The truck starts instantly and idles fine, but runs rough when attempting to accelerate above 1200 rpm. At 1500 rpm it feels like it's running on 5 cylinders. No codes. The truck has 225k miles. As the coolant temp increases the truck runs smoother, but does not run normally until reaching 190 deg. coolant temp. So far I have R&R'd the fuel lift pump, fuel filter, both coolant temp sensors, the air inlet temp sensor, the PMD/FSD (fuel pump computer), all 8 fuel injectors, the turbocharger, and the ECM (main computer). The truck still runs exactly as it did before I replaced all the above (yeah, I know, I wish I had junked it, but now I'm in too deep to quit until I fix it). Coincidentally, at idle, it takes approx. 20 minutes to reach 190 deg. coolant temp.

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Also, no white smoke, or blue or black for that matter. Radiator hose is not hard after start up. No coolant in the oil. No oil in the coolant.

 

A diesel burns very little fuel at idle so it takes a long time to warm up if left at idle.

What is the crankcase blow by like when cold and then when warm?

 

I will do a blowby test, both cold and warmed up, and post the results.

 

No black smoke?

Ever?

No quick puff on start or a light puff on heavy acceleration?

 

There is a puff of blueish smoke on initial start-up, but then the exhaust is clean. There is some black smoke on hard acceleration under load.

I performed the check. I warmed up the truck to 190 deg. coolant temp. and then removed the oil dipstick. I place a length of 3/8" clear plastic tubing over the oil dipstick tube. I then placed the other end of the tube into a pail of water. At idle, 630 rpm, the water moved approx. 3/8" up into the tube. At 2000 rpm the water moved approx 3 1/2" up into the tube.

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I also performed the test immediately after start when the coolant temp was 70 deg. At cold idle, approx. 800 rpm, yielded approx. 3/4" of water. At 1500 rpm, when the engine was running very rough, it yielded approx. 3" of water up the tube.

 

I was going to suggest a compression problem or a lack of fuel flow (clogged tank "sock"), but your response seems to rule that out.....


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I'm almost out of ideas. All I can think of now is that with 235k miles on the engine that there is some slack in the timing chain, which results in the fuel pump timing being retarded. The effects of late fuel injection would, of course, be more pronounced when the engine is cold, than when at normal operating temp.

The problem could also be the fuel temp sensor in the FI pump. Because the fuel pump has to be removed to change the timing chain, my next step will probably be to R&R the timing chain, gears, and the FI pump. B/c I already replaced/relocated the PMD/FSD I will buy a pump that does not have a PMD/FSD mounted on it -- so I will save a little bit there. I have already spent approx $1700 on parts, so what's another $700.

This is my plight unless anyone has any other ideas.

 

Before you buy a pump, take yours in and have it tested.

With your miles I would change the timing chain and gears. The OEM timing sets didn't sem to hold up all that great. Every vehicle that we opened up with more than 150,000 miles was at the sloppiness limit. At 500,000 miles you can just about take the chain off without removing the gears.
I also installed Fluidampers and new engine drive pullys at the same time.

I do not think any of this has a great amount to do with the issue you are having though.

 

Lucky me. So it sounds like I could spend a bunch more money, and spend a bunch more time, and I still will have a 6.5 that runs rough when cold.

 

Have you tried running it with the coolant temp sensors unplugged to see if the engine responds differently?

Cheap and quick check to make sure your PCM is responding properly to the sensors or that it is receiving correct info.

You can also try running it with the Optical sensor unplugged. If it runs well, then the OS is suspect (the OS is also the fuel temp sender).