Hey, I've got a 1999 F250 with a V10. Recently, I was on the highway and after driving a while I hit a big hill. I floored it, the truck down-shifted and it would not go over 3000RPM. I kept it floored and it slowly started to lose speed. I pulled off the highway and put it in park. With the gas pedal to the floor the truck would not rev over 3000RPM. I let it sit until the engine is cooled and it OK, as soon as it gets warm it does it again. So far I have changed the DPFE, all the plugs, I have checked the EGR valve, changed the fuel filter and checked the fuel pressure. Any suggestions what this could be? It seems to be worst when it is hot out.
Thanks in advance!

 

When my truck did this I eventually found out I had a partially clogged catalytic converter. Disconnect your exhaust ahead of the converter and take it for a quick spin to test that.

 

Converter or fuel delivery. Sure sounds like a converter though.

 

A bad coil can also cause the symptoms your truck is producing.

Note:
RE: "I let it sit until the engine is cooled and it's OK"

A bad coil can sometimes work ok when it's cool and act up when warmed up causing seamingly untracable gremlins in your engine.


Rick...

 

There are 10 coils on this truck. take 2 out it will still rev.

 

Well I took the truck out again today and of course it's not acting up. So two questions from your comments:
1) If it's the cat converter is it possible that it would only act up intermittently?
2) If it's one or more of the coils is there a way to check them or should I just replace them?

I should add that the truck currently has 250000km (155000miles). I am the second owner and I have had the truck since 185000km (115000miles). I HATE intermittent problems!!
Thanks for the help guys!
Trent

 

Could be the sock in the gas tank.. Usually converter will always do it and get worse over time. Keep an eye on it..
Coils do go bad but I don't think thats your problem...IMO

 

Take your fuel rail pressure when its hot. Well, not TOO hot, and watch the splash!

 

Fuel pressure is 34PSIG with truck off, 28PSIG when truck is on, hot or cold.

 

I'd be inclined to follow 99f350sd and redford's instruction on this one simply from thier lengthy history and experience here at FTE, but a bad coil or possibly even a damaged coil boot can cause the symptoms you described.

I'm in the process of waiting for my Motorcraft coils (DG-508) to arrive as I type this. The bad coil that's giving me grief acts up when warm/hot and causes different signs of problems from test drive to test drive.

- When it's been sitting over night or for a couple hours it runs like there is nothing wrong. Lots of power and idles like new.
BUT when warmed up/hot,,,
- Engine misses at idle sometimes and can barely stay running.
- After a short drive then slowing down to an idle (coasting) to park the truck it starts surging almost bucking.
- Driving down the road and all is good until it warms up then all of a sudden it will seem like there is no fuel pressure and it will not get over 2500 RPM. Not chugging, just no power and slowly gets worse until it's practically limping at idle speed.

Just something to consider if the other suggestions don't work out for you. It can be a real pita tracking down these problems sometimes when it can be one of several possible issues causing the symptoms you described.

As far as testing your coils,,, I personally find it easiest to have a known good/working coil to swap out each installed coil one at a time until the bad one is found. You can get lucky sometimes and find a misfire on the effected cylinder if you have access to a scanner, but since I normally try to have a good coil on hand for these trouble shooting issues I find it to work best for me just to have one in the parts box.

2002 vehicle and 9 of the coils in my truck are the originals so I'm replacing all them now. I think after over 70,000 miles of service they have served thier purpose and it's time to retire them before they start dropping on me.

Rick...

 

Yes, when my catalytic converter clogged up, it was intermittent at first, which made diagnosis very difficult.

It could also be a bad coil, but a scan of the PCM will show misfires in the pending codes if that was the case.

Your fuel pressure seems to be low also. Fuel filter or fuel pump?

 

The fuel pressure does seem a shade low if you checked it with no load. Testing pressure strictly under no load doesn't always reveal the problem. Have you checked pressure with the truck on the road accelerating? The pressure should be in the 30 to 45 psi range and stay steady or even rise a little under heavy load. If it falls off, you have a fuel delivery problem, possibly a bad pump or clogged intake screens.

 

I took a short video today. We were driving on a flat straight road, going about 60km/hr (35mph) and I floored it. As you can see the tach jumps up to about 3500RPM and stays there. No increase in speed, maybe even a slight decrease. If I took my foot off the throttle and then eased on it the truck would start to pick up speed and take off. Also, after doing this two or three times the 'overdrive off' light on my shifter started flashing and the truck shifted VERY hard for the rest of the drive home.
I'd be curious to know Rick if you had any codes show up when you were having your intermittent problems?
I posted a quick video below:
YouTube - VID 00001-20100710-1749.3GP

 

No codes at all. Not even a hint of pending misfires. No flashing OD light either. Stopped by my local mechanics shop twice to use his Snapon scanner (not sure of the model) but nothing showed up to help diagnos the issue. It was swapping the coils out one at a time and test driving each RE&RE that solved it for me.

Since you have the OD warning light indicator flashing I think there is a good chance you will find a code stored that will point you in the right direction. Get a scanner plugged into the OBDII port.

Rick...

 

looks almost like the trannys slipping. rpm jump with no mph jump...every time i've had a tranny go its been like that...slow at first then gets worse till it wont move under its own power. what also leads me to think this is the o/d light flashing meaning a issue with the tranny.