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Discussion Starter #1 (Edited)
Well I haven't posted here in many years. I purchased a '97 F250 18 months ago. I've never been really pleased with the power but it was adequate for the tasks I had. This is not my 1st diesel and I'd thought I had encountered most everything between my other 4 diesels over the years however I'm stumped here. Any insights would be much appreciated as this is my work truck and if it isn't running I'm not working.

Truck starts well. Will idle well. Start driving and in under a mile the power falls off so that full accelerator depression will result in about 1000 rpm idle that produces just enough white smoke to be visible. Release the accelerator and the engine will stall. Will restart easily. It will run this way for 4 to 7 minutes depending on ambient air temps. The warmer the air the faster the recovery to normal operation. It feels very much like the timing is not being advanced for some reason until the engine is warm.

If I let the truck idle on a cold start up until the engine is operationally warm the power fall off does not occur and it runs normally.

If I run the truck at highway speed for any length of time, typically 10 minutes, and pull off and stop for traffic stop sign the first 1-2 seconds the engine response on acceleration is very sluggish and then it picks up and resumes normal operation.

Things I've done in the order I've done them. Replaced Fuel Filter. Replaced Valve Cover Gaskets and the wiring harness within. Replaced fuel lift pump, associated rubber fuel lines, and cleaned particle screen in the pressure regulator. Checked the codes and none showed on the scanner.

Things I'm considering doing. Replace Throttle Position sensor but I'm not convinced this is the issue. Replace the entire Throttle Assembly thus getting a new Idle Verification Sensor in the process. Given the cost I'm really not convinced this will do anything. Replacing any sensor on the engine that may influence the computer in regards to timing. Replacing the computer but I put a new one in when I bought the truck and the power has been poor all along.

Any insight would be much appreciated.
 

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It could be the exhaust back pressure valve on the turbo. Its purpose is to aide in warming up the engine on cold starts but it usually causes more problems than it helps.

When there is a problem does it sound like a whooshing sound when you press the accelerator?

You might just want to unplug the electrical connection to it and see what happens. The plug is almost under the turbo. Or you can disconnect the rod on the back of the turbo and wire it open.
 

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Discussion Starter #3
I agree with you. Exhaust Back Pressure Sensor

At your suggestion of the exhuast back pressure sensor I've been searching and reading old posts and I stumbled across a link to a video on the back pressure sensor.

Have I heard a whooshing sound? I can't say that I did. I was focusing on listening to the actual engine and trying to feel and understand the vibration it had. Tomorrow I'll roll the window down and listen carefully.

I found this to be the best description of my problem.

For example, if the EBP valve gets stuck shut and you try accelerate, your 7.3 diesel's EBPS will read that the exhaust back pressure is too high.

High pressure increases EGT - exhaust gas temperatures - and high heat is the enemy of all engines. So the PCM opens the EBPV, reduces turbo boost, and "defuels" your engine to protect it.
I think I will move to the head of the list replacing the sensor since it's only $80 I'll go ahead and replace the back pressure tube as well. I saw in the video that the tube can have concealed damage.

I thank you for your insights. I have a path that makes more sense now.
 

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A lot of our trucks have it disconnected and there is a mod to pull it out completely.

I live at 6500' here in Colorado and personally don't believe that it is needed.

If you just unplug the electrical connection to see if that is the problem you may save some money.
 

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Remember there is a difference between the exhaust back pressure sensor ( front of engine ) and the exhaust back pressure solenoid (front of turbo pedestal ). You can unplug the latter and insert a resistor to prevent a code but you cannot unplug the former and expect the truck to run right.


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Your problem is real but not common. it pops up on the forum once or twice a year. I don't think it is a back pressure issue. I had back pressure delete it not help when I had this issue with my truck. I have never found the root cause, even had KLHANSON look at it!! I went to Different Strokes in Anchorage and talked to the owner Ron. Great guy (every town should have a Ron) he could have said bring it in and we will work on it, but, he said just run lighter oil in the winter. It solved the problem 100 % I started running 10w-30 Rotillia year round and it solved the problem. It is a oil temp/viscosity issue, that is why it gets better when warm or preheated. Before you start throwing parts run a light weight oil like Rotilla 10w-30 and see if that helps. If it works you are done. If you want to be the one that has the final answer to this issue consider looking at the low pressure oil pump. I just did not have the time to do it before I sold the tuck. Do you run 15w-40 oil now?
DENNY
 

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Sounds like one of three options; CPS can cause this, TPS will as well, and if it's like the previous comment and due to oil viscosity then that points to injectors, run an additive in the truck and replace the CPS and TPS. Those are the main culprits.

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You describe that this issue does not happen if you let the engine warm up at idle first.

CPS and TPS issues are not really temperature sensitive.

EBPV and oil viscosity are temperature sensitive.
 
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