engine control fuse issues

[llong66]

Hello, I have been having a reoccuring issue with fuse 17, the engine control fuse blowing. I have searched and found the various circuits controled through this fuse but have a cpl of questions before I start trouble shooting. I am unsure where to find the water in fuel solenoid, the cold advance, and the fast idle solenoid. I am guessing the fast idle is near the IP and the linkage for it, but the other two items I cannot seem to find a ref. to their location. I looked through the TM but no joy their. Can someone give me a better idea where in the TMs to look or tell me where these items are located? I have no problem finding the other items/circuits powered through this fuse. My first place to look will be the seatbelt buzzer and its associated wireing. This is because the truck will sometimes start and the fuse blow after I have let it run for a cpl min and get a little warm. It is not hooked up and the wires from the seatbelt re-tractor have been cut, so I am thinking the other ends could be causing the issue. I have a full rubber floor liner from LMC in the truck and I believe the wires are under it. If this is not the source of the problem, I will move to the other circuits, I know where the other things to look into are, but not those 3 items.
Thanks much!
Greg

 

[Keith_J]

Water in fuel is at the filter base. Green wires going to the injection pump are the fast idle and cold advance solenoids.

Fuses can blow due to excessive heat which can arise from dirty/poor connection at the fuse block. Fuse material has a positive temperature coefficient meaning resistance increases with temperature, leading to eventual melting of the fuse. Since current through the fuse is nearly constant, it can blow.

See the sticky thread on the alternator issues, the heater fuse supplies current to the alternator exciter circuit. It is an easy circuit to isolate and diagnose for short to ground.

 

[Hasdrubal]

There is a diode on the water in fuel sensor circuit. Apparently, it's taped up to prevent shorts, so maybe something to check out.

 

[Warthog]

The fast idle solenoid is the silver cylinder unit on the outside of the IP. When energized it pushes a plunger against the throttle lever. The Cold advance solenoid is inside the IP under the top cover. The water in fuel solenoid is part of the fuel filter base.

As you discovered the Engine Control fuse controls circuit #39. Diagrams E-3 and E-4 show the circuit.

A problem area is the Cold advance/Fast idle controller switch which is at the passenger rear of the engine. Sometimes the connector plug will come off and land on the exhaust manifold. Or the wires will melt on the manifold. Since circuit #39 is hot when the ignition is on the pink/black wire is hot all the time. If it grounds out it will blow the fuse.

 

[llong66]

Hello all! Thanks much for the help so far, life has gotten in the way an I have not had a chance to piddle with it until today. The first place I wanted to look was the seat belt buzzer wiring as its not hooked up an the wires were loose, however thats not the cause. I was thinking that one side of the fuse socket should be hot, the other side, being the "load" side, should not have continuity to ground unless there is an issue...checking this I do have continuity to ground on the load side. I then went and checked the fast idle/cold advance wires, both of them have continuity to ground so I thought I might have found the issue, all of this checking is being done with batts disconnected. Next I pulled the fuse block apart, looking inside for a possible cause...all looked good and clean. When I check the feed to the fast idle/cold adv. from the engine side of the socket, again, continuity to ground, but I also get this on many other tabs. Where is my logic failing? I will check the suggestions above next, but if they fail, which TM would be the best to guide me in trouble shooting this? I have a feeling this is going to be fun! lol...Thanks again!

Greg

 

[Warthog]

Remove the connector from the Cold Advance Temperature switch at the right rear of the engine (item #2) and make sure you check the wiring to see if it has melted to the exhaust manifold



Leave it unplugged and see if the fuse still blows.

 

[llong66]

Warthog, I did that and it looks fine, the connector was on quite tight and the wire looks good all the way into the plastic shield holding the wires. I did notice, after putting everything back together that the fuse does not blow immediately, the wait and water in fuel light come on as normal, the truck starts then maybe 30-45 sec after running, you hear the fuse go, is this a possible clue? It did this 3 times so I dont think its a by chance thing. I was unable to find the diode that Hasdrubal mentioned, the delay in the fuse blowing. I followed the two sets of wires off the fuel filter base and both of them go into the sheath before I see anything like he has pictured.http://www.steelsoldiers.com/member.php?1915-Hasdrubal

 

[llong66]

Warthog, I may have spoke to soon! As I said, the wire and connector are fine, but before my last post I had missed your suggestion to leave it unplugged,when I did that, all is fine! I went through 4 start cycles and the fuse held, I am going to let it sit and cool for a cpl hrs and go try again and see what happens. Thanks so much!!!

Greg

 

[Warthog]

Plug the sensor switch back in and then unplug the two green wires at the IP and see what happens

 

[llong66]

BINGO!!!! I plugged the sensor back in with the two wires at the inj. pump unplugged and all was good, plugged in the advance wire and everything was fine, unplugged it and plugged in the high idle...pop goes the fuse! The really wonderful( can I say that about a malfunction?? lol) thing is that I have installed a hand throttle kit from a humvee so I can set the idle where I choose! Thank you so uch for your help and time with this!!

 

[Warthog]

Good Job! You found it. The fast idle solenoid has a short. Sometimes you can take them apart and repair the internal coil.

All part of diagnosing the problem and stepping thru the individual items until the issue is found. Glad we could help.

 

[Warthog]

You may want to label the solenoid as bad so someone(you maybe) in the future does hook it back up. I know my memory plays tricks on me and I'll go back and ask myself why something isn't hooked up.