Getting this annoying engine shudder at highway speeds.

[spencnaz]

Hello all,

Had to do some long distance trips today and noticed something that I didn't much care for.

At around 55-65 there is a constant 'shudder' like there is a cylinder misfiring. When I back off the throttle it goes away or if I feather the throttle down the road, it smoothes out. At first I thought it might be a bad batch of biodiesel, but I filled up with diesel fuel later in the day and the shudder didn't go away.

Now I did notice tonight that my steering pump is on the verge of seizure, would this be causing this shudder? Or is there something not advancing correctly in the IP?

It's 0130 here right now, I'm really tired and need to sleep. I'll keep an eye on the posts here later for you guys' input.

 

[towcat]

couple of things you can check for. one is easy the other is not.
first, work the throttle arm and watch the advance plunger(driver's side of the pump, lower section) to see if it is following the lever as it moves in and out. If the plunger sticks, the nub on the plunger will not pop back out smoothly. there will be a gap between the nub and the lever.
second, using a peizo type timing meter check for 2deg advance from idle to 2k rpm. if no movement, you have a bad advance pump.
chances are you found your problem already in the bad p/s pump. yes, it will affect your motor.

 

[h2odrx]

chances are you found your problem already in the bad p/s pump. yes, it will affect your motor.

how?

 

[genchowford]

I have gotten shudder before when filter is about gone.

 

[93_E_350]

At around 55-65 there is a constant 'shudder' like there is a cylinder misfiring. When I back off the throttle it goes away or if I feather the throttle down the road, it smoothes out.

If you have a tach put the truck in park and try running the rpm up to the same range as when you are driving at 55/65. If the shudder persists more than likely its engine related or perhaps torque converter. If there is no shudder I would get a set of u-joints for your drive shaft. My truck did the same thing - under a load it sounded like the motor was firing unevenly. I tried to wiggle my drive shaft around and felt nothing but decided to change the u-joints as they were the cheapest. When removing the old u-joints I found one cap had gone bad and. Now it’s smooth again…

 

[spencnaz]

I'll check the static RPM idea later today. But definitely the power steering pump is not in good shape, I'm thinking it's the original.

I had a new IP put in a year ago and they put a timing light on it to time it. Unless they didn't tighten down the IP bolts, I can't see it really moving that far to cause this problem.

The PS pump was seizing up off and on when I had my friend turn the steering wheel last night. I was observing the pump pulley while she turned the steering wheel. I just replaced the fuel filter last week and before I did that I filled the new filter with injector cleaner/lube to make sure everything was greased up.

I checked the advance plunger last night and it was moving ok, didn't see anything sticking.

 

[rthomas]

sounds like the ps is the likely culprit but just last week a buddys psd developed a shudder and ended up being the harmonic balencer, it was only apparent at 2k+. i have seen a ip give a slight ocelating shudder as its only symtom but that was on a 6bt with 11.000 hours on it

 

[towcat]

The p/s pump as well as any other belt driven accessory will produce a harmonic if the bearings or pulley has issues. Often the vibration of the motor is the primary harmonic, the one you can see. The secondary harmonic is the one you don't see but can feel. Ever noticed any item touching a diesel motor gets worn down pretty quick? That's the physical evidence of the secondary at work. Add a accessory that is momentarily stopping and it will literally do so when you are looking at it with a strobe, the drive belt will slow down the rpm's just for the moment and then the motor will catch up again. Everything will go out of "phase" and back in. Done often enough, you will notice. Yup sounds crazy, but do the homework. It'll make sense.
the other thing is check is seeing if you can replicate this at a stop. If you don't feel it stopped, and is consistent with engine speed, you may have driveline issues. I don't remember if you have a slushbox or not, but if you do, try brake stalling the trans to see if it's in there too.

 

[spencnaz]

There is no vibration at idle. Only when the vehicle is moving. The seizing PS squeals of course when the belt tries to spin a stuck pulley.

The vibration is worst at about 60-65 and 2200-2500 RPM. It is constant at that speed range. I will try brake stalling the tranny today. I briefly tried to spin the rear driveline but didn't get any play out of the driveshaft.

I'll check the oil level in the rear diff just to make sure it's not low on oil. It had been leaking via a shaft seal but I topped it up a couple months ago to make sure.

 

[spencnaz]

Bump to top.

 

[Agnem]

You've got V belts. Why not just loosen the PS pump so the belts can't turn it, and then hit the road for a brief test? Obviously, this will have some level of difficulty, but if I were you, I'd pick the streightest quitest piece of road I could find, do the "mod" along the side of the road, complete the test with minimal turning of the steering wheel, and then hook the belts back up to get home.

 

[spencnaz]

Good idea, however the PS pump was on it's last legs. I'm almost done right now with the installation. Thank god for latex gloves, my keyboard would be a mess.

 

[spencnaz]

PS pump is now in. I need to clean up and get something to eat here. I also have to take the core back to the place I bought the Remanned unit from.

I'll let you guys know if I get any more shudder out of the truck.

 

[spencnaz]

Well just went for a quick drive. The shudder is still there and now it's not just at highway speeds but even at 30 and above.

I'm starting to lean towards the bad u-joint theory. Revving the engine up while parked, there is no shudder what so ever.

I'll climb underneath the truck tomorrow. There is no pressing need to have the truck running on the freeway right now anyway.

 

[93_E_350]

You need to remove the drive shaft and pop the caps and inspect them. The u-joints are less than $18.00 each. Also make sure the balance weight didn't come off - look for a clean spot...