Here's the issue...driving down the highway in traffic, stop and go, very light acceleration the truck shudders. Apply the throttle a bit more aggressively and the shudder goes away and the truck accelerates normally. A short time later in more traffic, the truck again shudders under light throttle acceleration. More aggressive throttle brought a metallic "tink, tink, tink" with what sounded like a toothed gear cutting into aluminum. Back out of the throttle immediately and resume light acceleration, no more shuddering present the rest of the way home.

No codes thrown. Transmission was rebuilt by a local shop 40k miles ago. The truck is mostly highway driven with no load, maybe 8000 miles towing a 4 horse trailer with tack room.

The truck has 261k miles and other than the transmission rebuild, is the bone stock truck delivered from the factory with the 250hp motor and the stock injectors.

I took the truck back to the transmission shop to rule out any potential issues there, as the tink, tink, tink sound reminded me of a cracked drive plate. On the way to the shop, it seemed as though there was more general engine noise forward of the transmission. No knocking or vibration and the engine was running smoothly.

There were no stored codes at the transmission shop and a test drive revealed no obvious cause. There was no noise or shuddering. At this point, I am at a loss. We have been relying on the truck to get back and forth to my wife's doctor's appointments, which is a 350 mile round trip weekly.

Ideas? Torque converter? Injectors?

-Joe

 

Did they drop the pan and look for metal?

 

I would check U joints and mounts of all kinds. Does your truck have a carrier bearing on the drive shaft?










47

 

The feel and sound is in the front of the truck, but I will check the mounts and u-joints. The front driveshaft is new and was installed after the transmission was done. The rear driveshaft is a one piece, so no carrier bearing.

-Joe

 

No, but I agree that will need to be done.

A few weeks ago, I started the truck and was letting it warm up before a trip. It was very cold out, so I wanted to get the cab warmed up and left it idling for about 15 minutes before I got in to leave. I remember hearing a noise that sounded like a piece of baling wire being whipped against a drive shaft as the truck sat idling. I couldn't hear it in the cab, but that "tink, tink, tink" noise was plain as day outside the truck, near the engine compartment. I was in a hurry and didn't have time to look for the source. I made a quick glance to look for leaks and all looked good. There was no issues during the trip and the noise went away on its own. The incident on the highway was obviously loud enough to be heard in the cab at 40 mph or so.

-Joe

 

Transmission pan dropped and all appears to be normal. Both drive lines are good to go with no u-joint issues or defects.

The issue seems to be injectors and is intermittent. It was a warm afternoon today and on a cold start after sitting for days, the engine was chugging at idle and upon starting from a stop. After a few minutes of running, the chugging went away. The truck ran smooth and quiet, shifting out normally with no issues. I drove it at mixed speed and into a 45 mph headwinds for twenty minutes or so.

The next question is oil pressure related. With a mechanical oil pressure gauge and fresh oil in the crankcase (Rotella 15w40), on start up, there is 0 oil pressure at idle for 30-45 seconds, at the to of the oil filter housing. Once oil pressure comes up, it goes straight up to 80 psi. Once warmed up after 20 minutes of mixed driving, oil psi at 70 mph, pressure is 65 psi (2100 rpm). At idle, in gear, psi is 20, and at idle in Park, psi is 25. My question is what is causing the long period of no oil psi at start up? Weak oil pump?

-Joe