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Hi Guys,

New to the forum (although I've been silently creeping in the background for a while now). I have a 1997 F350 7.3 Dually with 358,xxx miles and have slowly been fixing it up ever since I bought it. I bought the truck in March as a farm truck for myself, mainly to pull trailers. The truck is spotless from Georgia and was brought up in February and parked, because the owner decided he "changed his plans", which was short for the tranny is bad and I'm going to flip it before it blows. I was the sucker who made it 10 minutes after handing over the cash. :flame: Needless to say I built the trans and am in the process of Stage 1 injectors over my winter break from college. Once all is said and done, I will be very happy with where the truck is at.

Now that I've rambled long enough, here is the real question. When I bought the truck, only the rear tank worked. I knew that and figured I could fix it later. Now that I've got the time, I've been diagnosing it and am pretty sure it is the dreaded FTSV that I've read a lot of posts about. I have power from the switch all the way through the harness to the valve on both settings when it is unplugged from the valve, but when it is plugged in I will blow Fuse #6 when I switch from rear to front. Before I drop the $$ on a new valve, I want to see if anyone else has recommendations for anything else that could be causing the problem. Thanks in advance!

Aaron
 

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Welcome!

It does sound like the selector valve if it blows only when plugged in. Just in case you want the stuff from the factory service manual, here are the tests from that:

Tank Selector Valve (Diesel Only) Component Testing Procedure

On the Selector Valve Connector, the terminals are:
Pin 1: Not used
Pin 2: 789 (BR/W)
Pin 3: 786 (R)
Pin 4: 673 (DB/Y)
Pin 5: 29 (Y/W)
Pin 6: 675 (Y/LB)

To Test the Rear Tank Circuit:
Briefly Apply 12V Power to Terminals 789 (BR/W) (+) and 786 (R) (-)
Connect Self-Powered Test Lamp or Ohmmeter to Terminals 29 (Y/W) and 675 (Y/LB): A good Switch will indicate Closed Circuit
Connect Self-Powered Test Lamp or Ohmmeter to Terminals 29 (Y/W) and 673 (DB/Y): A good Switch will indicate Open Circuit

To Test the Front Tank Circuit:
Briefly Apply 12V Power to Terminals 786 (R) (+) and 789 (BR/W) (-)
Connect Self-Powered Test Lamp or Ohmmeter to Terminals 29 (Y/W) and 675 (Y/LB): A good Switch will indicate Open Circuit
Connect Self-Powered Test Lamp or Ohmmeter to Terminals 29 (Y/W) and 673 (DB/Y): A good Switch will indicate Closed Circuit

Check that the source and return valve transfer between front and rear positions. NOTE: A brief “zip” sound can be heard when the valve transfers.
Cheers!
 

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Remove it and back-blow the fittings, then test it with a direct battery connection to see if it will switch. You'll know it's switching right when it makes a "thwick" sound each time you reverse the polarity on the test leads. If that doesn't do it, there's a thread on one of the major diesel forums on taking apart the valve to clean it out; can't hurt, short of replacing it.
 

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I have never pulled one out or worked on one but you might want to mark which line goes where also when you pull it out
 
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