valve that could be fitted into the PVC line so that one could simply turn the boost signal on or off to the AFC housing at will... . Only concern I had was if the valve would flow enough volume of air to work the afc properly and not cause additional lags in the system... . Of course my simple threading of effectively a bolt into the area where the Banjo bolt fits onto the AFC housing still may allow a boost signal to get through (although mabe more delayed unless I can figure a way seal the threaded area).

 

[Moab4x4]

I don't see enough air getting past your "bolt" to run the AFC. I see the difficulty in finding a bolt that will work. That is a pretty small oddball banjo.



I would be concerned about the PVC tubing with the underhood temps, what is the PSI rating then?



The 1/8" OD nylon tubing Daniel recommends does work and even that tiny tube lets the AFC work fine so I don't see a needle valve causing enough restriction when open.



I finally got mine tuned the way I like it after a bit of experimentation. 24 psi with no AFC and 32 with it via solenoid. 24 = not too hot, 32 = watch the pyro.

 

[THeske]

It's a metric bolt, just make sure you have the right thread pitch, I believe it is a 1. 25 but I may be wrong on that one, But is definetly metric I made up a new banjo bolt using a metric die on a compression fitting ( re-threaded the fitting) When I made up a new flexeble AFC line,

 

[NYCEGUY01]

I just drilled out the threads and tapped the hole to 1/8 pipe thread. Worked perfect.

That made hooking up the valet switch real easy. I used 1/4" air brake hose with the quick connect fittings. No problems so far and it was super easy and fast.

 

[bgilbert]

It's metric and VERY close to 1/16 pipe thread. You could build your own afc hose in various ways by using ordinary pipe thread fittings.