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Old 04-19-2013, 03:40 PM
Roadkingjimmy Roadkingjimmy is offline
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Hesitation at constant speeds

Thanks for any help in advance!!

I have a 2000 F250 w/ 7.3L Powerstroke superduty. I was driving this past weekend out of state and after driving flawlessly for 5 hours the last hour I was driving the truck started freaking out.

The only item I knew not to be working upon my departure was the A/C, Vent, etc... selector switch. This was the first time this has not worked and it only blew air out the window defrost on the dash. The A/C compressor/clutch would not engage either.

So - despite the AC/vent switch not working what it would do, when using the accelerator manually at constant speeds, 35, 55, etc... it would just hesitate and "thunk" almost like for a split second like it wasn't getting fuel or a wire was intermittently not making a sound connection; as time went on it became worse and worse. However using cruise control it would never do it at all!!

After arriving to my destination the next day looking over potential reasons for this demise I found that a 10 amp fuse in fuse location 28 was bad. I replaced the fuse and everything seemed to be back to normal. While test driving the truck for over 7 miles it ran nicely, AC/vent switch came back to life, reverse lights were working, etc...

When leaving later that same day to drive back home immediately upon leaving the fuse blew again (very distinct because the truck ran like crap as described). I once again replaced the fuse, and again, and again. After replacing the same fuse 4 times in under a 1/2 mile I knew I had bigger issues.

I painstakingly drove the truck home the entire time on cruise control. When using the cruise the truck runs fantastic.

I recently have had all glow plugs and 5 of the 8 injectors replaced. New wiring harness and valve covers. All wiring looks good and solid. The vehicle is not throwing any codes (check engine light does not illuminate)...

I know many times that problems are because of something silly or complex. I am hoping this is silly and that someone has had a similar problem that can give me a clue as to where and look. Maybe replacing the AC/vent selector switch, which also uses vacuum connections??

Thanks for any impute!!!
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Old 04-19-2013, 04:12 PM
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A quick search for fuse 28 led me to a post where the 28 fuse kept blowing, effecting the A/C climate control. His problem ended up being a frayed wire in the trailer brake connector and corrosion in the trailer plug...

Can you tell me what fuse 28 is for your year? 02/03 can be different so I don't want to go look at my manual and it be wrong.
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Old 04-19-2013, 04:14 PM
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The owners manual for F-250 2000 says: for Fuse # 28 10A

Brake Shift Interlock, DRL Relay Coil, Speed Control Module, Backup Lamps, Trailer Tow Backup, lamp Relay Coil, Electronic Shift on The Fly Hub Lock Solenoid, Vacuum pump Motor.



Now to find out which one of these systems is giving you problems. One of them is shorting out and not working. It is interesting that you say that the cruise control works as this says something about 'Speed control Module'.
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Old 04-19-2013, 04:14 PM
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My initial instincts are pointing me to throttle position sensor in the pedal because it works fine on cruise.
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Old 04-19-2013, 04:16 PM
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Quote:
Originally Posted by Brother Les View Post
The owners manual for F-250 2000 says: for Fuse # 28 10A

Brake Shift Interlock, DRL Relay Coil, Speed Control Module, Backup Lamps, Trailer Tow Backup, lamp Relay Coil, Electronic Shift on The Fly Hub Lock Solenoid, Vacuum pump Motor.



Now to find out which one of these systems is giving you problems. One of them is shorting out and not working. It is interesting that you say that the cruise control works as this says something about 'Speed control Module'.

Well the vacuum pump motor explains why the A/C started working again.
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Old 04-19-2013, 04:20 PM
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Quote:
Originally Posted by jeffreyt View Post
My initial instincts are pointing me to throttle position sensor in the pedal because it works fine on cruise.
owners manual says that the 'Speed Control Module' is on that fuse. how can the cruise work? is that not the 'Speed Control Module/

what does DRL relay coil stand for...do..?
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Old 04-19-2013, 04:22 PM
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Daytime running lamps.
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Old 04-19-2013, 04:31 PM
Roadkingjimmy Roadkingjimmy is offline
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This is beginning to sound like two separate but linked problems. Fuse 10 was blown (I verified many times while driving) yet the cruise control worked fine. When taking the cruise off, the vehicle began to act up again while operating the accelerator manually.

I did replace just a couple months ago the TPS (throttle position sensor) so I am hoping it is not the problem.

Here is a kicker as well... I have replaced the fuse again, and ran the truck for 20 miles - not a hitch and the fuse is still good. Weird I know....

Would anyone suggest replacing the AC, Vent switch on the dash? Could this be a culprit?

Again thanks!!
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Old 04-19-2013, 04:31 PM
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I don't think the speed control module is the same as the cruise control. Cruise is set in the PCM IIRC and doesn't have a separate module. But now the question is what the speed control module is controlling the speed of???
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Old 04-19-2013, 04:38 PM
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Anyway, back to the issue. I would not replace the vent switch. I believe A/C is effected because of the vacuum pump being on that fuse. No vacuum, a/c defaults to defrost.

I would inspect the trailer plug and the harness leading to it. It's got several possible chafe points, and is vulnerable to corrosion. I think once the short is fixed and the fuse quits blowing, the rough running issue and the A/C issue will resolve themselves.

Also wouldn't hurt to check the wire harness going to the vacuum pump and the hub lock solenoid. Since those are all on the same fuse, there could be an issue there.

And somewhat related, there's a very common pinch point for wires behind the steering wheel from the shift lever. They cause issues when the break as well. Maybe not completely related, but another place to look for chaffed wires.
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Old 04-19-2013, 05:05 PM
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Quote:
Originally Posted by Roadkingjimmy View Post
This is beginning to sound like two separate but linked problems. Fuse 10 was blown (I verified many times while driving) yet the cruise control worked fine. When taking the cruise off, the vehicle began to act up again while operating the accelerator manually.

I did replace just a couple months ago the TPS (throttle position sensor) so I am hoping it is not the problem.

Here is a kicker as well... I have replaced the fuse again, and ran the truck for 20 miles - not a hitch and the fuse is still good. Weird I know....

Would anyone suggest replacing the AC, Vent switch on the dash? Could this be a culprit?

Again thanks!!
https://www.fleet.ford.com/maintenan...ls/default.asp owners manual, make, model, year... page 151 is the page for your fuse listing

When you said 'fuse 10' it seemed that now you are having problems with # 10 fuse....that reads 'Dual Fuel' tank'... I don't think you have a duel tank... now I understand that it is the 10amp fuse in #28 slot.

re-read the list that I wrote about. all of those systems are connected to #28. It could be any of them that blows the 10A fuse. Does the fuse pop when you turn your AC on? If it does, the AC electrical system is where to start looking.


follow jeffreyt advise and start by looking for corrosion on the trailer tow back up wires and then slowly move to the next. Don't replace 'parts' until you have narrowed it down to which system is causing the problem..
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Old 04-19-2013, 05:11 PM
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Doesn't the third brake light cause some kind of issue when it's out?
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Old 04-19-2013, 05:16 PM
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Quote:
Originally Posted by jeffreyt View Post
Doesn't the third brake light cause some kind of issue when it's out?
It is hard to see....


That 'High Center Stop Light' is on Fuse #13, not #28.
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Old 04-19-2013, 05:22 PM
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Originally Posted by Brother Les View Post
It is hard to see....


Haha, I'll give you props on that one. But it really seems like I read somewhere that it did something obscure. Like maybe weird shifts in the trans or something... Can't quite remember.

Edit: maybe it was a reverse light... Idk. And the pic is meant in complete jest, for the record
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Old 04-19-2013, 05:27 PM
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Quote:
Originally Posted by jeffreyt View Post


Haha, I'll give you props on that one. But it really seems like I read somewhere that it did something obscure. Like maybe weird shifts in the trans or something... Can't quite remember.

Edit: maybe it was a reverse light... Idk. And the pic is meant in complete jest, for the record

Its is Friday and almost 5:00, could not help myself, nothing at all at you Jeff.


Manual say: stop lamps, Top stop light, tow trailer stop lights, and speed control....
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