Ford F 750 with Cummins isb6.7

[BigWrench55]

Looking for some help with diagnosing a intermittent problem with losing power. What happens is I will put it in drive and it will accelerate as normal. But as soon as it shifts into 2nd gear it falls on its face and downshifts into 1st. When that happens if I keep my foot in it it won't hardly go. But as soon as I let up on the throttle it will pick back up and go until it shifts into 2nd. Then it falls on its face again. No codes and no other symptoms. It feels like a fuel issue like I'm not getting enough fuel delivery or maybe my rail pressure drops. But like I said absolutely no codes. This is totally random and I can't duplicate the problem, but when it happens I can't go anywhere. Any ideas are appreciated. Its being towed into a shop but I doubt that they would be able to duplicate the problem.

 

[funwithfuel]

One of the guys here at our show found a pregnant wire running over the top of the engine. It was red maybe 14 ga.where the harness runs under the air cleaner and above the valve cover.
BTW, mine is a 12 F750

 

[BigWrench55]

Mine is a 14. What was that wire for? And did yours do something similar?

 

[funwithfuel]

Failed upshifts, loss of power, no full throttle. I believe it was a power feed to ECU IIRC

 

[BigWrench55]

That makes sense. Thanks for the help. Truck is already heading to the shop. If they aren't able to find the problem then I have a idea as to where to look. Its frustrating because the company want us to work on our trucks. I see it from their point of view, but I rather spend a day diagnosing my truck than waiting a couple days/weeks to get my truck back.

 

[Tyler d4c]

Company I work for has one of these is the most miserable truck I've ever worked on who put the oil filter where it is needs smacked. Ok I feel better now.

 

[funwithfuel]

That makes sense. Thanks for the help. Truck is already heading to the shop. If they aren't able to find the problem then I have a idea as to where to look. Its frustrating because the company want us to work on our trucks. I see it from their point of view, but I rather spend a day diagnosing my truck than waiting a couple days/weeks to get my truck back.

Out here, it takes them a week or so to get it in and look at it. Plus you're without your livelihood for all that time. No thank you, not unless I absolutely positively have no other choice in the world.

 

[heymccall]

Mine would do that, but only in bursts.
The little tube at the EGR solenoid was soot plugged. No codes.

 

[BigWrench55]

Thank you for the idea. That makes sense because the Volvo articulated trucks will do the same thing and no codes. The engine ecm would adjust the vgt turbo based on the egr differential pressure (amongst other things ) if the reading was off it would drop boost and change the way it shifted. Exhaust gas would get trapped under the egr differential pressure sensor and give a false reading. I can't believe that I didn't think of that. This is how the last 10 days have been. Laptop issues, wifi issues, communications adapter issues, electronic drivers log issues, and now my service truck. How did mankind make it this far without computers, smartphones, and ecm's.

 

[kenh]

All mechanical or electronic devices contain malevolent molecules
The lay in ambush until an ideal time to smack you shows up

 

[heymccall]

All mechanical or electronic devices contain malevolent molecules
The lay in ambush until an ideal time to smack you shows up

The British, or more namely Lucas, started this practice ages ago.

 

[Spud_Monkey]

Thank you for the idea. That makes sense because the Volvo articulated trucks will do the same thing and no codes. The engine ecm would adjust the vgt turbo based on the egr differential pressure (amongst other things ) if the reading was off it would drop boost and change the way it shifted. Exhaust gas would get trapped under the egr differential pressure sensor and give a false reading. I can't believe that I didn't think of that. This is how the last 10 days have been. Laptop issues, wifi issues, communications adapter issues, electronic drivers log issues, and now my service truck. How did mankind make it this far without computers, smartphones, and ecm's.

It's not that they put them there cause we need them, they are there to stroke the governments $#*& on E.P.A. regulations. Love my mechanical engines...

 

[Vetech63]

One of the guys here at our show found a pregnant wire running over the top of the engine

Who's the father? LOL

 

[funwithfuel]

I personally think it was some prick that looked like this guy

Maybe it was you

 

[BigWrench55]

Laptop issues, wifi issues, communications adapter issues, electronic drivers log issues, and now my service truck. How did mankind make it this far without computers, smartphones, and ecm's.

Let's add new sewer line for my house to the list of things that are going wrong this past couple of weeks.

 

[BigWrench55]

Update on my service truck. I got a call yesterday and was told my truck is ready. I was 2.5 hours away near the Oklahoma border so I didn't get a chance to go and check it out. I asked the service manager what was wrong with it and he told me that the mechanic replaced a brake position sensor. I asked him if that would cause my engine to lose power. He didn't know . But the bill is 5k. I don't have a lot of confidence that my truck is fixed and if all they did was replace a brake position sensor. They are going to have to explain why it comes to 5k! Sounds like I might have a fight on my hands Monday if there isn't anything more that they did.

 

[Vetech63]

Update on my service truck. I got a call yesterday and was told my truck is ready. I was 2.5 hours away near the Oklahoma border so I didn't get a chance to go and check it out. I asked the service manager what was wrong with it and he told me that the mechanic replaced a brake position sensor. I asked him if that would cause my engine to lose power. He didn't know . But the bill is 5k. I don't have a lot of confidence that my truck is fixed and if all they did was replace a brake position sensor. They are going to have to explain why it comes to 5k! Sounds like I might have a fight on my hands Monday if there isn't anything more that they did.

Where did you take it?

 

[BigWrench55]

Update...
So the brake position sensor will derate the engine. Safety feature. I also verified this by applying the brake and accelerating, and it did exactly what I was experiencing. Also the bill wasn't 5k it was 500. I swore that I heard 5k, but anyways. I'm glad to be back into my service truck. Thanks for all of the suggestions.