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Discussion Starter #1
'97 F250HD,180k Pstroke, 2WD. I was driving out on the interstate today, and signaled to make an exit, and the RPMs suddenly shot up about 2-300 and then went back down. What? I did it several more times, just to check (more out of entertainment than anything else), and it did it each time.

Over the course of my trip, I discovered that it will do it with either directional, with OD on or off. It also occasionally unlocks the TQ at random, just driving down the road, if I've been on the highway for about a half hour.

I'm planning to change the fluid and filter this weekend. Is there anything I can do from the underside while the pan is off? I'd like to take the VBs out and clean them, but I worry about all those tiny check balls falling all over the place. Any suggestions?
 

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Check all your turn signal bulbs and the third brake light bulbs. A burned out bulb can cause your symptoms. If all is good there it could be a problem in the multi-function switch (on the steering column). Cheers!
 

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Discussion Starter #3
Thanks, I'll give them all a look. I'd also heard about a splice or ground below the driver's side battery, which is also blamed for kicking the trans out of OD (which may actually be a mistaken TQ unlock). Best to check it all!
 

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Check all your turn signal bulbs and the third brake light bulbs. A burned out bulb can cause your symptoms.
+1!!

Had the same problem resolved by changing the rear brake and turn bulbs. (On my previous '96 ext cab F150.) I always change both sides of the brake or turn bulbs so I don't have one brighter or dimmer than the other. But on the rears, why not change all four as you already have the lenses removed? Put one or two of the known good ones in your glove compartment as a spare.
 

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Also check the third brake light harness, they like to burn out. They're discontinued from Ford however...
 

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Discussion Starter #6
Haven't had a chance to check the bulbs yet, I'm replacing the front half-shafts on the wife's '97 Suby Outback. PITA... and it's raining, whee! And me with no garage... :(

Anyway, to tie the two issues together, yesterday we took the Suby to go to her doc's appt. We got about to the next town (12 miles away) and had to turn back, as the driveline vibration was horrendous, thought it was going to throw me out of my seat. I've had the new shafts for a couple months now, just haven't had the time to work on it, you know how it goes.

Anyway, we drove back and got the truck, and on the way back to the doc's, had the cruise control on and went to change lanes... woops! Cruise control disengaged at the same time the TQ unlocked! (I noted the tach jump just before the R's started down before I got my foot back on the pedal)

So that, IMO, lends some credence to the theory that it's a bad bulb in the brake circuit, or possibly the multifunction switch itself. I'll just replace all the bulbs as a matter of course, and save the ones that still look good. I'll clean the sockets and lube em up before putting in the new bulbs, and I'll check that splice/ground thing under the driver's batt while I'm at it.

If the new bulbs don't do it, does anyone know if the MFS can be rebuilt by mortal men such as I?
 

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Sorry to hijack, but...
I'm having sort of the same issue. Does yours "do it" when you hit your turn signal to the right, or any direction?

When I engage the turn signal to go RIGHT, it kicks up the RPM about 250 RPMs. If I hit the turn signal with Cruise Control, it bumps up the RPM again, and kicks off the Cruise Control.

Sounds like I'm replacing the bulb in my rear brake light & go from there. I was going to start checking out the wiring in the column. Good thing I saw this thread!
 

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Discussion Starter #8
No worries about the hijack, at least we're still on topic! :laugh:

Yes, mine "does it" primarily to the right as well. I don't know if it's a design thing, or just a thing. It does it *sometimes* to the left, but ordinarily not. I usually note it when I'm signalling to come back out of the passing lane into the right lane, or going onto a slip road or exit- all to the right.

Yesterday I had a load of 16' lumber and steel roofing sticking out the back of the bed (thank God for 8' beds!) and had the hazards on. The torque converter NEVER locked up; it was turning 2k RPM at only 50mph in OD, and had a lot of 'slip' (not trans slip, just unlocked TC slip). Once I got on the interstate and up to speed, I shut off the hazard lights, and bingo, the TC locked.

I'm going to stop by the LAPS and get some bulbs, and do both sides as was recommended. I'll post back with my results. You do so, too!
 

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:popcorn2:
 

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Simply inbelievable. I bought new bulbs for all my exterior lights.

I now have Back Up Lites (Whew. I was hoping that was all I needed...) and all my exterior lites are a LOT brighter.

So, my friends said I was full of BS when I said the 3rd Brake Lite COULD be causing my RPM issues.

Well, I jsut opened it up and the bulb housing was burnt. Plastic was black, contacts were black, bulb was black and burnt. I cleaned everything off and installed the new bulb & test drove it. Worked like a champ.

You guys are the HEAT! Beer's on me for that one!
 

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Discussion Starter #12
Wow, slepe, I'm glad it worked out for you!

I bought new tail/brake bulbs (3157LL's), but not the 197s for the 3rd brake. At first, once the tail/brake bulbs were replaced, the TQ unlocked on BOTH left and right signals, whereas before it only unlocked on the right signal. Then, it went back to right only. It unlocks when I engage the signal, then locks back up... then unlocks AGAIN when I CANCEL the signal! Goofy.

I've been working on the wife's Suby again (full brake job, all four corners... in the rain again!), so I haven't had a chance to check the 3rd brake light, but if I finish her car tomorrow, I'll check it. Hope that fixes it, it's almost as annoying as not having a reverse gear!
 
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