Tranny just started throwing a P0781 code - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 11 (permalink) Old 02-01-2010, 06:50 PM Thread Starter
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Tranny just started throwing a P0781 code

Last night my tranny started to ride 1st gear out up into the 2500 - 2800 RPM range without wanting to shift into second (under no load and driving slow). I am getting a P0781 1 - 2 shift error. I looked into troubleshooting with a pinpoint test but I don't have the Ford test gear. So I am using my gray matter test suite..

I had this issue back in September and flushed the tranny and it was fine until now.

I have a spare solenoid pack that I bought from a member a while back but never installed. All the solenoids in that pack ohm out ok using a DVM.

So I am wondering what you guys would do short of a BTS replacement.

Would you swap the solenoid pack?
Look for a bad wiring harness?
Drive it as is?
Look for something I have not considered?
Rebuild it?

2002 X PSD, Billy Boat 4", AirRaid, 38R,HO Outlet, IH Up-pipes, Gauges: Boost, EGT, Trans Temp, Fuel Pressure and Water Temp, Oil PSI at Turbo Pedestal

DP-Tuner 6 pos No Start - 140
Super Heavy Duty 4R100 / triple disc from ATO
Transmissions in Sacramento
ICON 5" Spring Pack Lift
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post #2 of 11 (permalink) Old 02-02-2010, 07:50 PM Thread Starter
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Re: Tranny just started throwing a P0781 code

Well, I have been driving the truck since it began shifting erratically. Basically everything but the 1-2 shift seems fine. from 1 - 2 it will drag the shift point into the 2500 rpm range and then shift into 2, from there it shifts pretty normal up through the gears.

I have 195K on the truck in the sig and this is the original transmission. I am running a DP tuner that does increase line pressure, but that is all I have done. Stock TC and stock VB.

This morning I was on my way home and pulling away from a stop sign. Got 'er up to about 2300 rpm easily and it shifted into 2 and then bucked a bit like it could not make up it's mind what gear to stay in, and then viola, Everything seemed fine. Stopped at the next stop sign, pulled away and it shifted from 1 - 2 in normal fashion, went through all the gears fine and is basically back to normal.

I have to believe something was plugging a passage in the VB and somehow became dislodged. My flashing OD light is no longer flashing and my codes are cleared and not coming back.

Any thoughts?? Like replace the VB with a new cleaner one. Replace the TC?

2002 X PSD, Billy Boat 4", AirRaid, 38R,HO Outlet, IH Up-pipes, Gauges: Boost, EGT, Trans Temp, Fuel Pressure and Water Temp, Oil PSI at Turbo Pedestal

DP-Tuner 6 pos No Start - 140
Super Heavy Duty 4R100 / triple disc from ATO
Transmissions in Sacramento
ICON 5" Spring Pack Lift
PSC Ram Assist Steering




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post #3 of 11 (permalink) Old 02-02-2010, 08:02 PM
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Re: Tranny just started throwing a P0781 code

I was going to say it was probibly a valve sticking in the VB. You could go through and clean up and the Valve body and the Accum. body and be ok for a while, but you may also find what is making the extra parts that got your valve stuck in the first place.

I like working on my own stuff and if you do to , I heard John Wood sells a DIY kit but I have not confirmed this with John.

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post #4 of 11 (permalink) Old 02-02-2010, 08:11 PM Thread Starter
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Re: Tranny just started throwing a P0781 code

I do like DIY, actually my truck has never been to the Ford dealer for anything since I bought it at 20k. I am going to be in SoCal and thought of going over to JW. IDK, at 200K I know the tranny is approaching the end, but I would sure like to get through the summer with it. I definitely don't have the money right now to drop on a new tranny as much as I wish I could.

This is the second time I have had the tranny act up. Back in Sept I had the same code, but the temps where up around 200 - 210. I flushed it back then and it returned to normal.

I am gonna play it by ear with my eye on a JW VB and maybe a new TC.

2002 X PSD, Billy Boat 4", AirRaid, 38R,HO Outlet, IH Up-pipes, Gauges: Boost, EGT, Trans Temp, Fuel Pressure and Water Temp, Oil PSI at Turbo Pedestal

DP-Tuner 6 pos No Start - 140
Super Heavy Duty 4R100 / triple disc from ATO
Transmissions in Sacramento
ICON 5" Spring Pack Lift
PSC Ram Assist Steering




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post #5 of 11 (permalink) Old 02-02-2010, 08:47 PM
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Re: Tranny just started throwing a P0781 code

most likely it is a sticking valve in the valve body. A new valve body would probably cure the situation.

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post #6 of 11 (permalink) Old 02-02-2010, 10:24 PM
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Re: Tranny just started throwing a P0781 code

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Originally Posted by NorCalDiesel View Post
I do like DIY, actually my truck has never been to the Ford dealer for anything since I bought it at 20k. I am going to be in SoCal and thought of going over to JW. IDK, at 200K I know the tranny is approaching the end, but I would sure like to get through the summer with it. I definitely don't have the money right now to drop on a new tranny as much as I wish I could.

This is the second time I have had the tranny act up. Back in Sept I had the same code, but the temps where up around 200 - 210. I flushed it back then and it returned to normal.

I am gonna play it by ear with my eye on a JW VB and maybe a new TC.

Sounds like you got somthing making a little metal in there or just crud from 200k miles and making your valve body stick here and there. If your gonna limp it along try what I suggested and clean everything you can from the bottom side.

Remove both the acc. and the main valve body and clean them, pulling all the valves out of every one, clean your cooler and install a new filter inside the trans as well as one on the cooler line. Put in new fluid and hope for the best.

If I had to wait a while to do a rebuild this is what Id do with a 200k trans. IMO

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post #7 of 11 (permalink) Old 02-02-2010, 11:09 PM Thread Starter
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Re: Tranny just started throwing a P0781 code

That seems to be the best route. I am thinking of just getting a JW VB and be done with it. Then when I rebuild I will have it already, plus it will be cleaner than if I had to do it.

Anyone in the NorCal area with a good VB they'd want to part with??

2002 X PSD, Billy Boat 4", AirRaid, 38R,HO Outlet, IH Up-pipes, Gauges: Boost, EGT, Trans Temp, Fuel Pressure and Water Temp, Oil PSI at Turbo Pedestal

DP-Tuner 6 pos No Start - 140
Super Heavy Duty 4R100 / triple disc from ATO
Transmissions in Sacramento
ICON 5" Spring Pack Lift
PSC Ram Assist Steering




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post #8 of 11 (permalink) Old 02-03-2010, 05:02 PM
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Re: Tranny just started throwing a P0781 code

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Originally Posted by NorCalDiesel View Post
That seems to be the best route. I am thinking of just getting a JW VB and be done with it. Then when I rebuild I will have it already, plus it will be cleaner than if I had to do it.

Anyone in the NorCal area with a good VB they'd want to part with??
How about getting a BTS VB. That way, when you have to get the full BTS trans, you get credit for the VB towards the trans?

01 Excursion 7.3L Powerstroke. Gauges with AIH Delete, AIS, CCV Mod, 4' MBRP, BTS Trans, 6.0L Trans Cooler and Intercooler, DP-Tuner F5 chip, ITP In Tank Mod and Boost Annihilator, Diesel Innovation's Regulated Fuel kit, BTS Big Oil system, GTP38R Turbo with 1.15 A/R housing and BPD Stage II AC injectors. Bilstein Shocks with U front and A Rear.
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post #9 of 11 (permalink) Old 02-03-2010, 05:24 PM Thread Starter
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Re: Tranny just started throwing a P0781 code

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How about getting a BTS VB. That way, when you have to get the full BTS trans, you get credit for the VB towards the trans?
Haha, That's awfully presumptuous.. that I would get a BTS.. Actually, I would love one.. just the money and right now time. I need the truck to go to SoCal on Monday, so whatever I do has to be done soon.

2002 X PSD, Billy Boat 4", AirRaid, 38R,HO Outlet, IH Up-pipes, Gauges: Boost, EGT, Trans Temp, Fuel Pressure and Water Temp, Oil PSI at Turbo Pedestal

DP-Tuner 6 pos No Start - 140
Super Heavy Duty 4R100 / triple disc from ATO
Transmissions in Sacramento
ICON 5" Spring Pack Lift
PSC Ram Assist Steering




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post #10 of 11 (permalink) Old 02-03-2010, 05:35 PM
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Re: Tranny just started throwing a P0781 code

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Originally Posted by NorCalDiesel View Post
Haha, That's awfully presumptuous.. that I would get a BTS.. Actually, I would love one.. just the money and right now time. I need the truck to go to SoCal on Monday, so whatever I do has to be done soon.
You mentioned you wanted suggestions short of getting one. Here is another suggestion. Give BTS a call and ask for help. He might have a simple answer and he doesn't mind giving tech support if you can hold. The time you have to work with is very short so not sure if anyone can help you at this time unless you want to "Next Day" a VB. Read $$$$. Call is cheaper. 870-422-3673

01 Excursion 7.3L Powerstroke. Gauges with AIH Delete, AIS, CCV Mod, 4' MBRP, BTS Trans, 6.0L Trans Cooler and Intercooler, DP-Tuner F5 chip, ITP In Tank Mod and Boost Annihilator, Diesel Innovation's Regulated Fuel kit, BTS Big Oil system, GTP38R Turbo with 1.15 A/R housing and BPD Stage II AC injectors. Bilstein Shocks with U front and A Rear.
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